1.
Artery
–
Arteries are blood vessels that carry blood away from the heart. While most arteries carry oxygenated blood, there are two exceptions to this, the pulmonary and the umbilical arteries, the effective arterial blood volume is that extracellular fluid which fills the arterial system. The anatomy of arteries can be separated into gross anatomy, at the level, and microscopic anatomy. The outermost layer is known as the tunica externa, also known as tunica adventitia, inside this layer is the tunica media, or media, which is made up of smooth muscle cells and elastic tissue. The innermost layer, which is in contact with the flow of blood, is the tunica intima. This layer is made up of endothelial cells. The hollow internal cavity in which the flows is called the lumen. Arterial formation begins when endothelial cells begin to express specific genes. Arteries form part of the circulatory system and they carry blood that is oxygenated after it has been pumped from the heart. Arteries also aid the heart in pumping blood, arteries carry oxygenated blood away from the heart to the tissues, except for pulmonary arteries, which carry blood to the lungs for oxygenation. Veins and pulmonary veins carry deoxygenated blood. )The pulmonary artery carries blood from the heart to the lungs and it is unique because the blood in it is not oxygenated, as it has not yet passed through the lungs. The other unique artery is the artery, which carries deoxygenated blood from a fetus to its mother. Arteries have a blood pressure than other parts of the circulatory system. The pressure in arteries varies during the cardiac cycle and it is highest when the heart contracts and lowest when heart relaxes. The variation in pressure produces a pulse, which can be felt in different areas of the body, arterioles have the greatest collective influence on both local blood flow and on overall blood pressure. They are the primary adjustable nozzles in the system, across which the greatest pressure drop occurs. The larger arteries are generally elastic and the smaller ones tend to be muscular, systemic arteries deliver blood to the arterioles, and then to the capillaries, where nutrients and gases are exchanged. After travelling from the aorta, blood travels through peripheral arteries into smaller arteries called arterioles, arterioles help in regulating blood pressure by the variable contraction of the smooth muscle of their walls, and deliver blood to the capillaries
Artery
–
Microscopic anatomy of the artery.
2.
Latin
–
Latin is a classical language belonging to the Italic branch of the Indo-European languages. The Latin alphabet is derived from the Etruscan and Greek alphabets, Latin was originally spoken in Latium, in the Italian Peninsula. Through the power of the Roman Republic, it became the dominant language, Vulgar Latin developed into the Romance languages, such as Italian, Portuguese, Spanish, French, and Romanian. Latin, Italian and French have contributed many words to the English language, Latin and Ancient Greek roots are used in theology, biology, and medicine. By the late Roman Republic, Old Latin had been standardised into Classical Latin, Vulgar Latin was the colloquial form spoken during the same time and attested in inscriptions and the works of comic playwrights like Plautus and Terence. Late Latin is the language from the 3rd century. Later, Early Modern Latin and Modern Latin evolved, Latin was used as the language of international communication, scholarship, and science until well into the 18th century, when it began to be supplanted by vernaculars. Ecclesiastical Latin remains the language of the Holy See and the Roman Rite of the Catholic Church. Today, many students, scholars and members of the Catholic clergy speak Latin fluently and it is taught in primary, secondary and postsecondary educational institutions around the world. The language has been passed down through various forms, some inscriptions have been published in an internationally agreed, monumental, multivolume series, the Corpus Inscriptionum Latinarum. Authors and publishers vary, but the format is about the same, volumes detailing inscriptions with a critical apparatus stating the provenance, the reading and interpretation of these inscriptions is the subject matter of the field of epigraphy. The works of several hundred ancient authors who wrote in Latin have survived in whole or in part and they are in part the subject matter of the field of classics. The Cat in the Hat, and a book of fairy tales, additional resources include phrasebooks and resources for rendering everyday phrases and concepts into Latin, such as Meissners Latin Phrasebook. The Latin influence in English has been significant at all stages of its insular development. From the 16th to the 18th centuries, English writers cobbled together huge numbers of new words from Latin and Greek words, dubbed inkhorn terms, as if they had spilled from a pot of ink. Many of these words were used once by the author and then forgotten, many of the most common polysyllabic English words are of Latin origin through the medium of Old French. Romance words make respectively 59%, 20% and 14% of English, German and those figures can rise dramatically when only non-compound and non-derived words are included. Accordingly, Romance words make roughly 35% of the vocabulary of Dutch, Roman engineering had the same effect on scientific terminology as a whole
Latin
–
Latin inscription, in the
Colosseum
Latin
–
Julius Caesar 's
Commentarii de Bello Gallico is one of the most famous classical Latin texts of the Golden Age of Latin. The unvarnished, journalistic style of this
patrician general has long been taught as a model of the urbane Latin officially spoken and written in the floruit of the
Roman republic.
Latin
–
A multi-volume Latin dictionary in the
University Library of Graz
Latin
–
Latin and Ancient Greek Language - Culture - Linguistics at
Duke University in 2014.
3.
Medical Subject Headings
–
Medical Subject Headings is a comprehensive controlled vocabulary for the purpose of indexing journal articles and books in the life sciences, it serves as a thesaurus that facilitates searching. Created and updated by the United States National Library of Medicine, it is used by the MEDLINE/PubMed article database, MeSH is also used by ClinicalTrials. gov registry to classify which diseases are studied by trials registered in ClinicalTrials. gov. MeSH was introduced in 1960, with the NLMs own index catalogue, the yearly printed version of MeSH was discontinued in 2007 and MeSH is now available online only. It can be browsed and downloaded free of charge through PubMed, originally in English, MeSH has been translated into numerous other languages and allows retrieval of documents from different languages. The 2009 version of MeSH contains a total of 25,186 subject headings, most of these are accompanied by a short description or definition, links to related descriptors, and a list of synonyms or very similar terms. This additional information and the structure make the MeSH essentially a thesaurus. The descriptors or subject headings are arranged in a hierarchy, a given descriptor may appear at several locations in the hierarchical tree. The tree locations carry systematic labels known as numbers. The tree numbers of a given descriptor are subject to change as MeSH is updated, every descriptor also carries a unique alphanumerical ID that will not change. Most subject headings come with a description or definition. See the MeSH description for diabetes type 2 as an example, the explanatory text is written by the MeSH team based on their standard sources if not otherwise stated. References are mostly encyclopaedias and standard textbooks of the subject areas, references for specific statements in the descriptions are not given, instead readers are referred to the bibliography. In addition to the hierarchy, MeSH contains a small number of standard qualifiers. For example, Measles is a descriptor and epidemiology is a qualifier, the epidemiology qualifier can be added to all other disease descriptors. Not all descriptor/qualifier combinations are allowed some of them may be meaningless. In all there are 83 different qualifiers, in addition to the descriptors, MeSH also contains some 139,000 supplementary concept records. These do not belong to the vocabulary as such, instead they enlarge the thesaurus. Many of these records describe chemical substances, by default, a search for a descriptor will include all the descriptors in the hierarchy below the given one
Medical Subject Headings
–
Medical Subject Headings
4.
Anatomical terminology
–
Anatomical terminology is a form of scientific terminology used by anatomists, zoologists, and health professionals such as doctors. Anatomical terminology uses many terms, suffixes, and prefixes deriving from Ancient Greek. These terms can be confusing to those unfamiliar with them, but can be more precise reducing ambiguity, also, since these anatomical terms are not used in everyday conversation, their meanings are less likely to change, and less likely to be misinterpreted. By using precise anatomical terminology such ambiguity is eliminated, an international standard for anatomical terminology, Terminologia Anatomica has been created. Anatomical terminology has quite regular morphology, the prefixes and suffixes are used to add meanings to different roots. The root of a term refers to an organ, tissue. For example, in the disorder hypertension, the prefix hyper- means high or over, the roots, prefixes and suffixes are often derived from Greek or Latin, and often quite dissimilar from their English-language variants. Latin names of such as musculus biceps brachii can be split up and refer to, musculus for muscle, biceps for two-headed. The first word tells us what we are speaking about, the second describes it, when describing the position of anatomical structures, structures may be described according to the anatomical landmark they are near. These landmarks may include structures, such as the umbilicus or sternum, or anatomical lines, the cephalon or cephalic region refers to the head. This area is differentiated into the cranium, facies, frons, oculus, auris, bucca, nausus, oris. The neck area is called the cervicis or cervical region, examples of structures named according to this include the frontalis muscle, submental lymph nodes, buccal membrane and orbicularis oculi muscle. Sometimes, unique terminology is used to reduce confusion in different parts of the body, for example, different terms are used when it comes to the skull in compliance with its embryonic origin and its tilted position compared to in other animals. Here, Rostral refers to proximity to the front of the nose, similarly, in the arms, different terminology is often used in the arms, in part to reduce ambiguity as what is the front, back, inner and outer surfaces. For this reason, the terms below are used, Radial referring to the radius bone, ulnar referring to the ulna bone, medially positioned when in the standard anatomical position. Other terms are used to describe the movement and actions of the hands and feet. International morphological terminology is used by the colleges of medicine and dentistry and it facilitates communication and exchanges between scientists from different countries of the world and it is used daily in the fields of research, teaching and medical care. The international morphological terminology refers to morphological sciences as a biological sciences branch, in this field, the form and structure are examined as well as the changes or developments in the organism
Anatomical terminology
–
The
anatomical position, with terms of relative location noted.
Anatomical terminology
–
The human body is shown in anatomical position in an anterior view and a posterior view. The regions of the body are labeled in boldface.
Anatomical terminology
–
Abdominal regions are used for example to localize pain.
5.
Pinna (anatomy)
–
The auricle or auricula is the visible part of the ear that resides outside of the head. It is also called the pinna, a term that is used more in zootomy and these hillocks develop into the folds of the auricle and gradually shift upwards and backwards to their final position on the head. En route accessory auricles may be left behind, the first three hillocks are derived from the 1st branchial arch and form the tragus, crus of the helix, and helix, respectively. Cutaneous sensation to these areas is via the nerve, the attendant nerve of the 1st branchial arch. The final three hillocks are derived from the branchial arch and form the antihelix, antitragus, and lobule. These portions of the ear are supplied by the cervical plexus and this explains why vesicles are classically seen on the auricle in herpes infections of the facial nerve. The auricles functions are to sound and transform it into directional. The auricle collects sound and, like a funnel, amplifies the sound, the filtering effect of the human pinnae preferentially selects sounds in the frequency range of human speech. Amplification of sound by the pinna, tympanic membrane and middle ear causes an increase in level of about 10 to 15 dB in a range of 1.5 kHz to 7 kHz. This amplification is an important factor in inner ear trauma resulting from elevated sound levels, due to its anatomy, the pinna largely eliminates a small segment of the frequency spectrum, this band is called the pinna notch. The pinna works differently for low and high frequency sounds, for low frequencies, it behaves similarly to a reflector dish, directing sounds toward the ear canal. For high frequencies, however, its value is thought to be more sophisticated, while some of the sounds that enter the ear travel directly to the canal, others reflect off the contours of the pinna first, these enter the ear canal after a very slight delay. This delay causes phase cancellation, virtually eliminating the frequency component whose wave period is twice the delay period, in the affected frequency band – the pinna notch – the pinna creates a band-stop or notch filtering effect. This filter typically affects sounds around 10 kHz, though it can affect any frequencies from 6 –16 kHz and it also is directionally dependent, affecting sounds coming from above more than those coming from straight ahead. This aids in sound localization. In animals the function of the pinna is to collect sound and it collects sound by acting as a funnel, amplifying the sound and directing it to the auditory canal. While reflecting from the pinna, sound also goes through a filtering process, in various species, the pinna can also signal mood and radiate heat
Pinna (anatomy)
–
The
fennec fox uses its distinctive oversized pinnae to radiate excess heat and to amplify the sound of small prey burrowing under the desert sand
Pinna (anatomy)
–
The
auricula. Lateral surface.
Pinna (anatomy)
–
To an impala, the pinna is useful in collecting sound
Pinna (anatomy)
–
Left human pinna
6.
Tragus (ear)
–
The tragus is a small pointed eminence of the external ear, situated in front of the concha, and projecting backward over the meatus. It also is the name of hair growing at the entrance of the ear and its name comes from the Greek, tragos, goat, and is descriptive of its general covering on its under surface with a tuft of hair, resembling a goats beard. The nearby antitragus projects forwards and upwards, because the tragus faces rearwards, it aids in collecting sounds from behind. These sounds are delayed more than sounds arriving from the front, in a positive fistula test, pressure on the tragus causes vertigo or eye deviation by inducing movement of perilymph. Tragal pressure Tragus piercing This article incorporates text in the domain from the 20th edition of Grays Anatomy MedlinePlus Image 1126 lesson3 at The Anatomy Lesson by Wesley Norman
Tragus (ear)
–
External ear. Right auricle.Lateral view.
Tragus (ear)
–
The ear — lateral surface
7.
Utricle (ear)
–
The utricle, or utriculus, along with the saccule, is one of the two otolith organs located in the vertebrate inner ear. The utricle and the saccule are parts of the balancing apparatus located within the vestibule of the bony labyrinth and these use small stones and a viscous fluid to stimulate hair cells to detect motion and orientation. The utricle detects linear accelerations and head-tilts in the horizontal plane, the gelatinous layer and the statoconia together are referred to as the otolithic membrane, where the tips of the stereocilia and kinocilium are embedded. When the head is tilted such that gravity pulls on the statoconia the gelatinous layer is pulled in the same direction causing the sensory hairs to bend. Within the utricle is a small 2 by 3 mm patch of hair called the macula of utricle. The macula of utricle, which lies horizontally on the floor of the utricle and these hair cells are mechanoreceptors which consist of 40 to 70 stereocilia and only one true cilium called a kinocilium. The kinocilium is the only aspect of the hair cell and is what causes hair cell polarization. The tips of stereocilia and kinocilium are embedded in a gelatinous otolithic membrane. This membrane is weighted with calcium carbonate-protein granules called otoliths, the otolithic membrane adds weight to the tops of the hair cells and increases their inertia. The addition in weight and inertia is vital to the ability to detect linear acceleration, as described below. The macula consists of three layers, the bottom layer is made of sensory hair cells which are embedded in bottom of a gelatinous layer. Each hair cells consists of 40 to 70 steriocilia and a kinocilium, on top of this layer lie calcium carbonate crystals called statoconia or otoconia. The otoliths are relatively heavy, providing weight to the membrane as well as inertia and this allows for a greater sense of gravity and motion. Labyrinthine activity responsible for the nystagmus induced by off-vertical axis rotation arises in the otolith organs, the cavity of the utricle communicates behind with the semicircular ducts by five orifices. The ductus utriculosaccularis comes off of the wall of the utricle. The utricle contains mechanoreceptors called hair cells that distinguish between degrees of tilting of the head, thanks to their apical stereocilia set-up and these are covered by otolith which, due to gravity, pull on the stereocilia and tilt them. Depending on whether the tilt is in the direction of the kinocilium or not, any orientation of the head causes a combination of stimulation to the utricles and saccules of the two ears. The inertia of the membranes is especially important in detecting linear acceleration
Utricle (ear)
–
Illustration of otolith organs showing detail of utricle,
otoconia,
endolymph,
cupula,
macula,
hair cell filaments, and
saccular nerve
Utricle (ear)
–
Posterior Canal
8.
Mammal
–
Mammals are any vertebrates within the class Mammalia, a clade of endothermic amniotes distinguished from reptiles by the possession of a neocortex, hair, three middle ear bones and mammary glands. All female mammals nurse their young with milk, secreted from the mammary glands, Mammals include the largest animals on the planet, the great whales. The basic body type is a quadruped, but some mammals are adapted for life at sea, in the air, in trees. The largest group of mammals, the placentals, have a placenta, Mammals range in size from the 30–40 mm bumblebee bat to the 30-meter blue whale. With the exception of the five species of monotreme, all modern mammals give birth to live young, most mammals, including the six most species-rich orders, belong to the placental group. The largest orders are the rodents, bats and Soricomorpha, the next three biggest orders, depending on the biological classification scheme used, are the Primates, the Cetartiodactyla, and the Carnivora. Living mammals are divided into the Yinotheria and Theriiformes There are around 5450 species of mammal, in some classifications, extant mammals are divided into two subclasses, the Prototheria, that is, the order Monotremata, and the Theria, or the infraclasses Metatheria and Eutheria. The marsupials constitute the group of the Metatheria, and include all living metatherians as well as many extinct ones. Much of the changes reflect the advances of cladistic analysis and molecular genetics, findings from molecular genetics, for example, have prompted adopting new groups, such as the Afrotheria, and abandoning traditional groups, such as the Insectivora. The mammals represent the only living Synapsida, which together with the Sauropsida form the Amniota clade, the early synapsid mammalian ancestors were sphenacodont pelycosaurs, a group that produced the non-mammalian Dimetrodon. At the end of the Carboniferous period, this group diverged from the line that led to todays reptiles. Some mammals are intelligent, with some possessing large brains, self-awareness, Mammals can communicate and vocalize in several different ways, including the production of ultrasound, scent-marking, alarm signals, singing, and echolocation. Mammals can organize themselves into fission-fusion societies, harems, and hierarchies, most mammals are polygynous, but some can be monogamous or polyandrous. They provided, and continue to provide, power for transport and agriculture, as well as commodities such as meat, dairy products, wool. Mammals are hunted or raced for sport, and are used as model organisms in science, Mammals have been depicted in art since Palaeolithic times, and appear in literature, film, mythology, and religion. Defaunation of mammals is primarily driven by anthropogenic factors, such as poaching and habitat destruction, Mammal classification has been through several iterations since Carl Linnaeus initially defined the class. No classification system is accepted, McKenna & Bell and Wilson & Reader provide useful recent compendiums. Though field work gradually made Simpsons classification outdated, it remains the closest thing to a classification of mammals
Mammal
–
Goat kids will stay with their mother until they are weaned.
Mammal
9.
Bony labyrinth
–
The bony labyrinth is the rigid, bony outer wall of the inner ear in the temporal bone. It consists of three parts, the vestibule, semicircular canals, and cochlea and these are cavities hollowed out of the substance of the bone, and lined by periosteum. They contain a fluid, the perilymph, in which the membranous labyrinth is situated. On radiographic images, the capsule is the most dense portion of the temporal bone. In otospongiosis, a cause of adult-onset hearing loss, the otic capsule is exclusively affected. This area normally undergoes no remodeling in adult life, and is extremely dense and this results in hypodensity on CT, with the portion first affected usually being the fissula ante fenestram. This article incorporates text in the domain from the 20th edition of Grays Anatomy
Bony labyrinth
–
Lateral view of right osseous labyrinth
10.
Temporal bone
–
The temporal bones are situated at the sides and base of the skull, and lateral to the temporal lobes of the cerebral cortex. The temporal bones are overlaid by the sides of the known as the temples. The lower seven cranial nerves and the vessels to and from the brain traverse the temporal bone. The temporal bone consists of four parts— the squamous, mastoid, petrous, the squamous part is the largest and most superiorly positioned relative to the rest of the bone. The zygomatic process is a long, arched process projecting from the region of the squamous part. Posteroinferior to the squamous is the mastoid part, fused with the squamous and mastoid parts and between the sphenoid and occipital bones lies the petrous part, which is shaped like a pyramid. The tympanic part is small and lies inferior to the squamous part, anterior to the mastoid part. The styloid, from the Greek stylos, is a thorn shaped pillar directed inferiorly and anteromedially between the parotid gland and internal jugular vein, an elongated or deviated styloid process can result from calcification of the stylohyoid ligament in a condition known as Eagle syndrome. The petromastoid part is developed from four centers, which make their appearance in the cartilaginous ear capsule about the fifth or sixth month, a third roofs in the tympanic cavity and antrum, while the fourth appears near the posterior semicircular canal and extends to form the mastoid process. The tympanic ring is a circle, in the concavity of which is a groove. This ring expands to form the part, and is ossified in membrane from a single center which appears about the third month. The tympanic ring unites with the squama shortly before birth, the part and squama join during the first year. The stylohyal does not unite with the rest of the bone until after puberty, apart from size increase, the chief changes from birth through puberty in the temporal bone are as follows, The tympanic ring extends outward and backward to form the tympanic part. This extension does not, however, take place at an equal rate all around the circumference of the ring, as these outgrowths meet, they create a foramen in the floor of the meatus, the foramen of Huschke. This foramen is usually closed about the year, but may persist throughout life. The mandibular fossa is at first extremely shallow, and looks lateral and inferior, it deepens, the part of the squama which forms the fossa lies at first below the level of the zygomatic process. The mastoid portion is at first flat, with the stylomastoid foramen, with air cell development, the outer part of the mastoid component grows anteroinferiorly to form the mastoid process, with the styloid and stylomastoid foramen now on the under surface. The descent of the foramen is accompanied by a lengthening of the facial canal
Temporal bone
–
Sphenoid and temporal bones
Temporal bone
–
Position of temporal bone (shown in green)
11.
Vestibular system
–
Together with the cochlea, a part of the auditory system, it constitutes the labyrinth of the inner ear in most mammals, situated in the vestibulum in the inner ear. The vestibular system sends signals primarily to the structures that control eye movements. The brain uses information from the system in the head. The semicircular canal system detects rotational movements, the semicircular canals are its main tools to achieve this detection. Since the world is three-dimensional, the system contains three semicircular canals in each labyrinth. They are approximately orthogonal to other, and are called the horizontal, the anterior semicircular canal. Anterior and posterior canals may be collectively called vertical semicircular canals, movement of fluid within the horizontal semicircular canal corresponds to rotation of the head around a vertical axis, as when doing a pirouette. The anterior and posterior canals detect rotations of the head in the sagittal plane. Both anterior and posterior canals are orientated at approximately 45° between frontal and sagittal planes, each of these three pairs works in a push-pull fashion, when one canal is stimulated, its corresponding partner on the other side is inhibited, and vice versa. Vertical canals are coupled in a fashion, i. e. stimulations that are excitatory for an anterior canal are also inhibitory for the contralateral posterior. For example, when the head moves to the right, the move to the left. The VOR reflex does not depend on visual input and works even in darkness or when the eyes are closed. The mechanics of the canals can be described by a damped oscillator. For humans, the time constants T1 and T2 are approximately 3 ms and 5 s, as a result, for typical head movements, which cover the frequency range of 0.1 Hz and 10 Hz, the deflection of the cupula is approximately proportional to the head-velocity. This is very useful, since the velocity of the eyes must be opposite to the velocity of the head in order to have clear vision, signals from the vestibular system also project to the cerebellum and to different areas in the cortex. The projections to the cortex are spread out over different areas, the vestibular nuclei on either sides of the brain stem exchange signals regarding movement and body position. These signals are sent down the following projection pathways, signals sent to the cerebellum are relayed back as muscle movements of the head, eyes, and posture. To nuclei of cranial nerves III, IV, and VI, signals sent to these nerves cause the vestibulo-ocular reflex
Vestibular system
–
Figure 2: Push-pull system of the semicircular canals, for a horizontal head movement to the right.
12.
Balance (ability)
–
In biomechanics, balance is an ability to maintain the line of gravity of a body within the base of support with minimal postural sway. Sway is the movement of the centre of gravity even when a person is standing still. A certain amount of sway is essential and inevitable due to small perturbations within the body or from external triggers, an increase in sway is not necessarily an indicator of dysfunctional balance so much as it is an indicator of decreased sensorimotor control. Maintaining balance requires coordination of input from sensory systems including the vestibular, somatosensory. There are environmental factors that can balance such as light conditions, floor surface changes, alcohol, drugs. There are balance impairments associated with aging, age-related decline in the ability of the above systems to receive and integrate sensory information contributes to poor balance in older adults. As a result, the elderly are at a risk of falls. In fact, one in three adults aged 65 and over will fall each year, in the case of an individual standing quietly upright, the limit of stability is defined as the amount of postural sway at which balance is lost and corrective action is required. Body sway can occur in all planes of motion, which make it an increasingly difficult ability to rehabilitate, there is strong evidence in research showing that deficits in postural balance is related to the control of medial-lateral stability and an increased risk of falling. To remain balanced, a person standing must be able to keep the vertical projection of their center of mass within their base of support, ankle sprains are one of the most frequently occurring injuries among athletes and physically active people. The most common residual disability post ankle sprain is instability along with body sway and it is found that nearly 40% of patients with ankle sprains suffer from instability and an increase in body sway. Injury to the causes an proprioceptive deficit and impaired postural control. Individuals with muscular weakness, occult instability, and decreased postural control are more susceptible to injury than those with better postural control. Balance can be affected in individuals with neurological conditions. Patients who suffer a stroke or a spinal cord injury for example and it has also been determined that impaired balance is strongly associated with future function and recovery in some cases, particularly in stroke patients. Additionally, balance problems have been identified as the strongest predictor of falls, another population where balance is severely affected is Parkinsons disease patients. Balance can also be affected in a normal population through fatigue in the musculature surrounding the ankles, knees. Studies have found, however, that muscle fatigue around the hips and it is thought that muscle fatigue leads to a decreased ability to contract with the correct amount of force or accuracy
Balance (ability)
–
A woman demonstrating the ability to balance
Balance (ability)
–
A
waiter balancing wine glasses
Balance (ability)
–
Balance
Balance (ability)
–
Balance Training
13.
Cranial nerve
–
Cranial nerves are the nerves that emerge directly from the brain, in contrast to spinal nerves. 10 of 12 of the cranial nerves originate in the brainstem, Cranial nerves relay information between the brain and parts of the body, primarily to and from regions of the head and neck. Spinal nerves emerge sequentially from the cord with the spinal nerve closest to the head emerging in the space above the first cervical vertebra. The cranial nerves, however, emerge from the nervous system above this level. Each cranial nerve is paired and is present on both sides, depending on definition in humans there are twelve or thirteen cranial nerves pairs, which are assigned Roman numerals I–XII, sometimes also including cranial nerve zero. The numbering of the nerves is based on the order in which they emerge from the brain. The terminal nerves, olfactory nerves and optic nerves emerge from the cerebrum or forebrain, and the ten pairs arise from the brainstem. Most typically, humans are considered to have pairs of cranial nerves. Cranial nerves are generally named according to their structure or function, for example, the olfactory nerve supplies smell, and the facial nerve supplies motor innervation to the face. The trigeminal nerve is named in accordance with its three components, and the nerve is named for its wandering course. Cranial nerves are numbered based on their position, when viewing the brain. If the brain is removed from the skull the nerves are typically visible in their numeric order. Cranial nerves have paths within and outside of the skull, the paths within the skull are called intracranial and the paths outside the skull are called extracranial. There are many holes in the skull called foramina by which the nerves can exit the skull, all cranial nerves are paired, which means that they occur on both the right and left sides of the body. The muscle, skin, or additional function supplied by a nerve on the side of the body as the side it originates from, is referred to an ipsilateral function. If the function is on the side to the origin of the nerve. The cell bodies of many of the neurons of most of the nerves are contained in one or more nuclei in the brainstem. These nuclei are important relative to cranial nerve dysfunction because damage to these nuclei such as from a stroke or trauma can mimic damage to one or more branches of a cranial nerve, the fibers of these cranial nerves exit the brainstem from these nuclei
Cranial nerve
–
View of the human brain from below showing the cranial nerves on an autopsy specimen
Cranial nerve
–
Left View of the human brain from below, showing origins of cranial nerves. Right Juxtaposed
skull base with
foramina in which many nerves exit the skull.
Cranial nerve
–
A case with unilateral hypoglossal nerve injury in branchial cyst surgery.
14.
Vestibule of the ear
–
The vestibule is the central part of the bony labyrinth, and is situated medial to the eardrum, behind the cochlea, and in front of the semicircular canals. The etymology comes from the Latin vestibulum, literally an entrance hall, the vestibule is somewhat oval in shape, but flattened transversely, it measures about 5 mm from front to back, the same from top to bottom, and about 3 mm across. In its lateral or tympanic wall is the window, closed, in the fresh state, by the base of the stapes. The orifice of the aquæductus vestibuli is the part of the medial wall. On the upper wall or roof there is an oval depression. The pyramid and adjoining part of the recessus ellipticus are perforated by a number of holes, the apertures in the pyramid transmit the nerves to the utricle, those in the recessus ellipticus are the nerves to the ampullæ of the superior and lateral semicircular ducts. Behind, the five orifices of the canals can be found. In the frontal view there is an opening which communicates with the scala vestibuli of the cochlea. This article incorporates text in the domain from the 20th edition of Grays Anatomy Inner ear Vestibular system
Vestibule of the ear
–
Posterior Canal
15.
Periosteum
–
The periosteum is a membrane that covers the outer surface of all bones, except at the joints of long bones. Endosteum lines the surface of all bones. The periosteum consists of irregular connective tissue. It is divided into a fibrous layer and inner cambium layer. The fibrous layer contains fibroblasts, while the layer contains progenitor cells that develop into osteoblasts. These osteoblasts are responsible for increasing the width of a long bone, after a bone fracture the progenitor cells develop into osteoblasts and chondroblasts, which are essential to the healing process. As opposed to osseous tissue, the periosteum has nociceptive nerve endings and it also provides nourishment by providing the blood supply to the body from the marrow. The periosteum is attached to the bone by strong collagenous fibers called Sharpeys fibres and it also provides an attachment for muscles and tendons. The periosteum that covers the surface of the bones of the skull is known as the pericranium. The word Periosteum is derived from the Greek Peri-, meaning surrounding, the Peri refers to the fact that the Periosteum is the outermost layer of long bones, surrounding other inner layers
Periosteum
–
The periosteum covers the outside of bones.
Periosteum
–
The periosteum consists of an inner osteogenic layer and an outer fibrous layer
16.
Membranous labyrinth
–
The membranous labyrinth is a collection of fluid filled tubes and chambers which contain the receptors for the senses of equilibrium and hearing. In certain places, it is fixed to the walls of the cavity, the membranous labyrinth contains fluid called endolymph. The walls of the labyrinth are lined with distributions of the cochlear nerve. The other branch is the vestibular nerve, within the vestibule, the membranous labyrinth does not quite preserve the form of the bony labyrinth, but consists of two membranous sacs, the utricle, and the saccule. The membranous labyrinth is also the location for the cells found in the inner ear. This article incorporates text in the domain from the 20th edition of Grays Anatomy
Membranous labyrinth
–
The membranous labyrinth.
17.
Perilymph
–
Perilymph is an extracellular fluid located within the cochlea in two of its three compartments, the scala tympani and scala vestibuli. The ionic composition of perilymph is comparable to that of plasma, the major cation in perilymph is sodium, The values of sodium and potassium concentration in the perilymph are 138 mM and 6.9 mM, respectively. The inner ear has two parts, the labyrinth and the membranous labyrinth. The membranous labyrinth is contained within the labyrinth, and contains a fluid called endolymph. Between the outer wall of the labyrinth and the wall of the bony labyrinth is the perilymphatic space which contains the perilymph. The membranous labyrinth is suspended in the perilymph, the perilymph in the bony labyrinth is continuous with the cerebrospinal fluid of the subarachnoid space via the perilymphatic duct. Perilymph and endolymph have unique ionic compositions suited to their functions in regulating electrochemical impulses of hair cells, the electric potential of endolymph is ~80-90 mV more positive than perilymph due to a higher concentration of potassium cations than sodium. Endolymph is the fluid contained within the labyrinth of the inner ear. It has also suggested that perilymph and endolymph participate in a unidirectional flow that is interrupted in Ménières disease
Perilymph
–
Cross-section of
cochlea. Perilymph is located in the
scala vestibuli and
scala tympani - the aqua regions at the top and bottom of the diagram.
18.
Sound pressure
–
Sound pressure or acoustic pressure is the local pressure deviation from the ambient atmospheric pressure, caused by a sound wave. In air, sound pressure can be measured using a microphone, the SI unit of sound pressure is the pascal. A sound wave in a medium causes a deviation in the local ambient pressure. Sound pressure, denoted p, is defined by p t o t a l = p s t a t + p, in a sound wave, the complementary variable to sound pressure is the particle velocity. Together they determine the intensity of the wave. Sound intensity, denoted I and measured in W·m−2 in SI units, is defined by I = p v. Consequently, the amplitude of the displacement is related to that of the acoustic velocity. This relationship is an inverse-proportional law, if the sound pressure p1 is measured at a distance r1 from the centre of the sphere, the sound pressure p2 at another position r2 can be calculated, p 2 = r 1 r 2 p 1. The inverse-proportional law for sound pressure comes from the law for sound intensity. Indeed, I = p v = p ∝ p 2, the sound pressure may vary in direction from the centre of the sphere as well, so measurements at different angles may be necessary, depending on the situation. An obvious example of a sound source whose spherical sound wave varies in level in different directions is a bullhorn, Sound pressure level or acoustic pressure level is a logarithmic measure of the effective pressure of a sound relative to a reference value. The commonly used reference sound pressure in air is p 0 =20 μ P a, which is often considered as the threshold of human hearing. The proper notations for sound pressure level using this reference are Lp/ or Lp, most sound level measurements will be made relative to this reference, meaning 1 Pa will equal an SPL of 94 dB. In other media, such as underwater, a level of 1 μPa is used. These references are defined in ANSI S1. 1-1994, the lower limit of audibility is defined as SPL of 0 dB, but the upper limit is not as clearly defined. Ears detect changes in sound pressure, human hearing does not have a flat spectral sensitivity relative to frequency versus amplitude. Humans do not perceive low- and high-frequency sounds as well as they perceive sounds between 3,000 and 4,000 Hz, as shown in the equal-loudness contour. Because the frequency response of human hearing changes with amplitude, three weightings have been established for measuring pressure, A, B and C. A-weighting applies to sound pressures levels up to 55 dB, B-weighting applies to sound levels between 55 dB and 85 dB, and C-weighting is for measuring sound pressure levels above 85 dB
Sound pressure
–
Sound pressure diagram: 1. silence; 2. audible sound; 3. atmospheric pressure; 4. sound pressure
19.
Pressure
–
Pressure is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure is the relative to the ambient pressure. Various units are used to express pressure, Pressure may also be expressed in terms of standard atmospheric pressure, the atmosphere is equal to this pressure and the torr is defined as 1⁄760 of this. Manometric units such as the centimetre of water, millimetre of mercury, Pressure is the amount of force acting per unit area. The symbol for it is p or P, the IUPAC recommendation for pressure is a lower-case p. However, upper-case P is widely used. The usage of P vs p depends upon the field in one is working, on the nearby presence of other symbols for quantities such as power and momentum. Mathematically, p = F A where, p is the pressure, F is the normal force and it relates the vector surface element with the normal force acting on it. It is incorrect to say the pressure is directed in such or such direction, the pressure, as a scalar, has no direction. The force given by the relationship to the quantity has a direction. If we change the orientation of the element, the direction of the normal force changes accordingly. Pressure is distributed to solid boundaries or across arbitrary sections of normal to these boundaries or sections at every point. It is a parameter in thermodynamics, and it is conjugate to volume. The SI unit for pressure is the pascal, equal to one newton per square metre and this name for the unit was added in 1971, before that, pressure in SI was expressed simply in newtons per square metre. Other units of pressure, such as pounds per square inch, the CGS unit of pressure is the barye, equal to 1 dyn·cm−2 or 0.1 Pa. Pressure is sometimes expressed in grams-force or kilograms-force per square centimetre, but using the names kilogram, gram, kilogram-force, or gram-force as units of force is expressly forbidden in SI. The technical atmosphere is 1 kgf/cm2, since a system under pressure has potential to perform work on its surroundings, pressure is a measure of potential energy stored per unit volume. It is therefore related to density and may be expressed in units such as joules per cubic metre. Similar pressures are given in kilopascals in most other fields, where the prefix is rarely used
Pressure
–
Mercury column
Pressure
–
Pressure as exerted by particle collisions inside a closed container.
Pressure
–
The effects of an external pressure of 700bar on an aluminum cylinder with 5mm wall thickness
Pressure
–
low pressure chamber in
Bundesleistungszentrum Kienbaum, Germany
20.
Hair cells
–
Hair cells are the sensory receptors of both the auditory system and the vestibular system in the ears of all vertebrates. Through mechanotransduction, hair cells detect movement in their environment, in mammals, the auditory hair cells are located within the spiral organ of Corti on the thin basilar membrane in the cochlea of the inner ear. They derive their name from the tufts of stereocilia called hair bundles that protrude from the surface of the cell into the fluid-filled cochlear duct. Mammalian cochlear hair cells are of two anatomically and functionally distinct types, known as outer, and inner hair cells, damage to these hair cells results in decreased hearing sensitivity, and because the inner ear hair cells cannot regenerate, this damage is permanent. However, other organisms, such as the frequently studied zebrafish, the human cochlea contains on the order of 3,500 inner hair cells and 12,000 outer hair cells at birth. Outer hair cells mechanically amplify low-level sound that enters the cochlea, the amplification may be powered by the movement of their hair bundles, or by an electrically driven motility of their cell bodies. This so-called somatic electromotility amplifies sound in all land vertebrates and it is affected by the closing mechanism of the mechanical sensory ion channels at the tips of the hair bundles. The deflection of the hair-cell stereocilia opens mechanically gated ion channels that allow any small, unlike many other electrically active cells, the hair cell itself does not fire an action potential. Instead, the influx of ions from the endolymph in the scala media depolarizes the cell. This receptor potential opens voltage gated calcium channels, calcium ions enter the cell. The neurotransmitters diffuse across the space between the hair cell and a nerve terminal, where they then bind to receptors and thus trigger action potentials in the nerve. In this way, the sound signal is converted into an electrical nerve signal. Repolarization of hair cells is done in a special manner, the perilymph in the scala tympani has a very low concentration of positive ions. The electrochemical gradient makes the positive ions flow through channels to the perilymph and this leakage causes a tonic release of neurotransmitter to the synapses. It is thought that this release is what allows the hair cells to respond so quickly in response to mechanical stimuli. The quickness of the cell response may also be due to the fact that it can increase the amount of neurotransmitter release in response to a change as little as 100 μV in membrane potential. In mammalian outer hair cells, the receptor potential triggers active vibrations of the cell body, outer hair cells are found only in mammals. While hearing sensitivity of mammals is similar to that of classes of vertebrates, without functioning outer hair cells
Hair cells
–
Inner ear illustration showing semicircular canal, hair cells, ampulla, cupula, vestibular nerve, & fluid
Hair cells
–
Section through the
spiral organ of Corti. Magnified. ("Outer hair cells" labeled near top; "inner hair cells" labeled near center).
Hair cells
–
Stereocilia of frog inner ear
21.
Embryonic development
–
Embryogenesis is the process by which the embryo forms and develops. In mammals, the term refers chiefly to early stages of development, whereas the terms fetus. Embryogenesis starts with the fertilization of the egg cell by a sperm cell, once fertilized, the ovum is referred to as a zygote, a single diploid cell. The zygote undergoes mitotic divisions with no significant growth and cellular differentiation, the egg cell is generally asymmetric, having an animal pole and a vegetal pole. It is covered with protective envelopes, with different layers, the first envelope - the one in contact with the membrane of the egg - is made of glycoproteins and is known as the vitelline membrane. Different taxa show different cellular and acellular envelopes englobing the vitelline membrane, fertilization is the fusion of gametes to produce a new organism. In animals, the process involves a sperm fusing with an ovum, depending on the animal species, the process can occur within the body of the female in internal fertilisation, or outside in the case of external fertilisation. The fertilized egg cell is known as the zygote, cell division with no significant growth, producing a cluster of cells that is the same size as the original zygote, is called cleavage. At least four initial cell divisions occur, resulting in a ball of at least sixteen cells called the morula. The different cells derived from cleavage, up to the stage, are called blastomeres. Depending mostly on the amount of yolk in the egg, the cleavage can be holoblastic or meroblastic, on the other hand, meroblastic cleavage occurs in animals whose eggs have more yolk, i. e. birds and reptiles. Because cleavage is impeded in the pole, there is a very uneven distribution and size of cells, being more numerous. In holoblastic eggs the first cleavage always occurs along the axis of the egg. Fluid collects between the trophoblast and the part of the inner cell-mass, and thus the morula is converted into a vesicle. After the 7th cleavage has produced 128 cells, the embryo is called a blastula, the blastula is usually a spherical layer of cells surrounding a fluid-filled or yolk-filled cavity. Mammals at this form a structure called the blastocyst, characterized by an inner cell mass that is distinct from the surrounding blastula. The blastocyst must not be confused with the blastula, even though they are similar in structure, their cells have different fates. On the deep surface of the cell mass, a layer of flattened cells, called the endoderm, is differentiated and quickly assumes the form of a small sac
Embryonic development
–
Dissection of human embryo
Embryonic development
–
Cell divisions (cleavage).
Embryonic development
–
Human embryo, 8-9 weeks, 38 mm
22.
Bipolar neuron
–
A bipolar cell is a type of neuron which has two extensions. Bipolar cells are specialized sensory neurons for the transmission of special senses, as such, they are part of the sensory pathways for smell, sight, taste, hearing and vestibular functions. Common examples are the cell of the retina, the ganglia of the vestibulocochlear nerve. The four types of neurons are bipolar cells, ganglion cells, horizontal cells. Oftentimes found in the retina, bipolar cells are crucial as they serve as direct and indirect cell pathways. The specific location of the bipolar cells allow them to facilitate the pathway of signals both where they start in the receptors as well as where they arrive at the ganglion cells. Bipolar cells in the retina are also unique as they do not fire impulses like the cells found within the retina. Rather, bipolar cells have a receptive-field that surrounds them, therefore, bipolar cells may exist as off-center or on-center. The off-center bipolar cells possess excitatory relationships with the synapses and are hyperpolarized by light, on-center bipolar cells have inhibitory synapses and therefore are suppressed in the dark. Bipolar neurons exist within the nerve as it is responsible for special sensory sensations including hearing, equilibrium. Bipolar cells are found in the spinal ganglia, when the cells are in an embryonic condition. Sometimes the extensions, also called processes, come off from opposite poles of the cell, interneuron Unipolar neuron Multipolar neuron Bipolar cell of the retina Diagram at howstuffworks. com This article incorporates text in the public domain from the 20th edition of Grays Anatomy
Bipolar neuron
–
Bipolar nerve cell from the
spinal ganglion of the pike.
23.
Auditory vesicle
–
Otic vesicle, or auditory vesicle, consists of either of the two sac-like invaginations formed and subsequently closed off during embryonic development. It is part of the ectoderm, which will develop into the membranous labyrinth of the inner ear. This labyrinth is a continuous epithelium, giving rise to the vestibular system, during the earlier stages of embryogenesis, the otic placode invaginates to produce the otic cup. Thereafter, the otic cup closes off, creating the otic vesicle, once formed, the otic vesicle will reside next to the neural tube medially, and on the lateral side will be paraxial mesoderm. Neural crest cells will migrate rostral and caudal to the placode, the general sequence in formation of the otic vesicle is relatively conserved across vertebrates, although there is much variation in timing and stages. The FGF, Bmp, Wnt and Pax genes are likely to be involved in otic induction, ffg and BMP signals help control patterning in the early otic vesicle. Fgf3 and Fgf10 are suggested to play a role in otic induction in mice, pax8 is expressed during the entirety of otic vesicle formation. Other genes found in the otic vesicle across species that may play a role in patterning include Hmx, Fox, Dlx, the otic vesicle is uniquely derived from the neural ectoderm. The early otic vesicle is characterized as having broad competence and can be subdivided into sensory, non-sensory, sensory epithelial cells and neurons are derived from the proneurosensory domain. This domain can be further sub-categorized into the neurogenic sub-domain and prosensory sub-domain, prosensory sub-domain eventually gives rise to the support cells and hair cells while the neurogenic sub-domain gives rise to the auditory neuron and vestibular neuron. The middle part of the otic vesicle develops into the ductus and saccus endolymphaticus, the anterior end of the otic vesicle gradually elongates as a tube and coils upon itself forming the beginnings of the cochlear duct. The vestibular extremity subsequently constricts to form the canalis reuniens, the dorsal component of the inner ear also consists of what will become the semicircular canals. The utricle and saccule communicate with each other by means of a Y-shaped canal, formation of the otic vesicle has been studied extensively in developmental model organisms including chick, Xenopus, zebrafish, axolotyl, & mouse. The transition from the otic placode to the otic vesicle occurs during the 19th somite stage in Zebrafish, Xenopus, in chick, invagination of the otic placode occurs passively due to the movements of the surrounding placode. The otic placode in zebrafish, on the hand, occurs by cavitation. Otic vesicle formation occurs later, during the 25-30 somite stage in mice
Auditory vesicle
–
Embryo between eighteen and twenty-one days
24.
Macula of utricle
–
The macula of the utricle, or utricular macula is the region of the utricle that receives the utricular filaments of the vestibulocochlear nerve. The portion of the utricle that forms the macula forms a sort of pouch or cul-de-sac, the macula of utricle allows a person to perceive changes in longitudinal acceleration. The macula consists of three layers, the bottom layer is made of sensory hair cells which are embedded in bottom of a gelatinous layer. Each hair cell has between 40 and 70 steriocilia and a kinocilium, which lies in the middle of the steriocilia and is the most important receptor, on top of this layer lie calcium carbonate crystals called statoconia or otoliths. The otoliths are relatively heavy, providing weight to the membrane as well as inertia and this allows for a greater sense of gravity and motion. The gelatinous layer and the statoconia together are referred to as the otolithic membrane, when the head is tilted such that gravity pulls on the statoconia the gelatinous layer is pulled in the same direction also causing the sensory hairs to bend. Unbent and at rest hairs in the macula have a rate of depolarization of 90-100 action potentials a second. The brain suppresses this, and we ignore it and know that our body is stabilized, if the head moves or the body accelerates or decelerates, then bending occurs. Depending on the direction of bending, the cells will either be excited or inhibited resulting in either an increase or decrease in firing frequency of the hair cells. The macula is also sensitive to linear acceleration as the inertia possessed by the statoconia can also shift the gelatinous layer during increases and decreases in linear velocity. This article incorporates text in the domain from the 20th edition of Grays Anatomy http
Macula of utricle
–
illustration of otolith organs showing detail of
utricle,
otoconia,
endolymph, cupula,
macula,
hair cell filaments, and
saccular nerve
25.
Linear acceleration
–
The principles for such machines were proposed by Gustav Ising in 1924, while the first machine that worked was constructed by Rolf Widerøe in 1928 at the RWTH Aachen University. The design of a linac depends on the type of particle that is being accelerated, linacs range in size from a cathode ray tube to the 3. 2-kilometre-long linac at the SLAC National Accelerator Laboratory in Menlo Park, California. A linear particle accelerator consists of the elements, The particle source. The design of the source depends on the particle that is being moved, electrons are generated by a cold cathode, a hot cathode, a photocathode, or radio frequency ion sources. Protons are generated in an ion source, which can have different designs. If heavier particles are to be accelerated, an ion source is needed. A high voltage source for the injection of particles. The length will vary with the application, if the device is used for the production of X-rays for inspection or therapy the pipe may be only 0.5 to 1.5 meters long. If the device is to be an injector for a synchrotron it may be about ten meters long, if the device is used as the primary accelerator for nuclear particle investigations, it may be several thousand meters long. Within the chamber, electrically isolated cylindrical electrodes are placed, whose length varies with the distance along the pipe, likewise, because its mass is so small, electrons have much less kinetic energy than protons at the same speed. One or more sources of radio energy, used to energize the cylindrical electrodes. A very high power accelerator will use one source for each electrode, the sources must operate at precise power, frequency and phase appropriate to the particle type to be accelerated to obtain maximum device power. If electrons are accelerated to produce X-rays then a water cooled tungsten target is used, various target materials are used when protons or other nuclei are accelerated, depending upon the specific investigation. For particle-to-particle collision investigations the beam may be directed to a pair of storage rings, the beams may then be extracted from the storage rings to create head on particle collisions. This accelerates the particle, imparting energy to it in the form of increased velocity, at speeds near the speed of light, the incremental velocity increase will be small, with the energy appearing as an increase in the mass of the particles. In portions of the accelerator where this occurs, the tubular electrode lengths will be almost constant, additional magnetic or electrostatic lens elements may be included to ensure that the beam remains in the center of the pipe and its electrodes. Very long accelerators may maintain an alignment of their components through the use of servo systems guided by a laser beam. The high density of the output makes the linac particularly attractive for use in loading storage ring facilities with particles in preparation for particle to particle collisions
Linear acceleration
–
The linac within the
Australian Synchrotron uses
radio waves from a series of
RF cavities at the start of the linac to accelerate the electron beam in bunches to energies of 100 MeV.
Linear acceleration
–
Quadrupole magnets surrounding the linac of the
Australian Synchrotron are used to help
focus the electron beam
Linear acceleration
–
The
Stanford University superconducting linear accelerator, housed on campus below the Hansen Labs until 2007. This facility is separate from
SLAC
Linear acceleration
–
Steel casting undergoing x-ray using the linear accelerator at
Goodwin Steel Castings Ltd
26.
Gravity
–
Gravity, or gravitation, is a natural phenomenon by which all things with mass are brought toward one another, including planets, stars and galaxies. Since energy and mass are equivalent, all forms of energy, including light, on Earth, gravity gives weight to physical objects and causes the ocean tides. Gravity has a range, although its effects become increasingly weaker on farther objects. The most extreme example of this curvature of spacetime is a hole, from which nothing can escape once past its event horizon. More gravity results in time dilation, where time lapses more slowly at a lower gravitational potential. Gravity is the weakest of the four fundamental interactions of nature, the gravitational attraction is approximately 1038 times weaker than the strong force,1036 times weaker than the electromagnetic force and 1029 times weaker than the weak force. As a consequence, gravity has an influence on the behavior of subatomic particles. On the other hand, gravity is the dominant interaction at the macroscopic scale, for this reason, in part, pursuit of a theory of everything, the merging of the general theory of relativity and quantum mechanics into quantum gravity, has become an area of research. While the modern European thinkers are credited with development of gravitational theory, some of the earliest descriptions came from early mathematician-astronomers, such as Aryabhata, who had identified the force of gravity to explain why objects do not fall out when the Earth rotates. Later, the works of Brahmagupta referred to the presence of force, described it as an attractive force. Modern work on gravitational theory began with the work of Galileo Galilei in the late 16th and this was a major departure from Aristotles belief that heavier objects have a higher gravitational acceleration. Galileo postulated air resistance as the reason that objects with less mass may fall slower in an atmosphere, galileos work set the stage for the formulation of Newtons theory of gravity. In 1687, English mathematician Sir Isaac Newton published Principia, which hypothesizes the inverse-square law of universal gravitation. Newtons theory enjoyed its greatest success when it was used to predict the existence of Neptune based on motions of Uranus that could not be accounted for by the actions of the other planets. Calculations by both John Couch Adams and Urbain Le Verrier predicted the position of the planet. A discrepancy in Mercurys orbit pointed out flaws in Newtons theory, the issue was resolved in 1915 by Albert Einsteins new theory of general relativity, which accounted for the small discrepancy in Mercurys orbit. The simplest way to test the equivalence principle is to drop two objects of different masses or compositions in a vacuum and see whether they hit the ground at the same time. Such experiments demonstrate that all objects fall at the rate when other forces are negligible
Gravity
–
Sir Isaac Newton, an English physicist who lived from 1642 to 1727
Gravity
Gravity
–
Two-dimensional analogy of spacetime distortion generated by the mass of an object. Matter changes the geometry of spacetime, this (curved) geometry being interpreted as gravity. White lines do not represent the curvature of space but instead represent the
coordinate system imposed on the curved spacetime, which would be
rectilinear in a flat spacetime.
Gravity
–
Ball falling freely under gravity. See text for description.
27.
Osseous ampullae
–
The semicircular canals or semicircular ducts are three semicircular, interconnected tubes located in the innermost part of each ear, the inner ear. The three canals are the horizontal, superior and posterior semicircular canals, the semicircular canals are a component of the bony labyrinth. At one end of each of the canals is a dilated sac called an osseous ampulla which is more than twice the diameter of the canal. Each ampulla contains an ampulla crest, the crista ampullaris which consists of a gelatinous cap called a cupula. The anterior and posterior canals are oriented vertically at right angles to each other. The lateral semicircular canal is about a 30-degree angle from the horizontal plane, the orientations of the canals cause a different canal to be stimulated by movement of the head in different planes. The horizontal canal detects angular acceleration of the head when the head is turned, when the head changes position, the endolymph in the canals lags behind due to inertia and this acts on the cupula which bends the cilia of the hair cells. The stimulation of the hair cells sends the message to the brain that acceleration is taking place, the ampullae open into the vestibule by five orifices, one of the apertures being common to two of the canals. Among species of mammals, the size of the canals is correlated with their type of locomotion. Specifically, species that are agile and have fast, jerky locomotion have larger canals relative to their size than those that move more cautiously. The lateral or horizontal canal is the shortest of the three canals, movement of fluid within this canal corresponds to rotation of the head around a vertical axis, or in other words rotation in the transverse plane. The lateral canal of one ear is nearly in the same plane as that of the other. The superior or anterior semicircular canal is a part of the system and detects rotations of the head in around the lateral axis. This occurs, for example, when nodding your head, as part of the vestibular system it detects rotation of the head around a rostral-caudal axis. It describes about two-thirds of a circle, the posterior semicircular canal is a part of the vestibular system detects rotation of the head around a rostral-caudal axis, or in other words rotation in the coronal plane. This occurs, for example, when you move your head to touch your shoulders and it is directed superiorly, as per its nomenclature, and posteriorly, nearly parallel to the posterior surface of the petrous bone. The vestibular aqueduct is immediately medial to it, the posterior canal is part of the bony labyrinth and is used by the vestibular system to detect rotations of the head in the sagittal plane. It is the longest of the three canals, measuring from 18 to 22 mm and its lower or ampullated end opens into the lower and back part of the vestibule, its upper into the crus commune
Osseous ampullae
–
Inner ear illustration showing semicircular canal,
hair cells, ampulla,
cupula,
vestibular nerve, & fluid
28.
Internal acoustic meatus
–
The internal auditory meatus is a canal within the petrous part of the temporal bone of the skull between the posterior cranial fossa and the inner ear. It also contains the vestibular ganglion, the opening to the meatus is called the porus acusticus internus, or its English translation, the internal acoustic opening. It is located inside the posterior fossa of the skull. The size varies considerably, its margins are smooth and rounded, the internal auditory meatus is short and runs laterally into the bone. At its end are the openings for three different canals, one of which is the facial canal, the facial nerve travels through the facial canal, eventually exiting the skull at the stylomastoid foramen. The antero-superior part transmits the nerve and nervus intermedius and is separated from the postero-superior section. The falciform crest or transverse crest separates the superior part from the inferior part, the cochlear nerve runs antero-inferiorly and the inferior vestibular nerve runs postero-inferiorly
Internal acoustic meatus
–
Internal acoustic meatus
Internal acoustic meatus
–
Left
temporal bone. Inner surface.
Internal acoustic meatus
–
Tympanic cavity. Facial canal. Internal carotid artery.
29.
Microtubule
–
Microtubules are a component of the cytoskeleton, found throughout the cytoplasm. These tubular polymers of tubulin can grow as long as 50 micrometres and are highly dynamic, the outer diameter of a microtubule is about 24 nm while the inner diameter is about 12 nm. They are found in cells, as well as some bacteria. Microtubules are very important in a number of cellular processes and they are involved in maintaining the structure of the cell and, together with microfilaments and intermediate filaments, they form the cytoskeleton. They also make up the structure of cilia and flagella. They are also involved in chromosome separation, and are the constituents of mitotic spindles. There are many proteins bind to microtubules, including the motor proteins kinesin and dynein, severing proteins like katanin. Recently an actin-like protein has found in a gram-positive bacterium Bacillus thuringiensis. Tubulin and microtubule-mediated processes, like cell locomotion, were seen by early microscopists, in eukaryotes, microtubules are long, hollow cylinders made up of polymerised α- and β-tubulin dimers. The inner space of the hollow microtubule cylinders is referred to as the lumen, the α and β-tubulin subunits are approximately 50% identical at the amino acid level, and each have a molecular weight of approximately 50 kDa. These α/β-tubulin dimers polymerize end-to-end into linear protofilaments that associate laterally to form a single microtubule, typically, microtubules are formed by the parallel association of thirteen protofilaments, although microtubules composed of fewer or more protofilaments have been observed in vitro. Microtubules have a polarity that is critical for their biological function. Tubulin polymerizes end to end, with the β-subunits of one tubulin dimer contacting the α-subunits of the next dimer, therefore, in a protofilament, one end will have the α-subunits exposed while the other end will have the β-subunits exposed. These ends are designated the and ends, respectively, while microtubule elongation can occur at both the and ends, it is significantly more rapid at the end. The lateral association of the protofilaments generates a pseudo-helical structure, with one turn of the helix containing 13 tubulin dimers, each from a different protofilament. In the most common 13-3 architecture, the 13th tubulin dimer interacts with the tubulin dimer with a vertical offset of 3 tubulin monomers due to the helicity of the turn. There are other alternative architectures, such as 11-3, 12-3, 14-3, 15-4, or 16-4, Microtubules can also morph into other forms such as helical filaments, which are observed in protist organisms like foraminifera. There are two types of interactions that can occur between the subunits of lateral protofilaments within the microtubule called the A-type and B-type lattices
Microtubule
–
Just as our bodies rely on bones for structural support, our cells rely on a cellular skeleton. In addition to helping cells keep their shape, this cytoskeleton transports material within cells and coordinates cell division. Microtubules are shown here as thin strands
Microtubule
–
Structure of a microtubule. The ring shape depicts a microtubule in cross-section, showing the 13 protofilaments surrounding a hollow center.
Microtubule
–
Components of the
eukaryotic cytoskeleton.
Actin filaments are shown in red,
microtubules are in green, and the
nuclei are in blue. The cystoskeleton provides the cell with an inner framework and enables it to move and change shape.
Microtubule
–
Image of a fibroblast cell containing fluorescently labeled actin (red) and microtubules (green).
30.
Actin
–
Actin is a family of globular multi-functional proteins that form microfilaments. It is found in all eukaryotic cells, where it may be present at a concentration of over 100 μM. Many of these processes are mediated by extensive and intimate interactions of actin with cellular membranes, in vertebrates, three main groups of actin isoforms, alpha, beta, and gamma have been identified. The alpha actins, found in tissues, are a major constituent of the contractile apparatus. The beta and gamma actins coexist in most cell types as components of the cytoskeleton and it is believed that the diverse range of structures formed by actin enabling it to fulfill such a large range of functions is regulated through the binding of tropomyosin along the filaments. Other enzymes or organelles such as cilia can be anchored to this scaffolding in order to control the deformation of the cell membrane. It can also produce movement either by itself or with the help of molecular motors, Actin therefore contributes to processes such as the intracellular transport of vesicles and organelles as well as muscular contraction and cellular migration. It therefore plays an important role in embryogenesis, the healing of wounds, the evolutionary origin of actin can be traced to prokaryotic cells, which have equivalent proteins. Actin homologs from prokaryotes and archaea polymerize into different helical or linear filaments consisting of one or multiple strands, however the in-strand contacts and nucleotide binding sites are preserved in prokaryotes and in archaea. Lastly, actin plays an important role in the control of gene expression, a large number of illnesses and diseases are caused by mutations in alleles of the genes that regulate the production of actin or of its associated proteins. The production of actin is also key to the process of infection by some pathogenic microorganisms, mutations in the different genes that regulate actin production in humans can cause muscular diseases, variations in the size and function of the heart as well as deafness. The make-up of the cytoskeleton is also related to the pathogenicity of bacteria and viruses. Actin was first observed experimentally in 1887 by W. D. Halliburton, in 1942, Straub developed a novel technique for extracting muscle protein that allowed him to isolate substantial amounts of relatively pure actin. Straubs method is essentially the same as used in laboratories today. Adding ATP to a mixture of both proteins causes a decrease in viscosity, the hostilities of World War II meant Szent-Gyorgyi and Straub were unable to publish the work in Western scientific journals. Actin therefore only became known in the West in 1945. Straub suggested that the transformation of ATP-bound actin to ADP-bound actin played a role in muscular contraction, in fact, this is true only in smooth muscle, and was not supported through experimentation until 2001. The amino acid sequencing of actin was completed by M. Elzinga, the crystal structure of G-actin was solved in 1990 by Kabsch and colleagues
Actin
–
Nobel Prize winning
physiologist Albert von Szent-Györgyi Nagyrápolt, co-discoverer of actin with
Brunó Ferenc Straub.
Actin
–
Ribbon diagram of G-actin.
ADP bound to actin's
active site (multi color sticks near center of figure) as well as a complexed
calcium dication (green sphere) are highlighted.
Actin
–
Fluorescence micrograph showing F-actin (in green) in rat
fibroblasts.
Actin
–
Structure of the C-terminal subdomain of
villin, a protein capable of splitting microfilaments.
31.
Basement membrane
–
The basement membrane is a thin, fibrous, extracellular matrix of tissue that separates the epithelium, mesothelium and endothelium from underlying connective tissue. As seen with electron microscope, the basement membrane is composed of two layers, the lamina and the underlying layer of reticular connective tissue. The underlying connective tissue attaches to the lamina with collagen VII anchoring fibrils. The two layers together are referred to as the basement membrane. The basal lamina layer can further be divided into two layers, the clear layer closer to the epithelium is called the lamina lucida, while the dense layer closer to the connective tissue is called the lamina densa. In addition to collagen, this supportive matrix contains intrinsic macromolecular components, the lamina densa, whose collagen IV fibers are coated with the heparan sulfate-rich proteoglycan perlecan, and the lamina lucida together make up the basal lamina. Integrins are not part of the lamina, they are part of desmosomes which are in the basement membrane. This is achieved by cell-matrix adhesions through substrate adhesion molecules, the basement membrane acts as a mechanical barrier, preventing malignant cells from invading the deeper tissues. Early stages of malignancy that are limited to the epithelial layer by the basement membrane are called carcinoma in situ. The basement membrane is essential for angiogenesis. Basement membrane proteins have been found to accelerate differentiation of endothelial cells, some diseases result from a poorly functioning basement membrane. The cause can be defects, injuries by the bodys own immune system. Genetic defects in the fibers of the basement membrane cause Alport syndrome. Non-collagenous domain basement membrane collagen type IV is autoantigen of autoantibodies in the autoimmune disease Goodpastures syndrome, a group of diseases stemming from improper function of basement membrane zone are united under the name epidermolysis bullosa. Intima Kefalides, Nicholas A. & Borel, Jacques P. eds, basement membranes, cell and molecular biology
Basement membrane
–
Illustration depicting basement membrane in relation to
epithelium and
endothelium. Also seen are other
extracellular matrix components
32.
Mechanoreceptor
–
A mechanoreceptor is a sensory receptor that responds to mechanical pressure or distortion. Normally there are four types in glabrous mammalian skin, lamellar corpuscles, tactile corpuscles, Merkel nerve endings. Invertebrate mechanoreceptors include campaniform sensilla and slit sensilla, among others, the third-order neurons then send the signal to the somatosensory cortex. More recent work has expanded the role of the cutaneous mechanoreceptors for feedback in fine motor control, in glabrous skin, there are four principal types of mechanoreceptors, each shaped according to its function. The tactile corpuscles respond to touch, and adapt rapidly to changes in texture. The bulbous corpuscles detect tension deep in the skin and fascia, the Merkel nerve endings detect sustained pressure. The lamellar corpuscles in the skin and fascia detect rapid vibrations, receptors in hair follicles sense when a hair changes position. Indeed, the most sensitive mechanoreceptors in humans are the cells in the cochlea of the inner ear. Mechanosensory free nerve endings detect touch, pressure, and stretching, baroreceptors are a type of mechanoreceptor sensory neuron that is excited by stretch of the blood vessel. Cutaneous mechanoreceptors respond to stimuli that result from physical interaction, including pressure. They are located in the skin, like other cutaneous receptors and they are all innervated by Aβ fibers, except the mechanorecepting free nerve endings, which are innervated by Aδ fibers. Cutaneous mechanoreceptors can be categorized by morphology, by kind of sensation they perceive. Furthermore, each has a different receptive field, the Slowly Adapting type 1 mechanoreceptor, with the Merkel corpuscle end-organ, underlies the perception of form and roughness on the skin. They have small receptive fields and produce sustained responses to static stimulation and they also produce sustained responses to static stimulation, but have large receptive fields. The Rapidly Adapting or Meissner corpuscle end-organ mechanoreceptor underlies the perception of flutter and they have small receptive fields and produce transient responses to the onset and offset of stimulation. The Pacinian corpuscle or Vater-Pacinian corpuscles or Lamellar corpuscles underlie the perception of high frequency vibration and they also produce transient responses, but have large receptive fields. Cutaneous mechanoreceptors can also be separated into categories based on their rates of adaptation, when a mechanoreceptor receives a stimulus, it begins to fire impulses or action potentials at an elevated frequency. The cell, however, will adapt to a constant or static stimulus
Mechanoreceptor
–
Tactile receptors.
33.
Microvillus
–
Thousands of microvilli form a structure called the brush border that is found on the apical surface of some epithelial cells, such as the small intestines. Microvilli are observed on the surface of eggs, aiding in the anchoring of sperm cells that have penetrated the extracellular coat of egg cells. Clustering of elongated microtubules around a sperm allows for it to be drawn closer and they are large objects that increase surface area for absorption. Microvilli are also of importance on the surface of white blood cells. Microvilli are covered in plasma membrane, which encloses cytoplasm and microfilaments, though these are cellular extensions, there are little or no cellular organelles present in the microvilli. Each microvillus has a bundle of cross-linked actin filaments, which serves as its structural core. 20 to 30 tightly bundled actin filaments are cross-linked by bundling proteins fimbrin, villin and espin to form the core of the microvilli. In the enterocyte microvillus, the core is attached to the plasma membrane along its length by lateral arms made of myosin 1a. Myosin 1a functions through a site for filamentous actin on one end. As mentioned, microvilli are formed as cell extensions from the membrane surface. Actin filaments, present in the cytosol, are most abundant near the cell surface and these filaments are thought to determine the shape and movement of the plasma membrane. The nucleation of actin fibers occurs as a response to external stimuli and this could account for the uniformity of the microvilli, which are observed to be of equal length and diameter. This nucleation process occurs from the end, allowing rapid growth from the plus end. Though the length and composition of microvilli is consistent within a group of homogenous cells. For example, the microvilli in the small and large intestines in mice are different in length. Microvilli function as the surface of nutrient absorption in the gastrointestinal tract. Because of this function, the microvillar membrane is packed with enzymes that aid in the breakdown of complex nutrients into simpler compounds that are more easily absorbed. For example, enzymes that digest carbohydrates called glycosidases are present at concentrations on the surface of enterocyte microvilli
Microvillus
–
Enterocytes with microvilli
34.
Aquaporin
–
The 2003 Nobel Prize in Chemistry was awarded jointly to Peter Agre for the discovery of aquaporins, and Roderick MacKinnon for his work on the structure and mechanism of potassium channels. Genetic defects involving aquaporin genes have been associated with human diseases including nephrogenic diabetes insipidus. The mechanism of facilitated water transport and the existence of water pores has attracted researchers since 1957. In most cells, water moves in and out by osmosis through the component of cell membranes. Due to the high water permeability of some epithelial cells. Solomon and his co-workers performed pioneering work on water permeability across the membrane in the late 1950s. Studies by Parisi, Edelman, Carvounis et al. accented not only the importance of the presence of water channels, in 1990, Verkmans experiments demonstrated functional expression of water channels, indicating that water channels are effectively proteins. It was not until 1992 that the first aquaporin, aquaporin-1, was reported by Peter Agre, in 1999, together with other research teams, Agre reported the first high-resolution images of the three-dimensional structure of an aquaporin, namely, aquaporin-1. The pioneering research and subsequent discovery of water channels by Agre, Agre said he discovered aquaporins by serendipity. He had been studying the Rh blood group antigens and had isolated the Rh molecule, at first they thought it was a Rh molecule fragment, or a contaminant, but it turned out to be a new kind of molecule with unknown function. It was present in such as kidney tubules and red blood cells, and related to proteins of diverse origins, such as in fruit fly brain, bacteria, the lens of the eye. However the first report of protein-mediated water transport through membranes was by Gheorghe Benga in 1986 and this led to a controversy that Bengas work had been adequately recognized neither by Agre nor by the Nobel Prize Committee. Aquaporins are the system for cells. Water moves through cells in a way, most rapidly in tissues that have aquaporin water channels. For many years, scientists assumed that water leaked through the cell membrane, however, this did not explain how water could move so quickly through some cells. Aquaporins selectively conduct water molecules in and out of the cell, while preventing the passage of ions, also known as water channels, aquaporins are integral membrane pore proteins. Some of them, known as aquaglyceroporins, also other small uncharged dissolved molecules including ammonia, CO2, glycerol. For example, the aquaporin 3 channel has a width of 8–10 Ångströms
Aquaporin
–
Illustration of aquaporin molecule
Aquaporin
–
Crystallographic structure of aquaporin 1 (
AQP1) PDB 1j4n
35.
Reptile
–
Reptiles are tetrapod animals in the class Reptilia, comprising todays turtles, crocodilians, snakes, amphisbaenians, lizards, tuatara, and their extinct relatives. The study of these traditional reptile orders, historically combined with that of amphibians, is called herpetology. Because some reptiles are more related to birds than they are to other reptiles. For this reason, many scientists prefer to consider the birds part of Reptilia as well. Some early examples include the lizard-like Hylonomus and Casineria, in addition to the living reptiles, there are many diverse groups that are now extinct, in some cases due to mass extinction events. In particular, the K–Pg extinction wiped out the pterosaurs, plesiosaurs, ornithischians, and sauropods, as well as species of theropods, crocodyliforms. Modern non-avian reptiles inhabit every continent with the exception of Antarctica, several living subgroups are recognized, Testudines, approximately 400 species, Sphenodontia,1 species, Squamata, over 9,600 species, Crocodilia,25 species, and Aves,10,000 species. Reptiles are tetrapod vertebrates, creatures that either have four limbs or, unlike amphibians, reptiles do not have an aquatic larval stage. As amniotes, reptile eggs are surrounded by membranes for protection and transport, many of the viviparous species feed their fetuses through various forms of placenta analogous to those of mammals, with some providing initial care for their hatchlings. In the 18th century, the reptiles were, from the outset of classification, the terms reptile and amphibian were largely interchangeable, reptile being preferred by the French. Josephus Nicolaus Laurenti was the first to use the term Reptilia for an expanded selection of reptiles. Today, the two groups are commonly treated under the same heading as herptiles. He subsequently proposed the names of Sauropsida and Ichthyopsida for the two groups. In 1866, Haeckel demonstrated that vertebrates could be divided based on their strategies, and that reptiles, birds. The terms Sauropsida and Theropsida were used again in 1916 by E. S, Goodrich to distinguish between lizards, birds, and their relatives on the one hand and mammals and their extinct relatives on the other. Goodrich supported this division by the nature of the hearts and blood vessels in each group, according to Goodrich, both lineages evolved from an earlier stem group, Protosauria in which he included some animals today considered reptile-like amphibians, as well as early reptiles. Watson observed that the first two groups diverged very early in history, so he divided Goodrichs Protosauria between them. He also reinterpreted Sauropsida and Theropsida to exclude birds and mammals, thus his Sauropsida included Procolophonia, Eosuchia, Millerosauria, Chelonia, Squamata, Rhynchocephalia, Crocodilia, thecodonts, non-avian dinosaurs, pterosaurs, ichthyosaurs, and sauropterygians
Reptile
Reptile
–
Reptiles, from Nouveau Larousse Illustré, 1897-1904: Notice the inclusion of
amphibians (below the crocodiles).
Reptile
–
An "antediluvian monster", a
Mosasaurus discovered in a
Maastricht limestone quarry, 1770 (contemporary engraving)
Reptile
–
The traditional class Reptilia (green field) includes all
amniotes which are not mammals or birds, making it a
paraphyletic group.
36.
Bird
–
Birds live worldwide and range in size from the 5 cm bee hummingbird to the 2.75 m ostrich. They rank as the class of tetrapods with the most living species, at ten thousand. As a subgroup of Reptilia, birds are the closest living relatives of crocodilians, while birds, the fossil record indicates that birds are also the last surviving representatives of dinosauria, having evolved from feathered ancestors within the theropod group of saurischian dinosaurs. True birds first appeared during the Cretaceous period, around 100 million years ago, dNA-based evidence finds that birds diversified dramatically around the time of the Cretaceous–Palaeogene extinction event which killed off all other dinosaur lineages. Birds, especially those in the continents, survived this event. Primitive bird-like dinosaurs that lie outside class Aves proper, in the broader group Avialae, have been found dating back to the mid-Jurassic period. Birds have wings which are more or less developed depending on the species, the digestive and respiratory systems of birds are also uniquely adapted for flight. Some bird species of aquatic environments, particularly seabirds and some waterbirds, have evolved for swimming. Many species annually migrate great distances, Birds are social, communicating with visual signals, calls, and bird songs, and participating in such social behaviours as cooperative breeding and hunting, flocking, and mobbing of predators. The vast majority of species are socially monogamous, usually for one breeding season at a time, sometimes for years. Other species have breeding systems that are polygynous or, rarely, Birds produce offspring by laying eggs which are fertilised through sexual reproduction. They are usually laid in a nest and incubated by the parents, most birds have an extended period of parental care after hatching. Some birds, such as hens, lay eggs even when not fertilised, songbirds, parrots, and other species are popular as pets. Guano is harvested for use as a fertiliser, Birds prominently figure throughout human culture. About 120–130 species have become extinct due to human activity since the 17th century, human activity threatens about 1,200 bird species with extinction, though efforts are underway to protect them. Recreational birdwatching is an important part of the ecotourism industry, the first classification of birds was developed by Francis Willughby and John Ray in their 1676 volume Ornithologiae. Carl Linnaeus modified that work in 1758 to devise the taxonomic classification system currently in use, Birds are categorised as the biological class Aves in Linnaean taxonomy. Phylogenetic taxonomy places Aves in the dinosaur clade Theropoda, Aves and a sister group, the clade Crocodilia, contain the only living representatives of the reptile clade Archosauria
Bird
–
Archaeopteryx lithographica is often considered the oldest known true bird.
Bird
Bird
–
Confuciusornis sanctus, a Cretaceous bird from China
Bird
–
The range of the
house sparrow has expanded dramatically due to human activities.
37.
Crocodilian
–
Crocodilia is an order of mostly large, predatory, semiaquatic reptiles. Crocodilians appeared 83.5 million years ago in the Late Cretaceous period and are the closest living relatives of birds, members of the orders total group, the clade Pseudosuchia, appeared about 250 million years ago in the Early Triassic period, and diversified during the Mesozoic era. The order Crocodilia includes the true crocodiles, the alligators and caimans, although the term crocodiles is sometimes used to refer to all of these, a less ambiguous vernacular term for this group is crocodilians. Large, solidly built, lizard-like reptiles, crocodilians have flattened snouts, laterally compressed tails, and eyes, ears. They swim well and can move on land in a high walk and their skin is thick and covered in non-overlapping scales. They have conical, peg-like teeth and a powerful bite and they have a four-chambered heart and, somewhat like birds, a unidirectional looping system of airflow within the lungs, but like other non-avian reptiles they are ectotherms. Crocodilians are found mainly in lowlands in the tropics, but alligators also live in the southeastern United States, Crocodilians are typically solitary and territorial, though cooperative feeding does occur. During breeding, dominant males try to monopolise available females, females lay eggs in holes or in mounds and, unlike most other reptiles, care for their hatched young. Eight species of crocodilians are known to have attacked humans, the largest number of attacks comes from the Nile crocodile. Artistic and literary representations of crocodilians have appeared in cultures around the world since at least Ancient Egypt. Crocodilia and Crocodylia have been used interchangeably for decades starting with Schmidts redescription of the group from the defunct term Loricata. Schmidt used the older term Crocodilia, based on Owens original name for the group, shortly after, Wermuth opted for Crocodylia as the proper name for this redescribed group, basing it on the type genus Crocodylus. Dundee—in a revision of many reptilian and amphibian names—argued strongly for Crocodylia to be the spelling for the group, however, it was not until the advent of cladistics and phylogenetic nomenclature that a more solid justification for assuming one spelling over the other was proposed. Prior to 2003, Crocodilia/Crocodylia was a group that encompassed the modern-day animals as well as their distant relatives now in the larger groups called Crocodylomorpha. Under its current definition Crocodylia is restricted to only the most recent ancestor of todays modern-day crocodilians and this distinction is more important for paleontologists studying crocodilian evolution. As such, the alternate spellings Crocodilia and Crocodylia are still used interchangeably in the neontological literature, Crocodilia appears to be a Latinizing of the Greek κροκόδειλος, which means both lizard and Nile crocodile. Crocodylia, as coined by Wermuth, in regards to the genus Crocodylus appears to be derived from the ancient Greek κρόκη —meaning shingle or pebble—and δρîλος or δρεîλος for worm, the name may refer to the animals habit of basking on the pebbled shores of the Nile. They tend to be sexually dimorphic, with much larger than females
Crocodilian
Crocodilian
–
Mounted skeleton and taxidermy of Nile crocodile
Crocodilian
–
Crocodilians, like this
spectacled caiman, can hide in water with only their nostrils, eyes and ears at the surface.
Crocodilian
–
Nile crocodile swimming. Sequence runs from right to left.
38.
Monotreme
–
Monotremes are basal mammals that lay eggs instead of giving birth to live young like marsupials and placental mammals. The only surviving examples of monotremes are all indigenous to Australia and New Guinea, the existing monotreme species are the platypus and four species of echidnas. There is currently debate regarding monotreme taxonomy. The word monotreme comes from the Greek μονός, monos and τρῆμα, trema, in common with reptiles and marsupials, monotremes lack the connective structure which in placental mammals is the primary communication route between the right and left brain hemispheres. Extant monotremes lack teeth as adults, fossil forms and modern platypus young have a tribosphenic form of molars, which is one of the hallmarks of extant mammals. Some recent work suggests that monotremes acquired this form of molar independently of placental mammals and marsupials, toothloss in modern monotremes might be related to their development of electrolocation. Monotreme jaws are constructed differently from those of other mammals. Nonetheless, findings on the extinct species Teinolophos confirm that suspended ear bones evolved independently among monotremes, the external opening of the ear still lies at the base of the jaw. DNA suggests that while this trait is shared and is synapomorphic with birds, platypuses are still mammals, l-ascorbic acid is synthesized only in the kidneys. The monotremes also have extra bones in the girdle, including an interclavicle and coracoid. Monotremes retain a reptile-like gait, with legs on the sides of, rather than underneath, the monotreme leg bears a spur in the ankle region, the spur is not functional in echidnas, but contains a powerful venom in the male platypus. This venom is derived from b-defensins, proteins that are present in mammals that create holes in viral and bacterial pathogens, some reptile venom is also composed of different types of b-defensins, another trait shared with reptiles. It is thought to be an ancient mammalian characteristic, as many non-monotreme archaic mammal groups also possess venomous spurs, the penis only carries semen, urine is excreted through the cloaca. The monotreme penis is similar to a penis, and is covered by a preputial sac. However, the egg is retained for some time within the mother, which provides the egg with nutrients. Newborn monotremes are larval and fetus-like, much like those of marsupials, Monotremes, like all mammals, lactate, but have no defined nipples, excreting the milk from their mammary glands via openings in their skin. All species are long-lived, with low rates of reproduction and relatively prolonged parental care of infants, the zygotes of monotremes, however, undergo meroblastic division, which causes the ovum to split but not completely. Monotremes metabolic rate is low by mammalian standards
Monotreme
Monotreme
–
Platypus
Monotreme
–
Long-beaked echidna
Monotreme
–
A 100-million-year-old
Steropodon jaw on display at the American Museum of Natural History, New York City, USA
39.
Amniote
–
Amniotes are a clade of tetrapod vertebrates comprising the reptiles, birds, and mammals that lay their eggs on land or retain the fertilized egg within the mother. They are distinguished from the anamniotes, which lay their eggs in water. Older sources, particularly prior to the 20th century, may refer to amniotes as higher vertebrates and anamniotes as lower vertebrates, based on the discredited idea of the Great Chain of Being. Amniotes are tetrapods that are characterised by having an egg equipped with an amnion, amniotes include synapsids and sauropsids, as well as their ancestors, back to amphibians. Amniote embryos, whether laid as eggs or carried by the female, are protected and aided by several extensive membranes, in eutherian mammals, these membranes include the amniotic sac that surrounds the fetus. These embryonic membranes and the lack of a larval stage distinguish amniotes from tetrapod amphibians, the first amniotes, referred to as basal amniotes, resembled small lizards and evolved from the amphibian reptiliomorphs about 312 million years ago, in the Carboniferous geologic period. Their eggs could survive out of the water, allowing amniotes to branch out into drier environments, the eggs could also breathe and cope with wastes, allowing the eggs and the amniotes themselves to evolve into larger forms. From this point the amniotes spread around the globe, eventually to become the dominant land vertebrates, very early in the evolutionary history of amniotes, basal amniotes diverged into two main lines, the synapsids and the sauropsids, both of which persist into the modern era. Amniotes can be characterized in part by embryonic development that includes the formation of several extensive membranes, the amnion, chorion, and allantois. Amniotes develop directly into a form with limbs and a thick stratified epithelium. In amniotes, the transition from a two-layered periderm to cornified epithelium is triggered by thyroid hormone during embryonic development and their kidneys and large intestines are also well-suited to water retention. Most mammals do not lay eggs, but corresponding structures may be found inside the placenta, the ancestors of true amniotes, such as Casineria kiddi, which lived about 340 million years ago, evolved from amphibian reptiliomorphs and resembled small lizards. At the late Devonian mass extinction 360 million years ago, all known tetrapods were essentially aquatic, indeed, many modern day amniotes are dependent on moisture to keep their eggs from desiccating. Although some modern amphibians lay eggs on land, they all lack advanced traits like an amnion, the amniotic egg was formed through a series of evolutionary steps. This allowed the egg to both its size and the rate of gas exchange, permitting a larger, metabolically more active embryo to reach full development before hatching. Further development of the design, like extraembryonic membranes and a shell, were not essential. The only way for the eggs to increase in size would be to develop new internal structures specialized for respiration, as this happened, it would also affect how much the juveniles could grow before they reached adulthood. In fish and amphibians there is one inner membrane, the embryonic membrane
Amniote
Amniote
–
Archaeothyris, one of the most
basal synapsids, first appears in the fossil records about 306 million years ago.
Amniote
–
By the early
Mesozoic, 250 million years ago, sauropsids included the largest animals anywhere. Shown are some
late Jurassic dinosaurs and the early bird
Archaeopteryx perched on a tree stump.
40.
Amphibian
–
Amphibians are ectothermic, tetrapod vertebrates of the class Amphibia. They inhabit a variety of habitats, with most species living within terrestrial, fossorial, arboreal or freshwater aquatic ecosystems. Thus amphibians typically start out as larvae living in water, the young generally undergo metamorphosis from larva with gills to an adult air-breathing form with lungs. Amphibians use their skin as a respiratory surface and some small terrestrial salamanders and frogs lack lungs. They are superficially similar to lizards but, along with mammals and birds, reptiles are amniotes, the earliest amphibians evolved in the Devonian period from sarcopterygian fish with lungs and bony-limbed fins, features that were helpful in adapting to dry land. They diversified and became dominant during the Carboniferous and Permian periods, over time, amphibians shrank in size and decreased in diversity, leaving only the modern subclass Lissamphibia. The three modern orders of amphibians are Anura, Urodela, and Apoda, the number of known amphibian species is approximately 7,000, of which nearly 90% are frogs. The smallest amphibian in the world is a frog from New Guinea with a length of just 7.7 mm. The largest living amphibian is the 1.8 m Chinese giant salamander, the study of amphibians is called batrachology, while the study of both reptiles and amphibians is called herpetology. The word amphibian is derived from the Ancient Greek term ἀμφίβιος, the term was initially used as a general adjective for animals that could live on land or in water, including seals and otters. Traditionally, the class Amphibia includes all tetrapod vertebrates that are not amniotes, the numbers of species cited above follows Frost and the total number of known amphibian species is over 7,000, of which nearly 90% are frogs. With the phylogenetic classification, the taxon Labyrinthodontia has been discarded as it is a group without unique defining features apart from shared primitive characteristics. Classification varies according to the phylogeny of the author and whether they use a stem-based or a node-based classification. The phylogeny of Paleozoic amphibians is uncertain, and Lissamphibia may possibly fall within groups, like the Temnospondyli or the Lepospondyli. If the common ancestor of amphibians and amniotes is included in Amphibia, all modern amphibians are included in the subclass Lissamphibia, which is usually considered a clade, a group of species that have evolved from a common ancestor. The three modern orders are Anura, Caudata, and Gymnophiona, although the fossils of several older proto-frogs with primitive characteristics are known, the oldest true frog is Prosalirus bitis, from the Early Jurassic Kayenta Formation of Arizona. It is anatomically similar to modern frogs. The oldest known caecilian is another Early Jurassic species, Eocaecilia micropodia, the earliest salamander is Beiyanerpeton jianpingensis from the Late Jurassic of northeastern China
Amphibian
–
Triadobatrachus massinoti, a proto-frog from the Early Triassic of Madagascar
Amphibian
Amphibian
–
Top: Restoration of Eusthenopteron, a fully aquatic lobe-finned fish Bottom: Restoration of
Tiktaalik, an advanced tetrapodomorph fish
Amphibian
41.
Osteichthyes
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Osteichthyes /ˌɒstiːˈɪkθi. iːz/, popularly referred to as the bony fish, is a diverse taxonomic group of fish that have skeletons primarily composed of bone tissue, as opposed to cartilage. The vast majority of fish are members of Osteichthyes, which is a diverse and abundant group consisting of 45 orders. It is the largest class of vertebrates in existence today, the group Osteichthyes is divided into the ray-finned fish and lobe-finned fish. The oldest known fossils of fish are about 420 million years ago. Osteichthyes can be compared to Euteleostomi, in paleontology, the terms are synonymous. However, recently published phylogenetic trees treat the Osteichthyes as a clade, bony fish are characterized by a relatively stable pattern of cranial bones, rooted, medial insertion of mandibular muscle in the lower jaw. The head and pectoral girdles are covered with large dermal bones, the eyeball is supported by a sclerotic ring of four small bones, but this characteristic has been lost or modified in many modern species. The labyrinth in the ear contains large otoliths. The braincase, or neurocranium, is divided into anterior and posterior sections divided by a fissure. Early bony fish had simple lungs which helped them breathe in low-oxygen water, in many bony fish these have evolved into swim bladders, which help the body create a neutral balance between sinking and floating. They do not have fin spines, but instead support the fin with lepidotrichia and they also have an operculum, which helps them breathe without having to swim. Bony fish have no placoid scales, most have smooth and overlapping ganoid, cycloid or ctenoid scales. Traditionally, Osteichthyes is considered a class, recognised on having a swim bladder, under this classification systems, the Osteichthyes are paraphyletic with regard to land vertebrates as the common ancestor of all Osteichthyes includes tetrapods amongst its descendants. The largest subclass, the Actinopterygii are monophyletic, but with the inclusion of the smaller sub-class Sarcopterygii and this has led to an alternative classification, splitting the Osteichthyes into two full classes. Paradoxically, Sarcopterygii is under this scheme monophyletic, as it includes the tetrapods, most bony fish belong to the ray-finned fish. The phylogeny of living bony fishes is shown in the cladogram, for the majority this is their sole or main means of respiration. Lungfish and other species are capable of respiration through lungs or vascularized swim bladders. Other species can respire through their skin, intestines, and/or stomach, Osteichthyes are primitively ectothermic, meaning that their body temperature is dependent on that of the water
Osteichthyes
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Blue runner
Osteichthyes
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Guiyu oneiros, the earliest known bony fish, lived during the
Late Silurian, 419 million years ago). It has the combination of both
ray-finned and
lobe-finned features, although analysis of the totality of its features place it closer to lobe-finned fish.
Osteichthyes
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ray-finned fish
42.
Swim bladder
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Also, the dorsal position of the swim bladder means the center of mass is below the center of volume, allowing it to act as a stabilizing agent. Additionally, the swim bladder functions as a chamber, to produce or receive sound. The swim bladder is evolutionarily homologous to the lungs, charles Darwin remarked upon this in On the Origin of Species. Darwin reasoned that the lung in air-breathing vertebrates had derived from a primitive swim bladder. In the embryonic stages some species, such as blenny, have lost the swim bladder again. Other fish like the Opah and the Pomfret use their fins to swim. The normally bottom dwelling sea robin can use their fins to produce lift while swimming. The gas/tissue interface at the swim bladder produces a reflection of sound. The cartilaginous fish do not have swim bladders, the swim bladder normally consists of two gas-filled sacs located in the dorsal portion of the fish, although in a few primitive species, there is only a single sac. It has flexible walls that contract or expand according to the ambient pressure, the walls of the bladder contain very few blood vessels and are lined with guanine crystals, which make them impermeable to gases. By adjusting the gas pressurising organ using the gas gland or oval window the fish can obtain neutral buoyancy, due to the dorsal position it gives the fish lateral stability. In physostomous swim bladders, a connection is retained between the bladder and the gut, the pneumatic duct, allowing the fish to fill up the swim bladder by gulping air. Excess gas can be removed in a similar manner, in more derived varieties of fish the connection to the digestive tract is lost. In order to introduce gas into the bladder, the gas gland excretes lactic acid, the resulting acidity causes the hemoglobin of the blood to lose its oxygen which then diffuses partly into the swim bladder. Thus a very high gas pressure of oxygen can be obtained, elsewhere, at a similar structure known as the oval window, the bladder is in contact with blood and the oxygen can diffuse back out again. Together with oxygen, other gases are salted out in the bladder which accounts for the high pressures of other gases as well. The combination of gases in the bladder varies, in shallow water fish, the ratios closely approximate that of the atmosphere, while deep sea fish tend to have higher percentages of oxygen. For instance, the eel Synaphobranchus has been observed to have 75. 1% oxygen,20. 5% nitrogen,3. 1% carbon dioxide, physoclist swim bladders have one important disadvantage, they prohibit fast rising, as the bladder would burst
Swim bladder
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The swim bladder of a
rudd
Swim bladder
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Swim bladder from a bony (teleost) fish
Swim bladder
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Internal positioning of the swim bladder of a
bleak S: anterior, S': posterior portion of the air bladder œ: œsophagus; l: air passage of the air bladder
Swim bladder
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The
West African lungfish possesses a lung homologous to swim bladders
43.
Gnathostome
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Gnathostomata /ˌneɪθoʊstoʊˈmɑːtə/ are the jawed vertebrates. The term derives from Greek, γνάθος jaw + στόμα mouth, gnathostome diversity comprises roughly 60,000 species, which accounts for 99% of all living vertebrates. Another is an immune system that uses VJ recombination to create antigen recognition sites. It is now assumed that Gnathostomata evolved from ancestors that possessed a pair of both pectoral and pelvic fins. The Osteostraci are generally considered the taxon of Gnathostomata. The mouth could then grow bigger and wider, making it possible to capture larger prey and this close and open mechanism would, with time, become stronger and tougher, being transformed into real jaws. Newer research suggests that a branch of Placoderms was most likely the ancestor of present-day gnathostomes and it also indicates that spiny sharks and Chondrichthyes represent a single sister group to the bony fishes. Late Ordovician-aged microfossils of what have been identified as scales of either acanthodians or shark-like fishes, undeniably unambiguous gnathostome fossils, mostly of primitive acanthodians, begin appearing by the early Silurian, and become abundant by the start of the Devonian. Some classification systems have used the term Amphirhina and it is a sister group of the jawless craniates Agnatha. Tree of Life discussion of Gnathostomata The Gill Arches, Meckels Cartilage
Gnathostome
Gnathostome
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Coccosteus
Gnathostome
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Great white shark
Gnathostome
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Acanthodes bronni
