1.
Lymph
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Lymph is the fluid that circulates throughout the lymphatic system. The lymph is formed when the fluid is collected through lymph capillaries. Since the lymph is derived from the fluid, its composition continually changes as the blood. It is generally similar to blood plasma except that it doesnt contain red blood cells, lymph returns proteins and excess interstitial fluid to the bloodstream. Lymph may pick up bacteria and bring them to lymph nodes, metastatic cancer cells can also be transported via lymph. Lymph also transports fats from the system to the blood via chylomicrons. The word lymph is derived from the name of the ancient Roman deity of fresh water, lymph has a composition comparable to that of blood plasma, but it may differ slightly. In particular, the lymph that leaves a lymph node is richer in lymphocytes, likewise, the lymph formed in the human digestive system called chyle is rich in triglycerides, and looks milky white because of its lipid content. As the blood and the surrounding cells continually add and remove substances from the interstitial fluid, thus, lymph when formed is a watery clear liquid with the same composition as the interstitial fluid. However, as it flows through the nodes it comes in contact with blood. Tubular vessels transport lymph back to the blood, ultimately replacing the volume lost during the formation of the interstitial fluid and these channels are the lymphatic channels, or simply lymphatics. Unlike the cardiovascular system, the system is not closed and has no central pump. Lymph transport, therefore, is slow and sporadic, despite low pressure, lymph movement occurs due to peristalsis, valves, and compression during contraction of adjacent skeletal muscle and arterial pulsation. Lymph that enters the lymph vessels from the interstitial spaces usually does not flow backwards along the vessels because of the presence of valves. If excessive hydrostatic pressure develops within the vessels, though, some fluid can leak back into the interstitial spaces. Flow of the lymph in the duct in an average resting person usually approximates 100ml per hour. Accompanied by another ~25ml per hour in other vessels, total lymph flow in the body is about 4 to 5 liters per day. Which can be elevated several folds in case of exercising, thus it can be estimated that without lymphatic flow, an average resting person would die within 24 hours
2.
Latin
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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
3.
Anatomical terminology
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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
4.
Brain
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The brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. The brain is located in the head, usually close to the organs for senses such as vision. The brain is the most complex organ in a vertebrates body, in a human, the cerebral cortex contains approximately 15–33 billion neurons, each connected by synapses to several thousand other neurons. Physiologically, the function of the brain is to exert centralized control over the other organs of the body, the brain acts on the rest of the body both by generating patterns of muscle activity and by driving the secretion of chemicals called hormones. This centralized control allows rapid and coordinated responses to changes in the environment, the operations of individual brain cells are now understood in considerable detail but the way they cooperate in ensembles of millions is yet to be solved. This article compares the properties of brains across the range of animal species. It deals with the human brain insofar as it shares the properties of other brains, the ways in which the human brain differs from other brains are covered in the human brain article. Several topics that might be covered here are instead covered there because more can be said about them in a human context. The most important is brain disease and the effects of brain damage, the shape and size of the brain varies greatly between species, and identifying common features is often difficult. Nevertheless, there are a number of principles of architecture that apply across a wide range of species. Some aspects of structure are common to almost the entire range of animal species, others distinguish advanced brains from more primitive ones. The simplest way to gain information about brain anatomy is by visual inspection, Brain tissue in its natural state is too soft to work with, but it can be hardened by immersion in alcohol or other fixatives, and then sliced apart for examination of the interior. Visually, the interior of the consists of areas of so-called grey matter, with a dark color, separated by areas of white matter. Further information can be gained by staining slices of tissue with a variety of chemicals that bring out areas where specific types of molecules are present in high concentrations. It is also possible to examine the microstructure of brain tissue using a microscope, the brains of all species are composed primarily of two broad classes of cells, neurons and glial cells. Glial cells come in types, and perform a number of critical functions, including structural support, metabolic support, insulation. Neurons, however, are considered the most important cells in the brain. The property that makes neurons unique is their ability to send signals to target cells over long distances
5.
Spinal cord
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The spinal cord is a long, thin, tubular bundle of nervous tissue and support cells that extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column. The brain and spinal cord make up the central nervous system. The spinal cord begins at the bone and extends down to the space between the first and second lumbar vertebrae, it does not extend the entire length of the vertebral column. It is around 45 cm in men and around 43 cm long in women, also, the spinal cord has a varying width, ranging from 13 mm thick in the cervical and lumbar regions to 6.4 mm thick in the thoracic area. The enclosing bony vertebral column protects the relatively shorter spinal cord, the spinal cord is the main pathway for information connecting the brain and peripheral nervous system. The length of the cord is much shorter as compared to the length of the vertebral column. The human spinal cord extends from the magnum and continues through to the conus medullaris near the second lumbar vertebra. It is about 45 cm long in men and around 43 cm in women, ovoid-shaped, the cervical enlargement, located from C5 to T1 spinal segments, is where sensory input comes from and motor output goes to the arms. The lumbar enlargement, located between L1 and S3 spinal segments, handles input and motor output coming from and going to the legs. The spinal cord is continuous with the portion of the medulla. It does not run the length of the vertebral column in adults. It is made of 31 segments that contain sensory nerve root. The first cervical segment is very small and may be absent in most individuals. Nerve roots merge into 31 bilaterally symmetric pairs of spinal nerves, the peripheral nervous system is made up of these spinal roots, nerves, and ganglia. Dorsal root ganglia hold the bodies of dorsal root ganglia in the spinal ganglia related with that spinal segment. Ventral roots only have efferent fibers that arise from motor neurons whose cell bodies are found in the ventral horns of the spinal cord. The spinal cord are protected by three layers of tissue or membranes called meninges, that surround the canal, the dura mater is the outermost layer, and it forms a tough protective coating. Between the dura mater and the bone of the vertebrae is a space called the epidural space
6.
Bilateria
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In contrast, radially symmetrical animals like jellyfish have a topside and a downside, but no identifiable front or back. The bilateria are a group of animals, including the majority of phyla but not sponges, cnidarians, placozoans. For the most part, bilateral embryos are triploblastic, having three germ layers, endoderm, mesoderm, and ectoderm. Nearly all are symmetrical, or approximately so, the most notable exception is the echinoderms, which achieve near-radial symmetry as adults. Except for a few phyla, bilaterians have complete digestive tracts with a separate mouth, some bilaterians lack body cavities, while others display primary body cavities or secondary cavities. The hypothetical most recent common ancestor of all bilateria is termed the Urbilaterian, the nature of the first bilaterian is a matter of debate. The first evidence of bilateria in the record comes from trace fossils in Ediacaran sediments. Earlier fossils are controversial, the fossil Vernanimalcula may be the earliest known bilaterian, fossil embryos are known from around the time of Vernanimalcula, but none of these have bilaterian affinities. Burrows believed to have created by bilaterian life forms have been found in the Tacuarí Formation of Uruguay. There are two main superphyla of Bilateria, the deuterostomes include the echinoderms, hemichordates, chordates, and a few smaller phyla. The protostomes include most of the rest, such as arthropods, annelids, mollusks, flatworms, there are a number of differences, most notably in how the embryo develops. In particular, the first opening of the embryo becomes the mouth in protostomes, many taxonomists now recognize at least two more superphyla among the protostomes, Ecdysozoa and Lophotrochozoa. Within the latter, some researchers also recognize another superphylum, Platyzoa, the arrow worms have proven particularly difficult to classify, with some taxonomists placing them among the deuterostomes and others placing them among the protostomes. The two most recent studies to address the question of chaetognath origins support protostome affinities, a modern consensus phylogeny for Bilateria is shown below, although the position of certain clades are still controversial and the tree has changed considerably between 2000 and 2010. Nodes marked with * have received broad consensus, a prominent alternative tree is championed by Nielsen. Embryological origins of the mouth and anus Tree of Life web project — Bilateria University of California Museum of Paleontology — Systematics of the Metazoa
7.
Sponge
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Sponges are the basalmost clade of animals of the phylum Porifera. Sponges have unspecialized cells that can transform into other types and that often migrate between the cell layers and the mesohyl in the process. Sponges do not have nervous, digestive or circulatory systems, instead, most rely on maintaining a constant water flow through their bodies to obtain food and oxygen and to remove wastes. Sponges are similar to animals in that they are multicellular, heterotrophic, lack cell walls. Unlike other animals, they lack true tissues and organs, and have no body symmetry, the shapes of their bodies are adapted for maximal efficiency of water flow through the central cavity, where it deposits nutrients, and leaves through a hole called the osculum. Many sponges have internal skeletons of spongin and/or spicules of calcium carbonate or silicon dioxide, all sponges are sessile aquatic animals. Although there are species, the great majority are marine species. A few species of sponge that live in food-poor environments have become carnivores that prey mainly on small crustaceans, most species use sexual reproduction, releasing sperm cells into the water to fertilize ova that in some species are released and in others are retained by the mother. The fertilized eggs form larvae which swim off in search of places to settle, sponges are known for regenerating from fragments that are broken off, although this only works if the fragments include the right types of cells. A few species reproduce by budding, the mesohyl functions as an endoskeleton in most sponges, and is the only skeleton in soft sponges that encrust hard surfaces such as rocks. More commonly, the mesohyl is stiffened by mineral spicules, by spongin fibers or both, demosponges use spongin, and in many species, silica spicules and in some species, calcium carbonate exoskeletons. Demosponges constitute about 90% of all known species, including all freshwater ones. The fragile glass sponges, with scaffolding of silica spicules, are restricted to polar regions, fossils of all of these types have been found in rocks dated from 580 million years ago. In addition Archaeocyathids, whose fossils are common in rocks from 530 to 490 million years ago, are now regarded as a type of sponge, the single-celled choanoflagellates resemble the choanocyte cells of sponges which are used to drive their water flow systems and capture most of their food. This along with studies of ribosomal molecules have been used as morphological evidence to suggest sponges are the sister group to the rest of animals. Some studies have shown that sponges do not form a group, in other words do not include all. Recent phylogenetic analyses suggest that comb jellies rather than sponges are the group to the rest of animals. By the 1950s, though, these had been overfished so heavily that the industry almost collapsed, sponges and their microscopic endosymbionts are now being researched as possible sources of medicines for treating a wide range of diseases
8.
Radiata
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Radiata is a taxonomic rank that has been used to classify radially symmetric animals. The term Radiata has united several different groupings of animals, some of which do not form a group under current views of animal phylogeny. Because of this and problems of homoplasy associated with using body symmetry as a phylogenetic character, in the early 19th century, Georges Cuvier united ctenophores and cnidarians in the Radiata. Thomas Cavalier-Smith, in 1983, redefined Radiata as a subkingdom consisting of Myxozoa, Placozoa, Cnidaria, lynn Margulis and K. V. Schwartz later redefined Radiata in their Five Kingdom classification, this time including only Cnidaria and Ctenophora. This definition is similar to the historical descriptor coelenterata which has also proposed as a group encompassing Cnidaria. Although radial symmetry is given as a defining characteristic in animals that have been classified in this group. Echinoderms, for example, exhibit unmistaken bilateral symmetry as larvae, ctenophores exhibit biradial or rotational symmetry, defined by tentacular and pharyngeal axes, on which two anal canals are located in two diametrically opposed quadrants. Some species within the cnidarian class Anthozoa are bilaterally symmetric
9.
Jellyfish
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Jellyfish or jellies are softbodied, free-swimming aquatic animals with a gelatinous umbrella-shaped bell and trailing tentacles. The bell can pulsate to acquire propulsion and locomotion, the tentacles may be utilized to capture prey or defend against predators by emitting toxins in a painful sting. Jellyfish species are classified in the subphylum Medusozoa which makes up a part of the phylum Cnidaria. Jellyfish are found in ocean, from the surface to the deep sea. Scyphozoans are exclusively marine, but some live in freshwater. Large, often colorful, jellyfish are common in coastal zones worldwide, Jellyfish have roamed the seas for at least 500 million years, and possibly 700 million years or more, making them the oldest multi-organ animal. The popular English name jellyfish has been in use since 1796 and it has traditionally also been applied to other animals sharing a superficial resemblance, for example ctenophores were included as jellyfishes. Even some scientists include the phylum ctenophora when they are referring to jellyfish, other scientists prefer to use the more all-encompassing term gelatinous zooplankton, when referring to these, together with other soft-bodied animals in the water column. As jellyfish are not true fish, which are vertebrates, the jellyfish is considered by some to be a misnomer. Public aquaria often use the terms jellies or sea jellies instead, the term jellies may have become more popular than jellyfish. In scientific literature, jelly and jellyfish are often used interchangeably, some sources may use the term jelly to refer to organisms in this taxon, as jellyfish may be considered inappropriate. Many textbooks and sources refer to only scyphozoans as true jellyfish, a group of jellyfish is sometimes called a bloom or a swarm. Bloom is usually used for a group of jellyfish that gather in a small area. Another collective name for a group of jellyfish is a smack, using swarm usually implies some kind of active ability to stay together, which a few species such as Aurelia, the moon jelly, demonstrate. Medusa jellyfish may be classified as scyphomedusae, stauromedusae, cubomedusae, or hydromedusae, the term medusa was coined by Linnaeus in 1752, alluding to the tentacled head of Medusa in Greek mythology. This term refers exclusively to the non-polyp life-stage which occurs in many cnidarians, all medusa-producing species belong to the sub-phylum Medusozoa. In biology, a medusa is a form of cnidarian in which the body is shaped like an umbrella, medusae vary from bell-shaped to the shape of a thin disk, scarcely convex above and only slightly concave below. The digestive cavity consists of the cavity and radiating canals which extend toward the margin, these canals may be simple or branching
10.
Cranial nerves
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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
11.
Ganglion
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In anatomy, a ganglion is a nerve cell cluster or a group of nerve cell bodies located in the autonomic nervous system and sensory system. Ganglia house the bodies of afferent nerves. A pseudoganglion looks like a ganglion but only has nerve fibers and has no nerve cell bodies, in a neurological context, ganglia are composed mainly of somata and dendritic structures which are bundled or connected. Ganglia often interconnect with other ganglia to form a system of ganglia known as a plexus. Ganglia provide relay points and intermediary connections between different neurological structures in the body, such as the peripheral and central nervous systems, among vertebrates there are three major groups of ganglia, Dorsal root ganglia contain the cell bodies of sensory neurons. Cranial nerve ganglia, contain the bodies of cranial nerve neurons. Autonomic ganglia contain the bodies of autonomic nerves. The term ganglion refers to the nervous system. Partly due to ambiguity, the Terminologia Anatomica recommends using the term basal nuclei instead of basal ganglia, however. A pseudoganglion is a thickening of the main part or trunk of a nerve that has the appearance of a ganglion but has only nerve fibers. Pseudoganglia are found in the teres minor muscle and radial nerve, sympathetic ganglion Ganglion cyst Nervous system Neuron
12.
Cranial cavity
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The cranial cavity, or intracranial space, is the space formed inside the skull. It is part of the body cavity. The brain occupies the cranial cavity, which is lined by the meninges, eight fused cranial bones together form the cranial cavity, the frontal, occipital, sphenoid and ethmoid bones, and two each of the parietal and temporal bones. The capacity of an adult human cranial cavity is 1, 200-1,700 cm3, neurocranium Intracranial pressure Anatomy of cranial cavity
13.
Skull
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The skull is a bony structure that forms the head of the skeleton in most vertebrates. It supports the structures of the face and provides a cavity for the brain. The skull is composed of two parts, the cranium and the mandible, in the human these two parts are the neurocranium and the viscerocranium or facial skeleton that includes the mandible as its largest bone. The skull forms the anterior most portion of the skeleton and is a product of cephalisation—housing the brain, and several sensory structures such as the eyes, ears, nose, in the human these sensory structures are part of the facial skeleton. In some animals such as horned ungulates, the skull also has a function by providing the mount for the horns. The English word skull is probably derived from Old Norse skulle, while the Latin word cranium comes from the Greek root κρανίον, the skull is made up of a number of fused flat bones, and contains many foramina and processes, and several cavities or sinuses. For details and the constituent bones, see neurocranium and viscerocranium, the human skull is the bony structure that forms the head in the human skeleton. It supports the structures of the face and forms a cavity for the brain, like the skulls of other vertebrates, it protects the brain from injury. The skull consists of two parts, of different embryological origin—the neurocranium and the facial skeleton, the neurocranium forms the protective cranial cavity that surrounds and houses the brain and brainstem. The facial skeleton is formed by the supporting the face. Except for the mandible, all of the bones of the skull are joined together by sutures—synarthrodial joints formed by bony ossification, sometimes there can be extra bone pieces within the suture known as wormian bones or sutural bones. The human skull is considered to consist of twenty-two bones—eight cranial bones. In the neurocranium these are the bone, two temporal bones, two parietal bones, the sphenoid, ethmoid and frontal bones. The bones of the skeleton are the vomer, two nasal conchae, two nasal bones, two maxilla, the mandible, two palatine bones, two zygomatic bones, and two lacrimal bones. Some of these bones—the occipital, parietal, frontal, in the neurocranium, and the nasal, lacrimal, the skull also contains sinus cavities and numerous foramina. The sinuses are lined with respiratory epithelium and their known functions are the lessening of the weight of the skull, the aiding of resonance to the voice and the warming and moistening of the air drawn through the nasal cavity. The foramina are openings in the skull, the largest of these is the foramen magnum that allows the passage of the spinal cord as well as nerves and blood vessels. The many processes of the include the mastoid process and the zygomatic process
14.
Vertebra
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The basic configuration of a vertebra varies, the large part is the body, and the central part is the centrum. The upper and lower surfaces of the vertebra body give attachment to the intervertebral discs, the posterior part of a vertebra forms a vertebral arch, in eleven parts, consisting of two pedicles, two laminae, and seven processes. The laminae give attachment to the ligamenta flava, there are vertebral notches formed from the shape of the pedicles, which form the intervertebral foramina when the vertebrae articulate. These foramina are the entry and exit conducts for the spinal nerves, the body of the vertebra and the vertebral arch form the vertebral foramen, the larger, central opening that accommodates the spinal canal, which encloses and protects the spinal cord. Vertebrae articulate with other to give strength and flexibility to the spinal column. Structurally, vertebrae are essentially alike across the species, with the greatest difference seen between an aquatic animal and other vertebrate animals. As such, vertebrates take their name from the vertebrae that compose the vertebral column, each vertebra is an irregular bone. The size of the vertebrae varies according to placement in the column, spinal loading, posture. Along the length of the spine the vertebrae change to different needs related to stress. Every vertebra has a body, which consists of a large anterior middle portion called the centrum, the body is composed of cancellous bone, which is the spongy type of osseous tissue, whose micro-anatomy has been specifically studied within the pedicle bones. This cancellous bone is in turn, covered by a coating of cortical bone. The vertebral arch and processes have thicker coverings of cortical bone, the upper and lower surfaces of the body of the vertebra are flattened and rough in order to give attachment to the intervertebral discs. These surfaces are the vertebral endplates which are in contact with the intervertebral discs. The endplates are formed from a layer of the cancellous bone of the vertebral body. The endplates function to contain the adjacent discs, to spread the applied loads. They also act as an interface for the exchange of water. The vertebral arch is formed by pedicles and laminae, two pedicles extend from the sides of the vertebral body to join the body to the arch. The pedicles are short thick processes that extend, one each side, posteriorly, from the junctions of the posteriolateral surfaces of the centrum
15.
Neuroanatomy
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Neuroanatomy is the study of the anatomy and stereotyped organization of nervous systems. In contrast to animals with radial symmetry, whose nervous system consists of a network of cells, animals with bilateral symmetry have segregated, defined nervous systems. Their neuroanatomy is therefore better understood, in vertebrates, the nervous system is segregated into the internal structure of the brain and spinal cord and the routes of the nerves that connect to the rest of the body. The delineation of distinct structures and regions of the system has been critical in investigating how it works. For example, much of what neuroscientists have learned comes from observing how damage or lesions to specific brain areas affects behavior or other neural functions, for information about the composition of animal nervous systems, see nervous system. For information about the structure of the human nervous system. This article discusses information pertinent to the study of neuroanatomy, the first known written record of a study of the anatomy of the human brain is the ancient Egyptian document the Edwin Smith Papyrus. The next major development in neuroanatomy came from the Greek Alcmaeon, who determined that the brain and not the heart ruled the body, herophilus and Erasistratus of Alexandria were perhaps the most influential Greek neuroscientists with their studies involving dissecting the brains. For several hundred years afterward, with the taboo of dissection. However, Pope Sixtus IV effectively revitalized the study of neuroanatomy by altering the papal policy and this resulted in a boom of research in neuroanatomy by artists and scientists of the Renaissance. In 1664, Thomas Willis, a physician and professor at Oxford University, the subsequent three hundred and fifty some years has produced a great deal of documentation and study of the neural systems. At the tissue level, the system is composed of neurons, glial cells. Both neurons and glial cells come in many types, glial cells maintain homeostasis, produce myelin, and provide support and protection for the brains neurons. Some glial cells can even propagate intercellular calcium waves over distances in response to stimulation. The extracellular matrix also provides support on the level for the brains cells. At the organ level, the system is composed of brain regions. These regions are often modular and serve a role within the general pathways of the nervous system. For example, the hippocampus is critical for forming memories, the nervous system also contains nerves, which are bundles of fibers that originate from the brain and spinal cord, and branch repeatedly to innervate every part of the body
16.
Lumbar vertebrae
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The lumbar vertebrae are, in human anatomy, the five vertebrae between the rib cage and the pelvis. They are designated L1 to L5, starting at the top, the lumbar vertebrae help support the weight of the body, and permit movement. The figure on the left depicts the characteristics of the first through fourth lumbar vertebrae. The fifth vertebra contains certain peculiarities, which are detailed below, as with other vertebrae, each lumbar vertebra consists of a vertebral body and a vertebral arch. The vertebral arch, consisting of a pair of pedicles and a pair of laminae, encloses the vertebral foramen, the vertebral body of each lumbar vertebra is large, wider from side to side than from front to back, and a little thicker in front than in back. It is flattened or slightly concave above and below, concave behind, the pedicles are very strong, directed backward from the upper part of the vertebral body, consequently, the inferior vertebral notches are of considerable depth. The pedicles change in morphology from the upper lumbar to the lower lumbar and they increase in sagittal width from 9 mm to up to 18 mm at L5. They increase in angulation in the plane from 10 degrees to 20 degrees by L5. The pedicle is sometimes used as a portal of entrance into the body for fixation with pedicle screws or for placement of bone cement as with kyphoplasty or vertebroplasty. The laminae are broad, short, and strong and they form the posterior portion of the vertebral arch. In the upper lumbar region the lamina are taller than wide, the lamina connects the spinous process to the pedicles. The vertebral foramen within the arch is triangular, larger than the thoracic vertebrae, the spinous process is thick, broad, and somewhat quadrilateral, it projects backward and ends in a rough, uneven border, thickest below where it is occasionally notched. The superior and inferior articular processes are well-defined, projecting respectively upward and downward from the junctions of pedicles, the facets on the superior processes are concave, and look backward and medialward, those on the inferior are convex, and are directed forward and lateralward. The former are wider apart than the latter, since in the column the inferior articular processes are embraced by the superior processes of the subjacent vertebra. The transverse processes are long and slender and they are horizontal in the upper three lumbar vertebrae and incline a little upward in the lower two. They are situated in front of the articular processes instead of them as in the thoracic vertebrae. Three portions or tubercles can be noticed in a process of a lower lumbar vertebrae, the lateral or costiform process, the mammillary process. The costiform is lateral, the mammillary is superior, and the accessory is inferior, the mammillary is connected in the lumbar region with the back part of the superior articular process
17.
Grey matter
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Grey matter is a major component of the central nervous system, consisting of neuronal cell bodies, neuropil, glial cells, synapses, and capillaries. The colour difference arises mainly from the whiteness of myelin, in living tissue, grey matter actually has a very light grey colour with yellowish or pinkish hues, which come from capillary blood vessels and neuronal cell bodies. Grey matter refers to unmyelinated neurons and other cells of the nervous system. It is present in the brain, brainstem and cerebellum, grey matter is distributed at the surface of the cerebral hemispheres and of the cerebellum, as well as in the depths of the cerebrum, cerebellar, brainstem. Grey matter in the cord is known as the grey column which travels down the spinal cord distributed in three grey columns that are presented in an H shape. The forward-facing column is the grey column, the rear-facing one is the posterior grey column. The grey matter on the left and right side is connected by the grey commissure, the grey matter in the spinal cord consists of interneurons, as well as cell bodies. Grey matter undergoes development and growth throughout childhood and adolescence, grey matter contains most of the brains neuronal cell bodies. The grey matter includes regions of the involved in muscle control, and sensory perception such as seeing and hearing, memory, emotions, speech, decision making. The grey matter in the cord is split into three grey columns, The anterior grey column contains motor neurons. These synapse with interneurons and the axons of cells that have travelled down the pyramidal tract and these cells are responsible for the movement of muscles. The posterior grey column contains the points where sensory neurons synapse and these receives sensory information from the body, including fine touch, proprioception, and vibration. This information is sent from receptors of the skin, bones and this information is then transmitted in axons up the spinal cord in spinal tracts, including the dorsal column-medial lemniscus tract and the spinothalamic tract. The lateral grey column is the column of the spinal cord. The grey matter of the cord can be divided into different layers. These describe, in general, the purpose of the cells within the matter of the spinal cord at a particular location. High alcohol consumption has been correlated with significant reductions in grey matter volume, in the current edition of the official Latin nomenclature, Terminologia Anatomica, substantia grisea is used for English grey matter. The adjective grisea for grey is however not attested in classical Latin, the adjective grisea is derived from the French word for grey, gris
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White matter
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White matter refers to areas of the central nervous system that are mainly made up of myelinated axons, also called tracts. White matter is named for its relatively light appearance resulting from the content of myelin. However, the tissue of the freshly cut brain appears pinkish white to the eye because myelin is composed largely of lipid tissue veined with capillaries. Its white color in prepared specimens is due to its preservation in formaldehyde. White matter is composed of bundles of myelinated nerve cell projections, which connect various gray matter areas of the brain to each other, and carry nerve impulses between neurons. Myelin acts as an insulator, which allows electrical signals to jump, rather than coursing through the axon, schüz and Braitenberg note As a rough rule, the number of fibres of a certain range of lengths is inversely proportional to their length. White matter in nonelderly adults is 1. 7–3. 6% blood, the other main component of the brain is grey matter, which is composed of neurons. The substantia nigra is a third colored component found in the brain that appears due to higher levels of melanin in dopaminergic neurons than its nearby areas. Note that white matter can sometimes appear darker than grey matter on a slide because of the type of stain used. Cerebral- and spinal white matter do not contain dendrites, neural cell bodies, or shorter axons, white matter forms the bulk of the deep parts of the brain and the superficial parts of the spinal cord. Aggregates of gray matter such as the ganglia and brain stem nuclei are spread within the cerebral white matter. The fluid-filled cerebral ventricles are also located deep within the white matter. Men have more white matter than females both in volume and in length of myelinated axons, at the age of 20, the total length of myelinated fibers in males is 176,000 km while that of a female is 149,000 km. There is a decline in length with age of about 10% each decade such that a man at 80 years of age has 97,200 km. Most of this reduction is due to the loss of thinner fibers, white matter is the tissue through which messages pass between different areas of gray matter within the central nervous system. The white matter is white because of the fatty substance that surrounds the nerve fibers and this myelin is found in almost all long nerve fibers, and acts as an electrical insulation. This is important because it allows the messages to pass quickly from place to place, unlike gray matter, which peaks in development in a persons twenties, the white matter continues to develop, and peaks in middle age. This claim has been disputed in recent years, however, multiple sclerosis is one of the most common diseases which affect white matter
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Peripheral nervous system
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The peripheral nervous system is one of the two main parts of the nervous system, the other part is the central nervous system. The PNS consists of the nerves and ganglia outside of the brain, the main function of the PNS is to connect the CNS to the limbs and organs, essentially serving as a relay between the brain and spinal cord and the rest of the body. Unlike the CNS, the PNS is not protected by the column and skull, or by the blood–brain barrier. The peripheral nervous system is divided into the nervous system. In the somatic nervous system, the nerves are part of the PNS with the exception of the optic nerve. The second cranial nerve is not a peripheral nerve but a tract of the diencephalon. Cranial nerve ganglia originate in the CNS, however, the remaining ten cranial nerve axons extend beyond the brain and are therefore considered part of the PNS. The autonomic nervous system is a control of smooth muscle. The connection between CNS and organs allows the system to be in two different functional states, sympathetic and parasympathetic, the peripheral nervous system is divided into the somatic nervous system, and the autonomic nervous system. The somatic nervous system is under control, and transmits signals from the brain to end organs such as muscles. The sensory nervous system is part of the nervous system and transmits signals from senses such as taste and touch to the spinal cord. The autonomic nervous system is a system which influences the function of organs outside of voluntary control. The somatic system includes the sensory system and the somatosensory system and consists of sensory nerves and somatic nerves. In the head and neck, cranial nerves carry somatosensory data, there are twelve cranial nerves, ten of which originate from the brainstem, and mainly control the functions of the anatomic structures of the head with some exceptions. The nuclei of the nerve and the optic nerves lie in the forebrain and thalamus, respectively. One unique cranial nerve is the nerve, which receives sensory information from organs in the thorax. The accessory nerve is responsible for innervating the sternocleidomastoid and trapezius muscles, for the rest of the body, Spinal nerves are responsible for somatosensory information. These arise from the spinal cord, usually these arise as a web of interconnected nerves roots that arrange to form single nerves
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Axon
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An axon, is a long, slender projection of a nerve cell, or neuron, that typically conducts electrical impulses away from the neurons cell body. Axons are also known as nerve fibers, the function of the axon is to transmit information to different neurons, muscles and glands. Axon dysfunction has caused many inherited and acquired neurological disorders which can affect both the peripheral and central neurons, nerve fibers are classed into three types – A delta fibers, B fibers, and C fibres. A and B are myelinated and C are unmyelinated, an axon is one of two types of protoplasmic protrusions that extrude from the cell body of a neuron, the other type being dendrites. Axons are distinguished from dendrites by several features, including shape, length, all of these rules have exceptions, however. Axons are covered by a known as axolemma, the cytoplasm of axon is called axoplasm. Some types of neurons have no axon and transmit signals from their dendrites, no neuron ever has more than one axon, however in invertebrates such as insects or leeches the axon sometimes consists of several regions that function more or less independently of each other. Most axons branch, in cases very profusely. Axons make contact with other cells—usually other neurons but sometimes muscle or gland cells—at junctions called synapses, at a synapse, the membrane of the axon closely adjoins the membrane of the target cell, and special molecular structures serve to transmit electrical or electrochemical signals across the gap. Some synaptic junctions appear partway along an axon as it extends—these are called en passant synapses, other synapses appear as terminals at the ends of axonal branches. A single axon, with all its branches together, can innervate multiple parts of the brain. Axons are the transmission lines of the nervous system. Some axons can extend up to one meter or more while others extend as little as one millimeter, the longest axons in the human body are those of the sciatic nerve, which run from the base of the spinal cord to the big toe of each foot. The diameter of axons is also variable, most individual axons are microscopic in diameter. The largest mammalian axons can reach a diameter of up to 20 µm, the squid giant axon, which is specialized to conduct signals very rapidly, is close to 1 millimetre in diameter, the size of a small pencil lead. Axonal arborization also differs from one nerve fiber to the next, axons in the central nervous system typically show complex trees with many branch points. In comparison, the granule cell axon is characterized by a single T-shaped branch node from which two parallel fibers extend. Elaborate arborization allows for the transmission of messages to a large number of target neurons within a single region of the brain
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Oligodendrocyte
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Oligodendrocytes, or oligodendroglia, are a type of neuroglia. Oligodendrocytes do this by creating the myelin sheath, which is 80% lipid, a single oligodendrocyte can extend its processes to 50 axons, wrapping approximately 1 μm of myelin sheath around each axon, Schwann cells, on the other hand, can wrap around only one axon. Each oligodendrocyte forms one segment of myelin for several adjacent axons, most oligodendrocytes develop during embryogenesis and early postnatal life from restricted periventricular germinal regions. Oligodendrocytes are found only in the nervous system, which comprises the brain. They are the last cell type to be generated in the CNS, myelination is only prevalent in a few brain regions at birth and continues into adulthood. The entire process is not complete until about 25–30 years of age, Oligodendrocyte formation in the adult brain is associated with glial-restricted progenitor cells, known as oligodendrocyte progenitor cells. SVZ cells migrate away from germinal zones to populate both developing white and gray matter, where they differentiate and mature into myelin-forming oligodendroglia, however, it is not clear whether all oligodendroglial progenitors undergo this sequence of events. It has been suggested that some undergo apoptosis and others fail to differentiate into mature oligodendroglia, remarkably, oligodendrocyte population originated in the subventricular zona can be dramatically expanded by administering epidermal growth factor. In addition, the system of mammals depends crucially on myelin sheaths. Myelin also increases speed, as saltatory propagation of action potentials occurs at the nodes of Ranvier in between Schwann cells and oligodendrocytes. Furthermore, impulse speed of myelinated axons increases linearly with the axon diameter, the insulation must be proportional to the diameter of the fiber inside. The optimal ratio of axon diameter divided by the fiber diameter is 0.6. In contrast, satellite oligodendrocytes are functionally distinct from other oligodendrocytes and they are not attached to neurons and, therefore, do not serve an insulating role. They remain apposed to neurons and regulate the extracellular fluid, satellite oligodendrocytes are considered to be a part of the gray matter whereas myelinating oligodendrocytes are a part of the white matter. Myelination is an important component of intelligence, neuroscientist Vincent J. Schmithorst proposes that there is a correlation with white matter and intelligence. People with greater white matter had higher IQs, a study done with rats by Janice M. Juraska showed that rats that were raised in an enriched environment had more myelination in their corpus callosum. Diseases that result in injury to the cells include demyelinating diseases such as multiple sclerosis. Trauma to the body, e. g. spinal cord injury, cerebral palsy, is largely congenital and caused by damage to the newly forming brain
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Neurogenesis
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Neurogenesis is the process by which neurons are generated from neural stem cells and progenitor cells. Through precise genetic mechanisms of cell fate determination, many different varieties of excitatory and inhibitory neurons are generated from different kinds of stem cells. Neurogenesis occurs during embryogenesis in all animals and is responsible for producing all the neurons of the organism, prior to the period of neurogenesis, neural stem cells first multiply until the correct number of progenitor cells is achieved. The process of neurogenesis then involves a cell division of the parent neural stem cell. The molecular and genetic factors influencing neurogenesis notably include the Notch pathway, all neurons are thus post-mitotic, and most neurons of the human central nervous system live the lifetime of the individual. In mammals, adult neurogenesis has been shown to occur in three places of the brain, the dentate gyrus of the hippocampus, subventricular zone. In some vertebrates, regenerative neurogenesis has also shown to occur. Likewise, many antidepressants have been shown to increase the rate of neurogenesis within the hippocampus
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Astrocyte
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Astrocytes, also known collectively as astroglia, are characteristic star-shaped glial cells in the brain and spinal cord. The proportion of astrocytes in the brain is not well defined, depending on the counting technique used, studies have found that the astrocyte proportion varies by region and ranges from 20% to 40% of all glia. Astrocytes are a type of cells and they hold various roles. Data suggest that astrocytes also signal to neurons through Ca2+-dependent release of glutamate, such discoveries have made astrocytes an important area of research within the field of neuroscience. Astrocytes are a sub-type of glial cells in the nervous system. They are also known as astrocytic glial cells, star-shaped, their many processes envelop synapses made by neurons. Astrocytes are classically identified using histological analysis, many of these express the intermediate filament glial fibrillary acidic protein. Several forms of astrocytes exist in the nervous system including fibrous, protoplasmic. The fibrous glia are located within white matter, have relatively few organelles. This type often has vascular feet that physically connect the cells to the outside of capillary walls when they are in proximity to them. The protoplasmic glia are the most prevalent and are found in grey matter tissue, possess a quantity of organelles. The radial glia are disposed in planes perpendicular to the axes of ventricles, one of their processes abuts the pia mater, while the other is deeply buried in gray matter. Radial glia are mostly present during development, playing a role in neuron migration, müller cells of the retina and Bergmann glia cells of the cerebellar cortex represent an exception, being present still during adulthood. When in proximity to the pia mater, all three forms of astrocytes send out processes to form the pia-glial membrane, Astrocytes are macroglial cells in the central nervous system. Astrocytes are derived from heterogeneous populations of cells in the neuroepithelium of the developing central nervous system. The resultant patterning along the neuraxis leads to segmentation of the neuroepithelium into progenitor domains for distinct types in the developing spinal cord. On the basis of several studies it is now believed that model also applies to macroglial cell specification. Studies carried out by Hochstim and colleagues have demonstrated that three distinct populations of astrocytes arise from the p1, p2 and p3 domains, previously in medical science, the neuronal network was considered the only important function of astrocytes, and they were looked upon as gap fillers
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Microglia
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Microglia are a type of glial cell located throughout the brain and spinal cord. Microglia account for 10–15% of all cells found within the brain, as the resident macrophage cells, they act as the first and main form of active immune defense in the central nervous system. Microglia are distributed in large non-overlapping regions throughout the CNS, Microglia are key cells in overall brain maintenance—they are constantly scavenging the CNS for plaques, damaged or unnecessary neurons and synapses, and infectious agents. Since these processes must be efficient to prevent potentially fatal damage and this sensitivity is achieved in part by the presence of unique potassium channels that respond to even small changes in extracellular potassium. The BBB prevents most infections from reaching the vulnerable nervous tissue, due to the unavailability of antibodies from the rest of the body, microglia must be able to recognize foreign bodies, swallow them, and act as antigen-presenting cells activating T-cells. Microglial cells differentiate in the marrow from hematopoietic stem cells. During hematopoiesis, some of these cells differentiate into monocytes and travel from the bone marrow to the brain. However, recent studies indicate microglia originate in the yolk sac during a remarkably restricted period, monocytes can also differentiate into myeloid dendritic cells and macrophages in the peripheral systems. Like macrophages in the rest of the body, microglia use phagocytic and cytotoxic mechanisms to destroy foreign materials, Microglia also differ from macrophages in that they are much more tightly regulated spatially and temporally in order to maintain a precise immune response. Another difference between microglia and other cells that differentiate from myeloid progenitor cells is the turnover rate, macrophages and dendritic cells are constantly being used up and replaced by myeloid progenitor cells which differentiate into the needed type. Due to the barrier, it would be fairly difficult for the body to constantly replace microglia. Once the infection has decreased the disconnect between peripheral and central systems is reestablished and only microglia are present for the recovery and regrowth period, the ability to view and characterize different neural cells including microglia began in 1880 when Nissl staining was developed by Franz Nissl. Franz Nissl and F. Robertson first described microglial cells during their histology experiments, the cell staining techniques in the 1880s showed that microglia are related to macrophages. The activation of microglia and formation of ramified microglial clusters was first noted by Victor Babeş while studying a rabies case in 1897, Babeş noted the cells were found in a variety of viral brain infections but did not know what the clusters of microglia he saw were. Pío del Río Hortega, a student of Santiago Ramón y Cajal and he went on to characterize microglial response to brain lesions in 1927 and note the fountains of microglia present in the corpus callosum and other perinatal white matter areas in 1932. After many years of research Rio-Hortega became generally considered as the Father of Microglia, for a long period of time little improvement was made in our knowledge of microglia. Then, in 1988, Hickey and Kimura showed that perivascular microglial cells are bone-marrow derived and this confirmed Pio Del Rio-Hortegas postulate that microglial cells functioned similarly to macrophages by performing phagocytosis and antigen presentation. Microglial cells are extremely plastic, and undergo a variety of structural changes based on location and this level of plasticity is required to fulfill the vast variety of functions that microglia perform
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Macrophage
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These large phagocytes are found in essentially all tissues, where they patrol for potential pathogens by amoeboid movement. They take various forms throughout the body, but all are part of the mononuclear phagocyte system, besides phagocytosis, they play a critical role in nonspecific defense and also help initiate specific defense mechanisms by recruiting other immune cells such as lymphocytes. For example, they are important as antigen presenters to T cells, in humans, dysfunctional macrophages cause severe diseases such as chronic granulomatous disease that result in frequent infections. Beyond increasing inflammation and stimulating the system, macrophages also play an important anti-inflammatory role. Macrophages that encourage inflammation are called M1 macrophages, whereas those that decrease inflammation, human macrophages are about 21 micrometres in diameter and are produced by the differentiation of monocytes in tissues. They can be identified using flow cytometry or immunohistochemical staining by their expression of proteins such as CD14, CD40, CD11b, CD64, F4/80 /EMR1, lysozyme M, MAC-1/MAC-3. Macrophages were first discovered by Élie Metchnikoff, a Russian zoologist, when a monocyte enters damaged tissue through the endothelium of a blood vessel, a process known as the leukocyte extravasation, it undergoes a series of changes to become a macrophage. At some sites such as the testis, macrophages have shown to populate the organ through proliferation. Unlike short-lived neutrophils, macrophages survive longer in the body up to a maximum of several months, macrophages are professional phagocytes and are highly specialized in removal of dying or dead cells and cellular debris. This role is important in inflammation, as the early stages of inflammation are dominated by neutrophils. The neutrophils are at first attracted to a site, where they proliferate, when a macrophage ingests a pathogen, the pathogen becomes trapped in a phagosome, which then fuses with a lysosome. Within the phagolysosome, enzymes and toxic peroxides digest the pathogen, however, some bacteria, such as Mycobacterium tuberculosis, have become resistant to these methods of digestion. Typhoidal Salmonellae too induce their own phagocytosis by host macrophages in vivo, macrophages can digest more than 100 bacteria before they finally die due to their own digestive compounds. Macrophages are versatile cells that play many roles, as scavengers, they rid the body of worn-out cells and other debris. Along with dendritic cells, they are foremost among the cells present antigens. At the same time, they carry receptors for lymphokines that allow them to be activated into single-minded pursuit of microbes, after digesting a pathogen, a macrophage will present the antigen of the pathogen to the corresponding helper T cell. In some cases, pathogens are very resistant to adhesion by the macrophages, the antigen presentation on the surface of infected macrophages in a lymph node stimulates TH1 to proliferate. When a B-cell in the lymph node recognizes the same unprocessed surface antigen on the bacterium with its surface bound antibody, the processed antigen is then presented in MHCII on the surface of the B-cell
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Immune system
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The immune system is a host defense system comprising many biological structures and processes within an organism that protects against disease. To function properly, a system must detect a wide variety of agents, known as pathogens, from viruses to parasitic worms. In many species, the system can be classified into subsystems, such as the innate immune system versus the adaptive immune system. In humans, the barrier, blood–cerebrospinal fluid barrier, and similar fluid–brain barriers separate the peripheral immune system from the neuroimmune system. Even simple unicellular organisms such as bacteria possess a rudimentary immune system in the form of enzymes that protect against bacteriophage infections, other basic immune mechanisms evolved in ancient eukaryotes and remain in their modern descendants, such as plants and invertebrates. These mechanisms include phagocytosis, antimicrobial peptides called defensins, and the complement system, jawed vertebrates, including humans, have even more sophisticated defense mechanisms, including the ability to adapt over time to recognize specific pathogens more efficiently. Adaptive immunity creates immunological memory after a response to a specific pathogen. This process of acquired immunity is the basis of vaccination, disorders of the immune system can result in autoimmune diseases, inflammatory diseases and cancer. Immunodeficiency occurs when the system is less active than normal. In humans, immunodeficiency can either be the result of a disease such as severe combined immunodeficiency, acquired conditions such as HIV/AIDS. In contrast, autoimmunity results from an immune system attacking normal tissues as if they were foreign organisms. Common autoimmune diseases include Hashimotos thyroiditis, rheumatoid arthritis, diabetes mellitus type 1, immunology covers the study of all aspects of the immune system. Immunology is a science that examines the structure and function of the immune system and it originates from medicine and early studies on the causes of immunity to disease. The earliest known reference to immunity was during the plague of Athens in 430 BC, thucydides noted that people who had recovered from a previous bout of the disease could nurse the sick without contracting the illness a second time. In the 18th century, Pierre-Louis Moreau de Maupertuis made experiments with scorpion venom and observed that certain dogs and this and other observations of acquired immunity were later exploited by Louis Pasteur in his development of vaccination and his proposed germ theory of disease. Pasteurs theory was in opposition to contemporary theories of disease. It was not until Robert Kochs 1891 proofs, for which he was awarded a Nobel Prize in 1905, viruses were confirmed as human pathogens in 1901, with the discovery of the yellow fever virus by Walter Reed. Immunology made an advance towards the end of the 19th century, through rapid developments, in the study of humoral immunity
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Capillary
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Capillaries are the smallest of a bodys blood vessels that make up the microcirculation. Their endothelial linings are only one layer thick. Lymph capillaries connect with larger vessels to drain lymph collected in the microcirculation. The term angiogenesis denotes the formation of new capillaries from pre-existing blood vessels, blood flows from the heart through arteries, which branch and narrow into arterioles, and then branch further into capillaries where nutrients and wastes are exchanged. The capillaries then join and widen to become venules, which in turn widen and converge to become veins, capillaries do not function on their own, but instead in a capillary bed, an interweaving network of capillaries supplying organs and tissues. The more metabolically active a cell or environment is, the capillaries are required to supply nutrients. Metarterioles are found primarily in the mesenteric microcirculation and were thought to be present in most or all capillary beds. The physiological mechanisms underlying precapillary resistance is no longer considered to be a result of precapillary sphincters outside of the mesentery organ, lymphatic capillaries are slightly larger in diameter than blood capillaries, and have closed ends. This structure permits interstitial fluid to flow into them but not out, lymph capillaries have a greater internal oncotic pressure than blood capillaries, due to the greater concentration of plasma proteins in the lymph. However lipid-soluble molecules can diffuse through the endothelial cell membranes along concentration gradients. Tight junctions can be divided into two subtypes, Those with numerous transport vesicles, which are found primarily in skeletal muscles, fingers, gonads. Those with few vesicles, which are found in the central nervous system. These capillaries are a constituent of the blood–brain barrier, fenestrated capillaries have pores in the endothelial cells that are spanned by a diaphragm of radially oriented fibrils and allow small molecules and limited amounts of protein to diffuse. In the renal glomerulus there are cells with no diaphragms, called foot processes or pedicels. Both of these types of vessels have continuous basal laminae and are primarily located in the endocrine glands, intestines, pancreas. Sinusoidal capillaries are a type of open-pore capillary, that have larger openings in the endothelium. These types of blood vessels allow red and white cells and various serum proteins to pass. These capillaries lack pinocytotic vesicles, and therefore utilize gaps present in cell junctions to permit transfer between cells, and hence across the membrane
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Gliosis
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Gliosis is a nonspecific reactive change of glial cells in response to damage to the central nervous system. In most cases, gliosis involves the proliferation or hypertrophy of several different types of cells, including astrocytes, microglia. In its most extreme form, the associated with gliosis leads to the formation of a glial scar. The process of gliosis involves a series of cellular and molecular events that occur over several days, typically, the first response to injury is the migration of macrophages and local microglia to the injury site. This process, which constitutes a form of known as microgliosis. Later, after 3–5 days, oligodendrocyte precursor cells are recruited to the site. The final component of gliosis is astrogliosis, the proliferation of surrounding astrocytes, gliosis has historically been given a negative connotation due to its appearance in many CNS diseases and the inhibition of axonal regeneration caused by glial scar formation. Like other forms of gliosis, astrogliosis accompanies traumatic brain injury as well as many neuropathologies, traditionally, astrogliosis has been defined as an increase in intermediate filaments and cellular hypertrophy as well as an increase in the proliferation of astrocytes. In fact, it is a spectrum of changes occur based on the type. Changes in astrocyte function or morphology which occur during astrogliosis may range from minor hypertrophy to major hypertrophy, domain overlap, changes in astrogliosis are regulated in a context-dependent fashion, and the signaling events which dictate these changes may modify both their nature and severity. It is these changes in astrogliosis which allow the process to be complex and multifaceted, some of the many signalling molecules used in these pathways include the cytokines interleukin 6, ciliary neurotrophic factor, and leukemia inhibitory factor. Generally, the effects of astrogliosis vary with the context of the initial CNS insult, a few of the most important effects of astrogliosis are listed below. The dense structure of proteins is a physically and chemically inhibitory barrier to axon regeneration. Secretion of neurotoxic substances — These may include pro-inflammatory and cytotoxic cytokines, examples of these molecules include nitric oxide radicals and TNF-α. Release of excitotoxic glutamate Hindrance of functional recovery and worsening of clinical signs Microglia, another type of glial cell, due to their fast response time, microgliosis, or the activation of microglia, is commonly the first observed stage of gliosis. Microgliosis following a CNS insult most commonly involves the development of an altered cellular morphology, the microglial immunological surface receptor CR3 is also upregulated within 24 hours after the initial injury. While in their state, microglia may serve a variety of beneficial functions. Active microglia also perform critical homeostatic activity, including the clearing of cell debris through phagocytosis, in addition, active microglia release anti-inflammatory factors and other molecules, such as IL-6 and TGF-β, which regulate neurogenesis after injury
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Cerebral cortex
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The cerebral cortex is the outer layer of neural tissue of the cerebrum of the brain, in humans and other mammals. It is separated into two cortices, by the fissure that divides the cerebrum into the left and right cerebral hemispheres. The two hemispheres are joined beneath the cortex by the corpus callosum, the cerebral cortex plays a key role in memory, attention, perception, awareness, thought, language, and consciousness. In large mammals, the cortex is folded, giving a much greater surface area in the confined volume of the skull. A fold or ridge in the cortex is termed a gyrus, in the human brain more than two-thirds of the cerebral cortex is buried in the sulci. The human cerebral cortex is 2 to 4 millimetres thick, the cerebral cortex is composed of gray matter, consisting mainly of cell bodies and capillaries. It contrasts with the white matter, consisting mainly of the white myelinated sheaths of neuronal axons. The most recent part of the cortex to develop in the evolutionary history of mammals is the neocortex. Neurons in various layers connect vertically to form small microcircuits, called cortical columns, Different neocortical regions known as Brodmann areas are distinguished by variations in their cytoarchitectonics and functional roles in sensation, cognition and behavior. The different cortical layers each contain a distribution of neuronal cell types. There are direct connections between different cortical areas and indirect connections via the thalamus, for example, one of the clearest examples of cortical layering is the stria of Gennari in the primary visual cortex. This is a band of tissue that can be observed with the naked eye in the fundus of the calcarine sulcus of the occipital lobe. The Stria of Gennari is composed of axons bringing visual information from the thalamus into layer four of the visual cortex, during development Cajal-Retzius and subpial granular layer cells are present in this layer. Also, some spiny stellate cells can be found here, inputs to the apical tufts are thought to be crucial for the ‘‘feedback’’ interactions in the cerebral cortex involved in associative learning and attention. Layer II, the granular layer, contains small pyramidal neurons. Layer V, the internal pyramidal layer, contains large pyramidal neurons which give rise to axons leaving the cortex and that is, layer VI neurons from one cortical column connect with thalamus neurons that provide input to the same cortical column. These connections are both excitatory and inhibitory, neurons send excitatory fibers to neurons in the thalamus and also send collaterals to the thalamic reticular nucleus that inhibit these same thalamus neurons or ones adjacent to them. One theory is that because the output is reduced by cholinergic input to the cerebral cortex
. PMID 22788696.
