Anatomical terms of bone
Many anatomical terms descriptive of bone are defined in anatomical terminology, are derived from Greek and Latin. A long bone is one, cylindrical in shape, being longer than it is wide. However, the term describes the shape of a bone, not its size, relative. Long bones are found in the legs, as well as in the fingers and toes. Long bones function as levers, they are responsible for the body's height. A short bone is one, cube-like in shape, being equal in length and thickness; the only short bones in the human skeleton are in the carpals of the wrists and the tarsals of the ankles. Short bones provide support as well as some limited motion; the term “flat bone” is something of a misnomer because, although a flat bone is thin, it is often curved. Examples include the cranial bones, the scapulae, the sternum, the ribs. Flat bones serve as points of attachment for muscles and protect internal organs. Flat bones do not have a medullary cavity. An irregular bone is one that does not have an classified shape and defies description.
These bones tend to have more complex shapes, like the vertebrae that support the spinal cord and protect it from compressive forces. Many facial bones the ones containing sinuses, are classified as irregular bones. A sesamoid bone is a round bone that, as the name suggests, is shaped like a sesame seed; these bones form in tendons. The sesamoid bones protect tendons by helping them overcome compressive forces. Sesamoid bones vary in number and placement from person to person but are found in tendons associated with the feet and knees; the only type of sesamoid bone, common to everybody is the kneecap, the largest of the sesamoid bones. A condyle is the round prominence at the end of a bone, most part of a joint – an articulation with another bone; the epicondyle refers to a projection near a condyle the medial epicondyle of the humerus. These terms derive from Greek. An eminence refers to a small projection or bump of bone, such as the medial eminence. A process refers to a large projection or prominent bump, as does a promontory such as the sacral promontory.
Both tubercle and tuberosity refer to a projection or bump with a roughened surface, with a "tubercle" smaller than a "tuberosity". These terms are derived from Tuber. A ramus refers to an extension of bone, such as the ramus of the mandible in the jaw or Superior pubic ramus. Ramus may be used to refer to nerves, such as the ramus communicans. A facet refers to a flattened articular surface. A line refers to a long, thin projection with a rough surface. Ridge and crest refer to a narrow line. Unlike many words used to describe anatomical terms, the word ridge is derived from Old English. A spine, as well as referring to the spinal cord, may be used to describe a long, thin projection or bump; these terms are used to describe bony protuberances in specific parts of the body. The Malleolus is the bony prominence on each side of the ankle; these are known as the lateral malleolus. Each leg is supported by two bones, the tibia on the inner side of the leg and the fibula on the outer side of the leg; the medial malleolus is the prominence on the inner side of the ankle, formed by the lower end of the tibia.
The lateral malleolus is the prominence on the outer side of the ankle, formed by the lower end of the fibula. The trochanters are parts of the femur, it may refer to the greater, lesser, or third trochanter The following terms are used to describe cavities that connect to other areas: A foramen is any opening referring to those in bone. Foramina inside the body of humans and other animals allow muscles, arteries, veins, or other structures to connect one part of the body with another. A canal is a long, tunnel-like foramen a passage for notable nerves or blood vessels; the following terms are used to describe cavities that do not connect to other areas: A fossa is a depression or hollow in a bone, such as the hypophyseal fossa, the depression in the sphenoid bone. A meatus is a short canal. A fovea is a small pit on the head of a bone. An example of a fovea is the fovea capitis of the head of the femur; the following terms are used to describe the walls of a cavity: A labyrinth refers to the bony labyrinth and membranous labyrinth, components of the inner ear, due to their fine and complex structure.
A sinus refers to a bony cavity within the skull. A joint, or articulation is the region where adjacent bones contact each other, for example the elbow, shoulder, or costovertebral joint. Terms that refer to joints include: articular process, referring to a projection that contacts an adjacent bone. Suture, referring to an articulation between cranial bones. Bones are described with the terms head, shaft and base The head of a bone refers to the proximal end of the bone; the shaft refers to the elongated sections of long bone, the neck the segment between the head and shaft. The end of the long bone opposite to the head is known as the base; the cortex of a bone is used to refer to its outer layers, medulla used to
Endochondral ossification is one of the two essential processes during fetal development of the mammalian skeletal system by which bone tissue is created. Unlike intramembranous ossification, the other process by which bone tissue is created, cartilage is present during endochondral ossification. Endochondral ossification is an essential process during the rudimentary formation of long bones, the growth of the length of long bones, the natural healing of bone fractures; the cartilage model will grow in length by continuous cell division of chondrocytes, accompanied by further secretion of extracellular matrix. This is called interstitial growth; the process of appositional growth occurs when the cartilage model grows in thickness due to the addition of more extracellular matrix on the peripheral cartilage surface, accompanied by new chondroblasts that develop from the perichondrium. The first site of ossification occurs in the primary center of ossification, in the middle of diaphysis. Then: Formation of periosteum The perichondrium becomes the periosteum.
The periosteum contains a layer of undifferentiated cells which become osteoblasts. Formation of bone collar The osteoblasts secrete osteoid against the shaft of the cartilage model; this serves as support for the new bone. Calcification of matrix Chondrocytes in the primary center of ossification begin to grow, they stop secreting collagen and other proteoglycans and begin secreting alkaline phosphatase, an enzyme essential for mineral deposition. Calcification of the matrix occurs and osteoprogenitor cells that entered the cavity via the periosteal bud, use the calcified matrix as a scaffold and begin to secrete osteoid, which forms the bone trabecula. Osteoclasts, formed from macrophages, break down spongy bone to form the medullary cavity. About the time of birth in mammals, a secondary ossification center appears in each end of long bones. Periosteal buds carry mesenchyme and blood vessels in and the process is similar to that occurring in a primary ossification center; the cartilage between the primary and secondary ossification centers is called the epiphyseal plate, it continues to form new cartilage, replaced by bone, a process that results in an increase in length of the bone.
Growth continues until the individual is about 20 years old or until the cartilage in the plate is replaced by bone. The point of union of the primary and secondary ossification centers is called the epiphyseal line; the growth in diameter of bones around the diaphysis occurs by deposition of bone beneath the periosteum. Osteoclasts in the interior cavity continue to resorb bone until its ultimate thickness is achieved, at which point the rate of formation on the outside and degradation from the inside is constant. During endochondral ossification, five distinct zones can be seen at the light-microscope level. During fracture healing, cartilage is formed and is called callus; this cartilage develops into new bone tissue through the process of endochondral ossification. It has been shown that biomimetic bone like apatite inhibits formation of bone through endochondral ossification pathway via hyperstimulation of extracellular calcium sensing receptor. Intramembranous ossification Ossification
The cranial vault is the space in the skull within the neurocranium, tenanted by the brain. In humans, the size and shape of the brain, may be affected by the size of the vault as shown in craniometry, but studies relating it to intelligence have found no conclusive evidence; the vault is alternatively called "skullcap" or calvaria, though these properly refer to the upper portion of the skull only. In humans, the cranial vault is imperfectly composed in newborns, to allow the large human head to pass through the birth canal. During birth, the various bones connected by cartilage and ligaments only will move to each other; the open portion between the major bones of the upper part of the vault, called fontanelles remain soft up to two years after birth. As the fontanelles close, the vault loses some of its plasticity; the sutures between the bones remain until 30 to 40 years of age, allowing for growth of the brain. Cranial vault size is developed early; the size and shape of the brain and the surrounding vault remain quite plastic as the brain grows in childhood.
In several ancient societies, head shape was altered for aesthetic or religious reasons by binding cloth or boards around the head during infancy. It is not known; the cranial vault is composed of the endocranium forming the basal parts, topped by the skull roof in land vertebrates. In fishes no distinct cranial vault as such exists. Instead, the skull is composed of loosely jointed bones; the cranial vault as a distinct unit arose with the fusion of the skull roof and the endocranium on the early Labyrinthodonts. In amphibians and reptiles the vault is rather small and inconspicuous, only forming proper vaults in mammals and birds. Skull Craniometry Phrenology
Tetrapods are four-limbed animals constituting the superclass Tetrapoda. It includes existing and extinct amphibians and mammals. Tetrapods evolved from a group of animals known as the Tetrapodomorpha which, in turn, evolved from ancient Sarcopterygii around 390 million years ago in the middle Devonian period; the first tetrapods appeared by the late Devonian, 367.5 million years ago. The change from a body plan for breathing and navigating in water to a body plan enabling the animal to move on land is one of the most profound evolutionary changes known; the first tetrapods were aquatic. Modern amphibians, which evolved from earlier groups, are semiaquatic. However, most tetrapod species today are amniotes, most of those are terrestrial tetrapods whose branch evolved from earlier tetrapods about 340 million years ago; the key innovation in amniotes over amphibians is laying of eggs on land or having further evolved to retain the fertilized egg within the mother. Amniote tetrapods drove most amphibian tetrapods to extinction.
One group of amniotes diverged into the reptiles, which includes lepidosaurs, crocodilians and extinct relatives. Amniotes include the tetrapods that further evolved for flight—such as birds from among the dinosaurs, bats from among the mammals; some tetrapods, such as the snakes, have lost some or all of their limbs through further speciation and evolution. Others, such as amphibians, returned to or aquatic lives, the first during the Carboniferous period. Tetrapods have numerous anatomical and physiological features that are distinct from their aquatic ancestors; these include the structure of the jaw and teeth for feeding on land, limb girdles and extremities for land locomotion, lungs for respiration in air, a heart for circulation, eyes and ears for seeing and hearing in air. Tetrapods can be defined in cladistics as the nearest common ancestor of all living amphibians and all living amniotes, along with all of the descendants of that ancestor; this is a node-based definition. The group so defined is crown tetrapods.
The term tetrapodomorph is used for the stem-based definition: any animal, more related to living amphibians, reptiles and mammals than to living dipnoi. The group so defined is known as the tetrapod total group. Stegocephalia is a larger group equivalent to some broader uses of the word tetrapod, used by scientists who prefer to reserve tetrapod for the crown group; such scientists use the term "stem-tetrapod" to refer to those tetrapod-like vertebrates that are not members of the crown group, including the tetrapodomorph fishes. The two subclades of crown tetrapods are Reptiliomorpha. Batrachomorphs are all animals sharing a more recent common ancestry with living amphibians than with living amniotes. Reptiliomorphs are all animals sharing a more recent common ancestry with living amniotes than with living amphibians. Tetrapoda includes four living classes: amphibians, reptiles and birds. Overall, the biodiversity of lissamphibians, as well as of tetrapods has grown exponentially over time. However, that diversification process was interrupted at least a few times by major biological crises, such as the Permian–Triassic extinction event, which at least affected amniotes.
The overall composition of biodiversity was driven by amphibians in the Palaeozoic, dominated by reptiles in the Mesozoic and expanded by the explosive growth of birds and mammals in the Cenozoic. As biodiversity has grown, so has the number of niches that tetrapods have occupied; the first tetrapods were aquatic and fed on fish. Today, the Earth supports a great diversity of tetrapods that live in many habitats and subsist on a variety of diets; the following table shows summary estimates for each tetrapod class from the IUCN Red List of Threatened Species, 2014.3, for the number of extant species that have been described in the literature, as well as the number of threatened species. The classification of tetrapods has a long history. Traditionally, tetrapods are divided into four classes based on gross anatomical and physiological traits. Snakes and other legless reptiles are considered tetrapods because they are sufficiently like other reptiles that have a full complement of limbs. Similar considerations apply to aquatic mammals.
Newer taxonomy is based on cladistics instead, giving a variable number of major "branches" of the tetrapod family tree. As is the case throughout evolutionary biology today, there is debate over how to properly classify the groups within Tetrapoda. Traditional biological classification sometimes fa
The pterion is the region where the frontal, parietal and sphenoid bones join together. It is located on the side of the skull, just behind the temple; the pterion is located in the temporal fossa 2.6 cm behind and 1.3 cm above the posterolateral margin of the frontozygomatic suture. It is the junction between four bones: the parietal bone the squamous part of temporal bone the greater wing of sphenoid bone the frontal boneThese bones are joined by five cranial sutures: the sphenoparietal suture joins the sphenoid and parietal bones the coronal suture joins the frontal bone to the sphenoid and parietal bones the squamous suture joins the temporal bone to the sphenoid and parietal bones the sphenofrontal suture joins the sphenoid and frontal bones the sphenosquamosal suture joins the sphenoid and temporal bones The pterion is known as the weakest part of the skull; the anterior division of the middle meningeal artery runs underneath the pterion. A traumatic blow to the pterion may rupture the middle meningeal artery causing an epidural haematoma.
The pterion may be fractured indirectly by blows to the top or back of the head that place sufficient force on the skull to fracture the pterion. The pterion receives its name from the Greek root pteron. In Greek mythology, messenger of the gods, was enabled to fly by winged sandals, wings on his head, which were attached at the pterion; this article incorporates text in the public domain from page 182 of the 20th edition of Gray's Anatomy Anatomy figure: 22:01-04 at Human Anatomy Online, SUNY Downstate Medical Center Diagram - look for #24
Human evolution is the evolutionary process that led to the emergence of anatomically modern humans, beginning with the evolutionary history of primates—in particular genus Homo—and leading to the emergence of Homo sapiens as a distinct species of the hominid family, the great apes. This process involved the gradual development of traits such as human bipedalism and language, as well as interbreeding with other hominins, which indicate that human evolution was not linear but a web; the study of human evolution involves several scientific disciplines, including physical anthropology, archaeology, neurobiology, linguistics, evolutionary psychology and genetics. Genetic studies show that primates diverged from other mammals about 85 million years ago, in the Late Cretaceous period, the earliest fossils appear in the Paleocene, around 55 million years ago. Within the Hominoidea superfamily, the Hominidae family diverged from the Hylobatidae family some 15–20 million years ago. Human evolution from its first separation from the last common ancestor of humans and chimpanzees is characterized by a number of morphological, developmental and behavioral changes.
The most significant of these adaptations are bipedalism, increased brain size, lengthened ontogeny, decreased sexual dimorphism. The relationship between these changes is the subject of ongoing debate. Other significant morphological changes included the evolution of a power and precision grip, a change first occurring in H. erectus. Bipedalism is the basic adaptation of the hominid and is considered the main cause behind a suite of skeletal changes shared by all bipedal hominids; the earliest hominin, of primitive bipedalism, is considered to be either Sahelanthropus or Orrorin, both of which arose some 6 to 7 million years ago. The non-bipedal knuckle-walkers, the gorilla and chimpanzee, diverged from the hominin line over a period covering the same time, so either of Sahelanthropus or Orrorin may be our last shared ancestor. Ardipithecus, a full biped, arose 5.6 million years ago. The early bipeds evolved into the australopithecines and still into the genus Homo. There are several theories of the adaptation value of bipedalism.
It is possible that bipedalism was favored because it freed the hands for reaching and carrying food, saved energy during locomotion, enabled long distance running and hunting, provided an enhanced field of vision, helped avoid hyperthermia by reducing the surface area exposed to direct sun. A new study provides support for the hypothesis that walking on two legs, or bipedalism, evolved because it used less energy than quadrupedal knuckle-walking. However, recent studies suggest that bipedality without the ability to use fire would not have allowed global dispersal; this change in gait saw a lengthening of the legs proportionately when compared to the length of the arms, which were shortened through the removal of the need for brachiation. Another change is the shape of the big toe. Recent studies suggest that Australopithecines still lived part of the time in trees as a result of maintaining a grasping big toe; this was progressively lost in Habilines. Anatomically, the evolution of bipedalism has been accompanied by a large number of skeletal changes, not just to the legs and pelvis, but to the vertebral column and ankles, skull.
The femur evolved into a more angular position to move the center of gravity toward the geometric center of the body. The knee and ankle joints became robust to better support increased weight. To support the increased weight on each vertebra in the upright position, the human vertebral column became S-shaped and the lumbar vertebrae became shorter and wider. In the feet the big toe moved into alignment with the other toes to help in forward locomotion; the arms and forearms shortened relative to the legs making it easier to run. The foramen magnum migrated under more anterior; the most significant changes occurred in the pelvic region, where the long downward facing iliac blade was shortened and widened as a requirement for keeping the center of gravity stable while walking. A drawback is that the birth canal of bipedal apes is smaller than in knuckle-walking apes, though there has been a widening of it in comparison to that of australopithecine and modern humans, permitting the passage of newborns due to the increase in cranial size but this is limited to the upper portion, since further increase can hinder normal bipedal movement.
The shortening of the pelvis and smaller birth canal evolved as a requirement for bipedalism and had significant effects on the process of human birth, much more difficult in modern humans than in other primates. During human birth, because of the variation in size of the pelvic region, the fetal head must be in a transverse position during entry into the birth canal and rotate about 90 degrees upon exit; the smaller birth canal became a limiting factor to brain size increases in early humans and prompted a shorter gestation period leading to the relative immaturity of human
The frontal lobe is the largest of the four major lobes of the brain in mammals, is located at the front of each hemisphere. It is separated from the parietal lobe by a groove between tissues called the central sulcus, from the temporal lobe by a deeper groove called the lateral sulcus; the most anterior rounded part of the frontal lobe is known as the frontal pole, one of the three poles of the cerebrum. The frontal lobe is covered by the frontal cortex; the frontal cortex includes the premotor cortex, the primary motor cortex – cortical parts of the motor cortex. The front part of the frontal lobe is covered by the prefrontal cortex. There are four principal gyri in the frontal lobe; the precentral gyrus, is directly anterior to the central sulcus, running parallel to it and contains the primary motor cortex, which controls voluntary movements of specific body parts. Three horizontally arranged subsections of the frontal gyrus are the superior frontal gyrus, the middle frontal gyrus, the inferior frontal gyrus.
The inferior frontal gyrus is divided into three parts – the orbital part, the triangular part, the opercular part. The frontal lobe contains most of the dopamine neurons in the cerebral cortex; the dopaminergic pathways are associated with reward, short-term memory tasks and motivation. Dopamine tends to select sensory information arriving from the thalamus to the forebrain; the frontal lobe is the largest lobe of the brain and makes up about a third of the surface area of each hemisphere. On the lateral surface of each hemisphere, the central sulcus separates the frontal lobe from the parietal lobe; the lateral sulcus separates the frontal lobe from the temporal lobe. The frontal lobe can be divided into a lateral, polar and medial part; each of these parts consists of a particular gyrus: Lateral part: lateral part of the superior frontal gyrus, middle frontal gyrus, inferior frontal gyrus. Polar part: Transverse frontopolar gyri, frontomarginal gyrus. Orbital part: Lateral orbital gyrus, anterior orbital gyrus, posterior orbital gyrus, medial orbital gyrus, gyrus rectus.
Medial part: Medial part of the superior frontal gyrus, cingulate gyrus. The gyri are separated by sulci. E.g. the precentral gyrus is in front of the central sulcus, behind the precentral sulcus. The superior and middle frontal gyri are divided by the superior frontal sulcus; the middle and inferior frontal gyri are divided by the inferior frontal sulcus. In humans, the frontal lobe reaches full maturity around the late 20s, marking the cognitive maturity associated with adulthood. A small amount of atrophy, however, is normal in the aging person’s frontal lobe. Fjell, in 2009, studied atrophy of the brain in people aged 60–91 years; the 142 healthy participants were scanned using MRI. Their results were compared to those of 122 participants with Alzheimer's disease. A follow-up one year showed there to have been a marked volumetric decline in those with Alzheimer's and a much smaller decline in the healthy group; these findings corroborate those of Coffey, who in 1992 indicated that the frontal lobe decreases in volume 0.5%–1% per year.
The frontal lobe plays a large role in voluntary movement. It houses the primary motor cortex; the function of the frontal lobe involves the ability to project future consequences resulting from current actions. Frontal lobe functions include override and suppression of unacceptable response as well as differentiation tasks; the frontal lobe plays an important part in integrating longer non-task based memories stored across the brain. These are memories associated with emotions derived from input from the brain's limbic system; the frontal lobe modifies those emotions to fit acceptable norms. Psychological tests that measure frontal lobe function include finger tapping, the Wisconsin Card Sorting Test, measures of language and numeracy skills. Damage to the frontal lobe can result in many different consequences. Transient ischemic attacks known as mini-strokes, strokes are common causes of frontal lobe damage in older adults; these strokes and mini-strokes can occur due to the blockage of blood flow to the brain or as a result of the rupturing of an aneurysm in a cerebral artery.
Other ways in which injury can occur include head injuries such as traumatic brain injuries incurred following accidents, diagnoses such as Alzheimer's disease or Parkinson's disease, frontal lobe epilepsy. Common effects of damage to the frontal lobe are varied. Patients who have experienced frontal lobe trauma may know the appropriate response to a situation but display inappropriate responses to those same situations in "real life". Emotions that are felt may not be expressed in the face or voice. For example, someone, feeling happy would not smile, the voice would be devoid of emotion. Along the same lines, the person may exhibit excessive, unwarranted displays of emotion. Depression is common in stroke patients. Common is a loss of or decrease in motivation. Someone might not want to carry out normal daily activities and would not feel "up to it"; those who are close to the person who has experienced the damage may notice changes in behavior. This personality change is characteristic of damage to the frontal lobe and was exemplified in the case of Phineas Gage.
The frontal lobe is the same part of the brain, responsible for executive functions