Misplaced Pages

#876123

82-427: In humans, cervical vertebrae are the smallest of the true vertebrae and can be readily distinguished from those of the thoracic or lumbar regions by the presence of a foramen (hole) in each transverse process, through which the vertebral artery , vertebral veins , and inferior cervical ganglion pass. The remainder of this article focuses upon human anatomy. By convention, the cervical vertebrae are numbered, with

164-408: A cervical rib can develop from C7 as an anatomical variation . The term cervicothoracic is often used to refer to the cervical and thoracic vertebrae together, and sometimes also their surrounding areas. The twelve thoracic vertebrae and their transverse processes have surfaces that articulate with the ribs . Some rotation can occur between the thoracic vertebrae, but their connection with

246-403: A lumbar vertebra is also sometimes called the costal or costiform process because it corresponds to a rudimentary rib ( costa ) which, as opposed to the thorax, is not developed in the lumbar region. There are superior and inferior articular facet joints on each side of the vertebra, which serve to restrict the range of movement possible. These facets are joined by a thin portion of

328-534: A radiograph is the distance between the basion and the top of the dens, used in the diagnosis of dissociation injuries. Genetic disorders can cause a prominent occiput as found in Edwards syndrome , and Beckwith–Wiedemann syndrome . The identification of the location of the fetal occiput is important in delivery . Occipital stems from Latin occiput "back of the skull", from ob "against, behind" + caput "head". Distinguished from sinciput (anterior part of

410-423: A complex structure composed of bone and some hyaline cartilage , that make up the vertebral column or spine, of vertebrates . The proportions of the vertebrae differ according to their spinal segment and the particular species. The basic configuration of a vertebra varies; the bone is the body, and the central part of the body is the centrum. The upper and lower surfaces of the vertebra body give attachment to

492-451: A disc, vertebra or scar tissue might be remedied by a foraminotomy to broaden the intervertebral foramina and relieve pressure. It can also be caused by a foramina stenosis , a narrowing of the nerve opening, as a result of arthritis . Another condition is spondylolisthesis when one vertebra slips forward onto another. The reverse of this condition is retrolisthesis where one vertebra slips backward onto another. The vertebral pedicle

574-453: A facet on each side of the vertebral body, which articulates with the head of a rib . There is also a facet on each of the transverse processes which articulates with the tubercle of a rib . The number of thoracic vertebrae varies considerably across the species. Most marsupials have thirteen, but koalas only have eleven. The usual number is twelve to fifteen in mammals , (twelve in the human ), though there are from eighteen to twenty in

656-433: A large range of motion. The atlanto-occipital joint allows the skull to move up and down, while the atlanto-axial joint allows the upper neck to twist left and right. The axis also sits upon the first intervertebral disc of the spinal column. Cervical vertebrae possess transverse foramina to allow for the vertebral arteries to pass through on their way to the foramen magnum to end in the circle of Willis . These are

738-539: A number of congenital vertebral anomalies , mostly involving variations in the shape or number of vertebrae, and many of which are unproblematic. Others though can cause compression of the spinal cord. Wedge-shaped vertebrae, called hemivertebrae can cause an angle to form in the spine which can result in the spinal curvature diseases of kyphosis , scoliosis and lordosis . Severe cases can cause spinal cord compression. Block vertebrae where some vertebrae have become fused can cause problems. Spina bifida can result from

820-567: A painfree condition but can also be very painful. In other animals, the vertebrae take the same regional names except for the coccygeal – in animals with tails, the separate vertebrae are usually called the caudal vertebrae . Because of the different types of locomotion and support needed between the aquatic and other vertebrates, the vertebrae between them show the most variation, though basic features are shared. The spinous processes which are backward extending are directed upward in animals without an erect stance. These processes can be very large in

902-438: A pair. The long spinous process of C7 is thick and nearly horizontal in direction. It is not bifurcated, and ends in a tubercle that the ligamentum nuchae attaches to. This process is not always the most prominent of the spinous processes, being found only about 70% of the time, C6 or T1 can sometimes be the most prominent. The transverse processes are of considerable size; their posterior roots are large and prominent, while

SECTION 10

#1732793606877

984-456: A posterior arch and two lateral masses. At the outside centre points of both arches there is a tubercle, an anterior tubercle and a posterior tubercle , for the attachment of muscles. The front surface of the anterior arch is convex and its anterior tubercle gives attachment to the longus colli muscle . The posterior tubercle is a rudimentary spinous process and gives attachment to the rectus capitis posterior minor muscle . The spinous process

1066-401: A vertebra is a backward extending spinous process (sometimes called the neural spine) which projects centrally. This process points dorsally and caudally from the junction of the laminae. The spinous process serves to attach muscles and ligaments . The two transverse processes, one on each side of the vertebral body, project laterally from either side at the point where the lamina joins

1148-406: Is a cranial dermal bone and the main bone of the occiput (back and lower part of the skull ). It is trapezoidal in shape and curved on itself like a shallow dish. The occipital bone overlies the occipital lobes of the cerebrum . At the base of the skull in the occipital bone, there is a large oval opening called the foramen magnum , which allows the passage of the spinal cord . Like

1230-437: Is an irregular bone. A typical vertebra has a body ( vertebral body ), which consists of a large anterior middle portion called the centrum ( vertebral centrum , plural centra ) and a posterior vertebral arch , also called a neural arch . The body is composed of cancellous bone , which is the spongy type of osseous tissue , whose microanatomy has been specifically studied within the pedicle bones. This cancellous bone

1312-401: Is comparatively mobile, and some component of this movement is due to flexion and extension of the vertebral column itself. This movement between the atlas and occipital bone is often referred to as the "yes joint", owing to its nature of being able to move the head in an up-and-down fashion. The movement of shaking or rotating the head left and right happens almost entirely at the joint between

1394-422: 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 from each side, posteriorly, from the junctions of the posteriolateral surfaces of the centrum, on its upper surface. From each pedicle a broad plate, a lamina , projects backward and medially to join and complete the vertebral arch and form

1476-410: Is in turn, covered by a thin coating of cortical bone (or compact bone), the hard and dense type of osseous tissue. 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 direct contact with

1558-473: Is often used as a radiographic marker and entry point in vertebroplasty , kyphoplasty , and spinal fusion procedures. The arcuate foramen is a common anatomical variation more frequently seen in females. It is a bony bridge found on the first cervical vertebra, the atlas where it covers the groove for the vertebral artery . Degenerative disc disease is a condition usually associated with ageing in which one or more discs degenerate. This can often be

1640-457: Is said to be ossified from two centers and the basilar portion from one. About the fourth year the squamous part and the two lateral parts unite, and by about the sixth year the bone consists of a single piece. Between the 18th and 25th years the occipital and sphenoid bone become united, forming a single bone. Trauma to the occiput can cause a fracture of the base of the skull, called a basilar skull fracture . The basion-dens line as seen on

1722-417: Is small so as not to interfere with the movement between the atlas and the skull . On the under surface is a facet for articulation with the dens of the axis. Specific to the cervical vertebra is the transverse foramen (also known as foramen transversarium ). This is an opening on each of the transverse processes which gives passage to the vertebral artery and vein and a sympathetic nerve plexus . On

SECTION 20

#1732793606877

1804-400: Is the mammillary process which connects with the superior articular process. The multifidus muscle attaches to the mammillary process and this muscle extends through the length of the vertebral column, giving support. The inferior, or lower tubercle is the accessory process and this is found at the back part of the base of the transverse process. The term lumbosacral is often used to refer to

1886-407: Is the strong odontoid process (dens) that rises perpendicularly from the upper surface of the body and articulates with C1. The body is deeper in front than behind, and prolonged downward anteriorly so as to overlap the upper and front part of the third vertebra. The vertebra prominens , or C7, has a distinctive long and prominent spinous process, which is palpable from the skin surface. Sometimes,

1968-448: Is thin, semitransparent, and without diploë. Near the middle of the outer surface of the squamous part of the occipital (the largest part) there is a prominence – the external occipital protuberance . The highest point of this is called the inion . From the inion, along the midline of the squamous part until the foramen magnum, runs a ridge – the external occipital crest (also called the medial nuchal line) and this gives attachment to

2050-411: The accessory nerves , the vertebral arteries , the anterior and posterior spinal arteries , the tectorial membrane and the alar ligaments . The superior angle of the occipital bone articulates with the occipital angles of the parietal bones and, in the fetal skull, corresponds in position with the posterior fontanelle . The lateral angles are situated at the extremities of the groove for

2132-455: The carotid artery from the vertebral artery and the carotid artery can be massaged against this tubercle to relieve the symptoms of supraventricular tachycardia . The carotid tubercle is also used as a landmark for anaesthesia of the brachial plexus and cervical plexus . The cervical spinal nerves emerge from above the cervical vertebrae. For example, the cervical spinal nerve 3 (C3) passes above C3. The atlas (C1) and axis (C2) are

2214-497: The cervical vertebrae bear ribs. In many groups, such as lizards and saurischian dinosaurs, the cervical ribs are large; in birds, they are small and completely fused to the vertebrae. The transverse processes of mammals are homologous to the cervical ribs of other amniotes . In the whale, the cervical vertebrae are typically fused, an adaptation trading flexibility for stability during swimming. All mammals except manatees and sloths have seven cervical vertebrae, whatever

2296-468: The chondrocranium throughout life. In most higher vertebrates , the foramen magnum is surrounded by a ring of four bones. The basioccipital lies in front of the opening, the two exoccipital condyles lie to either side, and the larger supraoccipital lies to the posterior, and forms at least part of the rear of the cranium. In many bony fish and amphibians , the supraoccipital is never ossified, and remains as cartilage throughout life. In primitive forms

2378-446: The cruciform (cross-shaped) eminence . At the midpoint where the lines intersect a raised part is formed called the internal occipital protuberance . From each side of this eminence runs a groove for the transverse sinuses . There are two midline skull landmarks at the foramen magnum . The basion is the most anterior point of the opening and the opisthion is the point on the opposite posterior part. The basion lines up with

2460-417: The dens . The foramen magnum ( Latin : large hole ) is a large oval foramen longest front to back; it is wider behind than in front where it is encroached upon by the occipital condyles . The clivus, a smooth bony section, travels upwards on the front surface of the foramen, and the median internal occipital crest travels behind it. Through the foramen passes the medulla oblongata and its membranes,

2542-438: The hangman's fracture , both of which are often treated with immobilization in a cervical collar or halo brace . A common practice is to immobilize a patient's cervical spine to prevent further damage during transport to hospital. This practice has come under review recently as incidence rates of unstable spinal trauma can be as low as 2% in immobilized patients. In clearing the cervical spine , Canadian studies have developed

Cervical vertebrae - Misplaced Pages Continue

2624-588: The horse , tapir , rhinoceros and elephant . In certain sloths, there is an extreme number of twenty-five and at the other end only nine in the cetacean . There are fewer lumbar vertebrae in chimpanzees and gorillas , which have three in contrast to the five in the genus Homo . This reduction in number gives an inability of the lumbar spine to lordose but gives an anatomy that favours vertical climbing, and hanging ability more suited to feeding locations in high-canopied regions. The bonobo differs by having four lumbar vertebrae. Caudal vertebrae are

2706-506: The internal occipital protuberance , and serves as a point of attachment to the falx cerebri . To the sides of the foramen sitting at the junction between the lateral and base of the occipital bone are the hypoglossal canals . Further out, at each junction between the occipital and petrous portion of the temporal bone lies a jugular foramen . The inner surface of the occipital bone is marked by dividing lines as shallow ridges, that form four fossae or depressions. The lines are called

2788-422: The intervertebral disc , which lets some of the soft gel-like material, the nucleus pulposus , bulge out in a hernia . This may be treated by a minimally-invasive endoscopic procedure called Tessys method . A laminectomy is a surgical operation to remove the laminae in order to access the spinal canal. The removal of just part of a lamina is called a laminotomy . A pinched nerve caused by pressure from

2870-436: The intervertebral discs . The posterior part of a vertebra forms a vertebral arch , in eleven parts, consisting of two pedicles ( pedicle of vertebral arch ), two laminae, and seven processes . The laminae give attachment to the ligamenta flava (ligaments of the spine). There are vertebral notches formed from the shape of the pedicles, which form the intervertebral foramina when the vertebrae articulate . These foramina are

2952-403: The lambdoidal suture . The inferior borders extend from the lateral angles to the inferior angle; the upper half of each articulates with the mastoid portion of the corresponding temporal , the lower half with the petrous part of the same bone. These two portions of the inferior border are separated from one another by the jugular process , the notch on the anterior surface of which forms

3034-426: The nuchal ligament . Running across the outside of the occipital bone are three curved lines and one line (the medial line) that runs down to the foramen magnum. These are known as the nuchal lines which give attachment to various ligaments and muscles. They are named as the highest , superior and inferior nuchal lines. The inferior nuchal line runs across the midpoint of the median nuchal line. The area above

3116-402: The paraxial mesoderm . The lower half of one sclerotome fuses with the upper half of the adjacent one to form each vertebral body. From this vertebral body, sclerotome cells move dorsally and surround the developing spinal cord , forming the vertebral arch . Other cells move distally to the costal processes of thoracic vertebrae to form the ribs. Functions of vertebrae include: There are

3198-422: The pedicle , between the superior and inferior articular processes. They also serve for the attachment of muscles and ligaments, in particular the intertransverse ligaments . There is a facet on each of the transverse processes of thoracic vertebrae which articulates with the tubercle of the rib . A facet on each side of the thoracic vertebral body articulates with the head of the rib . The transverse process of

3280-400: The rib cage prevents much flexion or other movement. They may also be known as "dorsal vertebrae" in the human context. The vertebral bodies are roughly heart-shaped and are about as wide anterio-posteriorly as they are in the transverse dimension. Vertebral foramina are roughly circular in shape. The top surface of the first thoracic vertebra has a hook-shaped uncinate process, just like

3362-498: The Canadian C-Spine Rule (CCR) for physicians to decide who should receive radiological imaging. The vertebral column is often used as a marker of human anatomy . This includes: [REDACTED] This article incorporates text in the public domain from page 97 of the 20th edition of Gray's Anatomy (1918) Transverse foramen Each vertebra ( pl. : vertebrae ) is an irregular bone with

Cervical vertebrae - Misplaced Pages Continue

3444-435: The anterior are small and faintly marked. The upper surface of each usually has a shallow sulcus for the eighth spinal nerve, and its extremity seldom presents more than a trace of bifurcation. The transverse foramen may be as large as that in the other cervical vertebrae, but it is generally smaller on one or both sides; occasionally, it is double, and sometimes it is absent. On the left side, it occasionally gives passage to

3526-422: The atlas and the axis, the atlanto-axial joint . A small amount of rotation of the vertebral column itself contributes to the movement. This movement between the atlas and axis is often referred to as the "no joint", owing to its nature of being able to rotate the head in a side-to-side fashion. Cervical degenerative changes arise from conditions such as spondylosis , stenosis of intervertebral discs , and

3608-401: The basioccipital and exoccipitals somewhat resemble the centrum and neural arches of a vertebra , and form in a similar manner in the embryo. Together, these latter bones usually form a single concave circular condyle for the articulation of the first vertebra . In mammals , however, the condyle has divided in two, a pattern otherwise seen only in a few amphibians. Most mammals also have

3690-514: The bones that make up the tails of vertebrates. They range in number from a few to fifty, depending on the length of the animal's tail. In humans and other tailless primates , they are called the coccygeal vertebrae , number from three to five and are fused into the coccyx . [REDACTED] This article incorporates text in the public domain from page 96 of the 20th edition of Gray's Anatomy (1918) Occipital bone The occipital bone ( / ˌ ɒ k ˈ s ɪ p ɪ t əl / )

3772-400: The brain." The occipital bone, like the other seven cranial bones , has outer and inner layers (also called plates or tables ) of cortical bone tissue between which is the cancellous bone tissue known in the cranial bones as diploë . The bone is especially thick at the ridges, protuberances, condyles , and anterior part of the basilar part ; in the inferior cerebellar fossae it

3854-419: The cervical spine are common at the level of the second cervical vertebrae, but neurological injury is uncommon. C4 and C5 are the areas that see the highest amount of cervical spine trauma. If it does occur, however, it may cause death or profound disability, including paralysis of the arms, legs, and diaphragm , which leads to respiratory failure . Common patterns of injury include the odontoid fracture and

3936-409: The cervical vertebrae other than the atlas, the anterior and posterior tubercles are on either side of the transverse foramen on each transverse process. The anterior tubercle on the sixth cervical vertebra is called the carotid tubercle because it separates the carotid artery from the vertebral artery . There is a hook-shaped uncinate process on the side edges of the top surface of the bodies of

4018-453: The cervical vertebrae. The thoracolumbar division refers to the thoracic and lumbar vertebrae together, and sometimes also their surrounding areas. The thoracic vertebrae attach to ribs and so have articular facets specific to them; these are the superior , transverse and inferior costal facets . As the vertebrae progress down the spine they increase in size to match up with the adjoining lumbar section. The five lumbar vertebrae are

4100-414: The coccyx. There are seven cervical vertebrae (but eight cervical spinal nerves ), designated C1 through C7. These bones are, in general, small and delicate. Their spinous processes are short (with the exception of C2 and C7, which have palpable spinous processes). C1 is also called the atlas , and C2 is also called the axis . The structure of these vertebrae is the reason why the neck and head have

4182-469: The convex articular feature of an anterior vertebra acts as the ball to the socket of a caudal vertebra. This type of connection permits a wide range of motion in most directions, while still protecting the underlying nerve cord. The central point of rotation is located at the midline of each centrum, and therefore flexion of the muscle surrounding the vertebral column does not lead to an opening between vertebrae. In many species, though not in mammals,

SECTION 50

#1732793606877

4264-469: The entry and exit conduits 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 each other to give strength and flexibility to the spinal column, and the shape at their back and front aspects determines the range of movement. Structurally, vertebrae are essentially alike across

4346-467: The first one (C1) closest to the skull and higher numbered vertebrae (C2–C7) proceeding away from the skull and down the spine. The general characteristics of the third through sixth cervical vertebrae are described here. The first, second, and seventh vertebrae are extraordinary, and are detailed later. The anterior tubercle of the sixth cervical vertebra is known as the carotid tubercle or Chassaignac tubercle (for Édouard Chassaignac ). This separates

4428-432: The foramen magnum and directed towards the pharynx . The squamous part is the curved, expanded plate behind the foramen magnum and is the largest part of the occipital bone. Due to its embryonic derivation from paraxial mesoderm (as opposed to neural crest, from which many other craniofacial bones are derived), it has been posited that "the occipital bone as a whole could be considered as a giant vertebra enlarged to support

4510-445: The formation of osteophytes . The changes are seen on radiographs , which are used in a grading system from 0–4 ranging from no changes (0) to early with minimal development of osteophytes (1) to mild with definite osteophytes (2) to moderate with additional disc space stenosis or narrowing (3) to the stage of many large osteophytes, severe narrowing of the disc space, and more severe vertebral end plate sclerosis (4). Injuries to

4592-418: The highest nuchal line is termed the occipital plane and the area below this line is termed the nuchal plane . The inner surface of the occipital bone forms the base of the posterior cranial fossa . The foramen magnum is a large hole situated in the middle, with the clivus , a smooth part of the occipital bone travelling upwards in front of it. The median internal occipital crest travels behind it to

4674-421: The incomplete formation of the vertebral arch. Spondylolysis is a defect in the pars interarticularis of the vertebral arch. In most cases this occurs in the lowest of the lumbar vertebrae (L5), but may also occur in the other lumbar vertebrae, as well as in the thoracic vertebrae. Spinal disc herniation , more commonly called a slipped disc , is the result of a tear in the outer ring ( anulus fibrosus ) of

4756-429: The intervertebral discs and form the joint. The endplates are formed from a thickened layer of the cancellous bone of the vertebral body, the top layer being more dense. The endplates function to contain the adjacent discs, to evenly spread the applied loads, and to provide anchorage for the collagen fibers of the disc. They also act as a semi-permeable interface for the exchange of water and solutes. The vertebral arch

4838-480: The intervertebral discs. The lumbar vertebrae are located between the ribcage and the pelvis and are the largest of the vertebrae. The pedicles are strong, as are the laminae, and the spinous process is thick and broad. The vertebral foramen is large and triangular. The transverse processes are long and narrow and three tubercles can be seen on them. These are a lateral costiform process , a mammillary process and an accessory process . The superior, or upper tubercle

4920-541: The larger animals since they attach to the muscles and ligaments of the body. In the elephant , the vertebrae are connected by tight joints, which limit the backbone's flexibility. Spinous processes are exaggerated in some animals, such as the extinct Dimetrodon and Spinosaurus , where they form a sailback or finback. Vertebrae with saddle-shaped articular surfaces on their bodies, called "heterocoelous", allow vertebrae to flex both vertically and horizontally while preventing twisting motions. Such vertebrae are found in

5002-419: The largest of the vertebrae, their robust construction being necessary for supporting greater weight than the other vertebrae. They allow significant flexion , extension and moderate lateral flexion (side-bending). The discs between these vertebrae create a natural lumbar lordosis (a spinal curvature that is concave posteriorly). This is due to the difference in thickness between the front and back parts of

SECTION 60

#1732793606877

5084-420: The length of the neck. This includes seemingly unlikely animals such as the giraffe, the camel, and the blue whale, for example. Birds usually have more cervical vertebrae with most having a highly flexible neck consisting of 13–25 vertebrae. In all mammals, the thoracic vertebrae are connected to ribs and their bodies differ from the other regional vertebrae due to the presence of facets. Each vertebra has

5166-435: The lumbar and sacral vertebrae together, and sometimes includes their surrounding areas. There are five sacral vertebrae (S1–S5) which are fused in maturity, into one large bone, the sacrum , with no intervertebral discs . The sacrum with the ilium forms a sacroiliac joint on each side of the pelvis , which articulates with the hips . The last three to five coccygeal vertebrae (but usually four) (Co1–Co5) make up

5248-423: The necks of birds and some turtles. "Procoelous" vertebrae feature a spherical protrusion extending from the caudal end of the centrum of one vertebra that fits into a concave socket on the cranial end of the centrum of an adjacent vertebra. These vertebrae are most often found in reptiles , but are found in some amphibians such as frogs. The vertebrae fit together in a ball-and-socket articulation, in which

5330-416: The occipital bone to the petrous-part of the temporal bone . The occipital plane [Fig. 3] of the squamous part of the occipital bone is developed in membrane , and may remain separate throughout life when it constitutes the interparietal bone ; the rest of the bone is developed in cartilage. The number of nuclei for the occipital plane is usually given as four, two appearing near the middle line about

5412-445: The other cranial bones, it is classed as a flat bone . Due to its many attachments and features, the occipital bone is described in terms of separate parts. From its front to the back is the basilar part , also called the basioccipital, at the sides of the foramen magnum are the lateral parts , also called the exoccipitals, and the back is named as the squamous part . The basilar part is a thick, somewhat quadrilateral piece in front of

5494-442: The posterior border of the vertebral foramen, which completes the triangle of the vertebral foramen. The upper surfaces of the laminae are rough to give attachment to the ligamenta flava . These ligaments connect the laminae of adjacent vertebra along the length of the spine from the level of the second cervical vertebra . Above and below the pedicles are shallow depressions called vertebral notches ( superior and inferior ). When

5576-454: The posterior margin of the foramen magnum during the fifth month; this forms a separate ossicle (sometimes double) which unites with the rest of the squamous part before birth. Each of the lateral parts begins to ossify from a single center during the eighth week of fetal life. The basilar portion is ossified from two centers, one in front of the other; these appear about the sixth week of fetal life and rapidly coalesce. The occipital plane

5658-410: The posterior part of the jugular foramen . The lambdoid suture joins the occipital bone to the parietal bones . The occipitomastoid suture joins the occipital bone and mastoid portion of the temporal bone . The sphenobasilar suture joins the basilar part of the occipital bone and the back of the sphenoid bone body. The petrous-basilar suture joins the side edge of the basilar part of

5740-422: The second month, and two some little distance from the middle line about the third month of fetal life . The nuchal plane of the squamous part is ossified from two centers, which appear about the seventh week of fetal life and soon unite to form a single piece. Union of the upper and lower portions of the squamous part takes place in the third month of fetal life. An occasional centre ( Kerckring ) appears in

5822-475: The seventh cervical vertebra is associated with an abnormal extra rib, known as a cervical rib , which develops from the anterior root of the transverse process. These ribs are usually small, but may occasionally compress blood vessels (such as the subclavian artery or subclavian vein ) or nerves in the brachial plexus , causing pain, numbness, tingling, and weakness in the upper limb, a condition known as thoracic outlet syndrome . Very rarely, this rib occurs in

5904-425: The skull). In many animals these parts stay separate throughout life; for example, in the dog as four parts: squamous part (supraoccipital); lateral parts –left and right parts (exoccipital); basilar part (basioccipital). The occipital bone is part of the endocranium , the most basal portion of the skull. In Chondrichthyes and Agnatha , the occipital does not form as a separate element, but remains part of

5986-415: The smallest, lightest vertebrae and the vertebral foramina are triangular in shape. The spinous processes are short and often bifurcated (the spinous process of C7 is not bifurcated, and is substantially longer than that of the other cervical spinous processes). The atlas differs from the other vertebrae in that it has no body and no spinous process. It has instead a ring-like form, having an anterior and

6068-414: The tailbone or coccyx . There are no intervertebral discs . Somites form in the early embryo and some of these develop into sclerotomes. The sclerotomes form the vertebrae as well as the rib cartilage and part of the occipital bone . From their initial location within the somite, the sclerotome cells migrate medially toward the notochord . These cells meet the sclerotome cells from the other side of

6150-420: The third to the seventh cervical vertebrae and of the first thoracic vertebra. Together with the vertebral disc, this uncinate process prevents a vertebra from sliding backward off the vertebra below it and limits lateral flexion (side-bending). Luschka's joints involve the vertebral uncinate processes. The spinous process on C7 is distinctively long and gives the name vertebra prominens to this vertebra. Also

6232-453: The total number of vertebrae ranges from 32 to 35. In about 10% of people, both the total number of pre-sacral vertebrae and the number of vertebrae in individual parts of the spine can vary. The most frequent deviations are eleven (rarely thirteen) thoracic vertebrae, four or six lumbar vertebrae and three or five coccygeal vertebrae (rarely up to seven). The regional vertebrae increase in size as they progress downward but become smaller in

6314-410: The transverse sinuses : each is received into the interval between the mastoid angle of the parietal bone , and the mastoid portion of the temporal bone . The inferior angle is fused with the body of the sphenoid bone . The superior borders extend from the superior to the lateral angles: they are deeply serrated for articulation with the occipital borders of the parietals, and form by this union

6396-433: The two topmost vertebrae. The atlas (C1) is the topmost vertebra, and along with the axis forms the joint connecting the skull and spine . It lacks a vertebral body, spinous process, and discs either superior or inferior to it. It is ring-like and consists of an anterior arch, posterior arch, and two lateral masses. The axis (C2) forms the pivot on which the atlas rotates. The most distinctive characteristic of this bone

6478-410: The vertebrae articulate the notches align with those on adjacent vertebrae and these form the openings of the intervertebral foramina . The foramina allow the entry and exit of the spinal nerves from each vertebra, together with associated blood vessels. The articulating vertebrae provide a strong pillar of support for the body. There are seven processes projecting from the vertebra: A major part of

6560-429: The vertebral arch called the pars interarticularis . Vertebrae take their names from the regions of the vertebral column that they occupy. There are usually thirty-three vertebrae in the human vertebral column — seven cervical vertebrae , twelve thoracic vertebrae , five lumbar vertebrae , five fused sacral vertebrae forming the sacrum and four coccygeal vertebrae , forming the coccyx . Excluding rare deviations,

6642-408: The vertebral artery; more frequently, the vertebral vein traverses it on both sides, but the usual arrangement is for both artery and vein to pass in front of the transverse process, not through the foramen. The movement of nodding the head takes place predominantly through flexion and extension at the atlanto-occipital joint between the atlas and the occipital bone . However, the cervical spine

6724-493: The vertebrate 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. In the human vertebral column , the size of the vertebrae varies according to placement in the vertebral column, spinal loading, posture and pathology. Along the length of the spine , the vertebrae change to accommodate different needs related to stress and mobility. Each vertebra

#876123