Spine - Anatomy Pictures and Information Home > Skeletal System > Spine Spine Stretching down the midline of the trunk from the base of the skull to the coccyx, the spine plays an extremely important role in our bodies as it supports the upper body’s weight; provides posture while allowing for movement and flexibility; and protects the spinal cord. The spine, also known as the vertebral column or spinal column, is a column of 26 bones in an adult body – 24 separate vertebrae interspaced with cartilage, and then additionally the sacrum and coccyx.... Move up/down/left/right: Click compass arrows Rotate image: Click and drag in any direction, anywhere in the frame Identify objects: Click on them in the image Vertebra and Spinal Cord, Cross-section Full Spine Description [Continued from above] . . . Prior to adolescence, the spine consists of 33 bones because the sacrum’s five bones and the coccyx’s four do not fuse together until adolescence. The vertebrae are named by the first letter of their region (cervical, thoracic, or lumbar) and with a number to indicate their position along the superior-inferior axis.

For example, the fifth lumbar vertebra (which is most inferior one, located beneath the fourth lumbar vertebra) is called the L5 vertebra. Each vertebra has several important parts: the body, vertebral foramen, spinous process, and transverse process. The body is the main weight-bearing region of a vertebra, making up the bulk of the bone’s mass. Extending from the body, the transverse processes are thin columns of bone that point out to the left and right sides of the body. The spinous process extends from the ends of the transverse processes in the posterior direction. Between the body, transverse processes and spinous process is the vertebral foramen, a hollow space that contains the spinal cord and meninges. Between the vertebrae of the spine are thin regions of cartilage known as the intervertebral discs. Intervertebral discs are made of an outer shell known as the annulus fibrosus and a soft, pulpy region known as the nucleus pulposus in the middle. The annulus fibrosus is made of tough fibrocartilage that binds the vertebrae together but is flexible enough to allow for our movements.

The inner nucleus pulposus acts as a shock absorber to support the body’s weight and prevent the vertebrae from painfully crashing into each other while under strain. The vertebrae of the spine align so that their vertebral canals form a hollow, bony tube to protect the spinal cord from external damage and infection. Between the vertebrae are small spaces known as intervertebral canals that allow spinal nerves to exit the spinal cord and connect to the various regions of the body. There are 5 major regions of the spine: Cervical: The 7 vertebrae in the neck form the cervical region of the spine. Cervical vertebrae are the thinnest and most delicate vertebrae in the spine but offer great flexibility to the neck. The first cervical vertebra, C1, supports the skull and is named “atlas” after the Greek titan who held the Earth on his shoulders. The skull pivots on the atlas when moving up and down. The second cervical vertebra, C2, is also known as the “axis” because it allows the skull and atlas to rotate to the left and right.

Thoracic: The 12 vertebrae in the chest region form the spine’s thoracic region. Thoracic vertebrae are larger and stronger than cervical vertebrae but are much less flexible. The spinous processes of the thoracic vertebrae point inferiorly to help lock the vertebrae together. A unique feature of the thoracic vertebrae is that each one forms joints with a pair of ribs to form the sturdy rib cage that protects the organs of the chest. Lumbar: The 5 vertebrae in the lower back form the lumbar region of the spine. Lumbar vertebrae are even larger and stronger than thoracic vertebrae, but are more flexible due to the lack of ribs in the lumbar region. All of the upper body’s weight bears down on the lumbar vertebrae, leading to many back problems in this region despite the size and strength of the vertebrae. Sacral: The sacral region of the spine contains only the sacrum, a single bone in the adult skeleton that is formed by the fusion of 5 smaller vertebrae during adolescence. The sacrum is a flat, triangular bone found in the lower back and wedged between the 2 hip bones.

Coccygeal: The spine’s coccygeal region contains only the coccyx, a single bone in the adult skeleton that is formed by the fusion of 4 tiny vertebrae during adolescence. The coccyx is often referred to as the human tailbone, as this region is homologous to the tail bones of animals that have tails. In humans, the coccyx bears our body weight when sitting down and provides attachment points for muscles of the pelvic and gluteal regions. While most people have a coccyx made of 4 fused vertebrae, the coccyx may consist of as few as 3 or as many as 5 vertebrae. The length of the coccyx has no effect on the body’s function.

Prepared by Tim Taylor, Anatomy and Physiology Instructor Chapter 39: The vertebral column Chapter 39: The vertebral column Vertebral column in general The vertebral column usually consists of 33 vertebrae: 24 presacral vertebrae (7 cervical, 12 thoracic, and 5 lumbar) followed by the sacrum (5 fused sacral vertebrae) and the coccyx (4 frequently fused coccygeal vertebrae). The 24 presacral vertebrae allow movement and hence render the vertebral column flexible. Stability is provided by ligaments, muscles, and the form of the bones. The abbreviations C., T., L., S., and Co. are used for the regions, and these are sometimes followed by V. for vertebra or N. for nerve. Curvatures. The adult vertebral column presents four anteroposterior curvatures: thoracic and sacral, both concave anteriorly, and cervical and lumbar, both concave posteriorly (fig. 39-1 ).

The thoracic and sacral curvatures, termed primary, appear during the embryonic period proper, whereas the cervical and lumbar curvatures, termed secondary, appear later (although before birth) and are accentuated in infancy by support of the head and by the adoption of an upright posture. Parts of a Vertebra. A typical vertebra consists of (1) a body and (2) a vertebral arch, which has several processes (articular, transverse, and spinous) for articular and muscular attachments. Between the body and the arch is the vertebral foramen: the sum of the vertebral foramina constitutes the vertebral canal, which houses the spinal cord (fig. 39-2 ). In addition to the transverse and spinous processes, which serve as short levers, the 12 thoracic vertebrae are connected by joints with paired, long levers, namely the ribs. The bodies of the vertebrae are separated from each other by intervertebral discs. The body is mainly spongy bone and red marrow, but the margins of the upper and lower surfaces consist of a ring of compact bone, the vertebral end-plates.

The body is marked on its sides by vascular foramina. The vertebral arch consists of right and left pedicles (which connect it to the body) and right and left laminae. The transverse processes emerge laterally at the junction of the pedicles and laminae, and the spinous process proceeds posteriorly from the union of the laminae. The superior and inferior articular processes project vertically from the vertebral arches on each side and bear articular facets. When vertebra are in their anatomical position, notches between adjacent pedicles form intervertebral foramina, each of which typically transmitsneural structures including a spinal ganglion and a ventral root of a spinal nerve. Relationship of Spinal Nerves to Vertebrae. The first cervical nerve emerges between the skull and the atlas, and cervical nerves C2 to 7 continue to leave the vertebral canal above the correspondingly numbered vertebrae. C8 emerges between the C7 and T1 vertebrae, and the remaining spinal nerves leave below the correspondingly numbered vertebrae. Regional characteristics of vertebrae The vertebrae of each region have special characteristics, which are now described. Cervical Vertebrae.

The seven vertebrae of the neck are characterized by an opening in each transverse process known as a foramen transversarium. The upper six pairs of foramina transversaria transmit the vertebral artery. The C1 vertebra, which supports the skull, is termed the atlas, and C2, which serves as a pivot for the atlas, is termed the axis. Atlas (fig. 39-3 ). The atlas (C1), which has neither body nor spinous process, consists of two lateral masses connected by a short anterior and a longer posterior arch. Each lateral mass presents upper and lower facets, for the occipital condyle of the skull and for the axis, respectively. The transverse processes are long and are vaguely palpable in vivo immediately below the auricle. The anterior arch presents an anterior tubercle in front (for the anterior longitudinal ligament) and a facet posteriorly (for the dens of the axis). The posterior arch is grooved above for the vertebral artery and the small C1 nerve on each side, and it presents a posterior tubercle behind. Axis (fig. 39-4 ).

The axis (C2) is characterized by the dens (or odontoid process), which projects upward from the body and articulates with the anterior arch of the atlas. The dens is anchored to the occipital bone (by apical and alar ligaments) and is limited behind by the transverse ligament of the atlas (fig. 39-3 ). It is frequently claimed that the dens represents the body of the atlas, but this is doubtful. * Remaining cervical vertebrae (fig. 39-5 ). The lower cervical vertebrae, C2 to 6 are typical and present short, bifid spinous processes. The bodies are small and oval in shape. There are superiorly-projecting lips at the superolateral borders of the vertebral bodies. These closely match indentations in the lateral border of inferior aspect of the vertebral body above. Each transverse process, pierced by a foramen transversarium, ends laterally in anterior and posterior tubercles, which are connected by an "intertubercular lamella" or bar. # The bars are grooved by the ventral primary rami of the spinal nerves, which pass posterior to the foramina transversaria.

The anterior tubercles of C6 vertebra are large and are termed the carotid tubercles, because the common carotid arteries can be compressed against them. C7 vertebra has a long, non-bifid spinous process and is known as the vertebra prominens. (The spinous processes of C6 and 7 and T1 are usually visible in vivo when the neck is flexed.) The anterior tubercles (costal processes) of C7 vertebra may develop separately as cervical ribs. (Lumbar ribs are less frequent.) Thoracic Vertebrae (figs. 39-5 , 39-6 and 39-7 ). It should be noted that all vertebrae are dorsal, although only 12 are thoracic. The 12 vertebrae of the thorax bear the ribs. The T1 vertebra (like C.V.7) is transitional in appearance. T2 to 8 vertebra are typical thoracic vertebrae with a kidney shaped body (fig. 39-5 ). Demifacets for the heads of the ribs (see fig.

20-3 ) are found supeiorly and inferiorly at the junction of the body and pedicle. The transverse processes of T1 to 10 have costal facets for the tubercles of the ribs. The spinous processes are long, slender, and sloping: their tips lie opposite the subjacent body or even at the level of the intervertebral disc below the subjacent body. The various facets for the ribs on T1 and on T9 to 12 veertebral bodies are arranged differently. T11 and 12 are transitional in form, i.e., partly resembling lumbar vertebrae. A humped back is termed kyphosis. Lumbar Vertebrae (figs. 39-8 and 39-9 ). The five vertebrae between the thorax and sacrum are large and present neither foramina transversaria nor costal facets (fig. 39-5 ). The body is kidney shpaed, and the pedicles and laminae are short and thick.

The part of the lamina between the superior and inferior articular processes is known as the pars interarticularis and is liable to injury in some people (resulting in spondylolisthesis, i.e., a slipping forward of the body of one vertebra on the vertebra or sacrum below it). A mamillary process projects posteriorward from the superior articular process. The transverse process, which corresponds to a rib, is long and thin, and an accessory process may project inferiorward from its root. The spinous processes are quadrilateral and project horizontally backward. The fifth lumbar vertebra, usually the largest vertebra, is mainly responsible for the lumbosacral angle (between the lumbar part of the column and the sacrum). Excessive "hollowing" of the back is termed lordosis. Sacrum (figs. 39-10 and 39-11 ). Five (sometimes six) vertebrae are fused in the adult to form the sacrum, which can be felt below the "small of the back." The sacrum articulates above with L5, laterally with the hip bones, and inferiorly with the coccyx.

It has a roughly triangular appearance with a pelvic and dorsal surface, a lateral mass on each side, and a base and apex. The pelvic surface, concave and facing antero-inferiorly, presents four paired sacral foramina for the ventral primary rami of sacral nerves 1 to 4. The dorsal surface, convex and facing posterosuperiorly, presents a modified series of spinous processes termed the median sacral crest and four paired sacral foramina for the dorsal primary rami of sacral nerves 1 to 4. Below, the sacrum shows right and left sacral cornua, which bound a variable gap termed the sacral hiatus. An anesthetic for the spinal nerves may be injected extradurally through the sacral hiatus (caudal analgesia). The cornua articulate with corresponding horns on the coccyx. The lateral part or mass of the sacrum, lateral to the sacral foramina, consists of the fused transverse processes (including their costal elements). Its superior surface is frequently termed the ala. The superolateral part of the lateral mass presents the auricular (ear-shaped) surface for articulation with the hip bone (sacro-iliac joint).

The surface is limited behind by an area (sacral tuberosity) for interosseous ligaments. The base, formed by the suprior part of the first sacral vertebra, presents a prominent anterior margin termed the promontory (fig. 39-11 ). Superior articular processes articulate with the fifth lumbar vertebra. The sacral canal (which contains the dura, cauda equina, and filum terminale) extends from the base to the sacral hiatus. The apex of the sacrum may be fused with the coccyx. Coccyx (fig. 39-10 ). The vertebrae (usually four) below the sacrum are variably fused in the adult to form the coccyx, which resembles a miniature sacrum in shape. Development of vertebrae (figs. 39-12 and 39-13 ) Vertebrae develop in mesenchyme and cartilage during the embryonic period proper, and most begin to ossify during fetal life. Typically, a vertebra at birth shows three ossific areas, one for the centrum (defined in fig.

39-14 ) and one for each half of the neural arch. At about puberty, ossific centers appear in the margins of the upper and lower surfaces of the body (ring epiphyses) and at the tips of the various processes. Developmental failure of half a vertebra (hemivertebra) is one cause of lateral curvature (scoliosis). Failure of fusion of the halves of one or more neural (future vertebral) arches is termed spina bifida. The meninges alone (meningocele), or the spinal cord and meninges (meningomyelocele), may protrude through the defect (spina bifida cystica). When the defect is skeletal rather than neural, it may be concealed by the skin (although sometimes marked by a tuft of hair) and is termed spina bifida occulta. In the sacrum, this is quite common. Surface anatomy The spinous processes of the vertebrae are palpable in the median furrow of the back. The external occipital protuberance is palpable in adults.

The spines of vertebrae C6, C7, and T1 are usually prominent and palpable, and they are made more conspicuous by flexion of the neck and trunk. In the thoracic region, the spinous process of each vertebra extends to the level of at least the body of the vertebra below. The inferior angle of the scapula is frequently at the level of the spinous process of T7. A horizontal plane between the highest points of the iliac crests (supracristal plane) is usually at the level of the spinous process of L4, and this is used as a landmark for lumbar puncture. A needle introduced here should enter the subarachnoid space after 4 to 6 cm. The posterior superior iliac spine is commonly marked by a skin dimple (fig. 39-15 ). Additional reading Kohler, A., and Zimmer, E. A. Borderlands of the Normal and Early Pathologic in Skeletal Roentgenology, 3rd ed" trans, by S. P. Wilk, Grone & Stratton, New York, 1968.

This classic study of the entire skeleton is available in a more recent edition in German. Schmorl, G., and Junghanns, H., The Human Spine in Health and Disease, 2nd ed., trans. by E. F. Besemann, Grone & Stratton, New York, 1971. This well known work is an important account of the normal and abnormal vertebral column. Questions 39-1 How many vertebrae are movable? 39-1 The 24 "presacral" vertebrae are movable. Eighty-nine per cent of people have 24 presacral vertebrae, 6 per cent have 23, and 5 per cent have 25 (P. E. Bomstein and R. R. Peterson, Am. J. Phys. Anthropol., 25:139-146, 1966). 39-2 Which curvatures first appear in the vertebral column? 39-2 The thoracic and sacral curvatures are primary (appearing during embryonic life).

The cervical and lumbar curvatures are secondary (appearing during fetal life and accentuated during infancy). 39-3 How many processes characterize a vertebral arch? 39-3 A typical vertebral arch is characterized by at least seven processes: four articular, two transverse, and one spinous. Lumbar vertebrae have small, additional (mamillary and accessory) processes. The axis has an odontoid process (the dens) but no superior articular processes (merely facets). The atlas has only transverse processes. 39-4 Where are the intervertebral foramina and what do they contain? 39-4 The intervertebral foramina are between adjacent pedicles, and typically each contains a spinal ganglion and a ventral root (or rootlets) of a spinal nerve (see fig. 41-3 ). 39-5 Between which vertebrae does the C8 nerve emerge? 39-5 C8 nerve root emerges between C7 and T1 vertebrae. Hence the remaining spinal nerves below leave inferior to the correspondingly numbered vertebrae.

39-6 What are the key features of the cervical, thoracic, lumbar, and sacral vertebrae? 39-6 The key features of cervical, thoracic, lumbar, and sacral vertebrae are, respectively, foramina transversaria, articulation with ribs, absence of both of the above features, and fusion. 39-7 How many dorsal vertebrae are present in the body? 39-7 All 33 vertebrae are dorsal. Twelve are thoracic. 39-8 What is the pars interarticularis? 39-8 The pars interarticularis, visible on oblique radiographs of the lumbar vertebrae (see fig. 39-9 ), is the part of the neural arch between the superior and inferior articular processes. The slipping forward of a vertebral body (e.g., L5) is termed spondylolisthesis (Gk, vertebral slipping) and usually involves fracture at the pars interarticularis. Case Report.

A 50-year-old nurse complained of numbness of the right big toe, a burning pain down the lateral side of the right leg and foot, bowel and bladder problems, and weakness of the lower limbs. She developed a marked depression over the spinous process of L5. At operation, spondylolisthesis of L5 on S1 was found, with defective partes interarticulares of L5 and protrusion of the L4/5 disc. The leg pains were caused by compression of L5 nerve roots from alterations of the L5/S1 facets. Bowel and bladder difficulties were produced by compression of the cauda equina from gross distortion of the vertebral canal. Decompression by removal of some bone near the pedicles relieved the symptoms (G. Austin, The Spinal Cord, Thomas, Springfield, Illinois, 1961). Numerous case studies on anatomy have been described by E. Lachman (Case Studies in Anatomy, 3rd ed., Oxford University Press, New York, 1981) and also by L. K. Schneider (Anatomical Case Histories, Year Book, Chicago, 1976).

39-9 What are the chief contents of the sacral canal? 39-9 The sacral canal contains the dura, cauda equina, and filum terminale. Above S2, a subarachnoid space is also present (see fig. 41-1 ). 39-10 What is the ossific status of a typical vertebra at birth? 39-10 At birth, a typical vertebra shows three primary ossific areas, one for the centrum and one for each half of the neural arch. (The centrum does not correspond to the whole of the body: see fig. 39-14 .) The three primary areas become united by bone in early childhood (3 to 6 years). A number of secondary centers (the ring epiphyses and centers for the tips of the transverse and spinous processes) appear at about puberty. 39-11 How is surgical access to the spinal cord achieved? 39-11 Surgical access to the spinal cord and nerve roots is achieved by sectioning the laminae (laminectomy) on each side of several vertebrae. 39-12 What is spina bifida?

39-12 Spina bifida is a developmental anomaly in which the halves of one or more neural (future vertebral) arches have failed to fuse. The spinal cord and meninges (myelomeningocele), or the meninges alone (meningocele), may protrude through the defect (spina bifida cystica). When the defect is skeletal rather than neural, it is termed spina bifida occulta; this defect is found in the sacrum in approximately one fifth of the general population (A. C. Berry, J. Anal., 120:519,1975), although the incidence is minute in certain peoples (J. I. Levy and C. Freed, J. Anal., 114:449, 1973). 39-13 Which Latin and Greek roots are used with reference to the vertebral column? 39-13 The Latin roots spino- and vertebro- are used with reference to the vertebral column (e.g., in spinotransverse and vertebrocostal).

Greek roots with a similar significance are spondyl- and rhachi- (e.g., in spondylolisthesis and rachischisis, the latter meaning "vertebral cleft" and used for an open spina bifida, especially one that extends along many vertebrae). Figure legends Figure 39-1 The primary (1, thoracic; 2, sacral) and secondary (3, cervical; 4, lumbar) curvatures of the vertebral column. Figure 39-2 The parts of a vertebra (T.V.6) seen from above and from the right side. Adjacent intervertebral notches form intervertebral foramina for the transmission of nerves. Figure 39-3 The atlas from above. Muscle origins and the superior vertebral artery are shown on the right side. (After Frazer.) Figure 39-4 lateral and posterosuperior views of the axis. Figure 39-5 Various vertebrae from lateral, superior, and posterior aspects. Figure 39-6 The positions, lengths, and directions of (A) the spinous processes and (B) the transverse processes.

The vertebrae in black mark the levels at which a change in direction of curvature occurs. Figure 39-7 Thoracic vertebrae (and C7 and L1). Note the bodies, pedicles, transverse and spinous processes, and costrotransverse joints. (Courtesy of V.C. Johnson, M.D., Detroit, Michigan.) Figure 39-8 Lumbar vertebrae and female pelvis. Figure 39-9 Oblique view of the lumbar vertebrae. Note the very small twelfth rib, the joints between the articular processes ofthe lumbar vertebrae (the arrow indicates the joint between L1 and L2), and the sacrum. In this view the outline of a Scotch terrier is formed by the transverse process (snout, overlapping the vertebral body), the superior articular process (ear), and the inferior articular process (forepaw). The neck of the dog corresponds to the important pars interarticularis, injury to which may result in spondylolisthesis. Figure 39-10 Female sacrum and coccyx. A, Pelvic and, B, dorsal aspects showing muscular and ligamentous attachments.

C, Right lateral aspect in the anatomical position. Figure 39-11 Female and male sacra from above. The superior aspect of the lateral part is the ala. Figure 39-12 Scheme of horizontal sections of vertebrae, showing what are thought to be corresponding parts. Note that the costal element forms a part of the transverse process of a cervical vertebra. It forms the rib in the thoracic region, most of the transverse process in the lumbar region, and the greater portion of the lateral part of the sacrum. In the cervical vertebra, the posterior tubercle of the transverse process should probably also be shaded as part of the costal element. Figure 39-13 Variations in vertebrae. B shows the common arrangement. In A, "cranial shift," a cervical rib articulates with C7 and rib 12 is small. In B, L5 is partially "sacralized" and S5 is partially freed. In C, "caudal shift," rib 12 is large and a small lumbar rib is present.

S1 vertebra is partially "lumbarized" and Co.1 is incorporated into the sacrum. (After Schinz et al.) Figure 39-14 The neural arch and centrum (left half of figure), and the vertebral arch and body (right half). The terms centrum and neural arch refer to those parts of a vertebra ossified from primary centers. The terms vertebral arch and body are descriptive terms generally applied to adult vertebrae. The body of a vertebra includes the centrum and part of the neural arch. The vertebral arch, therefore, is less extensive than the neural arch. Note that the rib articulates with the neural arch and not with the centrum. Figure 39-15 Some surface landmarks of the back. (From Royce, L Surface Anatomy, Davis, Philadelphia, 1965,) * See F. A. Jenkins, Anat. Rec., 164:173-184, 1969.

# The part of a cervical vertebra that corresponds to a rib is probably the transverse process lateral to the foramen transversarium and including the anterior and posterior tubercles as well as the "intertubercular lamella" (or so-called costotransverse bar). See A. J. E. Cave, J. Zool., 177:377-393, 1975. Only the anterior tubercle is shaded in figure 39-12 . Jump to: Anatomy of the Spine - Cedars-Sinai Anatomy of the Spine The human spine is a complex anatomic structure that is the scaffolding for the entire body. It provides several important functions, including: Protecting the spinal cord and nerves Structural support for the body, allowing us to stand upright. The spine supports about half the weight of the body. The average person is born with 33 individual bones (the vertebrae) that interact and connect with each other through flexible joints called facets. By the time a person becomes an adult most have only 24 vertebrae because some vertebrae at the bottom end of the spine fuse together during normal growth and development.

Sometimes a person may have an additional vertebra, which is called a transitional body and is usually found at the sixth level of the lumbar area (labeled L6). The bottom of the spine is called the sacrum. It is made up of several vertebral bodies usually fused together as one. The remaining small bones or ossicles below the sacrum are also fused together and called the tailbone or coccyx. The spine above the sacrum consists of: Seven bones in the neck - the cervical spine 12 bones in the chest - the thoracic spine Five bones in the lower back - the lumbar spine The spinal column combines strong bones, unique joints, flexible ligaments and tendons, large muscles and highly sensitive nerves. While many of us take the benefits of a healthy spine for granted, spinal pain is a sharp reminder of how much we depend on our back in daily life.

Some causes of spinal pain include: Irritation of the large nerves as they exit the bony confines of the spine leading to the arms and legs Irritation of the smaller nerves of the spine that involve innervate or supply the discs between the vertebrae, facets and ligaments Strain of the large muscles of the back that hold the spine upright Injuries to the bones, ligaments or joints Damage or disease to the discs that separate the vertebrae Abnormal movement between segments Tumors, infection, trauma, deformity or other spinal disorders The spinal column is made up of many parts, all designed to help the back move flexibly, support body weight and protect the spinal cord and nerves. These parts include the: How Many Vertebrae Does a Human Being Have? Test What You Know! Follow Us How Many Vertebrae Does a Human Being Have? Test What You Know! The human vertebral column comprises 33 vertebrae that collectively protect the spinal cord and support the entire skeletal framework of the body. The current article provides a brief description of the number of vertebrae in humans beings along with their respective location. Advertisement Gravity makes you look shorter!

Gravitational force compresses your vertebral column, and it can elongate by 2-3 inches in the absence of gravity. The vertebral column (backbone or spine) is a characteristic feature of vertebrates. Extending from the base of the skull to the pelvis, it forms the axis of their skeletons. It is made up of individual units called vertebrae, within which the spinal cord is enclosed. This structure provides protection to the spinal cord, and also influences the overall posture of the animal. Other functions include structural support for head, shoulders and chest; as well as balance and weight distribution for maintaining flexibility and mobility. The vertebral column of an adult human being is composed of 33 vertebrae, of which 24 are known as articulating or movable vertebrae, and are separated from each other by an intervertebral disc. The remaining 9 vertebrae lack the intervertebral disc and form two sets of fused structures. The total length of an adult vertebral column is about 71 cm in men and about 61 cm in women. Do you know how many vertebrae does a human being have?

Classified into five categories depending on their location in the body, the total number of vertebrae in human beings are: ♦ Cervical: 7 (C1 to C7) ♦ Thoracic: 12 (T1 to T12) ♦ Lumbar: 5 (L1 to L5) ♦ Sacral: 5 (S1 to S5, fused) ♦ Coccygeal: 4 (Co1 to Co4, fused) Total number = 33 A detailed account of the number of vertebrae in human beings as well as their names and characteristics have been provided below. Cervical (n = 7) Numbered as C1 to C7, the cervical vertebrae are present in the neck region with C1 present closest to the skull. These are smaller as compared to the other articulating vertebrae. C1 or atlas is the topmost vertebra of the spinal column, and supports the head. It freely rotates over a pivot formed by the next vertebra C2 which is termed axis or epistropheus. Together, the atlas and axis form the joint through which the skull and spine are connected.

The next four vertebrae, C3 to C6, share a similar structure, and have short and bifid spinous processes. The last vertebra in this region, C7, has long and prominent spinous process, and hence is also called vertebra prominens. Spinous process is the region for attachment of muscles and ligaments. Thoracic (n = 12) These are present in the chest region, and are designated as T1 to T12. These vertebrae have special facets for the attachment of ribs. The vertebral bodies are heart-shaped and intermediate in size as compared to the cervical and lumbar vertebrae. Being attached to the rib cage they provide lesser flexibility. Lumbar (n = 5) The five lumbar vertebrae are present in the lower back region between the rib cage and the pelvis, and are termed L1 to L5. They enable flexion and extension movements, and help to support body weight. The vertebra body is larger than the cervical and thoracic vertebrae, and is kidney-shaped. The fifth lumbar vertebra or L5, is generally the largest of all vertebrae.

Sacral (n = 5) Sacrum is a triangular, shield-shaped bony structure present below the lumbar vertebrae, and forms the posterior pelvic wall. It supports and strengthens the pelvis. The sacrum is formed by the fusion of 5 (sometimes 6) vertebrae known as the sacral vertebrae named as S1 to S5. Initially they exist as separate vertebrae, and begin to fuse after the age of 18. The fusion completes between the ages of 25 to 33. Coccygeal (n = 4) The last segment of the vertebral column is a structure called coccyx or tailbone, and represents a vestigial tail in humans. It is formed by the fusion of four small vertebrae designated as Co1 to Co4. Similar to the sacral vertebrae, these vertebrae too exist separately in the first two decades of life. The coccyx serves as an anchor for certain pelvic muscles and ligaments. The supporting structure called vertebral column is thus made up of 26 bones including 24 vertebrae and a sacrum and coccyx.

Reshma Jirage Spine Anatomy, Anatomy of the Human Spine Anatomy of the Human Spine Overview The spine is made of 33 individual bones stacked one on top of the other. This spinal column provides the main support for your body, allowing you to stand upright, bend, and twist, while protecting the spinal cord from injury. Strong muscles and bones, flexible tendons and ligaments, and sensitive nerves contribute to a healthy spine. Yet, any of these structures affected by strain, injury, or disease can cause pain. Spinal curves When viewed from the side, an adult spine has a natural S-shaped curve. The neck (cervical) and low back (lumbar) regions have a slight concave curve, and the thoracic and sacral regions have a gentle convex curve (Fig. 1). The curves work like a coiled spring to absorb shock, maintain balance, and allow range of motion throughout the spinal column. Figure 1. The spine has three natural curves that form an S-shape; strong muscles keep our spine in alignment. Figure 2. The five regions of the spinal column. The muscles and correct posture maintain the natural spinal curves.

Good posture involves training your body to stand, walk, sit, and lie so that the least amount of strain is placed on the spine during movement or weight-bearing activities (see Posture ). Excess body weight, weak muscles, and other forces can pull at the spine's alignment: An abnormal curve of the lumbar spine is lordosis, also called sway back. An abnormal curve of the thoracic spine is kyphosis, also called hunchback. An abnormal curve from side-to-side is called scoliosis. Muscles The two main muscle groups that affect the spine are extensors and flexors. The extensor muscles enable us to stand up and lift objects. The extensors are attached to the back of the spine. The flexor muscles are in the front and include the abdominal muscles. These muscles enable us to flex, or bend forward, and are important in lifting and controlling the arch in the lower back. The back muscles stabilize your spine. Something as common as poor muscle tone or a large belly can pull your entire body out of alignment. Misalignment puts incredible strain on the spine (see Exercise for a Healthy Back ). Vertebrae Vertebrae are the 33 individual bones that interlock with each other to form the spinal column.

The vertebrae are numbered and divided into regions: cervical, thoracic, lumbar, sacrum, and coccyx (Fig. 2). Only the top 24 bones are moveable; the vertebrae of the sacrum and coccyx are fused. The vertebrae in each region have unique features that help them perform their main functions. Cervical (neck) - the main function of the cervical spine is to support the weight of the head (about 10 pounds). The seven cervical vertebrae are numbered C1 to C7. The neck has the greatest range of motion because of two specialized vertebrae that connect to the skull. The first vertebra (C1) is the ring-shaped atlas that connects directly to the skull. This joint allows for the nodding or “yes” motion of the head. The second vertebra (C2) is the peg-shaped axis, which has a projection called the odontoid, that the atlas pivots around. This joint allows for the side-to-side or “no” motion of the head. Thoracic (mid back) - the main function of the thoracic spine is to hold the rib cage and protect the heart and lungs.

The twelve thoracic vertebrae are numbered T1 to T12. The range of motion in the thoracic spine is limited. Lumbar (low back) - the main function of the lumbar spine is to bear the weight of the body. The five lumbar vertebrae are numbered L1 to L5. These vertebrae are much larger in size to absorb the stress of lifting and carrying heavy objects. Sacrum - the main function of the sacrum is to connect the spine to the hip bones (iliac). There are five sacral vertebrae, which are fused together. Together with the iliac bones, they form a ring called the pelvic girdle. Coccyx region - the four fused bones of the coccyx or tailbone provide attachment for ligaments and muscles of the pelvic floor. While vertebrae have unique regional features, every vertebra has three functional parts (Fig. 3): Figure 3. While vertebrae have unique regional features, every vertebra has three main parts: body (purple), vertebral arch (green), and processes for muscle attachment (tan).

a drum-shaped body designed to bear weight and withstand compression (purple) an arch-shaped bone that protects the spinal cord (green) star-shaped processes designed as outriggers for muscle attachment (tan) Intervertebral discs Each vertebra in your spine is separated and cushioned by an intervertebral disc, keeping the bones from rubbing together. Discs are designed like a radial car tire. The outer ring, called the annulus, has criss-crossing fibrous bands, much like a tire tread. These bands attach between the bodies of each vertebra. Inside the disc is a gel-filled center called the nucleus, much like a tire tube (Fig. 4). Figure 4. Intervertebral discs (purple) are made of a gel-filled center called the nucleus and a tough fibrous outer ring called the annulus. The annulus pulls the vertebral bodies together against the resistance of the gel-filled nucleus. Discs function like coiled springs. The criss-crossing fibers of the annulus pull the vertebral bodies together against the elastic resistance of the gel-filled nucleus. The nucleus acts like a ball-bearing when you move, allowing the vertebral bodies to roll over the incompressible gel.

The gel-filled nucleus is composed mostly of fluid. This fluid absorbed during the night as you lie down and is pushed out during the day as you move upright. With age, our discs increasingly lose the ability to reabsorb fluid and become brittle and flatter; this is why we get shorter as we grow older. Also diseases, such as osteoarthritis and osteoporosis, cause bone spurs (osteophytes) to grow. Injury and strain can cause discs to bulge or herniate, a condition in which the nucleus is pushed out through the annulus to compress the nerve roots causing back pain. Vertebral arch & spinal canal On the back of each vertebra are bony projections that form the vertebral arch. The arch is made of two supporting pedicles and two laminae (Fig. 5). The hollow spinal canal contains the spinal cord, fat, ligaments, and blood vessels. Under each pedicle, a pair of spinal nerves exits the spinal cord and pass through the intervertebral foramen to branch out to your body. Figure 5. The vertebral arch (green) forms the spinal canal (blue) through which the spinal cord runs.

Seven bony processes arise from the vertebral arch to form the facet joints and processes for muscle attachment. Surgeons often remove the lamina of the vertebral arch (laminectomy) to access and decompress the spinal cord and nerves to treat spinal stenosis, tumors, or herniated discs. Seven processes arise from the vertebral arch: the spinous process, two transverse processes, two superior facets, and two inferior facets. Facet joints The facet joints of the spine allow back motion. Each vertebra has four facet joints, one pair that connects to the vertebra above (superior facets) and one pair that connects to the vertebra below (inferior facets) (Fig. 6). Figure 6. The superior and inferior facets connect each vertebra together. There are four facet joints associated with each vertebra. Ligaments The ligaments are strong fibrous bands that hold the vertebrae together, stabilize the spine, and protect the discs. The three major ligaments of the spine are the ligamentum flavum, anterior longitudinal ligament (ALL), and posterior longitudinal ligament (PLL) (Fig. 7).

The ALL and PLL are continuous bands that run from the top to the bottom of the spinal column along the vertebral bodies. They prevent excessive movement of the vertebral bones. The ligamentum flavum attaches between the lamina of each vertebra. Figure 7. The ligamentum flavum, anterior longitudinal ligament (ALL), and posterior longitudinal ligament (PLL) allow the flexion and extension of the spine while keeping the vertebrae in alignment. Spinal cord The spinal cord is about 18 inches long and is the thickness of your thumb. It runs within the protective spinal canal from the brainstem to the 1st lumbar vertebra. At the end of the spinal cord, the cord fibers separate into the cauda equina and continue down through the spinal canal to your tailbone before branching off to your legs and feet. The spinal cord serves as an information super-highway, relaying messages between the brain and the body. The brain sends motor messages to the limbs and body through the spinal cord allowing for movement. The limbs and body send sensory messages to the brain through the spinal cord about what we feel and touch. Sometimes the spinal cord can react without sending information to the brain.

These special pathways, called spinal reflexes, are designed to immediately protect our body from harm. The nerve cells that make up your spinal cord itself are called upper motor neurons. The nerves that branch off your spinal cord down your back and neck are called lower motor neurons. These nerves exit between each of your vertebrae and go to all parts of your body. Any damage to the spinal cord can result in a loss of sensory and motor function below the level of injury. For example, an injury to the thoracic or lumbar area may cause motor and sensory loss of the legs and trunk (called paraplegia). An injury to the cervical (neck) area may cause sensory and motor loss of the arms and legs (called tetraplegia, formerly known as quadriplegia). Spinal nerves Thirty-one pairs of spinal nerves branch off the spinal cord. The spinal nerves act as telephone lines, carrying messages back and forth between your body and spinal cord to control sensation and movement. Each spinal nerve has two roots (Fig. 8). The ventral (front) root carries motor impulses from the brain and the dorsal (back) root carries sensory impulses to the brain.

The ventral and dorsal roots fuse together to form a spinal nerve, which travels down the spinal canal, alongside the cord, until it reaches its exit hole - the intervertebral foramen (Fig. 9). Once the nerve passes through the intervertebral foramen, it branches; each branch has both motor and sensory fibers. The smaller branch (called the posterior primary ramus) turns posteriorly to supply the skin and muscles of the back of the body. The larger branch (called the anterior primary ramus) turns anteriorly to supply the skin and muscles of the front of the body and forms most of the major nerves. Figure 8. The ventral (motor) and dorsal (sensory) roots join to form the spinal nerve. The spinal cord is covered by three layers of meninges: pia, arachnoid and dura mater. The spinal nerves are numbered according to the vertebrae above which it exits the spinal canal. The 8 cervical spinal nerves are C1 through C8, the 12 thoracic spinal nerves are T1 through T12, the 5 lumbar spinal nerves are L1 through L5, and the 5 sacral spinal nerves are S1 through S5.

There is 1 coccygeal nerve. Figure 9. The spinal nerves exit the spinal canal through the intervertebral foramen below each pedicle. The spinal nerves innervate specific areas and form a striped pattern across the body called dermatomes (Fig. 10). Doctors use this pattern to diagnose the location of a spinal problem based on the area of pain or muscle weakness. For example leg pain ( sciatica ) usually indicates a problem near the L4-S3 nerves. Figure 10. A dermatome pattern shows which spinal nerves are responsible for sensory and motor control of specific areas of the body. Coverings & spaces The spinal cord is covered with the same three membranes as the brain, called meninges. The inner membrane is the pia mater, which is intimately attached to the cord. The next membrane is the arachnoid mater. The outer membrane is the tough dura mater (Fig. 8). Between these membranes are spaces used in diagnostic and treatment procedures. The space between the pia and arachnoid mater is the wide subarachnoid space, which surrounds the spinal cord and contains cerebrospinal fluid (CSF).

This space is most often accessed when performing a lumbar puncture to sample and test CSF or during a myelogram to inject contrast dye. The space between the dura mater and the bone is the epidural space. This space is most often accessed to deliver anesthetic numbing agents, commonly called an epidural, and to inject steroid medication (see Epidural Steroid Injections ). Sources & links How Many Bones are in the Spinal Column? Home » Spine Articles » Spinal Column Articles » How Many Bones are in the Spinal Column? How Many Bones are in the Spinal Column? Sections Your spine – also known as the vertebral column – stretches all the way from your skull down to your pelvis and contains 33 individual bones, known as vertebrae. These vertebrae are instrumental to the strength, support and flexibility that your spine provides. Cushioned by spongy intervertebral discs and connected at bony facet joints, these vertebrae are the building blocks of your spine.

Sections of the spine The 33 vertebrae are stacked within four regions of the spine: Cervical (neck) – seven vertebrae, labeled C1 through C7 Thoracic (mid-back) – 12 vertebrae, labeled T1 through T12 Lumbar (lower back) – five or six vertebrae, labeled L1 through L5 or L6 Sacrum (pelvis) – five fused vertebrae, labeled S1 through S5 You also have a tailbone, known as the coccyx, containing three fused vertebrae at the bottom of your spinal column. Vertebral problems and their treatments Over time, your vertebrae can fall prey to the natural deterioration associated with the aging process. This can cause a variety of degenerative spine conditions, which can potentially result in a number of painful symptoms. If you have chronic neck or back pain due to a degenerative spine condition, contact Laser Spine Institute. Our orthopedic surgeons and neurosurgeons perform a variety of minimally invasive procedures that are effective alternatives to traditional open neck or back surgery. Want to chat? A Laser Spine Institute team member is available now to answer any questions you may have.

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Question: How many vertebrae bones does a human usually have?
Answer: Thirty-three