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The spinal column, a defining
synapomorphy In phylogenetics, an apomorphy (or derived trait) is a novel character or character state that has evolved from its ancestral form (or plesiomorphy). A synapomorphy is an apomorphy shared by two or more taxa and is therefore hypothesized to hav ...
shared by nearly all
vertebrates Vertebrates () comprise all animal taxa within the subphylum Vertebrata () (chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, with c ...
,
Hagfish Hagfish, of the class Myxini (also known as Hyperotreti) and order Myxiniformes , are eel-shaped, slime-producing marine fish (occasionally called slime eels). They are the only known living animals that have a skull but no vertebral column, ...
are believed to have secondarily lost their spinal column
is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic
irregular bone The irregular bones are bones which, from their peculiar form, cannot be grouped as long, short, flat or sesamoid bones. Irregular bones serve various purposes in the body, such as protection of nervous tissue (such as the vertebrae protect th ...
whose complex structure is composed primarily of
bone A bone is a rigid organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red and white blood cells, store minerals, provide structure and support for the body, ...
, and secondarily of hyaline cartilage. They show variation in the proportion contributed by these two tissue types; such variations
correlate In statistics, correlation or dependence is any statistical relationship, whether causal or not, between two random variables or bivariate data. Although in the broadest sense, "correlation" may indicate any type of association, in statistic ...
on one hand with the cerebral/caudal rank (i.e., location within the
backbone The backbone is the vertebral column of a vertebrate. Arts, entertainment, and media Film * ''Backbone'' (1923 film), a 1923 lost silent film starring Alfred Lunt * ''Backbone'' (1975 film), a 1975 Yugoslavian drama directed by Vlatko Gilić ...
), and on the other with
phylogenetic In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...
differences among the vertebrate
taxa In biology, a taxon (back-formation from ''taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular nam ...
. The basic configuration of a vertebra varies, but the bone is its ''body'', with the central part of the body constituting the ''centrum''. The upper (closer to) and lower (further from), respectively, the cranium and its
central nervous system The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain and spinal cord. The CNS is so named because the brain integrates the received information and coordinates and influences the activity of all p ...
surfaces of the vertebra body support attachment to 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 The ligamenta flava (singular, ''ligamentum flavum'', Latin for ''yellow ligament'') are a series of ligaments that connect the ventral parts of the laminae of adjacent vertebrae. They help to preserve upright posture, preventing hyperflexion, a ...
, which are ligaments of the spine. There are vertebral notches, each constituted by the shape of the pedicles, which form the
intervertebral foramina The intervertebral foramen (also called neural foramen, and often abbreviated as IV foramen or IVF) is a foramen between two spinal vertebrae. Cervical, thoracic, and lumbar vertebrae all have intervertebral foramina. The foramina, or openin ...
when vertebrae articulate. These foramina are the entry and exit conduits accommodating the spinal nerves. The body of the vertebra, and its vertebral arch, form the vertebral
foramen In anatomy and osteology, a foramen (;Entry "foramen"
in
, which is the larger, stable and central opening: this accommodates the
spinal canal The spinal canal (or vertebral canal or spinal cavity) is the canal that contains the spinal cord within the vertebral column. The spinal canal is formed by the vertebrae through which the spinal cord passes. It is a process of the dorsal body ca ...
, and encloses and protects the
spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column (backbone). The backbone encloses the central canal of the sp ...
. 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 the vertebrate species, with the greatest difference seen between an
aquatic animal An aquatic animal is any animal, whether invertebrate or vertebrate, that lives in water for most or all of its lifetime. Many insects such as mosquitoes, mayflies, dragonflies and caddisflies have aquatic larvae, with winged adults. Aquatic ani ...
and other vertebrate animals. As such, vertebrates take their name from the vertebrae that compose the vertebral column.


Structure in humans


General structure

In the human
vertebral column The vertebral column, also known as the backbone or spine, is part of the axial skeleton. The vertebral column is the defining characteristic of a vertebrate in which the notochord (a flexible rod of uniform composition) found in all chordate ...
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 is an irregular bone. Every 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 A bone is a rigid organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red and white blood cells, store minerals, provide structure and support for the body, and ...
, which is the spongy type of
osseous tissue A bone is a rigid organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red and white blood cells, store minerals, provide structure and support for the body, ...
, whose microanatomy has been specifically studied within the pedicle bones. This cancellous bone is in turn, covered by a thin coating of
cortical bone A bone is a rigid organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red and white blood cells, store minerals, provide structure and support for the body, and ...
(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 An intervertebral disc (or intervertebral fibrocartilage) lies between adjacent vertebrae in the vertebral column. Each disc forms a fibrocartilaginous joint (a symphysis), to allow slight movement of the vertebrae, to act as a ligament to hold ...
. These surfaces are the vertebral endplates which are in direct contact with 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 Type I collagen is the most abundant collagen of the human body. It forms large, eosinophilic fibers known as collagen fibers. It is present in scar tissue, the end product when tissue heals by repair, as well as tendons, ligaments, the endo ...
of the disc. They also act as a semi-permeable interface for the exchange of water and solutes. The vertebral arch is formed by pedicles and laminae. Two pedicles extend from the sides of the vertebral body to join the body to the arch. The pedicles are short thick
process A process is a series or set of activities that interact to produce a result; it may occur once-only or be recurrent or periodic. Things called a process include: Business and management *Business process, activities that produce a specific se ...
es 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 backwards and medialwards to join and complete the vertebral arch and form 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 The ligamenta flava (singular, ''ligamentum flavum'', Latin for ''yellow ligament'') are a series of ligaments that connect the ventral parts of the laminae of adjacent vertebrae. They help to preserve upright posture, preventing hyperflexion, a ...
. 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 the vertebrae articulate the notches align with those on adjacent vertebrae and these form the openings of the
intervertebral foramina The intervertebral foramen (also called neural foramen, and often abbreviated as IV foramen or IVF) is a foramen between two spinal vertebrae. Cervical, thoracic, and lumbar vertebrae all have intervertebral foramina. The foramina, or openin ...
. 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.


Processes

There are seven processes projecting from the vertebra: * one spinous process * two transverse processes * four articular processes A major part of a vertebra is a backward extending spinous process (sometimes called the neural spine) which projects centrally. This process points
dorsally Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...
and
caudally Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...
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 the
pedicle Pedicle or pedicel may refer to: Human anatomy *Pedicle of vertebral arch, the segment between the transverse process and the vertebral body, and is often used as a radiographic marker and entry point in vertebroplasty and kyphoplasty procedures ...
, 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 a
lumbar vertebra The lumbar vertebrae are, in human anatomy, the five vertebrae between the rib cage and the pelvis. They are the largest segments of the vertebral column and are characterized by the absence of the foramen transversarium within the transverse ...
is also sometimes called the ''costal''Platzer (2004), pp 42–43Latin ''costa'' refers to either a "rib" or "side" of the body. (Diab (1999), p 76) or ''costiform process''Tweedie, A. ''The library of medicine'
p. 31
/ref> 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 The articular bone is part of the lower jaw of most vertebrates, including most jawed fish, amphibians, birds and various kinds of reptiles, as well as ancestral mammals. Anatomy In most vertebrates, the articular bone is connected to two oth ...
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 the vertebral arch called the ''
pars interarticularis Pars may refer to: * Fars Province of Iran, also known as Pars Province * Pars (Sasanian province), a province roughly corresponding to the present-day Fars, 224–651 * ''Pars'', for ''Persia'' or ''Iran'', in the Persian language * Pars News A ...
''.


Regional variation

Vertebrae take their names from the regions of the vertebral column that they occupy. There are thirty-three vertebrae in the human vertebral column—seven cervical vertebrae, twelve
thoracic vertebrae In vertebrates, thoracic vertebrae compose the middle segment of the vertebral column, between the cervical vertebrae and the lumbar vertebrae. In humans, there are twelve thoracic vertebrae and they are intermediate in size between the cervical ...
, five
lumbar vertebrae The lumbar vertebrae are, in human anatomy, the five vertebrae between the rib cage and the pelvis. They are the largest segments of the vertebral column and are characterized by the absence of the foramen transversarium within the transverse p ...
, five fused sacral vertebrae forming the sacrum and three to five
coccygeal vertebrae The coccyx ( : coccyges or coccyxes), commonly referred to as the tailbone, is the final segment of the vertebral column in all apes, and analogous structures in certain other mammals such as horses. In tailless primates (e.g. humans and other ...
, forming the
coccyx The coccyx ( : coccyges or coccyxes), commonly referred to as the tailbone, is the final segment of the vertebral column in all apes, and analogous structures in certain other mammals such as horses. In tailless primates (e.g. humans and othe ...
. The regional vertebrae increase in size as they progress downwards but become smaller in the coccyx.


Cervical vertebrae

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 An atlas is a collection of maps; it is typically a bundle of maps of Earth or of a region of Earth. Atlases have traditionally been bound into book form, but today many atlases are in multimedia formats. In addition to presenting geograp ...
, and C2 is also called the
axis An axis (plural ''axes'') is an imaginary line around which an object rotates or is symmetrical. Axis may also refer to: Mathematics * Axis of rotation: see rotation around a fixed axis * Axis (mathematics), a designator for a Cartesian-coordinat ...
. The structure of these vertebrae is the reason why the neck and head have a large range of motion. The
atlanto-occipital joint The atlanto-occipital joint (''Capsula articularis atlantooccipitalis'') is an articulation between the atlas bone and the occipital bone. It consists of a pair of condyloid joints. It is a synovial joint. Structure The atlanto-occipital join ...
allows the
skull The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, th ...
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 The circle of Willis (also called Willis' circle, loop of Willis, cerebral arterial circle, and Willis polygon) is a circulatory anastomosis that supplies blood to the brain and surrounding structures in reptiles, birds and mammals, including huma ...
. These are 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, however, 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 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 rectus capitis posterior minor (or rectus capitis posticus minor, both being Latin for ''lesser posterior straight muscle of the head'') arises by a narrow pointed tendon from the tubercle on the posterior arch of the atlas, and, widening as i ...
. The spinous process is small so as not to interfere with the movement between the atlas and the
skull The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, th ...
. 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 The vertebral arteries are major arteries of the neck. Typically, the vertebral arteries originate from the subclavian arteries. Each vessel courses superiorly along each side of the neck, merging within the skull to form the single, midline ba ...
and
vein Veins are blood vessels in humans and most other animals that carry blood towards the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are the pulmonary and umbilical veins, both of which carry oxygenat ...
and a sympathetic nerve plexus. On 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 The vertebral arteries are major arteries of the neck. Typically, the vertebral arteries originate from the subclavian arteries. Each vessel courses superiorly along each side of the neck, merging within the skull to form the single, midline ba ...
. There is a hook-shaped uncinate process on the side edges of the top surface of the bodies of 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 backwards 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 In tetrapods, cervical vertebrae (singular: vertebra) are the vertebrae of the neck, immediately below the skull. Truncal vertebrae (divided into thoracic and lumbar vertebrae in mammals) lie caudal (toward the tail) of cervical vertebrae. In sau ...
to this vertebra. Also a cervical rib can develop from C7 as an
anatomical variation An anatomical variation, anatomical variant, or anatomical variability is a presentation of body structure with morphological features different from those that are typically described in the majority of individuals. Anatomical variations are categ ...
. The term cervicothoracic is often used to refer to the cervical and thoracic vertebrae together, and sometimes also their surrounding areas.


Thoracic vertebrae

The twelve
thoracic vertebrae In vertebrates, thoracic vertebrae compose the middle segment of the vertebral column, between the cervical vertebrae and the lumbar vertebrae. In humans, there are twelve thoracic vertebrae and they are intermediate in size between the cervical ...
and their transverse processes have surfaces that articulate with the ribs. Some rotation can occur between the thoracic vertebrae, but their connection with the
rib cage The rib cage, as an enclosure that comprises the ribs, vertebral column and sternum in the thorax of most vertebrates, protects vital organs such as the heart, lungs and great vessels. The sternum, together known as the thoracic cage, is a sem ...
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 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.


Lumbar vertebrae

The five
lumbar vertebrae The lumbar vertebrae are, in human anatomy, the five vertebrae between the rib cage and the pelvis. They are the largest segments of the vertebral column and are characterized by the absence of the foramen transversarium within the transverse p ...
are 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 Lordosis is historically defined as an ''abnormal'' inward curvature of the lumbar spine. However, the terms ''lordosis'' and ''lordotic'' are also used to refer to the normal inward curvature of the lumbar and cervical regions of the human spin ...
(a spinal curvature that is concave posteriorly). This is due to the difference in thickness between the front and back parts of 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.Postacchini, Franco (1999) ''Lumbar Disc Herniation'
p. 19
/ref> The superior, or upper tubercle is the mammillary process which connects with the superior articular process. The
multifidus muscle The multifidus (multifidus spinae : ''pl. multifidi'' ) muscle consists of a number of fleshy and tendinous fasciculi, which fill up the groove on either side of the spinous processes of the vertebrae, from the sacrum to the axis. While very th ...
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 the lumbar and sacral vertebrae together, and sometimes includes their surrounding areas.


Sacrum

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 The sacroiliac joint or SI joint (SIJ) is the joint between the sacrum and the ilium bones of the pelvis, which are connected by strong ligaments. In humans, the sacrum supports the spine and is supported in turn by an ilium on each side. Th ...
on each side of the pelvis, which articulates with the
hips In vertebrate anatomy, hip (or "coxa"Latin ''coxa'' was used by Celsus in the sense "hip", but by Pliny the Elder in the sense "hip bone" (Diab, p 77) in medical terminology) refers to either an anatomical region or a joint. The hip region ...
.


Coccyx

The last three to five coccygeal vertebrae (but usually four) (Co1–Co5) make up the tailbone or
coccyx The coccyx ( : coccyges or coccyxes), commonly referred to as the tailbone, is the final segment of the vertebral column in all apes, and analogous structures in certain other mammals such as horses. In tailless primates (e.g. humans and othe ...
. There are no intervertebral discs.


Development

Somite The somites (outdated term: primitive segments) are a set of bilaterally paired blocks of paraxial mesoderm that form in the embryonic stage of somitogenesis, along the head-to-tail axis in segmented animals. In vertebrates, somites subdivide ...
s 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 towards the notochord. These cells meet the sclerotome cells from the other side of the
paraxial mesoderm Paraxial mesoderm, also known as presomitic or somitic mesoderm is the area of mesoderm in the neurulating embryo that flanks and forms simultaneously with the neural tube. The cells of this region give rise to somites, blocks of tissue running ...
. The lower half of one sclerotome fuses with the upper half of the adjacent one to form each vertebral body. Walker, Warren F., Jr. (1987) ''Functional Anatomy of the Vertebrate'' San Francisco: Saunders College Publishing. From this vertebral body, sclerotome cells move dorsally and surround the developing
spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column (backbone). The backbone encloses the central canal of the sp ...
, forming the
vertebral arch The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic ...
. Other cells move distally to the costal processes of
thoracic vertebrae In vertebrates, thoracic vertebrae compose the middle segment of the vertebral column, between the cervical vertebrae and the lumbar vertebrae. In humans, there are twelve thoracic vertebrae and they are intermediate in size between the cervical ...
to form the ribs.


Function

Functions of vertebrae include: #Support of the vertebrae function in the skeletomuscular system by forming the vertebral column to support the body #Protection. Vertebrae contain a
vertebral foramen In a typical vertebra, the vertebral foramen is the foramen (opening) formed by the anterior segment (the body), and the posterior part, the vertebral arch. The vertebral foramen begins at cervical vertebra #1 (C1 or atlas) and continues inferio ...
for the passage of the spinal canal and its enclosed
spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column (backbone). The backbone encloses the central canal of the sp ...
and covering meninges. They also afford sturdy protection for the spinal cord. The upper and lower surfaces of the centrum are flattened and rough in order to give attachment to the intervertebral discs. #Movement. The vertebrae also provide the openings, the intervertebral foramina which allow the entry and exit of the
spinal nerves A spinal nerve is a mixed nerve, which carries motor, sensory, and autonomic signals between the spinal cord and the body. In the human body there are 31 pairs of spinal nerves, one on each side of the vertebral column. These are grouped into the ...
. Similarly to the surfaces of the centrum, the upper and lower surfaces of the fronts of the laminae are flattened and rough to give attachment to the
ligamenta flava The ligamenta flava (singular, ''ligamentum flavum'', Latin for ''yellow ligament'') are a series of ligaments that connect the ventral parts of the laminae of adjacent vertebrae. They help to preserve upright posture, preventing hyperflexion, a ...
. Working together in the vertebral column their sections provide controlled movement and flexibility. #Feeding of the intervertebral discs through the reflex (hyaline ligament) plate that separates the cancellous bone of the vertebral body from each disk Spinal cord direv.svg, The
spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column (backbone). The backbone encloses the central canal of the sp ...
nested in the vertebral column. Gray298.png, Vertebral joint Gray313.png,
Costovertebral joint The costovertebral joints are the joints that connect the ribs to the vertebral column. The articulation of the head of the rib connects the head of the rib to the bodies of the thoracic vertebrae. Structure The costotransverse joint connects th ...
Gray90.png, A facet joint between the superior and inferior articular processes (labeled at top and bottom).


Clinical significance

There are 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 Kyphosis is an abnormally excessive convex curvature of the spine as it occurs in the thoracic and sacral regions. Abnormal inward concave ''lordotic'' curving of the cervical and lumbar regions of the spine is called lordosis. It can result ...
, scoliosis and
lordosis Lordosis is historically defined as an ''abnormal'' inward curvature of the lumbar spine. However, the terms ''lordosis'' and ''lordotic'' are also used to refer to the normal inward curvature of the lumbar and cervical regions of the human spin ...
. Severe cases can cause spinal cord compression. Block vertebrae where some vertebrae have become fused can cause problems.
Spina bifida Spina bifida (Latin for 'split spine'; SB) is a birth defect in which there is incomplete closing of the spine and the membranes around the spinal cord during early development in pregnancy. There are three main types: spina bifida occulta, men ...
can result from the incomplete formation of the vertebral arch.
Spondylolysis Spondylolysis is a defect or stress fracture in the pars interarticularis of the vertebral arch. The vast majority of cases occur in the lower lumbar vertebrae (L5), but spondylolysis may also occur in the cervical vertebrae.Dubousset, J. Trea ...
is a defect in the
pars interarticularis Pars may refer to: * Fars Province of Iran, also known as Pars Province * Pars (Sasanian province), a province roughly corresponding to the present-day Fars, 224–651 * ''Pars'', for ''Persia'' or ''Iran'', in the Persian language * Pars News A ...
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 Spinal disc herniation is an injury to the cushioning and connective tissue between vertebrae, usually caused by excessive strain or trauma to the spine. It may result in back pain, pain or sensation in different parts of the body, and physical ...
, more commonly called a ''slipped disc'', is the result of a tear in the outer ring ( anulus fibrosus) of the intervertebral disc, which lets some of the soft gel-like material, the
nucleus pulposus An intervertebral disc (or intervertebral fibrocartilage) lies between adjacent vertebrae in the vertebral column. Each disc forms a fibrocartilaginous joint (a symphysis), to allow slight movement of the vertebrae, to act as a ligament to hold t ...
, bulge out in a
hernia A hernia is the abnormal exit of tissue or an organ, such as the bowel, through the wall of the cavity in which it normally resides. Various types of hernias can occur, most commonly involving the abdomen, and specifically the groin. Groin herni ...
. This may be treated by a minimally-invasive endoscopic procedure called Tessys method. A
laminectomy A laminectomy is a surgical procedure that removes a portion of a vertebra called the lamina, which is the roof of the spinal canal. It is a major spine operation with residual scar tissue and may result in postlaminectomy syndrome. Depending ...
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 Radiculopathy, also commonly referred to as pinched nerve, refers to a set of conditions in which one or more nerves are affected and do not work properly (a neuropathy). Radiculopathy can result in pain (radicular pain), weakness, altered sensati ...
caused by pressure from a disc, vertebra or scar tissue might be remedied by a
foraminotomy Foraminotomy is a medical operation used to relieve pressure on nerves that are being compressed by the intervertebral foramina, the passages through the bones of the vertebrae of the spine that pass nerve bundles to the body from the spinal cord. ...
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 Spondylolisthesis is the displacement of one spinal vertebra compared to another. While some medical dictionaries define spondylolisthesis specifically as the forward or anterior displacement of a vertebra over the vertebra inferior to it (or t ...
when one vertebra slips forward onto another. The reverse of this condition is retrolisthesis where one vertebra slips backwards onto another. The vertebral pedicle is often used as a radiographic marker and entry point in
vertebroplasty Vertebral augmentation, including vertebroplasty and kyphoplasty, refers to similar percutaneous spinal procedures in which bone cement is injected through a small hole in the skin into a fractured vertebra in order to relieve back pain cause ...
,
kyphoplasty Vertebral augmentation, including vertebroplasty and kyphoplasty, refers to similar percutaneous spinal procedures in which bone cement is injected through a small hole in the skin into a fractured vertebra in order to relieve back pain caused ...
, and
spinal fusion Spinal fusion, also called spondylodesis or spondylosyndesis, is a neurosurgical or orthopedic surgical technique that joins two or more vertebrae. This procedure can be performed at any level in the spine (cervical, thoracic, or lumbar) and pre ...
procedures. The
arcuate foramen In human anatomy, arcuate foramen, also known as ponticulus posticus (Latin for "little posterior bridge") or Kimmerle's anomaly, refers to a bony bridge on the atlas (C1 vertebra) that covers the groove for the vertebral artery. It is a common a ...
is a common
anatomical variation An anatomical variation, anatomical variant, or anatomical variability is a presentation of body structure with morphological features different from those that are typically described in the majority of individuals. Anatomical variations are categ ...
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 The vertebral arteries are major arteries of the neck. Typically, the vertebral arteries originate from the subclavian arteries. Each vessel courses superiorly along each side of the neck, merging within the skull to form the single, midline ba ...
.
Degenerative disc disease Degenerative disc disease (DDD) is a medical condition typically brought on by the normal aging process in which there are anatomic changes and possibly a loss of function of one or more intervertebral discs of the spine. DDD can take place with ...
is a condition usually associated with ageing in which one or more discs degenerate. This can often be a painfree condition but can also be very painful.


Other animals

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 upwards in animals without an erect stance. These processes can be very large in the larger animals since they attach to the muscles and ligaments of the body. In the
elephant Elephants are the largest existing land animals. Three living species are currently recognised: the African bush elephant, the African forest elephant, and the Asian elephant. They are the only surviving members of the family Elephantidae ...
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 ''Spinosaurus'' (; ) is a genus of spinosaurid dinosaur that lived in what now is North Africa during the Cenomanian to upper Turonian stages of the Late Cretaceous period, about 99 to 93.5 million years ago. The genus was known first f ...
'', 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 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 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 The vertebral column, also known as the backbone or spine, is part of the axial skeleton. The vertebral column is the defining characteristic of a vertebrate in which the notochord (a flexible rod of uniform composition) found in all chordate ...
does not lead to an opening between vertebrae. In many species, though not in mammals, the cervical vertebrae bear ribs. In many groups, such as lizards and
saurischia Saurischia ( , meaning "reptile-hipped" from the Greek ' () meaning 'lizard' and ' () meaning 'hip joint') is one of the two basic divisions of dinosaurs (the other being Ornithischia), classified by their hip structure. Saurischia and Ornithis ...
n 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
manatee Manatees (family Trichechidae, genus ''Trichechus'') are large, fully aquatic, mostly herbivorous marine mammals sometimes known as sea cows. There are three accepted living species of Trichechidae, representing three of the four living speci ...
s and
sloth Sloths are a group of Neotropical xenarthran mammals constituting the suborder Folivora, including the extant arboreal tree sloths and extinct terrestrial ground sloths. Noted for their slowness of movement, tree sloths spend most of their l ...
s have seven cervical vertebrae, whatever 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 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
marsupial Marsupials are any members of the mammalian infraclass Marsupialia. All extant marsupials are endemic to Australasia, Wallacea and the Americas. A distinctive characteristic common to most of these species is that the young are carried in a ...
s have thirteen, but
koala The koala or, inaccurately, koala bear (''Phascolarctos cinereus''), is an arboreal herbivorous marsupial native to Australia. It is the only extant representative of the family Phascolarctidae and its closest living relatives are the w ...
s only have eleven. The norm is twelve to fifteen in mammals, (twelve in the
human Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedalism and exceptional cognitive skills due to a large and complex brain. This has enabled the development of advanced tools, cultu ...
), though there are from eighteen to twenty in the
horse The horse (''Equus ferus caballus'') is a domesticated, one-toed, hoofed mammal. It belongs to the taxonomic family Equidae and is one of two extant subspecies of ''Equus ferus''. The horse has evolved over the past 45 to 55 million yea ...
,
tapir Tapirs ( ) are large, herbivorous mammals belonging to the family Tapiridae. They are similar in shape to a pig, with a short, prehensile nose trunk. Tapirs inhabit jungle and forest regions of South and Central America, with one species inh ...
,
rhinoceros A rhinoceros (; ; ), commonly abbreviated to rhino, is a member of any of the five extant species (or numerous extinct species) of odd-toed ungulates in the family Rhinocerotidae. (It can also refer to a member of any of the extinct species ...
and
elephant Elephants are the largest existing land animals. Three living species are currently recognised: the African bush elephant, the African forest elephant, and the Asian elephant. They are the only surviving members of the family Elephantidae ...
. 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
gorilla Gorillas are herbivorous, predominantly ground-dwelling great apes that inhabit the tropical forests of equatorial Africa. The genus ''Gorilla'' is divided into two species: the eastern gorilla and the western gorilla, and either four or fi ...
s, which have three in contrast to the five in the genus ''
Homo ''Homo'' () is the genus that emerged in the (otherwise extinct) genus '' Australopithecus'' that encompasses the extant species ''Homo sapiens'' ( modern humans), plus several extinct species classified as either ancestral to or closely relat ...
''. 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 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
primate Primates are a diverse order of mammals. They are divided into the strepsirrhines, which include the lemurs, galagos, and lorisids, and the haplorhines, which include the tarsiers and the simians ( monkeys and apes, the latter including ...
s, they are called the
coccygeal vertebrae The coccyx ( : coccyges or coccyxes), commonly referred to as the tailbone, is the final segment of the vertebral column in all apes, and analogous structures in certain other mammals such as horses. In tailless primates (e.g. humans and other ...
, number from three to five and are fused into the
coccyx The coccyx ( : coccyges or coccyxes), commonly referred to as the tailbone, is the final segment of the vertebral column in all apes, and analogous structures in certain other mammals such as horses. In tailless primates (e.g. humans and othe ...
.


Additional images

File:Gray303.png, Vertebral arches of three thoracic vertebrae File:Gray312.png, Costovertebral joints seen from the front File:Sobo 1909 9.png, Lower thoracic and upper lumbar vertebrae seen from the side File:Sobo 1909 4.png, Cervical vertebrae seen from the back File:Vertebrae Anatomy by Jason Christian.webm, Vertebrae Anatomy


See also

* Limbus vertebra *
Functional spinal unit A functional spinal unit (FSU) (or motion segment) is the smallest physiological motion unit of the spine to exhibit biomechanical characteristics similar to those of the entire spine. A FSU consists of two adjacent vertebrae, the intervertebral d ...
*
Pott disease Pott disease is tuberculosis of the spine, usually due to haematogenous spread from other sites, often the lungs. The lower thoracic and upper lumbar vertebrae areas of the spine are most often affected. It causes a kind of tuberculous arthriti ...
*
Scheuermann's disease Scheuermann's disease is a Self-limiting (biology), self-limiting skeleton, skeletal disorder of childhood. Scheuermann's disease describes a condition where the vertebrae grow unevenly with respect to the sagittal plane; that is, the Posterior ( ...


References


External links

* – Axis & Atlas Articulated, Posterior View * * * *
Vertebra
- BlueLink Anatomy - University of Michigan Medical School * *

– University of the Cumberlands {{Authority control Irregular bones Skeletal system Vertebrate anatomy