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The vertebral column, also known as the backbone or spine, is part of the
axial skeleton Axial may refer to: * one of the describing relationships in an animal body * and submarine volcano off Oregon, USA * , a ghost town * In geometry: :* a :* an * the in China, India, etc. * a type of , in music * , a type of See also * *Axis ...
. The vertebral column is the defining characteristic of a
vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic ma ...
in which the
notochord In anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any in ...
(a flexible rod of uniform composition) found in all
chordates A chordate () is an animal of the phylum Chordata (). All chordates possess 5 Apomorphy and synapomorphy , synapomorphies, or primary characteristics, at some point during their larval or adulthood stages that distinguish them from all other ta ...

chordates
has been replaced by a segmented series of
bone A bone is a rigid tissue Tissue may refer to: Biology * Tissue (biology), an ensemble of similar cells that together carry out a specific function * ''Triphosa haesitata'', a species of geometer moth found in North America * ''Triphosa dubit ...

bone
:
vertebra In the vertebrate spinal 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 c ...
e separated by
intervertebral disc An intervertebral disc (or intervertebral fibrocartilage) lies between adjacent vertebrae in 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 ...
s. The vertebral column houses 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 cavi ...
, a cavity that encloses and protects the
spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue Nervous tissue, also called neural tissue, is the main tissue component of the nervous system In Biology, biology, the nervous system is a Complex system, high ...

spinal cord
. There are about 50,000 species of animals that have a vertebral column. The human vertebral column is one of the most-studied examples.


Structure

The number of vertebrae in a region can vary but overall the number remains the same. In a human's vertebral column, there are normally thirty-three vertebrae. The upper 24 pre-sacral vertebrae are articulating and separated from each other by
intervertebral disc An intervertebral disc (or intervertebral fibrocartilage) lies between adjacent vertebrae in 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 ...
s, and the lower nine are fused in adults, five in the
sacrum The sacrum (plural: ''sacra'' or ''sacrums''), in human anatomy The human body is the structure of a human being. It is composed of many different types of cells that together create tissues and subsequently organ systems. They ensure ho ...

sacrum
and four in the
coccyx The coccyx (plural: ''coccyges'' or ''coccyxes''), commonly referred to as the tailbone, is the final segment of the vertebral column The vertebral column, also known as the backbone or spine, is part of the axial skeleton. The vertebral c ...
, or ''tailbone''. The articulating vertebrae are named according to their region of the spine. There are seven
cervical vertebrae In tetrapod Tetrapods (; from Greek 'four' and 'foot') are four-limbed animals constituting the superclass Tetrapoda . It includes extant and extinct amphibians, reptiles (including dinosaurs and therefore birds), and synapsids (including ...

cervical vertebrae
, twelve
thoracic vertebrae In vertebrates Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, c ...

thoracic vertebrae
and five
lumbar vertebrae The lumbar vertebrae are, in human anatomy, the five vertebrae In the vertebrate spinal column, each vertebra (plural vertebrae) is an irregular bone with a complex structure composed of bone and some hyaline cartilage, the proportions of whic ...

lumbar vertebrae
. The number of those in the cervical region, however, is only rarely changed, while that in the coccygeal region varies most. One study of 908 human adults found 43 individuals with 23 pre-sacral vertebrae (4.7%), 826 individuals with 24 pre-sacral vertebrae (91%), and 39 with 25 pre-sacral vertebrae (4.3%). There are
ligament A ligament is the Connective tissue#Types, fibrous connective tissue that connects bones to other bones. It is also known as ''articular ligament'', ''articular larua'', ''fibrous ligament'', or ''true ligament''. Other ligaments in the body incl ...

ligament
s extending the length of the column at the front and the back, and in between the vertebrae joining the
spinous process In the vertebrate spinal 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 co ...
es, the
transverse process In the vertebrate spinal 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 c ...
es and the vertebral laminae.


Vertebrae

The vertebrae in the human vertebral column are divided into different regions, which correspond to the curves of the spinal column. The articulating vertebrae are named according to their region of the spine. Vertebrae in these regions are essentially alike, with minor variation. These regions are called the
cervical spine In tetrapod Tetrapods (; ) are four-limbed animals constituting the superclass Tetrapoda (). It includes extant Extant is the opposite of the word extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon ...

cervical spine
,
thoracic spine In vertebrates Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, c ...

thoracic spine
,
lumbar spine The lumbar vertebrae are, in human anatomy, the five vertebrae In the vertebrate spinal column The vertebral column, also known as the backbone or spine, is part of the axial skeleton. The vertebral column is the defining characteristic ...

lumbar spine
,
sacrum The sacrum (plural: ''sacra'' or ''sacrums''), in human anatomy The human body is the structure of a human being. It is composed of many different types of cells that together create tissues and subsequently organ systems. They ensure ho ...

sacrum
, and
coccyx The coccyx (plural: ''coccyges'' or ''coccyxes''), commonly referred to as the tailbone, is the final segment of the vertebral column The vertebral column, also known as the backbone or spine, is part of the axial skeleton. The vertebral c ...
. There are seven cervical vertebrae, twelve thoracic vertebrae, and five lumbar vertebrae. The number of vertebrae in a region can vary but overall the number remains the same. The number of those in the cervical region, however, is only rarely changed. The vertebrae of the cervical, thoracic, and lumbar spines are independent bones and generally quite similar. The vertebrae of the sacrum and coccyx are usually fused and unable to move independently. Two special vertebrae are the
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and
axis Axis may refer to: Politics *Axis of evil The phrase "axis of evil" was first used by U.S. President George W. Bush in his State of the Union address on January 29, 2002, less than five months after the 9/11 attacks, and often repeated t ...
, on which the head rests. A typical vertebra consists of two parts: the
vertebral body In the vertebrate spinal column, each vertebra is an irregular bone with a complex structure composed of bone and some hyaline cartilage, the proportions of which vary according to the segment of the backbone and the species of vertebrate. ...
and the
vertebral arch In the vertebrate spinal 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 co ...
. The vertebral arch is posterior, meaning it faces the back of a person. Together, these enclose the
vertebral foramen In a typical vertebra In the vertebrate spinal 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 fl ...
, which contains the
spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue Nervous tissue, also called neural tissue, is the main tissue component of the nervous system In Biology, biology, the nervous system is a Complex system, high ...

spinal cord
. Because the spinal cord ends in the lumbar spine, and the sacrum and coccyx are fused, they do not contain a central foramen. The vertebral arch is formed by a pair of pedicles and a pair of laminae, and supports seven
processes A process is a series or set of Action (philosophy), 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 pro ...
, four articular, two transverse, and one spinous, the latter also being known as the neural spine. Two
transverse process In the vertebrate spinal 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 c ...
es and one
spinous process In the vertebrate spinal 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 co ...
are posterior to (behind) the vertebral body. The spinous process comes out the back, one transverse process comes out the left, and one on the right. The spinous processes of the cervical and lumbar regions can be felt through the skin. Above and below each vertebra are joints called
facet joint The facet joints, (or zygapophysial joints, zygapophyseal, apophyseal, or Z-joints) are a set of synovial, plane joint A plane joint (arthrodial joint, gliding joint, plane articulation) is a synovial joint which, under physiological conditions ...
s. These restrict the range of movement possible, and are joined by a thin portion of the neural arch called the ''
pars interarticularis The ''pars interarticularis'', or pars for short, is the part of a vertebra In the vertebrate spinal column The vertebral column, also known as the backbone or spine, is part of the axial skeleton. The vertebral column is the defining charac ...
''. In between each pair of vertebrae are two small holes called
intervertebral foramina The intervertebral foramen (also called neural foramen, and often abbreviated as IV foramen or IVF), is a :wikt:foramen, foramen between two spinal vertebrae. Cervical vertebrae, Cervical, thoracic vertebrae, thoracic, and lumbar vertebrae all ...
. The
spinal nerve 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 ...

spinal nerve
s leave the
spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue Nervous tissue, also called neural tissue, is the main tissue component of the nervous system In Biology, biology, the nervous system is a Complex system, high ...

spinal cord
through these holes. Individual vertebrae are named according to their region and position. From top to bottom, the vertebrae are: *
Cervical spine In tetrapod Tetrapods (; ) are four-limbed animals constituting the superclass Tetrapoda (). It includes extant Extant is the opposite of the word extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon ...

Cervical spine
: 7 vertebrae (C1–C7) *
Thoracic spine In vertebrates Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, c ...

Thoracic spine
: 12 vertebrae (T1–T12) *
Lumbar spine The lumbar vertebrae are, in human anatomy, the five vertebrae In the vertebrate spinal column The vertebral column, also known as the backbone or spine, is part of the axial skeleton. The vertebral column is the defining characteristic ...

Lumbar spine
: 5 vertebrae (L1–L5) *
Sacrum The sacrum (plural: ''sacra'' or ''sacrums''), in human anatomy The human body is the structure of a human being Humans (''Homo sapiens'') are the most abundant and widespread species In biology, a species is the basic unit ...
: 5 (fused) vertebrae (S1–S5) *
Coccyx The coccyx (plural: ''coccyges'' or ''coccyxes''), commonly referred to as the tailbone, is the final segment of the vertebral column The vertebral column, also known as the backbone or spine, is part of the axial skeleton Axial may refer ...
: 4 (3–5) (fused) vertebrae (Tailbone) The combined region of the thoracic and lumbar vertebrae is known as the thoracolumbar division, or region.


Shape

The vertebral column is curved in several places, a result of human bipedal evolution. The curves allow the human spine to better stabilize the body in the upright position. The upper cervical spine has a curve, convex forward, that begins at the
axis Axis may refer to: Politics *Axis of evil The phrase "axis of evil" was first used by U.S. President George W. Bush in his State of the Union address on January 29, 2002, less than five months after the 9/11 attacks, and often repeated t ...
(second cervical vertebra) at the apex of the odontoid process or dens and ends at the middle of the second thoracic vertebra; it is the least marked of all the curves. This inward curve is known as a
lordotic 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 In tetrapod Tetrapods (; from Greek ...

lordotic
curve. The thoracic curve, concave forward, begins at the middle of the second and ends at the middle of the twelfth thoracic vertebra. Its most prominent point behind corresponds to the spinous process of the seventh thoracic vertebra. This curve is known as a curve. The lumbar curve is more marked in the female than in the male; it begins at the middle of the last thoracic vertebra, and ends at the sacrovertebral angle. It is convex anteriorly, the convexity of the lower three vertebrae being much greater than that of the upper two. This curve is described as a
lordotic 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 In tetrapod Tetrapods (; from Greek ...

lordotic
curve. The sacral curve begins at the sacrovertebral articulation, and ends at the point of the
coccyx The coccyx (plural: ''coccyges'' or ''coccyxes''), commonly referred to as the tailbone, is the final segment of the vertebral column The vertebral column, also known as the backbone or spine, is part of the axial skeleton. The vertebral c ...
; its concavity is directed downward and forward as a kyphotic curve. The thoracic and sacral kyphotic curves are termed primary curves, because they are present in the
fetus A fetus or foetus (; plural fetuses, feti, foetuses, or foeti) is the unborn offspring that develops from an animal embryo An embryo is the early stage of development of a multicellular organism A multicellular organism is an organism tha ...

fetus
. The cervical and lumbar curves are ''compensatory'', or ''secondary'', and are developed after birth. The cervical curve forms when the infant is able to hold up its head (at three or four months) and sit upright (at nine months). The lumbar curve forms later from twelve to eighteen months, when the child begins to walk.


Surfaces

;Anterior surface When viewed from in front, the width of the bodies of the vertebrae is seen to increase from the second cervical to the first thoracic; there is then a slight diminution in the next three vertebrae. Below this, there is again a gradual and progressive increase in width as low as the sacrovertebral angle. From this point there is a rapid diminution, to the apex of the coccyx.Gray's Anatomy (1918) ;Posterior surface From behind, the vertebral column presents in the median line the spinous processes. In the cervical region (with the exception of the second and seventh vertebrae), these are short, horizontal, and bifid. In the upper part of the thoracic region they are directed obliquely downward; in the middle they are almost vertical, and in the lower part they are nearly horizontal. In the lumbar region they are nearly horizontal. The spinous processes are separated by considerable intervals in the lumbar region, by narrower intervals in the neck, and are closely approximated in the middle of the thoracic region. Occasionally one of these processes deviates a little from the median line — which can sometimes be indicative of a fracture or a displacement of the spine. On either side of the spinous processes is the vertebral groove formed by the laminae in the cervical and lumbar regions, where it is shallow, and by the laminae and transverse processes in the thoracic region, where it is deep and broad; these grooves lodge the deep muscles of the back. Lateral to the spinous processes are the articular processes, and still more laterally the transverse processes. In the thoracic region, the transverse processes stand backward, on a plane considerably behind that of the same processes in the cervical and lumbar regions. In the cervical region, the transverse processes are placed in front of the articular processes, lateral to the pedicles and between the intervertebral foramina. In the thoracic region they are posterior to the pedicles, intervertebral foramina, and articular processes. In the lumbar region they are in front of the articular processes, but behind the intervertebral foramina. ;Lateral surfaces The sides of the vertebral column are separated from the posterior surface by the articular processes in the cervical and thoracic regions and by the transverse processes in the lumbar region. In the thoracic region, the sides of the bodies of the vertebrae are marked in the back by the facets for articulation with the heads of the ribs. More posteriorly are the intervertebral foramina, formed by the juxtaposition of the vertebral notches, oval in shape, smallest in the cervical and upper part of the thoracic regions and gradually increasing in size to the last lumbar. They transmit the special spinal nerves and are situated between the transverse processes in the cervical region and in front of them, in the thoracic and lumbar regions.


Ligaments

There are different ligaments involved in the holding together of the vertebrae in the column, and in the column's movement. The
anterior Standard anatomical terms of location deal unambiguously with the anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organism In biology, an organism (from Ancient ...
and
posterior longitudinal ligament The posterior longitudinal ligament is situated within the vertebral canal The spinal canal (or vertebral canal or spinal cavity) is the canal that contains the spinal cord The spinal cord is a long, thin, tubular structure made up of nervous ...
s extend the length of the vertebral column along the front and back of the vertebral bodies. The
interspinous ligament The interspinous ligaments (interspinal ligaments) are thin and membranous ligaments, that connect adjoining spinous processes of the vertebra in the human vertebral column, spine. They extend from the root to the apex of each spinous process. They ...
s connect the adjoining spinous processes of the vertebrae. The
supraspinous ligament The supraspinous ligament, also known as the supraspinal ligament, is a ligament A ligament is the Connective tissue#Types, fibrous connective tissue that connects bones to other bones. It is also known as ''articular ligament'', ''articular larua' ...
extends the length of the spine running along the back of the spinous processes, from the sacrum to the seventh
cervical vertebra In tetrapod Tetrapods (; from Greek 'four' and 'foot') are four-limbed animals constituting the superclass Tetrapoda . It includes extant and extinct amphibians, reptiles (including dinosaurs and therefore birds), and synapsids (including ...

cervical vertebra
. From there it is continuous with the
nuchal ligament The nuchal ligament is a ligament A ligament is the Connective tissue#Types, fibrous connective tissue that connects bones to other bones. It is also known as ''articular ligament'', ''articular larua'', ''fibrous ligament'', or ''true ligament ...
.


Development

The striking segmented pattern of the spine is established during
embryogenesis An embryo is the early stage of development of a multicellular organism A multicellular organism is an organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms ar ...

embryogenesis
when
somites 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 segmentation (biology), segmented animals. In vertebrat ...

somites
are rhythmically added to the posterior of the embryo. Somite formation begins around the third week when the embryo begins
gastrulation Gastrulation is the stage in the early embryonic development of most animals, during which the blastula (a single-layered hollow sphere of Cell (biology), cells) is reorganized into a multilayered structure known as the gastrula. Before gastrulat ...

gastrulation
and continues until all somites are formed. Their number varies between species: there are 42 to 44 somites in the human embryo and around 52 in the chick embryo. The somites are spheres, formed from the
paraxial mesoderm Paraxial mesoderm, also known as presomitic or somitic mesoderm is the area of mesoderm In all bilaterian animals, the mesoderm is one of the three primary germ layers in the very early embryo. The other two layers are the ectoderm (outside la ...
that lies at the sides of the neural tube and they contain the precursors of spinal bone, the vertebrae ribs and some of the skull, as well as muscle, ligaments and skin.
Somitogenesis Somitogenesis is the process by which 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 segmente ...
and the subsequent distribution of somites is controlled by a
clock and wavefront modelThe clock and wavefront model is a model used to describe the process of somitogenesis in vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom ...
acting in cells of the paraxial mesoderm. Soon after their formation,
sclerotome The somites (outdated term: primitive segments) are a set of bilaterally paired blocks of paraxial mesoderm that form in the embryogenesis, embryonic stage of somitogenesis, along the head-to-tail axis in segmentation (biology), segmented animals. ...
s, which give rise to some of the bone of the skull, the vertebrae and ribs, migrate, leaving the remainder of the somite now termed a dermamyotome behind. This then splits to give the myotomes which will form the muscles and
dermatomes A dermatome is an area of skin that is mainly supplied by afferent nerve fibres from the dorsal root of spinal nerve, dorsal root of any given spinal nerve. There are 8 cervical nerves (C1 being an exception with no dermatome), 12 thoracic nerves ...
which will form the skin of the back. Sclerotomes become subdivided into an anterior and a posterior compartment. This subdivision plays a key role in the definitive patterning of vertebrae that form when the posterior part of one somite fuses to the anterior part of the consecutive somite during a process termed resegmentation. Disruption of the somitogenesis process in humans results in diseases such as congenital scoliosis. So far, the human homologues of three genes associated to the mouse segmentation clock, (MESP2, DLL3 and LFNG), have been shown to be mutated in cases of congenital scoliosis, suggesting that the mechanisms involved in vertebral segmentation are conserved across vertebrates. In humans the first four somites are incorporated in the base of the
occipital bone The occipital bone () is a neurocranium, cranial dermal bone and the main bone of the occiput (back and lower part of the skull). It is Trapezoid, trapezoidal in shape and curved on itself like a shallow dish. The occipital bone overlies the occi ...

occipital bone
of the skull and the next 33 somites will form the vertebrae, ribs, muscles, ligaments and skin. The remaining posterior somites degenerate. During the fourth week of
embryogenesis An embryo is the early stage of development of a multicellular organism A multicellular organism is an organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms ar ...

embryogenesis
, the
sclerotome The somites (outdated term: primitive segments) are a set of bilaterally paired blocks of paraxial mesoderm that form in the embryogenesis, embryonic stage of somitogenesis, along the head-to-tail axis in segmentation (biology), segmented animals. ...
s shift their position to surround the
spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue Nervous tissue, also called neural tissue, is the main tissue component of the nervous system In Biology, biology, the nervous system is a Complex system, high ...

spinal cord
and the
notochord In anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any in ...
. This column of tissue has a segmented appearance, with alternating areas of dense and less dense areas. As the sclerotome develops, it condenses further eventually developing into the
vertebral body In the vertebrate spinal column, each vertebra is an irregular bone with a complex structure composed of bone and some hyaline cartilage, the proportions of which vary according to the segment of the backbone and the species of vertebrate. ...
. Development of the appropriate shapes of the vertebral bodies is regulated by ''
HOX gene Hox genes, a subset of homeobox genes, are a group of related genes that specify regions of the body plan of an embryo An embryo is the early stage of development of a multicellular organism. In general, in organism In biology, an ...
s''. The less dense tissue that separates the sclerotome segments develop into the
intervertebral disc An intervertebral disc (or intervertebral fibrocartilage) lies between adjacent vertebrae in 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 ...
s. The notochord disappears in the sclerotome (vertebral body) segments but persists in the region of the intervertebral discs as the
nucleus pulposus An intervertebral disc (or intervertebral fibrocartilage) lies between adjacent vertebrae in 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 ...
. The nucleus pulposus and the fibers of the anulus fibrosus make up the intervertebral disc. The primary curves (thoracic and sacral curvatures) form during fetal development. The secondary curves develop after birth. The cervical curvature forms as a result of lifting the head and the lumbar curvature forms as a result of walking.


Function


Spinal cord

The vertebral column surrounds the spinal cord which travels within 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 cavi ...
, formed from a central hole within each
vertebra In the vertebrate spinal 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 c ...
. The spinal cord is part of the
central nervous system The central nervous system (CNS) is the part of the nervous system In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecu ...

central nervous system
that supplies nerves and receives information from the
peripheral nervous system The peripheral nervous system (PNS) is one of two components that make up the nervous system In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, ...
within the body. The spinal cord consists of
grey Grey or gray (American English American English (AmE, AE, AmEng, USEng, en-US), sometimes called United States English or U.S. English, is the set of varieties of the English language native to the United States. Currently, American Eng ...
and
white matter White matter refers to areas of the central nervous system The central nervous system (CNS) is the part of the nervous system In biology Biology is the natural science that studies life and living organisms, including their anato ...
and a central cavity, the
central canal The central canal, also known as ependymal canal, is the cerebrospinal fluid Cerebrospinal fluid (CSF) is a clear, colorless body fluid found within the tissue that surrounds the brain A brain is an organ (anatomy), organ that serves as ...
. Adjacent to each vertebra emerge
spinal nerve 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 ...

spinal nerve
s. The spinal nerves provide sympathetic nervous supply to the body, with nerves emerging forming the
sympathetic trunk The sympathetic trunks (sympathetic chain, gangliated cord) are a paired bundle of nerve fibers that run from the base of the skull The skull is a bone A bone is a rigid tissue Tissue may refer to: Biology * Tissue (biology), an ensemb ...

sympathetic trunk
and the
splanchnic nerve The splanchnic nerves are paired visceral nerves (nerves that contribute to the innervation of the internal organs), carrying fibers of the autonomic nervous system (visceral efferent fibers) as well as sensory fibers from the organs (visceral affe ...
s. 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 cavi ...
follows the different curves of the column; it is large and triangular in those parts of the column that enjoy the greatest freedom of movement, such as the cervical and lumbar regions, and is small and rounded in the thoracic region, where motion is more limited. The spinal cord terminates in the
conus medullaris The conus medullaris (Latin for "medullary cone") or conus terminalis is the tapered, lower end of the spinal cord. It occurs near lumbar vertebrae, lumbar vertebral levels 1 (L1) and 2 (L2), occasionally lower. The upper end of the conus medullar ...
and
cauda equina The cauda equina () is a bundle of spinal nerves and spinal nerve rootlets, consisting of the second through fifth lumbar nerve pairs, the first through fifth sacral nerve pairs, and the coccygeal nerve, all of which arise from the lumbar enlar ...
.


Clinical significance


Disease

Spina bifida Spina bifida (Latin for "split spine"; SB) is a in which there is incomplete closing of the and the around the during . There are three main types: spina bifida occulta, meningocele and myelomeningocele. Meningocele and myelomeningocele may ...
is a
congenital disorder A birth defect, also known as a congenital disorder, is a condition present at birth Birth is the act or process of bearing or bringing forth offspring, also referred to in technical contexts as parturition. In mammals, the process is initiat ...
in which there is a defective closure of the vertebral arch. Sometimes the spinal
meninges In anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of concerned with the study of the structure of s and their parts. Anatomy is a branch of natural science which deals with the structural organization of living things. I ...

meninges
and also the spinal cord can protrude through this, and this is called ''Spina bifida cystica''. Where the condition does not involve this protrusion it is known as ''Spina bifida occulta''. Sometimes all of the vertebral arches may remain incomplete. Another, though rare, congenital disease is
Klippel–Feil syndrome Klippel–Feil syndrome (KFS), also known as cervical vertebral fusion syndrome, is a Rare disease, rare congenital condition characterized by the abnormal fusion of any two of the seven bones in the neck (cervical vertebrae). It results in a limi ...

Klippel–Feil syndrome
, which is the fusion of any two of the cervical vertebrae.
Spondylolisthesis Spondylolisthesis is the displacement of one spinal vertebra In the vertebrate spinal 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 ...

Spondylolisthesis
is the forward displacement of a vertebra and retrolisthesis is a posterior displacement of one
vertebral body In the vertebrate spinal column, each vertebra is an irregular bone with a complex structure composed of bone and some hyaline cartilage, the proportions of which vary according to the segment of the backbone and the species of vertebrate. ...
with respect to the adjacent vertebra to a degree less than a dislocation.
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. Treatme ...

Spondylolysis
, also known as a pars defect, is a defect or fracture at the pars interarticularis of the vertebral arch.
Spinal disc herniation Spinal disc herniation is an injury Injury, also known as physical trauma, is damage Damage is any change in a thing, often a physical object, that degrades it away from its initial state. It can broadly be defined as "changes introduced ...
, more commonly called a "slipped disc", is the result of a tear in the outer ring ( anulus fibrosus) of the
intervertebral disc An intervertebral disc (or intervertebral fibrocartilage) lies between adjacent vertebrae in 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 ...
, 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 The vertebral column, also known as the backbone or spine, is part of the axial skeleton. The vertebral column is the defining ...
, bulge out in a
hernia A hernia is the abnormal exit of tissue or an organ Organ may refer to: Biology * Organ (anatomy) An organ is a group of Tissue (biology), tissues with similar functions. Plant life and animal life rely on many organs that co-exist in organ ...

hernia
.
Spinal stenosis Spinal stenosis is an abnormal narrowing of the spinal canal or neural foramen that results in pressure on the spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblonga ...
is a narrowing of the spinal canal which can occur in any region of the spine though less commonly in the thoracic region. The stenosis can constrict the spinal canal giving rise to a neurological deficit. Pain at the
coccyx The coccyx (plural: ''coccyges'' or ''coccyxes''), commonly referred to as the tailbone, is the final segment of the vertebral column The vertebral column, also known as the backbone or spine, is part of the axial skeleton. The vertebral c ...
(tailbone) is known as
coccydynia Coccydynia is a medical term meaning pain Pain is a distressing feeling often caused by intense or damaging stimuli. The International Association for the Study of Pain defines pain as "an unpleasant sensory and emotional experience associated wi ...
.
Spinal cord injury A spinal cord injury (SCI) is damage to 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. ...
is damage to the
spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue Nervous tissue, also called neural tissue, is the main tissue component of the nervous system In Biology, biology, the nervous system is a Complex system, high ...

spinal cord
that causes changes in its function, either temporary or permanent. Spinal cord injuries can be divided into categories: complete transection, hemisection, central spinal cord lesions, posterior spinal cord lesions, and anterior spinal cord lesions. Scalloping vertebrae is the increase in the concavity of the posterior vertebral body. It can be seen on lateral X-ray and sagittal views of CT and MRI scans. Its concavity is due to the increased pressure exerting on the vertebrae due to a mass. Internal spinal mass such as spinal astrocytoma, ependymoma, schwannoma, neurofibroma, and
achondroplasia Achondroplasia is a genetic disorder A genetic disorder is a health problem caused by one or more abnormalities in the genome In the fields of molecular biology and genetics, a genome is all genetic information of an organism. It ...
causes vertebrae scalloping.


Curvature

Excessive or abnormal spinal curvature is classed as a spinal disease or dorsopathy and includes the following abnormal curvatures: *
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 fr ...

Kyphosis
is an exaggerated kyphotic (convex) curvature of the thoracic region in the sagittal plane, also called hyperkyphosis. This produces the so-called "humpback" or "dowager's hump", a condition commonly resulting from
osteoporosis Osteoporosis is a systemic skeletal disorder characterized by low bone massImage:Bone density scanner.jpg, A scanner used to measure bone density using dual energy X-ray absorptiometry Bone density, or bone mineral density (BMD), is the amount ...
. *
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 vertebrae, cervical region ...

Lordosis
is an exaggerated lordotic (concave) curvature of the lumbar region in the sagittal plane, is known as
lumbar hyperlordosis 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 spi ...
and also as "swayback". Temporary lordosis is common during
pregnancy Pregnancy, also known as gestation, is the time during which one or more offspring In biology, offspring are the young creation of living organisms, produced either by a Asexual reproduction, single organism or, in the case of sexual repr ...
. *
Scoliosis Scoliosis is a medical condition in which a person's spine has a sideways curve. The curve is usually "S"- or "C"-shaped over three dimensions. In some, the degree of curve is stable, while in others, it increases over time. Mild scoliosis doe ...

Scoliosis
, lateral curvature, is the most common abnormal curvature, occurring in 0.5% of the population. It is more common among
female Female (symbol: ♀) is the sex Sex is either of two divisions, typically male Male (♂) is the sex of an organism that produces the gamete known as sperm. A male gamete can fuse with a larger female gamete, or ovum, in the process of ...

female
s and may result from unequal growth of the two sides of one or more vertebrae, so that they do not fuse properly. It can also be caused by pulmonary
atelectasis Atelectasis is the collapse or closure of a lung resulting in reduced or absent gas exchange. It is usually unilateral, affecting part or all of one lung. It is a condition where the alveoli are deflated down to little or no volume, as distinct ...

atelectasis
(partial or complete deflation of one or more lobes of the lungs) as observed in
asthma Asthma is a long-term Long-Term Capital Management L.P. (LTCM) was a hedge fund''A financial History of the United States Volume II: 1970–2001'', Jerry W. Markham, Chapter 5: "Bank Consolidation", M. E. Sharpe, Inc., 2002 based in Greenwich, ...

asthma
or
pneumothorax A pneumothorax is an abnormal collection of air in the pleural space between the lung and the chest wall. Symptoms typically include sudden onset of sharp, one-sided chest pain and dyspnea, shortness of breath. In a minority of cases, a one-way ...

pneumothorax
. *
Kyphoscoliosis Kyphoscoliosis describes an abnormal curvature of the spine in both a coronal and sagittal In anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organism In biolo ...
, a combination of kyphosis and scoliosis.


Anatomical landmarks

Individual vertebrae of the human vertebral column can be felt and used as
surface anatomy Surface anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any ...
, with reference points are taken from the middle of the vertebral body. This provides
anatomical landmark Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, mo ...
s that can be used to guide procedures such as a
lumbar puncture Lumbar puncture (LP), also known as a spinal tap, is a medical procedure in which a needle is inserted into the spinal canal The spinal canal (or vertebral canal or spinal cavity) is the canal that contains the spinal cord within the vertebral c ...
and also as vertical reference points to describe the locations of other parts of human anatomy, such as the positions of
organs An organ is a group of tissues with similar functions. Plant life and animal life rely on many organs that co-exist in organ systems. A given organ's tissues can be broadly categorized as parenchyma Parenchyma () is the bulk of functional ...
.


Other animals


Variations in vertebrae

The general structure of vertebrae in other animals is largely the same as in humans. Individual vertebrae are composed of a centrum (body), arches protruding from the top and bottom of the centrum, and various processes projecting from the centrum and/or arches. An arch extending from the top of the centrum is called a neural arch, while the haemal arch or
chevron Chevron (often relating to V-shaped patterns) may refer to: Science and technology * Chevron (aerospace), sawtooth patterns on some jet engines * Chevron (anatomy), a bone * ''Eulithis testata'', a moth * Chevron (geology), a fold in rock laye ...
is found underneath the centrum in the caudal (tail) vertebrae of
fish Fish are aquatic Aquatic means relating to water Water (chemical formula H2O) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the ...

fish
, most
reptile Reptiles, as most commonly defined, are the animals in the class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or ...

reptile
s, some birds, some dinosaurs and some
mammal Mammals (from Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meaning "to share" or "to be i ...
s with long tails. The vertebral processes can either give the structure rigidity, help them articulate with ribs, or serve as muscle attachment points. Common types are transverse process, diapophyses, parapophyses, and zygapophyses (both the cranial zygapophyses and the caudal zygapophyses). The centrum of the vertebra can be classified based on the fusion of its elements. In temnospondyls, bones such as the
spinous process In the vertebrate spinal 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 co ...
, the pleurocentrum and the intercentrum are separate ossifications. Fused elements, however, classify a vertebra as having holospondyly. A vertebra can also be described in terms of the shape of the ends of the centrum. Centra with flat ends are ''acoelous'', like those in mammals. These flat ends of the centra are especially good at supporting and distributing compressive forces. ''Amphicoelous'' vertebra have centra with both ends concave. This shape is common in fish, where most motion is limited. Amphicoelous centra often are integrated with a full
notochord In anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any in ...
. ''Procoelous'' vertebrae are anteriorly concave and posteriorly convex. They are found in frogs and modern reptiles. ''Opisthocoelous'' vertebrae are the opposite, possessing anterior convexity and posterior concavity. They are found in salamanders, and in some non-avian dinosaurs. ''Heterocoelous'' vertebrae have
saddle The saddle is a supportive structure for a rider of an animal, fastened to Mammal#Anatomy, an animal's back by a girth (tack), girth. The most common type is the equestrian saddle designed for a Back (horse), horse. However, specialized sad ...

saddle
-shaped articular surfaces. This type of configuration is seen in turtles that retract their necks, and birds, because it permits extensive lateral and vertical flexion motion without stretching the nerve cord too extensively or wringing it about its long axis. In horses, the
Arabian The Arabian Peninsula (; ar, شِبْهُ الْجَزِيرَةِ الْعَرَبِيَّة, , "Arabian Peninsula" or , , "Island of the Arabs The Arabs (singular Arab ; singular ar, عَرَبِيٌّ, ISO 233: , Arabic pronunciati ...

Arabian
(breed) can have one less vertebrae and pair of ribs. This anomaly disappears in foals that are the product of an Arabian and another breed of horse.Edwards, ''The Arabian'', pp. 27–28


Regional vertebrae

Vertebrae are defined by the regions of the vertebral column that they occur in, as in humans. Cervical vertebrae are those in the neck area. With the exception of the two
sloth Sloths are a group of arboreal Neotropical xenarthran mammals, constituting the suborder Folivora. Noted for their slowness of movement, they spend most of their lives hanging upside down in the trees of the tropical rainforest File:Kop ...

sloth
genera ('' Choloepus'' and '''') and the
manatee Manatees (family In , family (from la, familia) is a of people related either by (by recognized birth) or (by marriage or other relationship). The purpose of families is to maintain the well-being of its members and of society. Ideal ...

manatee
genus, ('' Trichechus''), all mammals have seven cervical vertebrae. In other vertebrates, the number of cervical vertebrae can range from a single vertebra in
amphibian Amphibians are ectothermic, tetrapod vertebrates of the Class (biology), class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most species living within terrestrial animal, ter ...
s to as many as 25 in
swan Swans are birds of the family (biology), family Anatidae within the genus ''Cygnus''. The swans' closest relatives include the goose, geese and ducks. Swans are grouped with the closely related geese in the subfamily Anserinae where they form th ...

swan
s or 76 in the
extinct Extinction is the termination of a kind of organism In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biol ...
plesiosaur The Plesiosauria (; Greek: πλησίος, ''plesios'', meaning "near to" and ''sauros'', meaning "lizard") or plesiosaurs are an order or clade A clade (; from grc, , ''klados'', "branch"), also known as a monophyletic group or natural ...

plesiosaur
''
Elasmosaurus ''Elasmosaurus'' (;) is a genus Genus (plural genera) is a taxonomic rank Taxonomy (general) is the practice and science of classification of things or concepts, including the principles that underlie such classification. The term may also re ...
''. The dorsal vertebrae range from the bottom of the neck to the top of the
pelvis The pelvis (plural pelves or pelvises) is the lower part of the trunk, between the abdomen The abdomen (colloquially called the belly, tummy, midriff or stomach) is the part of the body between the thorax (chest) and pelvis, in humans and in ...

pelvis
. Dorsal vertebrae attached to the
rib In vertebrate anatomy, ribs ( la, costae) are the long curved bones which form the rib cage, part of the axial skeleton. In most tetrapods, ribs surround the chest, enabling the lungs to expand and thus facilitate breathing by expanding the chest ...
s are called thoracic vertebrae, while those without ribs are called lumbar vertebrae. The sacral vertebrae are those in the pelvic region, and range from one in amphibians, to two in most birds and modern reptiles, or up to three to five in mammals. When multiple sacral vertebrae are fused into a single structure, it is called the sacrum. The
synsacrum The synsacrum is a skeletal structure of birds Birds are a group of warm-blooded vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the King ...

synsacrum
is a similar fused structure found in birds that is composed of the sacral, lumbar, and some of the thoracic and caudal vertebra, as well as the
pelvic girdle The pelvis (plural pelves or pelvises) is the lower part of the trunk, between the abdomen The abdomen (colloquially called the belly, tummy, midriff or stomach) is the part of the body between the thorax (chest) and pelvis, in humans and in o ...
. Caudal vertebrae compose the tail, and the final few can be fused into the
pygostyle Pygostyle describes a skeletal condition in which the final few caudal vertebra In the vertebrate spinal column, each vertebra is an irregular bone with a complex structure composed of bone and some hyaline cartilage, the proportions of wh ...
in birds, or into the
coccygeal The coccyx (plural: ''coccyges'' or ''coccyxes''), commonly referred to as the tailbone, is the final segment of the vertebral column The vertebral column, also known as the backbone or spine, is part of the axial skeleton. The vertebral co ...
or tail bone in
chimpanzee The chimpanzee (''Pan troglodytes''), also known simply as chimp, is a species of Hominidae, great ape native to the forest and savannah of tropical Africa. It has four confirmed subspecies and a fifth proposed subspecies. The chimpanzee and t ...
s (and
human Humans (''Homo sapiens'') are the most abundant and widespread species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A speci ...

human
s).


Fish and amphibians

The vertebrae of
lobe-finned fishes Sarcopterygii (; ) — sometimes considered synonymous with Crossopterygii () — is a taxon (traditionally a class (biology), class or subclass) of the Osteichthyes, bony fishes whose members are known as lobe-finned fishes. The group Tetrapoda, ...

lobe-finned fishes
consist of three discrete bony elements. The vertebral arch surrounds the spinal cord, and is of broadly similar form to that found in most other vertebrates. Just beneath the arch lies a small plate-like pleurocentrum, which protects the upper surface of the
notochord In anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any in ...
, and below that, a larger arch-shaped intercentrum to protect the lower border. Both of these structures are embedded within a single cylindrical mass of cartilage. A similar arrangement was found in the primitive
Labyrinthodonts Labyrinthodontia (Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is approximately 10.7 mil ...

Labyrinthodonts
, but in the evolutionary line that led to reptiles (and hence, also to mammals and birds), the intercentrum became partially or wholly replaced by an enlarged pleurocentrum, which in turn became the bony vertebral body. In most
ray-finned fishes Actinopterygii (New Latin New Latin (also called Neo-Latin or Modern Latin) is the revival of Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was origi ...
, including all
teleost Teleostei (Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is approximat ...
s, these two structures are fused with, and embedded within, a solid piece of bone superficially resembling the vertebral body of mammals. In living
amphibian Amphibians are ectothermic, tetrapod vertebrates of the Class (biology), class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most species living within terrestrial animal, ter ...
s, there is simply a cylindrical piece of bone below the vertebral arch, with no trace of the separate elements present in the early tetrapods. In
cartilaginous fish Chondrichthyes (; ) is a class (biology), class that contains the cartilaginous fishes that have skeletons primarily composed of cartilage. They can be contrasted with the Osteichthyes or ''bony fishes'', which have skeletons primarily composed ...

cartilaginous fish
, such as
shark Sharks are a group of elasmobranch fish characterized by a Chondrichthyes#Skeleton, cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. Modern sharks are classified withi ...

shark
s, the vertebrae consist of two cartilaginous tubes. The upper tube is formed from the vertebral arches, but also includes additional cartilaginous structures filling in the gaps between the vertebrae, and so enclosing the spinal cord in an essentially continuous sheath. The lower tube surrounds the notochord, and has a complex structure, often including multiple layers of
calcification Calcification is the accumulation of calcium Calcium is a chemical element with the Symbol (chemistry), symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when expose ...
.
Lamprey Lampreys (sometimes inaccurately called lamprey eels) are an ancient extant lineage of Agnatha, jawless fish of the order (biology), order Petromyzontiformes , placed in the superclass Cyclostomata. The adult lamprey may be characterized by ...

Lamprey
s have vertebral arches, but nothing resembling the vertebral bodies found in all
higher vertebrates Amniotes (from Greek ἀμνίον ''amnion'', "membrane surrounding the fetus", earlier "bowl in which the blood of sacrificed animals was caught", from ἀμνός ''amnos'', "lamb") are a clade A clade (; from grc, , ''klados'', "bran ...
. Even the arches are discontinuous, consisting of separate pieces of arch-shaped cartilage around the spinal cord in most parts of the body, changing to long strips of cartilage above and below in the tail region.
Hagfish Hagfish, of the class Myxini (also known as Hyperotreti) and order Myxiniformes , are eel Eels are ray-finned fish belonging to the order Anguilliformes (), which consists of eight suborders, 19 families, 111 genera Genus (plural ...

Hagfish
es lack a true vertebral column, and are therefore not properly considered vertebrates, but a few tiny neural arches are present in the tail.


Other vertebrates

The general structure of human vertebrae is fairly typical of that found in
mammal Mammals (from Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meaning "to share" or "to be i ...
s,
reptile Reptiles, as most commonly defined, are the animals in the class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or ...

reptile
s, and
bird Birds are a group of warm-blooded vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With ...

bird
s. The shape of the vertebral body does, however, vary somewhat between different groups. In mammals, such as humans, it typically has flat upper and lower surfaces, while in reptiles the anterior surface commonly has a concave socket into which the expanded convex face of the next vertebral body fits. Even these patterns are only generalisations, however, and there may be variation in form of the vertebrae along the length of the spine even within a single species. Some unusual variations include the saddle-shaped sockets between the cervical vertebrae of birds and the presence of a narrow hollow canal running down the centre of the vertebral bodies of
gecko Geckos are small, mostly carnivorous lizards that have a wide distribution, found on every continent except Antarctica. Belonging to the infraorder#Hierarchy of ranks, infraorder Gekkota, geckos are found in warm climates throughout the world. T ...

gecko
s and
tuatara Tuatara (''Sphenodon punctatus'') are reptiles Endemism, endemic to New Zealand. Although resembling most lizards, they are part of a distinct lineage, the order Rhynchocephalia. Their name derives from the Māori language, and means "peaks on ...

tuatara
s, containing a remnant of the notochord. Reptiles often retain the primitive intercentra, which are present as small crescent-shaped bony elements lying between the bodies of adjacent vertebrae; similar structures are often found in the caudal vertebrae of mammals. In the tail, these are attached to chevron-shaped bones called '' haemal arches'', which attach below the base of the spine, and help to support the musculature. These latter bones are probably homologous with the ventral ribs of fish. The number of vertebrae in the spines of reptiles is highly variable, and may be several hundred in some species of
snake Snakes are elongated, limbless, carnivore, carnivorous reptiles of the suborder Serpentes . Like all other Squamata, squamates, snakes are ectothermic, amniote vertebrates covered in overlapping Scale (zoology), scales. Many species of snakes ...

snake
. In birds, there is a variable number of cervical vertebrae, which often form the only truly flexible part of the spine. The thoracic vertebrae are partially fused, providing a solid brace for the wings during flight. The sacral vertebrae are fused with the lumbar vertebrae, and some thoracic and caudal vertebrae, to form a single structure, the ''
synsacrum The synsacrum is a skeletal structure of birds Birds are a group of warm-blooded vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the King ...

synsacrum
'', which is thus of greater relative length than the sacrum of mammals. In living birds, the remaining caudal vertebrae are fused into a further bone, the
pygostyle Pygostyle describes a skeletal condition in which the final few caudal vertebra In the vertebrate spinal column, each vertebra is an irregular bone with a complex structure composed of bone and some hyaline cartilage, the proportions of wh ...
, for attachment of the tail feathers. Aside from the tail, the number of vertebrae in mammals is generally fairly constant. There are almost always seven cervical vertebrae (
sloth Sloths are a group of arboreal Neotropical xenarthran mammals, constituting the suborder Folivora. Noted for their slowness of movement, they spend most of their lives hanging upside down in the trees of the tropical rainforest File:Kop ...

sloth
s and
manatee Manatees (family In , family (from la, familia) is a of people related either by (by recognized birth) or (by marriage or other relationship). The purpose of families is to maintain the well-being of its members and of society. Ideal ...

manatee
s are among the few exceptions), followed by around twenty or so further vertebrae, divided between the thoracic and lumbar forms, depending on the number of ribs. There are generally three to five vertebrae with the sacrum, and anything up to fifty caudal vertebrae.


Dinosaurs

The vertebral column in
dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 annum, million years ago, although the exact origin and timing of the evolution ...

dinosaur
s consists of the cervical (neck), dorsal (back), sacral (hips), and caudal (tail) vertebrae.
Saurischia Saurischia ( , meaning "reptile-hipped" from the Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its popu ...

Saurischia
n dinosaur vertebrae sometimes possess features known as '' pleurocoels'', which are hollow depressions on the lateral portions of the vertebrae, perforated to create an entrance into the air chambers within the vertebrae, which served to decrease the weight of these bones without sacrificing strength. These pleurocoels were filled with air sacs, which would have further decreased weight. In
sauropod Sauropoda (), whose members are known as sauropods (; from ''sauro- This is a list of common affixes used when scientific name, scientifically naming species, particularly extinct species for whom only their scientific names are used, along wit ...

sauropod
dinosaurs, the largest known land vertebrates, pleurocoels and air sacs may have reduced the animal's weight by over a ton in some instances, a handy evolutionary adaption in animals that grew to over 30 metres in length. In many
hadrosaur Hadrosaurids ( el, ἁδρός, ''hadrós'', "stout, thick"), or duck-billed dinosaurs, are members of the ornithischian family Hadrosauridae. This group is known as the duck-billed dinosaurs for the flat duck-bill appearance of the bones in thei ...

hadrosaur
and
theropod Theropoda ( from Ancient Greek, Greek 'wild beast' and 'foot'), whose members are known as theropods, is a dinosaur clade that is characterized by hollow bones and three-toed limbs. Theropods are generally classed as a group of saurischian d ...
dinosaurs, the caudal vertebrae were reinforced by ossified tendons. The presence of three or more sacral vertebrae, in association with the hip bones, is one of the defining characteristics of dinosaurs. The
occipital condyle The occipital condyles are undersurface protuberances of the occipital bone The occipital bone () is a cranial dermal bone and the main bone of the occiput (back and lower part of the skull). It is Trapezoid, trapezoidal in shape and curved on i ...
is a structure on the posterior part of a dinosaur's skull that articulates with the first cervical vertebra.


See also

*
Low back pain Low back pain (LBP) or lumbago is a common musculoskeletal disorders, disorder involving the muscles, nerves, and bones of the back, inbetween the lower edge of the ribs and the lower fold of the buttocks. Pain can vary from a dull constant ache ...

Low back pain
* Neuromechanics of idiopathic scoliosis *
Neutral spine Good posture refers to the "three natural curves hatare present in a healthy spine.". It is also called neutral spine. Looking directly at the front or back of the body, the 33 vertebrae in the spinal column should appear completely vertical. F ...


References


External links


Spinal Term Glossary


{{DEFAULTSORT:Vertebral Column Bones of the vertebral column Vertebrate anatomy
Skeletal system {{Commons cat, Skeletal system A skeleton (endoskeleton) is made up of bones. ''See also:'' :Bone products Musculoskeletal system ...
Bones of the thorax Irregular bones Human back