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[[Image:Medulla spinalis - Section - Latin.png|thumb|right||Cross-section through cervical spinal cord.]]
The '''spinal cord''' is a part of the [[vertebrate]] [[nervous system]] that is enclosed in and protected by the [[spine (anatomy)|vertebral column]] (it passes through the [[spinal canal]]). It consists of [[neuron|nerve cells]]. The cord conveys the 31 [[spinal nerve]] pairs of the [[peripheral nervous system]], as well as [[central nervous system]] pathways that innervate [[skeletal muscle]]s.
[[Image:Gray 111 - Vertebral column.png|thumb|150px|The vertebral column seen from the side]]
The vertebral column consists of [[vertebra]]e described as belonging to 5 groups (called segments). These segments are (in order from top to bottom): the [[cervical]], thoracic, and lumbar vertebrae, and the [[sacrum]] and [[coccyx]].
[[Image:Spinal column curvature.png|thumb|150px|Different regions (curvatures) of the vertebral column]]
== Embryology ==
In [[human anatomy]], the '''vertebral column''' ('''backbone''' or '''spine''') is a column of 24 [[vertebra]]e, the [[sacrum]], [[intervertebral disc]]s, and the [[coccyx]] situated in the [[dorsum (biology)|dorsal]] aspect of the [[torso]], separated by [[spinal disc]]s. It houses the [[spinal cord]] in its [[spinal canal]].
In the human [[fetus]], the spinal cord extends all the way down to the [[sacral vertebrae]]. As a person matures, the spinal cord shortens relative to the rest of the body, so at adulthood, the spinal cord only reaches down to around the level of L1 (the first, i.e. highest, [[lumbar vertebrae|lumbar vertebra]]), where it terminates and the [[cauda equina]] begin - this is why [[lumbar puncture]]s are usually carried out on an adult at the (lower) level of L3/L4.
== Curves ==
== Anatomy ==
The spinal cord originates inside the [[brain]] at the inferior end of the [[medulla oblongata]], exiting the [[skull]] via the [[foramen magnum]]. It is wrapped in three layers of membranes, called [[meninges]].
The spinal cord carries [[sensory]] signals and [[motor]] innervation to most of the [[skeletal muscle]]s in the body. Just about every [[voluntary muscle]] in the body below the head depends on the spinal cord for control. Similarly, most cutaneous sensation below the neck is transmitted via the spinal cord. Most of the [[sympathetic nervous system|sympathetic pathway]]s and the lower (i.e. non-[[vagus nerve|vagal]]) [[parasympathetic nervous system|parasympathetic pathway]]s also go through the spinal cord.
Viewed laterally the vertebral column presents several curves, which correspond to the different regions of the column, and are called [[Cervical vertebrae|cervical]], [[Thoracic vertebrae|thoracic]], [[Lumbar vertebrae|lumbar]], and pelvic.
A cross-section through the spinal cord reveals that there is a [[central canal]] that carries [[cerebrospinal fluid]] (CSF) surrounded by [[grey matter]] on the inside, and this is surrounded by [[white matter]]. (This is the opposite to the [[brain]]'s [[cerebral cortex]].) A section of the cord can be divided into neat symmeterical halves by the dorsal median sulcus and ventral median fissure.
The cervical curve, convex forward, begins at the apex of the odontoid (''tooth-like'') process, and ends at the middle of the second thoracic vertebra; it is the least marked of all the curves.
The dorsal (towards the back) side of the spinal cord carries sensory information. The neurons that bring somatosensory information to the spinal cord reside in the [[dorsal root ganglion]]. Sensation from the lower body travels up the ''gracile tract'', while sensation from the upper body and arms travels up the ''cuneate tract'', which lies lateral to the gracile tract. There is no cuneate tract in the lumbar part of the spinal cord as sensory information from the arms does not travel through this area.
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 ''tt curve.
Motor information (signals coming from the brain to move the muscles) travels down the ventral (toward the front) half of the spinal cord. [[Motor neuron]]s are located in the anterior (this means close to the front, in humans it means the same as ventral) horn of the grey matter. There are two main columns of neurons in the anterior horn, the ''medial'' and ''lateral motor columns''.
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 curve''.
The spinal cord proper ends at the level of L1. It terminates at a conical point known as the [[conus medullaris]], from which the pia mater extends caudally as the '''''filum terminale''''' and attaches to the dorsal surface of the first cocygeal vertebra. After the termination of the cord, the spinal nerves continue as dangling nerves called the [[cauda equina]] (literally "horse's tail").
The pelvic curve begins at the sacrovertebral articulation, and ends at the point of the [[coccyx]]; its concavity is directed downward and forward.
The actual cord is approxiamately [[cylinder (geometry)|cylindrical]] in shape, but the diameter varies at different vetebral levels. There are two enlargements, cervical and lumbar. The ''cervical enlargement'' is due to the cord segments from C5 to T1 which innervates the upper limb via the [[brachial plexus]]. The ''[[lumbar]] enlargement'' arise from segments L1 to S3 (only the region around L1/L2 is part of the spinal cord proper) and innervates the lower limbs via the [[lumbar plexus|lumbar]] and [[sacral plexus|sacral]] plexi.
The thoracic and pelvic curves are termed <b>primary curves</b>, because they alone are present during [[fetus|fetal]] life. . The cervical and lumbar curves are ''compensatory'' or ''secondary'', and are developed after [[childbirth|birth]], the former when the [[child]] is able to hold up its [[head]] (at three or four months) and to sit upright (at nine months), the latter at twelve or eighteen months, when the child begins to [[walk]].
There is a higher proportion of white matter in the [[cervical]] (neck) part of the spinal cord. This is because information to and from the whole body (such as the feet) must pass through here. In contrast, the lumbar and sacral areas do not carry information from anywhere above them, so have less white matter.
=== Names of individual vertebrae ===
Individual vertebrae named according to region and position, from superior to inferior
<!-- Image with unknown copyright status removed: [[Image:Typical Cervival Vertebra.jpg|thumb|Typical cervical vertebra]] -->
*Cervical &ndash; 7 vertebrae (C1-C7)
** C1 is known as "atlas" and supports the head, C2 is known as "axis"
** Possesses bifid spinous processes, which is absent in C7
** Small-bodied
*Thoracic &ndash; 12 vertebrae (T1-T12)
** Distinguished by the presence of costal facets for the articulation of the heads of ribs
** Body is intermediate in size between the cervical and lumbar vertebrae
*Lumbar &ndash; 5 vertebrae (L1-L5)
** Has a large body
** Does not have costal facets nor transverse process foramina
*Sacral &ndash; 5 (fused) vertebrae (S1-S5)
*Coccygeal &ndash; 4 (3-5) (fused) vertebrae (Tailbone)
== 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.
[[Image:Gray204.png|thumb|right|200px|Orientation of the [[rib cage]] on the vertebral column]]
=== Posterior surface ===
The posterior surface of 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 and horizontal, with bifid extremities. 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 &mdash; a fact to be remembered in practice, as irregularities of this sort are attendant also on fractures or displacements of the vertebral column. 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 vertebral grooves 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 lateral surfaces are separated from the posterior surface by the articular processes in the cervical and lumbar regions, and by the transverse processes in the thoracic region. They present, in front, the sides of the bodies of the vertebrae, marked in the thoracic region 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 spinal nerves and are situated between the transverse processes in the cervical region, and in front of them in the thoracic and lumbar regions.
[[Image:Orientation.PNG|thumb|right|300px|Orientation of vertebral column on surface.]] T3 is at level of medial part of [[spine of scapula]]. T7 is at [[inferior angle of the scapula]]. L4 is at highest point of [[iliac crest]]. S2 is at the level of [[posterior superior iliac spine]]. T12 can be found by identifying the lowest pair of ribs and tracing them to their thoracic attachment.<ref>Swash, M, Glynn, M.(eds). 2007. Hutchison's Clinical Methods. Edinburgh. Saunders Elsevier.</ref> Furthermore, C7 is easily localized as a prominence at the lower part of the neck. <ref>Anatomy Compendium (Godfried Roomans and Anca Dragomir)</ref>
== Vertebral canal ==
The vertebral canal follows the different curves of the column; it is large and triangular in those parts of the column which 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.
== Abnormalities ==
Occasionally the coalescence of the laminae is not completed, and consequently a cleft is left in the arches of the vertebrae, through which a protrusion of the spinal membranes (''[[dura mater]]'' and [[arachnoid (brain)|arachnoid]]), and generally of the [[spinal cord]] (''medulla spinalis'') itself, takes place, constituting the malformation known as ''[[spina bifida]]''. This condition is most common in the lumbosacral region, but it may occur in the thoracic or cervical region, or the arches throughout the whole length of the canal may remain incomplete.
The following abnormal curvatures may occur in some people:
* [[Kyphosis]] is an exaggerated kyphotic (posterior) curvature in the thoracic region. This produces the so-called "humpback" or "dowager's hump", a condition commonly observed in osteoporosis.
* [[Lordosis]] is an exaggerated lordotic (anterior) curvature of the lumbar region, "swayback". Temporary lordosis is common among [[pregnant]] [[women]].
* [[Scoliosis]], lateral curvature, is the most common abnormal curvature, occurring in 0.5% of the population. It is more common among [[female]]s and may result from unequal growth of the two sides of one or more vertebrae. It can also be caused by pulmonary atelectasis (partial or complete deflation of one or more lobes of the lungs) as observed in asthma or pneumothorax.
== Pathology ==
== Pathology ==
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* [[Brown-Sequard syndrome]]
* [[Brown-Sequard syndrome]]
==Additional images==
Image:Illu vertebral column.jpg|Vertebral column.
Image:Spinal cord direv.svg|The [[spinal cord]] nested in the vertebral column.
Image:Human skeleton back.svg|Human [[skeleton]] back
Image:Gray409.png|Relation of the vertebral column to the surrounding muscles.
Image:Gray 111 - Vertebral column-coloured.png|Vertebral column.
== See also ==
* [[Low back pain]]
* [[Vertebral subluxation]]
* [[Spinal cord injuries]]
* [[Scoliosis]]
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*[ Nerve Structures of the Spine]
*[ Nerve Structures of the Spine]
[[it:Midollo spinale]]
[[it:Midollo spinale]]
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[[uk:Спинний мозок]]
[[uk:Спинний мозок]]
{{enWP| Spinal_cord}}
{{enWP|Vertebral column}}

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