[[Image:Medulla spinalis - Section - Latin.png|thumb|right||Cross-section through cervical spinal cord.]]
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{{BioPsy}}
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The '''spinal cord''' is a part of the [[vertebrate]][[nervoussystem]]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 cordconveysthe31 [[spinal nerve]] pairs of the [[peripheral nervous system]], as well as [[central nervous system]] pathways that innervate [[skeletal muscle]]s.
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[[Image:Gray111-Vertebral column.png|thumb|150px|The vertebralcolumnseenfrom the side]]
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The vertebral column consists of [[vertebra]]edescribedas 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]].
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[[Image:Spinalcolumncurvature.png|thumb|150px|Differentregions (curvatures) of the vertebralcolumn]]
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==Embryology==
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In[[humananatomy]], 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]].
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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.
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== Anatomy ==
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== Curves ==
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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]].
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Thespinal cord carries [[sensory]] signals and [[motor]] innervation to most of the [[skeletalmuscle]]sinthebody.Justaboutevery [[voluntary muscle]] in the bodybelowthe head depends on the spinal cord for control. Similarly, mostcutaneoussensation below the neck is transmitted via the spinal cord. Most of the [[sympatheticnervous system|sympathetic pathway]]sand the lower (i.e. non-[[vagusnerve|vagal]]) [[parasympatheticnervous system|parasympathetic pathway]]salsogothrough the spinal cord.
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Viewedlaterally the vertebralcolumnpresentsseveralcurves,whichcorrespondto the differentregionsof the column, andarecalled [[Cervicalvertebrae|cervical]], [[Thoracicvertebrae|thoracic]], [[Lumbarvertebrae|lumbar]],andpelvic.
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Across-sectionthroughthespinalcordrevealsthatthereisa[[central canal]] that carries [[cerebrospinal fluid]] (CSF) surrounded by [[grey matter]] on the inside, and thisis surrounded by [[white matter]]. (This is the oppositeto the [[brain]]'s[[cerebralcortex]].)Asection of the cordcanbedivided into neat symmeterical halves by the dorsalmedian sulcus and ventral median fissure.
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Thecervicalcurve,convexforward,beginsattheapexoftheodontoid (''tooth-like'') process, and endsat the middleof the secondthoracicvertebra;itis the leastmarkedofall the curves.
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The dorsal(towardstheback)sideof the spinalcordcarriessensoryinformation.Theneurons that bring somatosensory information to the spinalcord reside in the [[dorsalrootganglion]]. Sensationfromthelowerbodytravelsup the ''graciletract'',whilesensationfromtheupperbodyandarmstravelsupthe ''cuneatetract'', 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.
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The thoraciccurve,concaveforward,beginsat the middleofthesecondandendsat the middleof the twelfththoracicvertebra. Itsmostprominentpointbehindcorrespondsto the spinousprocessofthesevenththoracicvertebra.Thiscurveisknownasa ''ttcurve.
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Motorinformation(signalscomingfrom the braintomove the muscles)travelsdownthe ventral (toward the front) half of the spinalcord.[[Motorneuron]]sarelocated in the anterior(thismeansclosetothe front, in humans it means the same as ventral) horn of the greymatter.Therearetwomaincolumns of neuronsintheanteriorhorn,the''medial''and ''lateral motorcolumns''.
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Thelumbarcurveismore marked in the [[female]]thanin the [[male]];itbeginsat the middle of the lastthoracicvertebra,andendsat the sacrovertebralangle.Itisconvexanteriorly, the convexity of the lowerthreevertebraebeingmuchgreaterthan that of theuppertwo.Thiscurveisdescribedas a ''lordoticcurve''.
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The spinalcordproper ends at the levelofL1.It terminates at a conical point known as the [[conus medullaris]],fromwhichthepiamater 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").
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The pelviccurvebegins at the sacrovertebralarticulation,andends at the point of the [[coccyx]];itsconcavityisdirecteddownward and forward.
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The actualcordisapproxiamately[[cylinder(geometry)|cylindrical]]inshape, butthediametervariesatdifferentvetebrallevels. Thereare two enlargements, cervical and lumbar.The ''cervical enlargement'' isduetothecordsegmentsfrom C5 to T1 which innervates the upperlimb via the [[brachial plexus]].The''[[lumbar]] enlargement''arisefromsegmentsL1 to S3 (onlytheregion around L1/L2 is part of the spinalcordproper)andinnervatesthelower limbs via the [[lumbarplexus|lumbar]]and [[sacral plexus|sacral]] plexi.
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The thoracicandpelviccurvesaretermed<b>primarycurves</b>, becausetheyalonearepresentduring[[fetus|fetal]]life. .The cervical and lumbar curves are ''compensatory'' or''secondary'',andaredevelopedafter[[childbirth|birth]], the formerwhen the [[child]] is able to hold up its [[head]] (atthreeorfourmonths) and to sit upright (atninemonths), the latterattwelveoreighteenmonths,when the childbeginsto [[walk]].
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Thereis 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 lesswhitematter.
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===Names of individualvertebrae===
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Individual vertebrae named according to region and position, from superior to inferior
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<!-- Image with unknown copyright status removed: [[Image:Typical Cervival Vertebra.jpg|thumb|Typical cervical vertebra]] -->
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*Cervical – 7 vertebrae (C1-C7)
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** C1 is known as "atlas" and supports the head, C2 is known as "axis"
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** Possesses bifid spinous processes, which is absent in C7
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** Small-bodied
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*Thoracic – 12 vertebrae (T1-T12)
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** Distinguished by the presence of costal facets for the articulation of the heads of ribs
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** Body is intermediate in size between the cervical and lumbar vertebrae
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*Lumbar – 5 vertebrae (L1-L5)
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** Has a large body
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** Does not have costal facets nor transverse process foramina
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.
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[[Image:Gray204.png|thumb|right|200px|Orientation of the [[rib cage]] on the vertebral column]]
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=== Posterior surface ===
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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 — 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.
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=== Lateral surfaces ===
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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.
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[[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>
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== Vertebral canal ==
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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.
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== Abnormalities ==
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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.
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The following abnormal curvatures may occur in some people:
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* [[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.
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* [[Lordosis]] is an exaggerated lordotic (anterior) curvature of the lumbar region, "swayback". Temporary lordosis is common among [[pregnant]] [[women]].
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* [[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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Line 28:
* [[Brown-Sequard syndrome]]
* [[Brown-Sequard syndrome]]
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{{BioPsy}}
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==Additional images==
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<gallery>
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Image:Illu vertebral column.jpg|Vertebral column.
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Image:Spinal cord direv.svg|The [[spinal cord]] nested in the vertebral column.
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Image:Human skeleton back.svg|Human [[skeleton]] back
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Image:Gray409.png|Relation of the vertebral column to the surrounding muscles.
Viewed laterally the vertebral column presents several curves, which correspond to the different regions of the column, and are called cervical, thoracic, lumbar, and pelvic.
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 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.
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 pelvic curve begins at the sacrovertebral articulation, and ends at the point of the coccyx; its concavity is directed downward and forward.
The thoracic and pelvic curves are termed primary curves, because they alone are present during fetal life. . The cervical and lumbar curves are compensatory or secondary, and are developed after 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.
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.
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 — 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.
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.
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.
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), 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 pregnantwomen.
Scoliosis, lateral curvature, is the most common abnormal curvature, occurring in 0.5% of the population. It is more common among females 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.
Added by Dr Joe Kiff
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