Examine individual changes

'{{short description|Long, tubular central nervous system structure in the vertebral column}} {{More citations needed|date=January 2012}} {{Infobox anatomy | Name = Spinal cord | Latin = medulla spinalis | Image = Nervous system diagram-en.svg | Caption = The spinal cord (in yellow) connects the brain to nerves throughout the body. | Width = 244 | Image2 = | Caption2 = | Precursor = | System = | part_of = [[Central nervous system]] | Artery = spinal artery | Vein = spinal vein | Nerve = | Lymph = }} 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]]. It encloses the [[central canal]] of the spinal cord, which contains [[cerebrospinal fluid]]. The [[brain]] and spinal cord together make up the [[central nervous system]] (CNS). In [[human]]s, the spinal cord begins at the [[occipital bone]], passing through the [[foramen magnum]] and entering the [[spinal canal]] at the beginning of the [[cervical vertebrae]]. The spinal cord extends down to between the first and second [[lumbar vertebrae]], where it ends. The enclosing bony vertebral column protects the relatively shorter spinal cord. It is around {{convert|45|cm|in|abbr=on}} in men and around {{convert|43|cm|in|abbr=on}} long in women. The diameter of the spinal cord ranges from {{convert|1/2|in|mm|order=flip|abbr=on}} in the [[cervical vertebrae|cervical]] and lumbar regions to {{convert|1/4|in|mm|order=flip|abbr=on}} in the [[thoracic vertebrae|thoracic]] area. The spinal cord functions primarily in the transmission of [[Action potential|nerve signals]] from the [[motor cortex]] to the body, and from the [[afferent nerve fiber|afferent fibers]] of the [[sensory neuron]]s to the [[sensory cortex]]. It is also a center for coordinating many [[reflex]]es and contains [[reflex arc]]s that can independently control reflexes.<ref name="Maton">{{cite book|last1=Maton|display-authors=etal|first1=Anthea|title=Human biology and health|date=1993|publisher=Prentice Hall|location=Englewood Cliffs, N.J.|isbn=978-0-13-981176-0|pages=[https://archive.org/details/humanbiologyheal00scho/page/132 132–144]|edition=1st|url-access=registration|url=https://archive.org/details/humanbiologyheal00scho/page/132}}</ref> It is also the location of groups of [[spinal interneuron]]s that make up the [[neural circuit]]s known as [[central pattern generator]]s. These circuits are responsible for controlling motor instructions for rhythmic movements such as walking.<ref name="Guertin">{{cite journal |last1=Guertin |first1=PA |title=Central pattern generator for locomotion: anatomical, physiological, and pathophysiological considerations. |journal=Frontiers in Neurology |date=2012 |volume=3 |pages=183 |doi=10.3389/fneur.2012.00183 |pmid=23403923|pmc=3567435 }}</ref> ==Structure== [[File:Diagram of the spinal cord CRUK 046.svg|thumb|left|240px|Diagram of the spinal cord showing segments]] The spinal cord is the main pathway for information connecting the brain and [[peripheral nervous system]].<ref>{{Cite book|title = Exploring Psychology|last = Myers|first = Gary|publisher = Worth Publishers|isbn = 978-1429216357|location = |pages = 41|date = 2009-12-25}}</ref><ref name="Squire">{{cite book|last1=Squire |display-authors=etal |first1=Larry Squire|title=Fundamental neuroscience|date=2013|publisher=Elsevier/Academic Press|location=Amsterdam|isbn=978-0-12-385-870-2|page=628|edition=4th}}</ref> Much shorter than its protecting spinal column, the human spinal cord originates in the brainstem, passes through the [[foramen magnum]], and continues through to the [[conus medullaris]] near the second [[lumbar vertebra]] before terminating in a fibrous extension known as the [[filum terminale]]. It is about {{convert|45|cm|in|abbr=on}} long in men and about {{convert|43|cm|in|abbr=on}} in women, [[oval|ovoid]]-shaped, and is enlarged in the cervical and lumbar regions. The cervical enlargement, stretching from the C5 to T1 vertebrae, is where sensory input comes from and motor output goes to the arms and trunk. The lumbar enlargement, located between L1 and S3, handles sensory input and motor output coming from and going to the legs. The spinal cord is continuous with the caudal portion of the medulla, running from the base of the [[skull]] to the body of the first lumbar vertebra. It does not run the full length of the vertebral column in adults. It is made of 31 segments from which branch one pair of sensory nerve roots and one pair of motor nerve roots. The nerve roots then merge into bilaterally symmetrical pairs of [[spinal nerve]]s. The peripheral nervous system is made up of these spinal roots, nerves, and [[ganglion|ganglia]]. The dorsal roots are afferent [[nerve fascicle|fascicles]], receiving sensory information from the skin, muscles, and visceral organs to be relayed to the brain. The roots terminate in [[dorsal root ganglia]], which are composed of the cell bodies of the corresponding neurons. Ventral roots consist of [[Efferent nerve fiber|efferent fibers]] that arise from motor neurons whose cell bodies are found in the ventral (or anterior) gray horns of the spinal cord. The spinal cord (and brain) are protected by three layers of tissue or membranes called [[meninges]], that surround the canal . The [[dura mater]] is the outermost layer, and it forms a tough protective coating. Between the dura mater and the surrounding bone of the [[vertebra (anatomy)|vertebrae]] is a space called the [[epidural space]]. The epidural space is filled with [[adipose tissue]], and it contains a network of [[blood vessel]]s. The [[arachnoid mater]], the middle protective layer, is named for its open, spiderweb-like appearance. The space between the arachnoid and the underlying [[pia mater]] is called the [[subarachnoid space]]. The subarachnoid space contains [[cerebrospinal fluid]] (CSF), which can be sampled with a [[lumbar puncture]], or "spinal tap" procedure. The delicate pia mater, the innermost protective layer, is tightly associated with the surface of the spinal cord. The cord is stabilized within the dura mater by the connecting [[denticulate ligaments]], which extend from the enveloping pia mater laterally between the dorsal and ventral roots. The [[dural sac]] ends at the vertebral level of the second [[sacrum|sacral]] vertebra. In cross-section, the peripheral region of the cord contains neuronal [[white matter]] tracts containing [[sensory neuron|sensory]] and [[motor neuron|motor]] [[axon]]s. Internal to this peripheral region is the [[grey matter]], which contains the [[neuron|nerve cell bodies]] arranged in the three [[grey column]]s that give the region its butterfly-shape. This central region surrounds the [[central canal]], which is an extension of the [[fourth ventricle]] and contains cerebrospinal fluid. The spinal cord is elliptical in cross section, being compressed dorsolaterally. Two prominent grooves, or sulci, run along its length. The [[posterior median sulcus of spinal cord|posterior median sulcus]] is the groove in the dorsal side, and the [[anterior median fissure of spinal cord|anterior median fissure]] is the groove in the ventral side. ===Spinal cord segments=== [[File:Gray 111 - Vertebral column-coloured.png|right|150px]] The human spinal cord is divided into segments where pairs of spinal nerves (mixed; sensory and motor) form. Six to eight motor nerve rootlets branch out of right and left ventro lateral sulci in a very orderly manner. Nerve rootlets combine to form nerve roots. Likewise, sensory nerve rootlets form off right and left dorsal lateral sulci and form sensory nerve roots. The ventral (motor) and dorsal (sensory) roots combine to form [[spinal nerve]]s (mixed; motor and sensory), one on each side of the spinal cord. Spinal nerves, with the exception of C1 and C2, form inside the [[intervertebral foramen]] (IVF). These rootlets form the demarcation between the central and peripheral nervous systems.[[File:Spinal readjustment 3.jpg|thumb|left|200px|right|alt=Model of a section of a spine.|A model of segments of the human spine and spinal cord, nerve roots can be seen extending laterally from the (not visible) spinal cord.]] The [[grey column]], (as three regions of grey columns) in the center of the cord, is shaped like a butterfly and consists of cell bodies of [[Spinal interneuron|interneurons]], motor neurons, [[neuroglia]] cells and [[unmyelinated]] axons. The [[anterior grey column|anterior]] and [[posterior grey column]] present as projections of the grey matter and are also known as the horns of the spinal cord. Together, the grey columns and the [[gray commissure]] form the "grey H." The white matter is located outside of the grey matter and consists almost totally of [[myelinated]] motor and sensory axons. "Columns" of white matter carry information either up or down the spinal cord. The spinal cord proper terminates in a region called the [[conus medullaris]], while the [[pia mater]] continues as an extension called the [[filum terminale]], which anchors the spinal cord to the [[coccyx]]. The [[cauda equina]] ("horse's tail") is a collection of nerves inferior to the conus medullaris that continue to travel through the vertebral column to the coccyx. The cauda equina forms because the spinal cord stops growing in length at about age four, even though the vertebral column continues to lengthen until adulthood. This results in sacral spinal nerves originating in the upper lumbar region. Within the Central Nervous System (CNS), nerve cell bodies are generally organized into functional clusters, called nuclei. Axons within the CNS are grouped into tracts. There are 31 spinal cord nerve segments in a human spinal cord: * 8 cervical segments forming 8 pairs of [[cervical nerves]] (C1 spinal nerves exit the spinal column between the foramen magnum and the C1 vertebra; C2 nerves exit between the posterior arch of the C1 vertebra and the lamina of C2; C3–C8 spinal nerves pass through the IVF above their corresponding cervical vertebrae, with the exception of the C8 pair which exit between the C7 and T1 vertebrae) * 12 thoracic segments forming 12 pairs of [[thoracic nerves]] * 5 lumbar segments forming 5 pairs of [[lumbar nerves]] * 5 sacral segments forming 5 pairs of [[sacral nerves]] * 1 coccygeal segment {| class="wikitable" |+Spinal cord segments in some common species <ref>{{cite web|url=http://vanat.cvm.umn.edu/neurLab2/SpCdGross.html|title=Spinal Cord Gross Anatomy|accessdate=December 27, 2015}}</ref> |- ! Species !! Cervical !! Thoracic !! Lumbar !! Sacral !! Caudal/Coccygeal !! Total |- | Dog || 8 || 13 || 7 || 3 || 5 || 36 |- | Cat || 8 || 13 || 7 || 3 || 5 || 36 |- | Cow || 8 || 13 || 6 || 5 || 5 || 37 |- | Horse || 8 || 18 || 6 || 5 || 5 || 42 |- | Pig || 8 || 15/14 || 6/7 || 4 || 5 || 38 |- | Human || 8 || 12 || 5 || 5 || 1 || 31 |- |Mouse<ref>{{Cite journal|last=Harrison|first=Megan|last2=O'Brien|first2=Aine|last3=Adams|first3=Lucy|last4=Cowin|first4=Gary|last5=Ruitenberg|first5=Marc J.|last6=Sengul|first6=Gulgun|last7=Watson|first7=Charles|date=March 2013|title=Vertebral landmarks for the identification of spinal cord segments in the mouse|journal=NeuroImage|volume=68|pages=22–29|doi=10.1016/j.neuroimage.2012.11.048|pmid=23246856|issn=1053-8119|hdl=20.500.11937/41041|hdl-access=free}}</ref> |8 |13 |6 |4 |3 |35 |} In the fetus, vertebral segments correspond with spinal cord segments. However, because the [[vertebra|vertebral column]] grows longer than the spinal cord, spinal cord segments do not correspond to vertebral segments in the adult, particularly in the lower spinal cord. For example, lumbar and sacral spinal cord segments are found between vertebral levels T9 and L2, and the spinal cord ends around the L1/L2 vertebral level, forming a structure known as the conus medullaris. Although the spinal cord cell bodies end around the L1/L2 vertebral level, the spinal nerves for each segment exit at the level of the corresponding vertebra. For the nerves of the lower spinal cord, this means that they exit the vertebral column much lower (more caudally) than their roots. As these nerves travel from their respective roots to their point of exit from the vertebral column, the nerves of the lower spinal segments form a bundle called the cauda equina. There are two regions where the spinal cord enlarges: * [[Cervical enlargement]] – corresponds roughly to the [[brachial plexus]] nerves, which innervate the [[upper limb]]. It includes spinal cord segments from about C4 to T1. The vertebral levels of the enlargement are roughly the same (C4 to T1). * [[Lumbar enlargement]] – corresponds to the [[lumbosacral plexus]] nerves, which innervate the [[lower limb]]. It comprises the spinal cord segments from L2 to S3 and is found about the vertebral levels of T9 to T12. ===Development=== [[File:Sobo 1909 621.png|thumb|140px|Spinal cord seen in a midsection of a five-week-old embryo]] [[File:Sobo 1909 622.png|thumb|140px|Spinal cord seen in a midsection of a 3 month old fetus]] The spinal cord is made from part of the [[neural tube]] during development. There are four stages of the spinal cord that arises from the neural tube: The neural plate, neural fold, neural tube, and the spinal cord. Neural differentiation occurs within the spinal cord portion of the tube.<ref>{{cite web|last1=Kaufman|first1=Bard|title=Spinal Cord – Development and Stem Cells|url=http://discovery.lifemapsc.com/in-vivo-development/spinal-cord|website=Life Map Discovery Compendium|accessdate=12 Dec 2015}}</ref> As the neural tube begins to develop, the [[notochord]] begins to secrete a factor known as [[Sonic hedgehog]] or SHH. As a result, the [[floor plate]] then also begins to secrete SHH, and this will induce the basal plate to develop [[motor neurons]]. During the maturation of the neural tube, its lateral walls thicken and form a longtitudinal groove called the [[sulcus limitans]]. This extends the length of the spinal cord into dorsal and ventral portions as well.<ref>{{cite web|last1=Kaufman|first1=Bard|title=Spinal Cord-Development and Stem Cells|url=http://discovery.lifemapsc.com/in-vivo-development/spinal-cord|website=Stem Cell Development Compendium|accessdate=2 Dec 2015}}</ref> Meanwhile, the overlying [[ectoderm]] secretes [[bone morphogenetic protein]] (BMP). This induces the [[roof plate]] to begin to secrete BMP, which will induce the [[alar plate]] to develop [[sensory neurons]]. Opposing gradients of such morphogens as BMP and SHH form different domains of dividing cells along the dorsal ventral axis.<ref>{{Cite journal|last=Than-Trong|first=Emmanuel|last2=Bally-Cuif|first2=Laure|date=2015-08-01|title=Radial glia and neural progenitors in the adult zebrafish central nervous system|journal=Glia|volume=63|issue=8|pages=1406–1428|doi=10.1002/glia.22856|issn=1098-1136|pmid=25976648}}</ref> Dorsal root ganglion neurons differentiate from neural crest progenitors. As the dorsal and ventral column cells proliferate, the lumen of the neural tube narrows to form the small central canal of the spinal cord.<ref>{{cite book|last1=Saladin|title=Anatomy & Physiology The Unity of Form and Function|url=https://archive.org/details/anatomyphysiolog0000sala|url-access=registration|publisher=Mc Graw Hill}}</ref> The alar plate and the basal plate are separated by the sulcus limitans. Additionally, the floor plate also secretes [[netrin]]s. The netrins act as chemoattractants to [[decussation]] of pain and temperature sensory neurons in the alar plate across the anterior white commissure, where they then ascend towards the [[thalamus]]. Following the closure of the caudal neuropore and formation of the brain's ventricles that contain the choroid plexus tissue, the central canal of the caudal spinal cord is filled with cerebrospinal fluid. Earlier findings by Viktor Hamburger and Rita Levi-Montalcini in the chick embryo have been confirmed by more recent studies which have demonstrated that the elimination of neuronal cells by [[programmed cell death]] (PCD) is necessary for the correct assembly of the nervous system.<ref>{{cite journal|last1=Cowan|first1=WM|title=Viktor Hamburger and Rita Levi-Montalcini: the path to the discovery of nerve growth factor.|journal=Annual Review of Neuroscience|date=2001|volume=24|pages=551–600|pmid=11283321|doi=10.1146/annurev.neuro.24.1.551|url=https://semanticscholar.org/paper/2c96e7e2b57ad0e78c003dc4458a49c4a08fcd6a}}</ref> Overall, spontaneous embryonic activity has been shown to play a role in neuron and muscle development but is probably not involved in the initial formation of connections between spinal neurons. ===Blood supply=== The spinal cord is supplied with blood by three arteries that run along its length starting in the brain, and many arteries that approach it through the sides of the spinal column. The three longitudinal arteries are the [[anterior spinal artery]], and the right and left [[posterior spinal artery|posterior spinal arteries]].<ref name=Moore298>{{cite book|last=Moore|first=Keith|title=Essential Clinical Anatomy, Third Edition|year=2007|publisher=Lippincott Williams & Wilkins|isbn=978-0-7817-6274-8|pages=298|author2=Anne Agur }}</ref> These travel in the [[Subarachnoid space|subarachnoid]] space and send branches into the spinal cord. They form [[anastamosis|anastamoses]] (connections) via the anterior and posterior [[segmental medullary artery|segmental medullary arteries]], which enter the spinal cord at various points along its length.<ref name=Moore298 /> The actual blood flow caudally through these arteries, derived from the posterior cerebral circulation, is inadequate to maintain the spinal cord beyond the cervical segments. The major contribution to the arterial blood supply of the spinal cord below the cervical region comes from the radially arranged posterior and anterior [[radicular artery|radicular arteries]], which run into the spinal cord alongside the dorsal and ventral nerve roots, but with one exception do not connect directly with any of the three longitudinal arteries.<ref name=Moore298 /> These intercostal and lumbar radicular arteries arise from the aorta, provide major anastomoses and supplement the blood flow to the spinal cord. In humans the largest of the anterior radicular arteries is known as the [[artery of Adamkiewicz]], or anterior radicularis magna (ARM) artery, which usually arises between L1 and L2, but can arise anywhere from T9 to L5.<ref>{{cite journal|last=Biglioli|first=Paolo |display-authors=etal |title=Upper and lower spinal cord blood supply: the continuity of the anterior spinal artery and the relevance of the lumbar arteries|journal=Journal of Thoracic and Cardiovascular Surgery|date=April 2004|volume=127|issue=4|pages=1188–1192|doi=10.1016/j.jtcvs.2003.11.038|pmid=15052221|url=https://air.unimi.it/bitstream/2434/143447/2/2004%20JTCVS%20midollo.pdf}}</ref> Impaired blood flow through these critical radicular arteries, especially during surgical procedures that involve abrupt disruption of blood flow through the aorta for example during aortic aneurysm repair, can result in spinal cord infarction and paraplegia. ==Function== ===Somatosensory organization=== {{anchor|tracts}} [[File:Spinal cord tracts - English.svg|thumb|360px|right|Spinal cord tracts.]] In the dorsal column-medial leminiscus tract, a primary neuron's axon enters the spinal cord and then enters the dorsal column. If the primary axon enters below spinal level T6, the axon travels in the [[fasciculus gracilis]], the medial part of the column. If the axon enters above level T6, then it travels in the [[fasciculus cuneatus]], which is lateral to the fasciculus gracilis. Either way, the primary axon ascends to the lower [[medulla oblongata|medulla]], where it leaves its fasciculus and synapses with a secondary neuron in one of the dorsal column nuclei: either the [[nucleus gracilis]] or the [[nucleus cuneatus]], depending on the pathway it took. At this point, the secondary axon leaves its nucleus and passes anteriorly and medially. The collection of secondary axons that do this are known as [[internal arcuate fibers]]. The internal arcuate fibers [[decussate]] and continue ascending as the contralateral [[medial lemniscus]]. Secondary axons from the medial lemniscus finally terminate in the [[ventral posterolateral nucleus]] (VPLN) of the [[thalamus]], where they synapse with tertiary neurons. From there, tertiary neurons ascend via the posterior limb of the [[internal capsule]] and end in the [[primary sensory cortex]]. The proprioception of the lower limbs differs from the upper limbs and upper trunk. There is a four-neuron pathway for lower limb proprioception. This pathway initially follows the dorsal spino-cerebellar pathway. It is arranged as follows: proprioceptive receptors of lower limb&nbsp;→&nbsp;peripheral process&nbsp;→&nbsp;dorsal root ganglion&nbsp;→&nbsp;central process&nbsp;→&nbsp;[[Clarke's column]]&nbsp;→&nbsp;2nd order neuron&nbsp;→&nbsp;medulla oblongata ([[Caudate nucleus]])&nbsp;→&nbsp;3rd order neuron&nbsp;→&nbsp;VPLN of thalamus&nbsp;→&nbsp;4th order neuron&nbsp;→&nbsp;posterior limb of internal capsule&nbsp;→&nbsp;corona radiata&nbsp;→&nbsp;sensory area of cerebrum. The anterolateral system works somewhat differently. Its primary neurons axons enter the spinal cord and then ascend one to two levels before synapsing in the [[substantia gelatinosa of Rolando|substantia gelatinosa]]. The tract that ascends before synapsing is known as [[Lissauer's tract]]. After synapsing, secondary axons decussate and ascend in the anterior lateral portion of the spinal cord as the [[spinothalamic tract]]. This tract ascends all the way to the VPLN, where it synapses on tertiary neurons. Tertiary neuronal axons then travel to the primary sensory cortex via the posterior limb of the internal capsule. Some of the "pain fibers" in the ALS deviate from their pathway towards the VPLN. In one such deviation, axons travel towards the [[reticular formation]] in the midbrain. The reticular formation then projects to a number of places including the [[hippocampus]] (to create memories about the pain), the [[centromedian nucleus]] (to cause diffuse, non-specific pain) and various parts of the cortex. Additionally, some ALS axons project to the [[periaqueductal gray]] in the pons, and the axons forming the periaqueductal gray then project to the [[nucleus raphes magnus]], which projects back down to where the pain signal is coming from and inhibits it. This helps control the sensation of pain to some degree. ===Motor organization=== {{Vertebral column}} The [[corticospinal tract]] serves as the motor pathway for upper motor neuronal signals coming from the cerebral cortex and from primitive brainstem motor nuclei. Cortical upper motor neurons originate from [[Brodmann area]]s 1, 2, 3, 4, and 6 and then descend in the posterior limb of the [[internal capsule]], through the [[crus cerebri]], down through the pons, and to the [[medullary pyramids]], where about 90% of the axons cross to the contralateral side at the decussation of the pyramids. They then descend as the lateral corticospinal tract. These axons synapse with lower motor neurons in the ventral [[spinal cord horn|horns]] of all levels of the spinal cord. The remaining 10% of axons descend on the ipsilateral side as the ventral corticospinal tract. These axons also synapse with lower motor neurons in the ventral horns. Most of them will cross to the contralateral side of the cord (via the [[anterior white commissure]]) right before synapsing. The midbrain nuclei include four motor tracts that send upper motor neuronal axons down the spinal cord to lower motor neurons. These are the [[rubrospinal tract]], the [[vestibulospinal tract]], the [[tectospinal tract]] and the [[reticulospinal tract]]. The rubrospinal tract descends with the lateral corticospinal tract, and the remaining three descend with the anterior corticospinal tract. The function of lower motor neurons can be divided into two different groups: the lateral corticospinal tract and the anterior cortical spinal tract. The lateral tract contains upper motor neuronal [[axons]] which synapse on dorsal lateral (DL) lower motor neurons. The DL neurons are involved in [[Anatomical terms of location#Proximal and distal|distal]] limb control. Therefore, these DL neurons are found specifically only in the cervical and lumbosacral enlargements within the spinal cord. There is no decussation in the lateral corticospinal tract after the decussation at the medullary pyramids. The anterior corticospinal tract descends [[ipsilateral]]ly in the anterior column, where the axons emerge and either synapse on lower ventromedial (VM) motor neurons in the ventral horn ipsilaterally or descussate at the [[anterior white commissure]] where they synapse on VM lower motor neurons [[contralateral]]ly . The tectospinal, vestibulospinal and reticulospinal descend ipsilaterally in the anterior column but do not synapse across the anterior white commissure. Rather, they only synapse on VM lower motor neurons ipsilaterally. The VM lower motor neurons control the large, postural muscles of the [[axial skeleton]]. These lower motor neurons, unlike those of the DL, are located in the ventral horn all the way throughout the spinal cord. ===Spinocerebellar tracts=== [[Proprioceptive]] information in the body travels up the spinal cord via three tracks. Below L2, the proprioceptive information travels up the spinal cord in the [[ventral spinocerebellar tract]]. Also known as the anterior spinocerebellar tract, sensory receptors take in the information and travel into the spinal cord. The cell bodies of these primary neurons are located in the [[dorsal root ganglia]]. In the spinal cord, the axons synapse and the secondary neuronal axons decussates and then travel up to the [[superior cerebellar peduncle]] where they decussate again. From here, the information is brought to deep nuclei of the cerebellum including the [[fastigial]] and [[Interposed nucleus|interposed nuclei]]. From the levels of L2 to T1, proprioceptive information enters the spinal cord and ascends ipsilaterally, where it synapses in [[Clarke's nucleus]]. The secondary neuronal axons continue to ascend ipsilaterally and then pass into the cerebellum via the [[inferior cerebellar peduncle]]. This tract is known as the dorsal spinocerebellar tract. From above T1, proprioceptive primary axons enter the spinal cord and ascend ipsilaterally until reaching the [[accessory cuneate nucleus]], where they synapse. The secondary axons pass into the cerebellum via the inferior cerebellar peduncle where again, these axons synapse on cerebellar deep nuclei. This tract is known as the [[cuneocerebellar tract]]. Motor information travels from the brain down the spinal cord via descending spinal cord tracts. Descending tracts involve two neurons: the upper motor neuron (UMN) and lower motor neuron (LMN).<ref name="SaladinAnatomy">Saladin. Anatomy and Physiology, 5th Ed.</ref> A nerve signal travels down the upper motor neuron until it synapses with the lower motor neuron in the spinal cord. Then, the lower motor neuron conducts the nerve signal to the spinal root where efferent nerve fibers carry the motor signal toward the target muscle. The descending tracts are composed of white matter. There are several descending tracts serving different functions. The corticospinal tracts (lateral and anterior) are responsible for coordinated limb movements.<ref name="SaladinAnatomy" /> {{Clear}} ==Clinical significance== A [[congenital disorder]] is [[diastematomyelia]] in which part of the spinal cord is split usually at the level of the upper lumbar vertebrae. Sometimes the split can be along the length of the spinal cord. ===Injury=== {{main|Spinal cord injuries}} Spinal cord injuries can be caused by trauma to the spinal column (stretching, bruising, applying pressure, severing, laceration, etc.). The vertebral bones or [[intervertebral disk]]s can shatter, causing the spinal cord to be punctured by a sharp fragment of [[bone]]. Usually, victims of spinal cord injuries will suffer loss of feeling in certain parts of their body. In milder cases, a victim might only suffer loss of [[hand]] or foot function. More severe injuries may result in [[paraplegia]], [[tetraplegia]] (also known as quadriplegia), or full body [[paralysis]] below the site of injury to the spinal cord. Damage to upper motor neuron axons in the spinal cord results in a characteristic pattern of ipsilateral deficits. These include [[hyperreflexia]], [[hypertonia]] and muscle weakness. Lower motor neuronal damage results in its own characteristic pattern of deficits. Rather than an entire side of deficits, there is a pattern relating to the [[myotome (anatomy)|myotome]] affected by the damage. Additionally, lower motor neurons are characterized by muscle weakness, [[hypotonia]], [[hyporeflexia]] and [[muscle atrophy]]. [[Spinal shock]] and [[neurogenic shock]] can occur from a spinal injury. Spinal shock is usually temporary, lasting only for 24–48 hours, and is a temporary absence of sensory and motor functions. Neurogenic shock lasts for weeks and can lead to a loss of muscle tone due to disuse of the muscles below the injured site. The two areas of the spinal cord most commonly injured are the [[cervical spine]] (C1–C7) and the [[lumbar spine]] (L1–L5). (The notation C1, C7, L1, L5 refer to the location of a specific [[vertebra]] in either the cervical, thoracic, or lumbar region of the spine.) Spinal cord injury can also be non-traumatic and caused by disease ([[transverse myelitis]], [[polio]], [[spina bifida]], [[Friedreich's ataxia]], [[spinal cord tumor]], [[spinal stenosis]] etc.)<ref name=":0" /> In the U.S., 10,000–12,000 people become paralyzed annually as a result of various injuries to the spinal cord. <ref>{{cite web |title=Spinal Cord |url=https://en.wikipedia.org/wiki/Spinal_cord}}</ref> ===Treatment=== Real or suspected spinal cord injuries need immediate immobilisation including that of the head. [[Medical imaging|Scans]] will be needed to assess the injury. A steroid, [[methylprednisolone]], can be of help as can physical therapy and possibly [[antioxidant]]s.{{citation needed|date=December 2016}} Treatments need to focus on limiting post-injury cell death, promoting cell regeneration, and replacing lost cells. Regeneration is facilitated by maintaining electric transmission in neural elements. ===Lumbar puncture=== The spinal cord ends at the level of vertebrae L1–L2, while the [[subarachnoid space]] —the compartment that contains [[cerebrospinal fluid]]— extends down to the lower border of S2.<ref name=":0" /> [[Lumbar puncture]]s in adults are usually performed between L3–L5 ([[cauda equina]] level) in order to avoid damage to the spinal cord.<ref name=":0">{{cite book|last1=Le|first1=Tao|title=First Aid for the USMLE Step 1 2014 / Edition 24|date=10 January 2014|publisher=McGraw-Hill Professional Publishing|isbn=9780071831420}}</ref> In the fetus, the spinal cord extends the full length of the spine and regresses as the body grows. ===Tumours=== [[Spinal tumor|Spinal tumour]]s can occur in the spinal cord and these can be either inside (intradural) or outside (extradural) the [[dura mater]]. ==Additional images== <gallery> Image:Spinal Cord Sectional Anatomy.png|Spinal Cord Sectional Anatomy. Animation in the reference. Image:Gray663.png|Diagrams of the spinal cord. Image:Gray664.png|Cross-section through the spinal cord at the mid-thoracic level. Image:Gray666.png|Cross-sections of the spinal cord at varying levels. Image:Cervical vertebra english.png|Cervical vertebra Image:Gray796.png|A portion of the spinal cord, showing its right lateral surface. The dura is opened and arranged to show the nerve roots. Image:Sobo 1909 611.png|The spinal cord with [[dura mater|dura]] cut open, showing the exits of the spinal nerves. Image:Sobo 1909 612.png|The spinal cord showing how the anterior and posterior roots join in the spinal nerves. Image:Sobo 1909 613.png|The spinal cord showing how the anterior and posterior roots join in the spinal nerves. Image:Sobo 1909 614.png|A longer view of the spinal cord. Image:Sobo 1909 615.png|Projections of the spinal cord into the nerves (red motor, blue sensory). Image:Sobo 1909 616.png|Projections of the spinal cord into the nerves (red motor, blue sensory). Image:Rabbitspinalcord100x1.jpg|Cross-section of rabbit spinal cord. File:Adult mouse spinal cord.tif|Cross-section of adult mouse spinal cord: astrocytes (red) and neurons (green) File:Neurons-spinal-cord-rat.jpg|Cross section of adult rat spinal cord stained using Cajal method. </gallery> {| class="wikitable collapsible collapsed" |- ! Dissection images |- | <gallery> File:Human brain and spinal cord.jpg|An overview of the spinal cord. Image:Sus barbatus 01 - Sagittal Section of Vertebral Column - sharp focus.jpg|Sagittal section of pig vertebrae showing a section of the spinal cord. File:Slide12ee.JPG|The base of the brain and the top of the spinal cord File:Slide1drdr.GIF|Spinal cord. Spinal membranes and nerve roots.Deep dissection. Posterior view. File:Slide2drdr.GIF|Spinal cord. Spinal membranes and nerve roots.Deep dissection. Posterior view. File:Slide3dsdd.GIF|Spinal cord. Spinal membranes and nerve roots.Deep dissection. Posterior view. File:Slide2fer.JPG|Spinal cord. Spinal membranes and nerve roots.Deep dissection. Posterior view. File:Slide3fer.JPG|Spinal cord. Spinal membranes and nerve roots.Deep dissection. Posterior view. File:Slide4rer.JPG|Spinal cord. Spinal membranes and nerve roots.Deep dissection. Posterior view. File:Slide5rer.JPG|Spinal cord. Spinal membranes and nerve roots.Deep dissection. Posterior view. File:Slide2PIT.JPG|Cerebrum.Inferior view.Deep dissection File:Slide3PIT.JPG|Cerebrum.Inferior view.Deep dissection File:Slide2ZEO.JPG|Spinal cord. Brachial plexus. Cerebrum.Inferior view.Deep dissection. File:Slide3ZEO.JPG|Spinal cord. Brachial plexus. Cerebrum.Inferior view.Deep dissection. File:Dissection of spinal cord.jpg|Spinal cord File:Human embryo 8 weeks 6.JPG|Medulla spinalis of 8-week-old human embryo </gallery> |} ==See also== {{commons category|Spinal cord}} {{Anatomy-terms}} * [[Neutral spine]] * [[Brown-Séquard syndrome]] * [[Hereditary spastic paraplegia]] <small>(HSP, or familial spastic paraplegia – FSP, Strümpell–Lorrain syndrome)</small> * [[Poliomyelitis]], [[Post-polio syndrome]] * [[Upper-limb surgery in tetraplegia]] * [[Redlich–Obersteiner's zone]] * [[Subacute combined degeneration of spinal cord]] * [[Tethered spinal cord syndrome]] * [[Myelomere]] ==References== {{reflist|2}} ==External links== * [https://web.archive.org/web/20060910185213/http://biology.clc.uc.edu/fankhauser/Labs/Anatomy_%26_Physiology/A%26P202/CNS_Histology/Spinal_Cord/Spinal_Cord_Histology.htm Spinal Cord Histology] – A multitude of great images from the [[University of Cincinnati]] * {{cite web|title=The Nervous System: Sensory and Motor Tracts of the Spinal Cord|url=http://www.napavalley.edu/people/briddell/Documents/BIO%20218/15_lecture_presentation.pdf|publisher=Napa Valley College / Southeast Community College Lincoln, Nebraska|accessdate=20 May 2013}} * [http://www.emedicine.com/neuro/topic657.htm eMedicine: Spinal Cord, Topographical and Functional Anatomy] * WebMD. May 17, 2005. [https://web.archive.org/web/20070302083650/http://children.webmd.com/tc/Spina-Bifida-Topic-Overview Spina Bifida – Topic Overview] Information about spina bifida in fetuses and throughout adulthood. WebMD children's health. Retrieved March 19, 2007. * [http://news.bbc.co.uk/2/hi/uk_news/wales/6274960.stm Potential for spinal injury repair] Retrieved February 6, 2008. * [http://mousespinal.brain-map.org/ 4000 sets of digital images, showing spatial expression patterns for various genes in adult and juvenile mouse spinal cords] from the [[Allen Institute for Brain Science]] *[http://www.histology-world.com/photoalbum/thumbnails.php?album=78 Spinal cord photomicrographs] {{Organ systems}} {{nervous system}} {{Spinal cord}} {{Authority control}} {{DEFAULTSORT:Spinal Cord}} [[Category:Spinal cord| ]] [[Category:Sensory systems]] [[Category:Motor system]] [[Category:Bones of the vertebral column]] [[Category:Skeletal system]]'