Spinal cord
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The spinal cord is a thin, tubular structure that is an extension of the central nervous system from the brain and is enclosed in and protected by the bony vertebral column. The main function of the spinal cord is transmission of neural inputs between the periphery and the brain.
[[Image: == [[<nowiki>'''Bold text''''''Bold text'''==Structure== The spinal cord extends from the [[medulla oblongata]] in the brain and continues to the [[conus medullaris]] near the lumbar level at L1-2, terminating in a fibrous extension known as the [[filum terminale]]. The spinal cord is about 45 cm long in men and 43 cm long in women, ovoid-shaped, and is enlarged in the cervical and lumbar regions. The peripheral regions of the cord contains neuronal white matter tracts containing sensory and motor neurons. The central region is four-leaf clover shaped that surrounds the central canal (an anatomic extension of the [[fourth ventricle]]) and contains nerve cell bodies. The three [[meninges]] that cover the spinal cord -- the outer [[dura mater]], the [[arachnoid membrane]], and the innermost [[pia mater]] -- are continuous with that in the brainstem and cerebral hemispheres, with [[cerebrospinal fluid]] found in the [[subarachnoid space]]. The cord within the pia mater is stabilized within the dura mater by the connecting [[denticulate ligaments]] which extends from the [[pia mater]] laterally between the dorsal and ventral roots. ===Spinal cord segments=== The human spinal cord is divided into 31 different segments, with motor nerve roots exiting in the [[ventral]] aspects and sensory nerve roots entering in the [[dorsal]] aspects. The ventral and dorsal roots later join to form paired [[spinal nerve]]s, one on each side of the spinal cord. There are 31 spinal cord nerve segments in a human spinal cord: * 8 cervical segments * 12 thoracic segments * 5 lumbar segments * 5 sacral segments * 1 coccygeal segment Because the vertebral column grows longer than the spinal cord, spinal cord segments become higher than the corresponding [[vertebra]], especially in the lower spinal cord segments in adults. In a fetus, the vertebral levels originally correspond with the spinal cord segments. In the adult, the cord ends around the L1/L2 vertebral level at the [[conus medullaris]], with all of the spinal cord segments located superiorly to this. For example, the segments for the lumbar and sacral regions are found between the vertebral levels of T9 and L2. The S4 spinal nerve roots arise from the cord around the upper lumbar/lower thoracic vertebral region, and descend downward in the vertebral canal. After they pass the end of the spinal cord, they are considered to be part of the [[cauda equina]]. The roots for S4 finally leave the vertebral canal in the [[sacrum]]. 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). * [[Lumbosacral 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. ===Embryology=== {{sect-num-stub|3}} In the human [[fetus]], the spinal cord extends all the way down to the [[sacral vertebrae]]. As a person matures, the rest of the body grows faster than the spinal cord, so that by [[adulthood]], the spinal cord reaches only to the level of the first or second lumbar vertebrae. There is no spinal cord below this level, only the collection of individual [[spinal nerve]]s that exit at lower levels, called the cauda equina.</nowiki>]] ==]]
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[edit] Injury
Spinal cord injuries can be caused by falling on the neck or back, or having the spinal cord moved or disrupted in another way. The vertebral bones or intervertebral disks 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 injury may result in paraplegia, tetraplegia, or full body paralysis below the site of injury to the spinal cord.
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.)
[edit] Additional images
 Diagrams of the spinal cord. |
 Cross-section through the spinal cord at the mid-thoracic level. |
 Cross-sections of the spinal cord at varying levels. |
[edit] See also
[edit] External links
- Spinal Cord Histology - A multitude of great Images from the University of Cincinnati
- eMedicine: Spinal Cord, Topographical and Functional Anatomy
- WebMD. May 17, 2005. Spina Bifida - Topic Overview Information about Spina Bifida in fetuses and throughout adulthood. WebMD children's health. Retrieved March 19, 2007.
