Webster, Douglas B. Department of Otorhinolaryngology and Biocommunication, Louisiana State University Medical Center, Baton Rouge, Louisiana.
Last reviewed:May 2020
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The portion of the central nervous system within the spinal canal of the vertebral column. In vertebrates, the central nervous system is composed of the brain and spinal cord (Fig. 1). The spinal cord extends from the foramen magnum at the base of the skull to a variable level of the spinal canal; it terminates at the lumbar level in humans and extends well into the caudal region in fishes. Paired spinal nerves enter the spinal canal between each pair of vertebrae and connect with the spinal cord. The number of spinal nerves varies widely in vertebrates; for example, in humans, there are 31 pairs of spinal nerves (8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal). In tetrapods, there are spinal cord enlargements where the large spinal nerves extend to the limbs, as well as a cervical enlargement cranially and a lumbosacral enlargement caudally. Functionally, the spinal cord consists of nerve fibers that convey signals between the brain and the rest of the body. Various disorders of form and function that affect the spinal cord are known. See also: Brain; Central nervous system; Nerve; Nervous system (vertebrate); Spinal cord disorders; Vertebra; Vertebrata
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