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[TA] spinal cord: that part of the central nervous system that is lodged in the vertebral canal. It extends from the foramen magnum, where it is continuous with the medulla oblongata, to the upper part of the lumbar region, ending between the twelfth thoracic and third lumbar vertebrae, often at or near the first and second lumbar vertebrae. It is composed of an inner core of gray substance, in which nerve cells predominate, and an outer layer of white substance, in which myelinated nerve fibers predominate, and is enclosed in three protective membranes, or meninges: the dura mater, arachnoid, and pia mater. Thirty-one spinal nerves originate from the spinal cord: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal. It conducts impulses to and from the brain, and controls many automatic muscular activities (reflexes). See also Rexed laminae, under lamina, and Plates 9 and 42.Medical dictionary. 2011.