Spinal cord

The major column of nerve tissue that is connected to the brain, lies within the vertebral canal, and from which the spinal nerves emerge. The spinal cord and the brain constitute the central nervous system (CNS). The spinal cord consists of nerve fibers that transmit impulses to and from the brain. Like the brain, the spinal cord is covered by three connective-tissue envelopes called the meninges. The space between the outer and middle envelopes is filled with cerebrospinal fluid (CSF), a clear colorless fluid that cushions the spinal cord against jarring shock. Thirty-one pairs of spinal nerves originate in the spinal cord: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal. In the spinal cord, information about internal and external conditions travels up the ascending tracts to the brain. This information is processed by the brain and corresponding responses are induced by nerve impulses traveling down the descending tracts of the spinal cord to stimulate motor neurons or to initiate secretions by glands. The spinal cord is sometimes referred to simply as "the cord."

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spinal cord n the thick longitudinal cord of nervous tissue that in vertebrates extends along the back dorsal to the bodies of the vertebrae and is enclosed in the vertebral canal formed by their neural arches, is continuous anteriorly with the medulla oblongata, gives off at intervals pairs of spinal nerves to the various parts of the trunk and limbs, serves not only as a pathway for nervous impulses to and from the brain but as a center for carrying out and coordinating many reflex actions independently of the brain, and is composed largely of white matter arranged in columns and tracts of longitudinal fibers about a large central core of gray matter somewhat H-shaped in cross section and pierced centrally by a small longitudinal canal continuous with the ventricles of the brain called also medulla spinalis

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the portion of the central nervous system enclosed in the vertebral column, consisting of nerve cells and bundles of nerves connecting all parts of the body with the brain. It contains a core of grey matter surrounded by white matter. It is enveloped in three layers of membrane, the meninges, and extends from the medulla oblongata in the skull to the level of the second lumbar vertebra. From it arise 31 pairs of spinal nerves.

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medulla spinalis.