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Purves D, Augustine GJ, Fitzpatrick D, et al., editors. Neuroscience. 2nd edition. Sunderland (MA): Sinauer Associates; 2001.

By agreement with the publisher, this book is accessible by the search feature, but cannot be browsed.

The spinal cord extends caudally from the brainstem, running from themedullary-spinal junction at about the level of the first cervical vertebra to aboutthe level of the twelfth thoracic vertebra (see Figure 1.10). The vertebral column (and the spinal cord within it) isdivided into cervical, thoracic, lumbar,sacral, and coccygeal regions. The peripheral nerves(called the spinal or segmental nerves) that innervate much of the bodyarise from the spinal cord"s 31 segmental pairs. The cervical region of the cordgives rise to eight cervical nerves (C1—C8), the thoracic to twelvethoracic nerves (T1—T12), the lumbar to five lumbar nerves(L1—L5), the sacral to five sacral nerves (S1—S5), and thecoccygeal to one coccygeal nerve. The segmental spinal nerves leave the vertebralcolumn through the intervertebral foramina that lie adjacent to the respectivelynumbered vertebral body. Sensory information carried by the afferent axons of thespinal nerves enters the cord via the dorsal roots, and motor commands carried bythe efferent axons leave the cord via the ventral roots (see Figure 1.10C). Once the dorsal and ventral roots join, sensoryand motor axons (with some exceptions) travel together in the segmental spinalnerves.

Two regions of the spinal cord are enlarged to accommodate the greater number ofnerve cells and connections needed to process information related to the upper andlower limbs (see Figure 1.10B). The spinalcord expansion that corresponds to the arms is called the cervicalenlargement and includes spinal segments C5—T1; the expansionthat corresponds to the legs is called the lumbar enlargement andincludes spinal segments L2—S3. Because the spinal cord is considerablyshorter than the vertebral column (see Figure1.10A), lumbar and sacral nerves run for some distance in the vertebralcanal before emerging, thus forming a collection of nerve roots known as the cauda equina. This region is the target for an important clinical procedure called a“lumbar puncture” that allows for the collection ofcerebrospinal fluid by placing a needle into the space surrounding these nerves towithdraw fluid for analysis. In addition, local anesthetics can be safely introducedto produce spinal anesthesia; at this level, the risk of damage to the spinal cordfrom a poorly placed needle is minimized.

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By agreement with the publisher, this book is accessible by the search feature, but cannot be browsed.