 Section No. 1 of Gray's Anatomy Part 4 This is a LibriVox recording. All LibriVox recordings are in the public domain. For more information or to volunteer, please visit LibriVox.org. Recording by M. L. Cohen. Anatomy of the Human Body Part 4 by Henry Gray Structure of the Nervous System Part 1 The nervous system is the most complicated and highly organized of the various systems which make up the human body. It is the mechanism concerned with the correlation and integration of various bodily processes and the reactions and adjustments of the organism to its environment. In addition, the cerebral cortex is concerned with conscious life. It may be divided into two parts, central and peripheral. The central nervous system consists of the encephalon or brain contained within the cranium and the medulla spinalis or spinal cord lodged in a vertebral canal. The two portions are continuous one another at the level of the upper border of the atlas vertebra. The peripheral nervous system consists of a series of nerves by which the central nervous system is connected with the various tissues of the body. For descriptive purposes, these nerves may be arranged in two groups, cerebrospinal and sympathetic. The arrangement, however, being an arbitrary one, since the two groups are intimately connected and closely intermingled. Both the cerebrospinal and sympathetic nerves have nuclei of origin, the somatic efferent and sympathetic efferent, as well as nuclei of termination, somatic afferent and sympathetic afferent, in the central nervous system. Cerebrospinal nerves are 43 in number on either side, 12 cranial attached to the brain and 31 spinal to the medulla spinalis. They are associated with the functions of the special and general senses and with the voluntary movements of the body. The sympathetic nerves transmit the impulses which regulate the movements of the viscera, determine the caliber of the blood vessels and control the phenomena of secretion. In relation with them are two rows of central ganglia, situated one on either side of the middle line in front of the vertebral columns. These ganglia are intimately connected with the medulla spinalis and the spinal nerves and are also joined to each other by vertical strands of nerve fibers, so as to constitute a pair of knotted cords, the sympathetic trunks, which reach from the base of the skull to the coccyx. The sympathetic nerves issuing from the ganglia form three great pre-vertebral plexuses which supply the thoracic, abdominal and pelvic... Sample complete. Ready to continue?