The essentials of healthA text-book of anatomy, physiology, hygiene, alcohol, and narcotics . ly shadedbodies; these are the large nerve cells, a representationof which is given in Fig. 90. Outside the central gray matter is the white matter,which is composed of fibers. The fibers extend up anddown the cord, so that a transverse section of the cord,as seen in Fig. 97, shows the fibers to be circular andwhite, with a dot or dark spot in the center. This darkspot represents a cross section of that part of a nervefiber which transmits the nerve force; the white sub-stance around it is for insulat
The essentials of healthA text-book of anatomy, physiology, hygiene, alcohol, and narcotics . ly shadedbodies; these are the large nerve cells, a representationof which is given in Fig. 90. Outside the central gray matter is the white matter,which is composed of fibers. The fibers extend up anddown the cord, so that a transverse section of the cord,as seen in Fig. 97, shows the fibers to be circular andwhite, with a dot or dark spot in the center. This darkspot represents a cross section of that part of a nervefiber which transmits the nerve force; the white sub-stance around it is for insulation and protection. Thesefibers finally enter the brain and are distributed to allparts of it, being at last connected with the nerve cells. The Spinal Nerves. Each one of the spinal nerves orig-inates in the spinal cord by two roots. One root, the an- THE NERVOUS SYSTEM. 205 tenor, originates from the anterior part of the graymatter, as illustrated at 1, Fig. 98. The oilier origi-nates from the posterior part, as shown at 2. Both theseroots unite to form one nerve, at 3. On the posterior. Fig. 98. A diagram illustrating the origin of the spinal nerves fromthe spinal cord- (3) is a spinal nerve; (1) and (2) are the roots, whichoriginate from the gray matter of the cord, G, a collection of nerve cells;(1) the motory root, (2) the sensory root. root is a ganglion, G, or a collection of nerve nerve fibers, at 3, continue together as a spinalnerve until they reach the distant parts of the body,when they separate again. Those fibers which origi-nated from the anterior part, known as motory fibers,terminate in muscles; while those from the posteriorpart, known as sensory fibers, terminate in the skin. QUESTIONS. 1. Xame the two nervous systems. 2. What composes the cerebro-spinal system? 3. What composes the sympathetic system? What are ganglia? 266 THE ESSENTIALS OF HEALTH. 4. What does the sympathetic system preside over and control? 5. Give the two kinds of nerve tissue.
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectphysiology, bookyear1
