The outlines of anatomy, physiology, and hygiene Being an edition of The essentials of anatomy, physiology, and hygiene, rev to conform to the legislation making the effects of alcohol and other narcotics upon the human system a mandatory study in public schools . effect what-ever is produced. There are no convulsive move-ments of the muscles, and no indication of sensa-tion. This seems to show that, in the fibers of theanterior root, the nervous impulse is transmittedfrom within outward, and gives rise to the phe-nomena of motion, while they have nothing to dowith sensation. 274. Division of
The outlines of anatomy, physiology, and hygiene Being an edition of The essentials of anatomy, physiology, and hygiene, rev to conform to the legislation making the effects of alcohol and other narcotics upon the human system a mandatory study in public schools . effect what-ever is produced. There are no convulsive move-ments of the muscles, and no indication of sensa-tion. This seems to show that, in the fibers of theanterior root, the nervous impulse is transmittedfrom within outward, and gives rise to the phe-nomena of motion, while they have nothing to dowith sensation. 274. Division of the Posterior Root.—If, now,instead of the anterior root, posterior root is theinjured one (Fig. 56), we find that the part suppliedby the nerve has lost sensation, but retains thepower of motion. If it be pinched, pricked, or in-jured in any way, no effect is produced, and nonotice is taken of it whatever. This shows that THE SPINAL CORD. 213 sensation in the part is abolished. If, now, the endsof the root be irritated, we find the following- re-sults : On irritation of the end nearest the part, noeffect whatever is produced. If, on the other hand,the end nearest the cord be irritated, there are im-mediate indications of pain, and the muscles sup-. Fig. 56.—Cross section of spinal cord and roots of spinal nerves, with pos-terior root cut. plied by the injured nerve are still able to contractas powerfully as ever. This shows that the ofmotion has not been interfered with by the injury,and it also shows that, in the posterior roots of thespinal nerves, the nervous impulse is transmittedfrom without inward, and has to do with sensa-tion. 275. Two Kinds of Fibers in Each Nerve.—Theanterior roots, then, are composed of motor fibers,and the posterior roots of sensory fibers. The twounite, as has been shown, to form a single cord,which afterward divides again to supply the frontand back of the body. Every spinal nerve in thisway is made up of both sensory and motor
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