. Public School Physiology and Temperance. rve tissue scattered through the body, called are all connected together and form the sympatheticsystem. There are therefore three classes of nerves, spinal,cranial and sympathetic. All three classes convey impres-sions of a twofold kind. There are those fibres along whichimpressions travel to the brain, and by which it is made8 114 PHYSIOLOGY AND TEMPERANCE, conscious of what is going on. These are called sensorynerves. Also, fibres by which impressions travel from thebrain and cause muscles to contract or cells to take onincreased acti
. Public School Physiology and Temperance. rve tissue scattered through the body, called are all connected together and form the sympatheticsystem. There are therefore three classes of nerves, spinal,cranial and sympathetic. All three classes convey impres-sions of a twofold kind. There are those fibres along whichimpressions travel to the brain, and by which it is made8 114 PHYSIOLOGY AND TEMPERANCE, conscious of what is going on. These are called sensorynerves. Also, fibres by which impressions travel from thebrain and cause muscles to contract or cells to take onincreased action. These are called motor nerves. 12. Spinal Nerves.—-Thirty-one pairs of nerves are givenofi by the spinal cord. The openings in the bones of thespine on each side allow them to pass out. Each nerve hastwo roots, one in front and one behind. The anterior rootconsists of motor fibres, the posterior of sensory fibres. Thetwo roots unite or are bound together in one sheath. If theanterior root were cut or destroyed by disease, the person. Fi9. 36.—Section of Spinal Cord, with roots of spinal nerves. Front view. would lose the power of motion in the part supplied by thatnerve, that is, that part would be paralyzed. If the posteriorroot were divided, the power of feeling would be lost. Thespinal nerves, after leaving the spinal column, are formedinto several groups, where they join together and then branchoff to different parts. This collection of nerves is called aflexus. 13. Cranial Nerves. — Arising from the base of thebrain, the medulla oblongata, and one pair from the upperpart of the spinal cord, are the twelve pairs of cranialnerves. They all emerge from the skull, through smallchannels in the bone. Nearly all of these nerves have their THE NERVOUS SYSTEM. 115 deep origin in the medulla oblongata, althougli the superficialorigin of some of them is some distance off. The first pair are known as the olfactory, or nerves ofsmell. They pass out through the roof of t]\e no
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