Human physiology : designed for colleges and the higher classes in schools and for general reading . quent condition of thebrain, that the sensation does not occur—one link in the neces-sary chain is defective. 227. The same can be said, in regard to the necessity ofeach of these links of the chain, in relation to voluntary mo-tion, as well as sensation. The brain must be in a conditionto be acted upon by the mind; the nervous trunk must becapable of transmitting the impression; and the muscle mustbe in such a state, and in such connection with the extremenervous fibres, that it can respond to
Human physiology : designed for colleges and the higher classes in schools and for general reading . quent condition of thebrain, that the sensation does not occur—one link in the neces-sary chain is defective. 227. The same can be said, in regard to the necessity ofeach of these links of the chain, in relation to voluntary mo-tion, as well as sensation. The brain must be in a conditionto be acted upon by the mind; the nervous trunk must becapable of transmitting the impression; and the muscle mustbe in such a state, and in such connection with the extremenervous fibres, that it can respond to the call of the brain. 228. Before going further, I will give you some idea of theproportions and arrangement of the central organs of thenervous system. In Fig. 72 you have presented a generalview of this system,—the central organs with the nerves goingout from them. At a is the cerebrum, the upper large brain,filling up a considerable portion of the skull; at b is thecerebellum, the lesser brain, lying beneath the cerebrum at its THE NERVOUS SYSTEM. 143 General plan of the nervous NERVOUS TRUNKS TN MAN. 144 HUMAN PHYSIOLOGY. Hemispheres and lobes of the brain. back part: at c is the great facial nerve, the chief nerve of theface; the spinal marrow, d, sends off branches on either sidein its whole length ; at e is the brachial plexus, a bundle ofnerves coming from the spinal marrow, which here unitetogether, and are then distributed to all parts of the arm; at iis a similar plexus from which are distributed nerves to thelower extremity; /, g, and h point to different nerves in thearm, and I, m, n, and o to different nerves in the leg. Youobserve that the whole of this nervous system is divided intoexactly similar halves. The cerebrum and the cerebellum areboth double organs, and the nerves of one side are just likethose of the other. 229. Having thus observed the general arrangement of thenervous system, I call your attention next to the arrangementand structure
Size: 1161px × 2152px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookauthorhookerwo, bookcentury1800, bookdecade1850, bookyear1854
