The Nervous System.
MAN is brought into connection with the outward world through the senses of feeling, seeing, hearing, etc. These communicate with the brain and mind through the nerves of sensation.
The nervous system is divided into two great central portions,
the brain and the spinal cord; and these together are called, by the
learned, the cerebrospinal centre. There are numerous pulpy white
cords, called nerves, which at one end are connected with this great
axis or centre, and from thence run to all parts of the system. A
portion of these nerves start from the base of the brain and run to
the eye, the ear, the tongue, etc. (Fig. 48) ; while another, and a
larger part spring from the cord which runs through the backbone,
and are distributed over the body and the lower extremities (Figs.
50 and 60). One portion of these cords produce feeling; another
part, motion. The former we call sensitive; the latter, motor. Both
kinds are widely distributed over the body. Those which spring
from the spinal cord have two roots, one uniting with the back, the
other with the front part of the cord. part to which it is distributed loses it feeling. As we say in common language, it becomes numb, though it may move as well as before. Cut the front root, which is motion producing, and the part to which it goes cannot move. It is palsied, though it may still feel acutely. The numerous nerves that spring from the spinal column are pretty well represented in Fig. 60.
If the cranial nerves of motion which go to the face be cut, no emotion or passion can be expressed. The features will all be immovable, like statuary. To smile, to laugh, to frown, to give expression to the feeling of pity, or anguisb, or love, is alike impossible. And yet a breath of air upon the face will be felt as readily as before. Paralysis, or palsy, as it is called, partial or general, is the result of injury upon few or many of these motion producing nerves. Neuralgia, tic douloureux, etc., arise from some disease, perhaps inflammation, of the nerves of sensation.
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