. Applied anatomy and kinesiology. anglion along the posterior root into the spinal cord,where it penetrates the posterior white column for a short dis-tance and then divides into an ascending and a descending two branches extend vertically in the posterior whitecolumn, giving off at intervals horizontal branches called collafrralft 48 MUSCULAR CONTROL which penetrate the gray portions of the cord and terminate amongthe cells and dendrites there (Fig. 24). The ends of these sensoryfibers are often brush-like, and they often intertwine with similarbrush-like endings of the dendrite
. Applied anatomy and kinesiology. anglion along the posterior root into the spinal cord,where it penetrates the posterior white column for a short dis-tance and then divides into an ascending and a descending two branches extend vertically in the posterior whitecolumn, giving off at intervals horizontal branches called collafrralft 48 MUSCULAR CONTROL which penetrate the gray portions of the cord and terminate amongthe cells and dendrites there (Fig. 24). The ends of these sensoryfibers are often brush-like, and they often intertwine with similarbrush-like endings of the dendrites of the motor neurones, thusforming what is called a synapse, or point of communication betweenone neurone and another. Everyone knows how a light touch upon the hand of a personwho is asleep may cause the hand to be moved without awakingthe sleeper and without his being aware of it. Such movements,commonly called reflexes because the influence of the touch uponthe skin seems to be reflected back from the central nervous 7771V mw. Fig. 24.—A sensory neurone and its branches in the cord. (Kolliker.) system to the region, from which it originated, can be explainedonly through a knowledge of the nervous mechanism we are justconsidering. The contact or pressure upon the skin stimulates oneor more of the delicate sensory nerve endings in it and as a resulta message or impulse passes up the corresponding nerve fibersto the spinal ganglion, thence to the spinal cord, up and down thevertical branches of the sensory axone, and along the horizontalbranches to the synapses at their ends. The close intertwining ofthe sensory brush endings with the similar endings of the motordendrites here makes it possible for the message to pass to themotor neurone, and once started upon the motor path it can only ASSOCIATION NEURONES 49 }>ass out to the muscles and give rise to a contraction. Such anervous path, including a sensory neurone, a motor neurone, andthe synapse that connects them, is ca
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