. Applied anatomy and kinesiology. en on only one side. ASSOCIATION NEURONES. Association neurones lie wholly within the central nervous sys-tem. Their cells are seen in the gray matter of all levels of the spinalcord and brain. They are by far the most numerous class of neu-rones in man, including a very large percentage of those in thespinal cord and practically all those in the brain. The superiorityof man over other animals is due to the more extensive develop-ment of this class of neurones. They are best studied in separategroups, of which there are many, each with its peculiarities offor
. Applied anatomy and kinesiology. en on only one side. ASSOCIATION NEURONES. Association neurones lie wholly within the central nervous sys-tem. Their cells are seen in the gray matter of all levels of the spinalcord and brain. They are by far the most numerous class of neu-rones in man, including a very large percentage of those in thespinal cord and practically all those in the brain. The superiorityof man over other animals is due to the more extensive develop-ment of this class of neurones. They are best studied in separategroups, of which there are many, each with its peculiarities ofform, location, and 50 MUSCULAR CONTROL We have just seen, in the preceding paragraphs and in Fig. 24,how the sensory axones branch in the spinal cord with the apparentpurpose of spreading the effect of each sensory stimulus to a widerange of muscles. It is evident, however, that Nature does notconsider the mechanism of the sensory branching sufficient for thepurpose, for she has provided a group of association neurones to. Fig. 15,—An association neurone of the spinal cord. S, sensory neurone; A, associa-tion neurone; M, M, M, motor neurones. aid in the same way, making still more intimate connection pos-sible between sensory and motor neurones and spreading the incom-ing messages still wider. These cells are smaller than either thesensory or motor cells; they are located in the gray part of the cbrdabout midway between the anterior and posterior gray columns;their axones pass out horizontally into the lateral white columns,where they divide into ascending and descending vertical brancheslike the sensory axones. These, like the sensory fibers, have hori-zontal branches that penetrate the gray part of the cord at all ASSOCIATION NEURONES 51 levels, with synapses connecting them with motor and other half of the axones of these cells cross to the opposite sideof the cord, where they divide and end in like matter, making themost complete and intimate connecti
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