The anatomy of the nervous system, from the standpoint of development and function . d the extrapyramidal motor path (see p. 324). In these diseases voluntarymovements are impeded by tremor, rigidity, and athetosis; and in all probabilitythese disturbances arise because the pyramidal system is deprived of the co-operation of one of the subordinate partners in the motor EFFERENT PATHS AND REFLEX ARCS 317 Even after cerebral control has been entirely eliminated in the dog by de-cerebration, many reflex functions remain, which represent the unguided activityof the lower elements in th
The anatomy of the nervous system, from the standpoint of development and function . d the extrapyramidal motor path (see p. 324). In these diseases voluntarymovements are impeded by tremor, rigidity, and athetosis; and in all probabilitythese disturbances arise because the pyramidal system is deprived of the co-operation of one of the subordinate partners in the motor EFFERENT PATHS AND REFLEX ARCS 317 Even after cerebral control has been entirely eliminated in the dog by de-cerebration, many reflex functions remain, which represent the unguided activityof the lower elements in the motor mechanism; and we now know that a similarindependent reflex activity may occur in the spinal cord of man after total trans-verse lesions (Riddoch, 1917). THE GREAT MOTOR PATH The great motor path from the cerebral cortex to the skeletal musculature,through which the bodily activities are placed directly under voluntary control,is in man and mammals the dominant factor in the motor mechanism. Wehave seen that afferent channels from the various exteroceptors reach the cere-. Fig. 236.—Cortical localization upon the lateral aspect of the human cerebral hemisphere. (Starr.) bral cortex; and that through the correlation of the olfactory, auditory, visual,tactile, thermal, and painful afferent impulses which pour into it, there is builtup within the cortex a representation of the outer world and its constantly chang-ing conditions. The responses appropriate to meet the entire situation in whichthe individual finds himself from moment to moment are in large part at leastinitiated in the cerebral cortex and are executed through the motor these responses the great motor path is the dominant factor, although otherparts of the mechanism are secondarily called into action, especially the pro-prioceptive reflex arcs, including the coordinating and tonic mechanism of thecerebellum. This great motor path consists of two-unit chains. The so-called uppermotor neurons cond
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