Nervous and mental diseases . we may see that all skeletal-muscle groups are outlines must be taken as suggestive rather than actual. Thereis no sharp boundary between the adjoining centers, and these fieldsoverlap. The dippings of the sulci also serve to interfere with sharplimitations of the cortical areas and obstruct the experimental stim-ulation of individual movements. Every muscular movement, ap-parently, has a locus of principal or major representation in the cortex,but such a movement is so wrapped up with other coordinate movements,and so widely related functionally,
Nervous and mental diseases . we may see that all skeletal-muscle groups are outlines must be taken as suggestive rather than actual. Thereis no sharp boundary between the adjoining centers, and these fieldsoverlap. The dippings of the sulci also serve to interfere with sharplimitations of the cortical areas and obstruct the experimental stim-ulation of individual movements. Every muscular movement, ap-parently, has a locus of principal or major representation in the cortex,but such a movement is so wrapped up with other coordinate movements,and so widely related functionally, that its representation in a minor de-gree may spread over great areas. The thumb, for instance, is princi-pally represented in a given small cortical center, but the prehensileaction of the thumb is related to the grasp of the fingers, the fixationof the wrist, the rigidity of the whole upper extremity, and even toaction of the trunk and lower limbs in strongest efforts, during whichthe opposite members also come into Fig. 67.—Functional areas of the cerebral cortex of the left side (after Campbell). The most recent investigation of cortical localization in anthropoidsby Sherrington and Griinbaum, and the histological studies of A. ,1 indicate that the true motor region of the cortex is much lessextensive than was formerly thought. The functional groups of skeletalmuscles are represented in the precentral or ascending frontal convolu-tion from the lower end of Rolandos fissure up to the midline of the brain,and to a slight extent on the mesial surface of the hemisphere, in a con-1 Histological Studies of the Localization of Cerebral Functions, 1905. THE CEREBRAL CORTEX—LOCALIZATION. 165 tinuous narrow zone. The bottom of the fissure of Rolando sharplybounds the motor area behind and it extends forward not to exceed thewidth of the precentral gyre.
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