CHAPTEE LIV 



MOTORIAL AND VISCERAL SENSATIONS 



WE shall in the present chapter deal with the motorial or muscular 

 sense, and with sensations from the viscera. 



The Motorial or Kinaesthetic Sense. 



By this sense we become aware that movement is taking place in 

 some part of the body. We are especially conscious of willed muscular 

 action, and the sense has thus been confused and identified with the 

 rt feeling of innervation," or " sense of effort," which accompanies voli- 

 tional movements. By some this feeling has been attributed to a direct 

 discharge from the motor to the sensory cells of the cerebral cortex 

 occurring at the very birth of the efferent impulse. No doubt part of 

 the effect involved in movement is of central origin, and this part is 

 the effect inherent in all conative (p. 758) processes, and characterises 

 all forms of mental activity, for instance, reasoning or imagination ; 

 but its physiological basis is quite unknown. Most, however, of the 

 sense of effort is unquestionably due to afferent impulses peripherally 

 generated by the accompanying respiratory and other strains. 



It is in the estimation of weights that the value of these peripheral 

 sensations can be most clearly seen. When a weight is first handled, 

 the amount of force necessary to lift it is estimated in the light of 

 past experience. As it is being lifted, sensations from the moving 

 limb guide the expenditure of force : a weight which flies up too fast 

 or does not move at once, calls for less or more muscular force. 

 Similarly, the motorial sense is invoked when we estimate the extent 

 to which we have moved our limbs, or to which they have been 

 passively moved by others. 



These guiding sensations are not merely of cutaneous origin. 

 Persons whose skin has been rendered insensitive by cocaine, or by 

 certain diseases, yet retain the power of estimating weights and the 

 extent of their movements. In locomotor ataxy the motorial sense 

 may be destroyed while the skin retains its usual sensitiveness to 

 touch. On the other hand, we must remember that it is not at all 

 certain that the muscles are solely or even predominantly the seat of 

 these peripheral sensations ; the term " motorial " or " kinsesthetic " 

 is therefore preferable to that of " muscular " sense, by which name 



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