CHAPTER VI 



SKELETAL MUSCLE AND THE NERVOUS SYSTEM 



The statement has been made that the contractile 

 tissue of the heart and also that which we call smooth 

 muscle may be considered " automatic" that is, having 

 an inherent tendency to keep contracting and relaxing. 

 These tissues are subject to ner- 

 vous regulation which may either 

 augment or repress the native prop- 

 erty. Skeletal muscle has been 

 said not to be automatic. All 

 its movements in life are caused 

 through the central nervous system 

 and we must now give our atten- 

 tion to this relationship. It is one 

 which holds as truly for the single 

 muscle fiber as for the multiple ar- 

 rangement. 



Each muscle fiber is believed to 

 have one and only one point at 

 which the stimulus from the ner- 

 vous system affects it. This is 

 about its middle. A theoretic ad- 

 vantage may be connected with 

 this position : the whole length' of 

 the fiber will be more quickly in- 

 volved if it is "touched off" at an intermediate point 

 than it would be if it were excited at one end. The dis- 

 turbance, spreading in two directions along the fiber, 

 will traverse it in less time than if it ran from one ex- 

 tremity to the other. However, the saving of time is 

 less than would be supposed and is perhaps of no prac- 

 tical' significance. The point at which the stimulus is 

 6 . 81 



FIG. 18. The segment 

 is from a fiber of skeletal 

 muscle near its middle. 

 The motor nerve fiber 

 (nf) comes into relation 

 with the muscle proto- 

 plasm through the pecu- 

 liar j unction known as the 

 motor end-plate (e.p.). 



