GENERAL PHYSIOLOGY OF MUSCLE-TISSUE 61 



PHENOMENA FOLLOWING A MUSCLE STIMULATION 

 PHYSICAL PHENOMENA 



Physiologic investigation has made it apparent that when a nerve impulse 

 -caches a muscle, it occasions a disruption of certain complex energy- 

 tiolding compounds and their subsequent oxidation to simpler compounds. 

 Coincidently with the chemic changes there is a transformation of the 

 potential energy of the molecules into kinetic energy which manifests 

 itself under three forms, heat, electricity and mechanic motion, or a change 

 of shape of the muscle. These phenomena vary in extent in accordance with 

 the intensity of the impulse as well as the frequency of its repetition. 

 Though the chemic changes are the first effects of the action of the nerve 



FIG. 2i. SHOWING THE CHANGES IN A MUSCLE AND MUSCLE-FIBER DURING 



CONTRACTION. 



impulse and the ones on which other phenomena depend, it will ^be found 

 convenient to consider the most evident effect, the physical change m t] 



shape of the muscle, first. ii,,; tho 



Change of Shape.-The most obvious change m a muscle followmg the 

 arrival of a nerve impulse is that relating to its form. The muscle no only 

 becomes shorter, but at the same time thicker. The extent to wh ch t may 

 shorten when unopposed may amount to 30 per cent, or more of Us or^mal 

 length. The increase in thickness practically compensates for the di 

 tion in length, for there is no observable diminution ^ volume. ^ Th, chw ge 

 in form of the entire muscle results from a corresponding change of iorm 

 its individual fibers as determined by microscopic examination, each of 

 which becomes shorter and thicker. The successive changes in t 

 muscle and the individual fibers are represented in _Fig. ^ 21 



When the contraction begins both the dim an , d , bn ^ s a ^ n ^ J n ^ 

 length, but at the same time increase m breadth This continues un m 

 the contraction reaches its maximum. The diminution m 

 bright band is greater proportionally than the diminution m th length .ot the 

 dim band, a fact which gave rise to the supposition on the part of Engemann 

 that there is at the time of the contraction a passage of .fluid ^ mate ^ ^ 

 the bright into the dim band or from the sarcoplas m into *? s cost ^ e d S s 

 When fhe relaxation begins, a reverse change in the dim and bright bands 

 sets in and continues until they regain their former shape and volume. Com 

 cidently there is a passage of fluid material from the sarcostyle 



