CHAPTER III. 

 PHYSIOLOGICAL CHARACTERISTICS OF MUSCLE. 



WHEN a muscle is acted upon by a weight it extends quite 

 readily, but as soon as the weight is removed the muscle re- 

 sumes its normal shape. This illustrates the extensibility and 

 elasticity of muscular tissue. The muscles all over the body 

 are in a constant state of elastic tension, which causes them to 

 be of greater value as a support to the body skeleton. A muscle 

 which is in a state of elastic tension contracts more readily and 

 forcibly than one which is relaxed. 



Under ordinary conditions a muscle receives the stimulus 

 which causes it to contract through its motor nerve from the 

 central nervous system. If this nerve be cut, the muscle is 

 paralyzed. However, it has been demonstrated that a muscle 

 which has its nerve cut may still be made to contract by applying 

 an artificial stimulus, as an electrical shock. But such a muscle 

 would still have its nerve endings in the muscle undestroyed, 

 and hence, this would not prove that the muscle has independent 

 contractility. Still, if the nerve is severed and the nerve endings 

 are destroyed, e. g., by a drug, we find that the muscle will still 

 respond to an electrical stimulus. This shows that muscular 

 tissue has independent irritability. Hence, striated muscular 

 tissue possesses independent contractility, by which is meant 

 that its power of shortening is due to active processes developed 

 in its own tissue, and independent irritability, by which is 

 meant that it may enter into contraction by artificial stimuli 

 applied directly to its own substance. 



If we isolate a muscle and stimulate it, we get a simple con- 

 traction. If the end of this muscle is attached to a lever con- 



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