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 mus- 

 cle resumes its normal shape. This illustrates the extensi- 

 bility 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 con- 

 tracts 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 mus- 

 cle 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 mus- 

 cle 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 stim- 

 ulus. This shows that muscular tissue has independent irri- 

 tability. Hence, striated muscular tissue possesses indepen- 

 dent contractility, by which is meant that its power of short- 

 ening 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 

 contraction. If the end of this muscle is attached to a lever 



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