GENERAL ZOOLOGY 



Axon of efferent neuron flL--^ Myelin sheath 



Striated muscle cell 



Terminal filaments 



Neuromuscular junction 



End bulb 



Rg. 4.22. Neuromuscular junctions. The terminal filaments of an efferent neuron may end on 

 specialized areas in a number of different striated muscle cells. 



ATP molecules, muscle glycogen is metabolized to lactic acid (p. 36). Some 

 of this is released to the blood stream in man and converted to glycogen in 

 the liver. But most of it accumulates in the muscle cell during muscular 

 work and must eventually be run through the TCA cycle for elimination 

 (p. 36). This is vs'hy the oxygen requirement is high during exercise. After 

 contraction, the actomyosin dissociates into actin and myosin and is ready to 

 be reused. An important by-product of muscular contraction in warm- 

 blooded animals is the heat necessary for maintenance of body temperature, 

 under normal conditions as well as under circumstances of excessive loss of 

 heat from the body (p. 125). 



Muscular fatigue is a feeling familiar to all of us. We might suppose that 

 it resulted from depletion of the energy stores of the muscle cells or of the 

 nerve fibers innervating them. However, muscle and nerve cells have reserves 

 capable of powering their reactions for relatively long periods of time. The 

 weakest link in the nerve-muscle reaction system is the neuromuscular 

 junction. It does not have the capacity to respond to the discharge of nerve 

 impulses for long periods of time without rest. This is the area that is 

 fatigued by continued muscular work. 



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