THE MUSCULAR SYSTEM 

 THE PHYSIOLOGY OF MUSCLES 



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The great size of the muscular system is an indication of its 

 physiologic importance. The most essential properties and 

 functions of muscles will now be discussed. 



Extensibility and elasticity are characteristic properties of all 

 kinds of muscle. The former is the property of stretching; the 

 latter the property of returning to the original shape after stretch- 

 ing. These properties can be demonstrated best by applying a 



Fig. 14.- Curve of extension of a rubber band, to show the equal exten- 

 sions for equal increments of weight. The band had an initial load of 17 gms., 

 and this was increased by increments of 3 gms. in each of the nine extensions, 

 the final load being 44 gms. The line joining the ends of the ordinates is a 

 straight line, b, Curve of extension of a frog's muscle (gastrocnemius). The 

 initial load and the increment of weight were the same as with the rubber. 

 The curve shows a decreasing extension for equal increments. The line joining 

 the ends of the ordinates is curved. (Howell's Physiology.) 



weight to living voluntary muscle, which, will extend under the 

 strain. When the weight is removed, the muscle returns to its 

 original form by virtue of its elasticity. The extensibility of such 

 a muscle is great, but the elasticity, though perfect, is slight. In 

 the living animal muscles are normally on the stretch. This 

 is seen by cutting across the belly of a muscle when a noticeable 

 gap occurs between the severed ends. This elastic tension insures 

 almost instantaneous action when the muscle is brought into 

 play for there is no slack to be taken up. The muscle stands as 

 if it were at full cock, We have seen that muscles are arranged 



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