CHAPTER 7 



THE MUSCULAR SYSTEM 



One of the intrinsic properties of protoplasm is that of movement. 

 It is a property that is found in all plants and animals. In some plants, 

 this movement can be detected only as the flowing of the cytoplasm 

 within the cells; among animals, movements are much more easily 

 discerned. For an animal, the ability to move from one spot to an- 

 other is of great importance, chiefly due to the fact that food must be 

 obtained and protective sites must be discovered. For this reason, 

 organs capable of bringing about movement are often highly developed. 



Muscle tissue is simply groups of cells in which the basic prop- 

 erty of contractility to bring about movements is highly developed. 

 Muscle tissue of at least a simple type is found in nearly all phyla of 

 the metazoans. Among the higher invertebrates such as the insects, the 

 muscular system is extremely well developed and rapid wing and leg 

 movements are possible. The greatest diversity of muscular develop- 

 ment is, however, found among the vertebrates. 



To bring about movements, the muscles of necessity are intimately 

 associated with the skeletal system. Bodily movements are possible 

 because of the manner in which these two systems are functionally 

 combined. 



FUNCTIONS OF THE MUSCULAR SYSTEM 



Fundamentally the muscular system has but one function, that of 

 bringing about movements. The most conspicuous movements are, of 

 course, those associated with the skeletal system. Movements such 

 as walking, lifting, running, and the handling of objects are all examples 

 of these. 



Of equal importance are the unconscious movements of the in- 

 ternal organs. Food is moved down the digestive tract, the heart beats, 

 respiration takes place, all due to muscular activity. 



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