MUSCLE TISSUE 



85 



Muscle tissue. It is impossible to discuss muscles without 

 bringing in a discussion of other tissues. When a large muscle is 

 dissected there is found not only the basic muscle cells, but several 

 other related tissues. The muscle is completely covered by a 

 sheath of connective tissue which extends in through the muscle, 

 dividing it into large bundles, then smaller and smaller ones, until 

 the bundles, or fasciculi, are so tiny that they are almost micro- 

 scopical. This connective tissue furnishes support for the blood 

 vessels and nerves which run through the muscles. Deposits of 

 fat cells may sometimes be found within the muscular tissue. 



Three kinds of muscles may be identified : cross-striated or skele- 

 tal, unstriated or smooth, and a specialized type which forms the 

 substances of the heart, called cardiac muscle. The units in stri- 

 ated muscle are probably the fibers. They have many nuclei in 

 contrast to the single nucleus in the elongated spindle-shaped 

 cells of the smooth muscle fibers. Skeletal muscle is voluntary 

 muscle. It is under the control of the will. Smooth muscle and 

 cardiac muscle are involuntary or independent of the will. Car- 

 diac muscle resembles vol- 



iS?&5 



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striates. 





cccrcliac 



untary muscle in having 

 cross striations. 



The special function of 

 all muscles is the produc- 

 tion of motion or the ex- 

 ertion of physical force. 

 This is brought about by 

 the shortening or contrac- 

 tion of the muscles which 

 have the abilitv of return- 

 ing to normal condition. 

 These changes are known 

 as contraction and relaxation. Normal muscle cells are always 

 in a slight state of contraction knowi:w as muscular tone. This 



smooth 



There are three types of muscle cells. Those having 

 many nuclei and cross markings are called striated cells. 

 The spindle-shaped ones with a single nucleus are 

 smooth muscle cells. An intermediate form, cross- 

 striated with a single nucleus, is found in the cardiac 

 muscle cells. Compare the three types. 



