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MUSCLE-NERVE PHYSIOLOGY 



cardiac muscle the time of a contraction is over a second, but in the warm- 

 blooded cardiac muscle the time is shorter, perhaps from 0.4 to 0.5 of a 

 second for the human ventricular muscle. 



Smooth Muscle. The physiology of smooth muscle has been given 

 to some extent in previous chapters, particularly in connection with the move- 

 ments of the stomach and intestines. As compared with skeletal and cardiac 

 muscle it is a much more slowly acting contractile tissue. Isolated strips of 

 smooth muscle, as a rule, contract only when stimulated, though preparations 

 of certain tissues, like the stomach muscle of the frog, give off rhythmic con- 

 tractions occasionally. In this regard smooth muscle stands intermediate 

 between skeletal and cardiac muscle ; the former is normally never automatic, 

 the latter always. 



Smooth muscle requires a different type of stimulus to produce contraction ; 

 the stimulus must be more prolonged and more intense. For example, 



FIG. 333- Contraction Area in Smooth Muscle. A, Showing the contraction nodes of the 

 fibers, the deep staining of the nodes, the condensation of surrounding connective tissue; B, 

 diagrammatic, showing the thickening of the longitudinal fibrillae. Intestine of dog. (Unpub- 

 lished figure by Caroline McGill.) 



smooth muscle is not readily responsive to induction currents of short duration, 

 but is readily stimulated by galvanic currents or induction currents of longer 

 duration. The stimulus must be applied through a longer interval of time. 



