530 



MUSCLE-NERVE PHYSIOLOGY 



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 



F IG 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. T : ~* 

 dog. (Caroline McGiil.) 



Intestine of 



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

 contractions occasionally. In this regard smooth muscle stands intermedi- 

 ate between skeletal and cardiac muscle; the former is normally never 

 automatic, the latter always. 



Smooth muscle requires a different type of stimulus to produce contrac- 

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

 smooth muscle is not readily responsive to induction currents of short dura- 

 tion, but is readily stimulated by galvanic currents or induction currents of 

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

 of time. Preparations of the stomach muscle can scarcely be made to 



