496 



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 



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 nbrillae. Intestine of 

 dog. (Caroline McGill.) 



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 



