THE RECEPTORS AND EFFECTORS 



93 



IV. VISCERAL EFFECTORS 



25. End-organs on the Involuntary Visceral Muscles. These muscles 

 may be unstriated or striated (as in heart muscle). They are innervated 



Fig. 37. Two unstriated involuntary muscle-fibers, showing the nerve- 

 endings: a, Axon; b, its termination; n, nucleus of the smooth muscle 

 cell. (After Huber and DeWitt, from Barker's Nervous System.) 



through the sympathetic nervous system and typically by a chain of two 

 neurons, the preganglionic and the postganglionic neurons (see p. 229). 



Fig. 38. Three striated cardiac muscle cells, with their nerve-endings. 

 (After Huber and DeWitt, from Barker's Nervous System.) 



The body of the preganglionic neuron lies in the central nervous system and 

 its axon passes out into the sympathetic nervous system, where it ends in a 

 sympathetic ganglion. The efferent impulse is here taken up by a post- 

 ganglionic neuron, whose body lies in the sympathetic ganglion in question 



