150 



PHYSIOLOGY OF CENTRAL NERVOUS SYSTEM. 



the nerve cells have dendritic processes, and, so far as their his- 

 tology is concerned, it would seem possible that in any ganglion 

 of this type there might be sensory and motor neurons so con- 

 nected as to make the ganglion an independent reflex center. 

 Numerous experiments have been made to determine experiment- 

 ally whether reflexes can be obtained through such ganglia. Per- 

 haps the most successful of these experiments have been made 

 upon the inferior mesenteric ganglion. 



This ganglion may be isolated from all connections with 

 the central nervous system and left attached to the bladder 

 through the two hypogastric nerves (see Fig. 287). If now one 

 of these nerves is cut and the central stump is stimulated, a 

 contraction of the bladder follows. Obviously in this case the 

 impulse has traveled to the ganglion and down the other hy- 

 pogastric nerve; the reaction has every appearance of being a 

 true reflex. Nevertheless, Langley and Anderson, f who have 

 studied the matter with especial care, are convinced that in this 



SenSQi-y Nerye 



SKtn 



^ioo' 



ess'' 



Fig. 69. — Schemata of axon-reflex producing local vascular dilatation from the applica- 

 tion of an irritant — A, Bardy's schema: n, the sensory fiber; c, the conjunctiva; d, the per- 

 ipheral sympathetic ganglion; /, the blood-vessel. The reflex runs from c over o 6 and d to 

 /; », a vaso-constrictor fiber. B, Bruce's schema (modified): The arrows indicate the course 

 ■of the axon-reflex. 



•and similar cases we have to do with what they call pseudo- 

 reflexes or axon reflexes. The idea underlying this term may 

 be explained in this way: Every sympathetic ganglion is 

 connected with the central nervous system, brain and cord, 

 by efferent spinal fibers, preganglionic fibers, which terminate by 

 arborization around the dendrites of the sympathetic cells. The 

 efferent fibers arising from the latter may be designated as post- 

 ganglionic fibers. These authors give reasons to believe that any 

 one preganglionic fiber, a, Fig. 68, may connect by collaterals with 

 several sympathetic cells. If such a fiber were stimulated at rr, 

 then the impulse passing back along the axon in a direction the 

 reverse of normal would stimulate cells b and c, giving effects that 

 are apparently reflex, but which differ from true reflexes in that 

 * Langley and Anderson, "Journal of Physiology," 16, 410, 1894. 



