3io 



COORDINATION AND SENSATION 



2. Through the central system (spinal cord or base of 

 brain). This, the intermediate division, may be composed 

 of mon-axonic neurons, or it may consist of branches from 

 the afferent neurons. In the case of separate neurons, 

 these are acted upon by impulses from the afferent 

 neurons, while their impulses serve in turn as stimuli to 

 other neurons within the cord (Fig. 129). 



3. From the central nervous system to the muscles. This, 

 the efferent division, is made up of mon-axonic neurons. 

 Most of these have their cell-bodies in the gray matter of 

 the cord, while their fibers pass into the spinal nerves by 

 the ventral roots. 1 They may be stimulated by impulses 

 either from the intermediate neurons, or from branches of 

 the afferent neurons. Their impulses reach and stimulate 

 the muscles. 



Reflex Action in Digestion. The flowing of the saliva, when food 

 is present in the mouth, is an example of reflex action. In this case, 



however, the organ 

 excited to activity is 

 a gland instead of a 

 muscle. The food 

 starts the impulses, 

 and these, acting 

 through the bulb, 

 reach and stimulate 

 the salivary glands. 

 In a similar manner 

 food excites the 

 glands that empty 

 their fluids into the 



stomach and intestines, and stimulates the muscular coats of these 

 organs to do their part in the digestive process. To a considerable 

 extent, neurons having their cell-bodies in the sympathetic ganglia are 

 concerned in these actions (Fig. 139). 



Reflex Action in the Circulation of the Blood. On sudden exposure 



1 Review description of the spinal nerves, page 295. 



FIG. 139. Diagram illustrating reflex action 

 in its relation to the food canal. The nerve path in 

 this case includes sympathetic neurons. 



