72 HUMAN PHYSIOLOGY. 



the end tufts of the collateral branches, which may extend for some distance 

 up and down the cord before passing into the various segments. 



For the excitation of a reflex action it is essential that the stimulus applied 

 to the sentient surface be of an intensity sufficient to develop in the terminals 

 of the afferent nerve a series of nerve impulses, which, raveling inward, will 

 be distributed to and received by the dendrites of the emissive or motor cell. 

 With the reception of these impulses there is apparently a disturbance of the 

 equilibrium of its molecules, a liberation of energy, and, in consequence, a 



M 



FIG. 10. DIAGRAM ILLUSTRATING REFLEX ACTION. (Kirke.) 

 S. Receptive surface from which proceeds the afferent nerve. M. C. Motor or 

 emissive cell giving origin to efferent nerve which terminates in M. M. Motor 

 organ. G. Ganglion cell on afferent nerve. 



transmission outward of impulses through the efferent nerve to muscle, gland, 

 or blood-vessel, separately or collectively, with the production of muscular 

 contraction, glandular secretion, vascular dilatation or contraction, etc. The 

 reflex actions take place, for the most part, through the spinal cord and med- 

 ulla oblongata, which, in virtue of their contained centers, coordinate the 

 various organs and tissues concerned in the performance of the organic func- 

 tions. The movements of mastication; the secretion of saliva; the muscular, 

 glandular, and vascular phenomena of gastric and intestinal digestion; the 

 vascular and respiratory movements; the mechanism of micturition, etc., are 

 illustrations of reflex activity. 



