CHAPTER V. 



THE AFFERENT AND EFFERENT NEURONS. 



The cell-bodies of the afferent neurons (so-called 'sensory' neurons) 

 are found in : ( 1 ) the spinal ganglia, the ganglia of the cranial nerve 

 roots, and the sympathetic and collateral ganglia. Here are located the 

 bodies of the neurons whose dendrites extend to the skin, subcutaneous 

 tissues, muscles, bones and tendons and viscera of the body. ( 2 ) the retina 

 of the eye, the cochlea of the ear, and the olfactory membrane of the nose. 



Posterolateral 

 groove 



Anterior nerve-root 

 Posterior nerve-root ' 



Spinal ganglion 



Anterior primary 

 division of nerve 

 Posterior primary 

 division of nerve 



Fig. 43. Portion of cord, showing the roots and spinal ganglia of the seventh 

 thoracic nerve. Enlarged about two diameters. (Cunningham, Anatomy.) 



RECEPTORS. 



The first, or most peripheral cell in an afferent chain is called a receptor. 

 A receptor (in other words) is a cell which receives the stimulus, whether 

 the stimulus be external to the body (as are light and sound), or internal 



