RECEPTORS AND EFFECTORS 



103 



fibers, each composed of an axon, myelin, neurolennna, and sheath 

 of Ilenle. The fibers are arranged in bundles, or fasciculi, of varying 

 size, bound together by loose fibroelastic connective tissue, and the 

 entire nerve is supported by similar tissue. (Fig. 59.) The con- 

 nective tissue immediately around all the fasciculi is called epi- 

 neurium, or external perineurium, and as the internal perineurium 

 it continues in between the bundles and merges with a more dense 

 connective tissue around each bimdle. There is also a loose delicate 



-External perineurium 



Internal perineurium 



Fig. 59. — Drawdng of cross-section of a peripheral nerve. Two large and a number 

 of smaller fasciculi of fibers are sho-w-n. External and internal perineurium are 

 shown around and between the bundles. 



extension of connecti\'e tissue between adjacent single fibers to 

 form the endoneurium. Delicate fibers from the endoneurium 

 continue to the .sheath of Henle. 



As the nerve extends out from its central origin, it branches, and 

 each branching represents a sorting out of bundles and a gradual 

 diminution in number of fibers in a bundle. The connective tissue 

 of a nerve has a special nerve supply, called the nervi nervorum, 

 and a vascular supply, the vasi nervorum. 



RECEPTORS AND EFFECTORS. 



The reception of external stimuli l)y nerve cell processes and the 

 transforming of these into nerve impulses necessitate some organiza- 

 tion of the other tissues located at each of these end-points. As an 

 example, there are receptors in the eye which receive stimuli from 

 light and others in the skin which receive stimuli from pressure. The 



