TERMINAL BRANCHES OF NERVES 283 



made several divisions, when certain of the sensory fibers are no 

 longer found in the same sheath with the others, but are grouped 

 into nerves which belong to sensitive surfaces. 



The terminal branches of all nerve fibers differ with their func- 

 tion. The fibrils of motor spinal nerves end as tiny expanded 

 plates (end plates) which are applied to muscle fibers. (See Fig. 

 178.) Those of sensory spinal nerves are modified for the purpose 

 of receiving impressions from skin, mucous membranes, joints, 

 periosteum and, to a lesser extent, from muscle and bone tissues. 



Sensory 

 nerve-fiber. 



Nerve-fiber 

 bundle. 



FIG. 178. MOTOR NERVE-ENDINGS OF INTERCOSTAL MUSCLE-FIBERS OF A 

 RABBIT. Xi5o.(Siohr.) 



The terms origin and distribution are employed in the description of indi- 

 vidual nerves. When applied to motor nerves they are used appropriately 

 and are easily understood, but in connection with sensory nerves it must be 

 remembered that their origin or nerve beginning is by the "terminal branches. " 

 The impulse transmitted by sensory nerves is aroused by the stimulus 

 of impressions on these "branches" and received by the central cell; while 

 that of a motor nerve originates in the central cell, to be transmitted to a muscle 

 where it is really distributed. 



In describing mixed nerves it is necessary to conform to custom and speak 

 of the whole nerve as arising by its central connections and as being distributed 

 at the periphery (by which is meant the place where its function is manifested) . 



By the above it is evident that the conductivity of the tissue is 

 specialized in the axon fibers; the sensibility in the terminals and 

 cell bodies. The chemical changes in these parts are supposed to 

 be the origin of nerve impulse or nerve force. 



