CHAPTER XVI 

 GENERAL NERVE PHYSIOLOGY 



1. THE CONSTRUCTION AND FUNCTION OF THE 

 NERVE ELEMENTS 



THE nervous system is composed of nerve units called 

 neurons. The neuron is made up of: 



(i) A nerve cell, and (2) its processes, which may be 

 divided into: 



(a] Protoplasmic processes or dendrites, which are short, 

 much-branching processes, rapidly decreasing in size. 



(V) An axis-cylinder process or neurite, which differs from 

 the dendrites in its hyaline, smooth appearance. Its thick- 

 ness is uniform throughout its course. At the end it splits 

 tip into a group of brushes, the so-called end-tufts. Many 

 axis-cylinders give off lateral branches (collaterals) which 

 also end in tufts. The axis-cylinder, the most important 

 part of each nerve fibre, is sometimes longitudinally striated 

 owing to the fibrils of which it is composed. Between the 

 fibrils is found the neuroplasma, a finely granular substance. 



The physiological processes in this nerve unit are such 

 that when the cell is stimulated either automatically (without 

 any outside stimulation) or by some outside stimulation, 

 the stimulation is taken up by the protoplasmic processes 

 and carried to the cell. By the cell it is transmitted to the 

 axis-cylinder which conducts it to the end-tufts. Thence 

 it is communicated to the organ with which the end-tufts are 

 connected (cells of other nerve elements, muscle fibres, or 

 gland cells). 



The protoplasmic processes carry the stimulation celluli- 



215 



