THE STRUCTURE OF THE CEREBRUM. 



171 



2. The second order has cell-body or distal process in relation 

 with neurone- of first order. It conducts to a neurone of the 

 first order or conducts centrally from it. In like manner there 

 are neurones of the third, fourth, fifth order, etc. 



Functions of Neurones. i. Afferent. 2. Associative. 3. 

 Efferent. 



A neurone is afferent in function when its dendrites are directed 

 toward the periphery; if its axone is peripherally directed, its 



;Jeurilemma 



Nerve-cell 



Dendrite 



Terminal 

 branches 



A B 



Fig. 51. An efferent neurone and an afferent neurone. (After Brubaker.) 

 A. Efferent neurone. B. Afferent neurone. 



function is efferent (Fig. 51). An association neurone connects 

 other neurones together. 



Degeneration. If a neurone is prevented from functionating, 

 it undergoes a slow atrophic change, called degeneration of Nissl. 

 Rapid Wallerian degeneration occurs in an axone or dendrite w r hich 

 is completely cut off from all other parts of the neurone. In all 

 probability neurones differ in chemical constitution and in electric 



