382 



ANATOMY FOR NURSES [Chap. XIX 



understood from a study of the accompanying diagrams (Figs. 

 181 and 182). 



Degeneration and regeneration of nerves. — Since, as has been 

 stated, tlu' cc'll-hody is essential for tlie nutrition of the whole cell, 

 it follows that if the processes of a neurone are cut oft", they will 

 suffer from malnutrition and die. If, for instance, a spinal nerve 

 be cut, all the peripheral part will die, since the fibres composing 

 it have been cut oft" from their cell-bodies situated in the cord, or in 

 the spinal ganglia. The divided ends of a nerve that has been cut 

 across readily reunite by cicatricial tissue, — that is to say, the 

 connective tissue framework unites, but the cut ends of tlie fibres 

 themselves do not unite. On the contrary, the peripheral or 

 severed portion of the nerve begins to degenerate, the medullary 



Fig. 182. — Degeneration of Spinal Nerves and Nerve-roots after 

 Section. A, section of ncrvo-trunk beyond the ganglion; B, section of anterior 

 root ; C, section of posterior root ; D, excision of ganglion ; a, anterior root ; p, 

 posterior root ; g, ganglion. 



sheath breaks up into a mass of fatty molecules and is gradually 

 absorbed, and finally the axis cylinder also disappears. In regen- 

 eration, the new fibres grow afresh from the axis cylinder of the 

 central end of the severed nerve-trunk, and penetrating into the 

 peripheral end of the neurilemma, grow along this as the axis 

 cylinder of the new nerve, each axis cylinder becoming after a time 

 surrounded with a medullary sheath. Restoration of function in 

 the nerve may not occur for several months, during which time it is 

 presumed the new nerve-fibres are slowly finding their way along 

 the course of those which have been destroyed. 



Distribution of the terminal branches of the spinal nerves. — 

 After leaving the spinal canal each spinal nerve divides into two 

 main trunks known as the anterior and posterior divisions. Each 

 of these contain sensorv and motor fibres. The anterior division 



