370 



ANATOMY FOR NURSES 



[Chap. XIX 



and these enter and terminate in the organules. The different 

 varieties of tactile corpuscles, the organ of Corti, for the auditory 

 nerve, and the rods and cones of the retina 

 may be cited as examples of organules. 



Motor plates. — A nerve intended to 

 stimulate a muscle to activity terminates 

 by a subdivision of the axis cylinder (the 

 neurilemma and medullary sheath fading 

 out), each branch of the axis cylinder end- 

 ing in a flat nodule of granular material 

 lying on the muscle fibre. This terminal 

 mass is the motor plate. 



Plexus. — The nerve-fibres which are 

 distributed to the viscera are non-medul- 

 lated, antl near their terminations each one 

 divides into a number of branches which 

 arborize with each other and form a net- 

 work or plexus. From this plexus smaller 

 branches are given off, these subdivide to 

 form fibrils, and the fibrils terminate on the 

 surface of the muscle cells. (See page 

 377.) 



Nature of nerve-impulse. — Having ex- 

 amined the make-uj) of a complete ner- 

 vous entity (the neurone), it now seems 

 best to study the nature of nerve-impulses. 

 The nature of a nerve-impulse is not known. We know that 

 nerve-fibres may be stimulated by several means, and the practical 

 result is similar to the result obtained were the nerve stimulated 

 by the natural physiological impulse. The nerve-fibre has no 

 power to initiate a nerve-impulse, but serves merely as a conveyor 

 of the impulse which has been started either in the end organs or 

 in the nerve-cell. 



Artificial nerve stimulation. — There are four means usually 

 applied to the artificial stimulation of a nerve-fibre, viz. : 

 chemical, thermal, mechanical, and electrical, — the latter the 

 most usual. That the true physiological impulse is none of 

 these can be readily proven. (See any standard work of physi- 

 ology.), 



Fig. 177. — Pacini's Cor- 

 puscle, a, stalk; b, nerve- 

 fibre entering it ; a, d, con- 

 nective-tissue envrlope ; e, 

 axis cylinder, with its end 

 divided at /. (Collins.) 



