MOTOR NERVE-ENDING 1 95 



endings in general, the gathering of the undifferentiated muscle cyto- 

 plasm, or sarcoplasm, around the end-organ. The whole mass, partly 

 nerve substance and partly muscle substance, is included when we use 

 the term end-plate. 



A further complexity and development is seen in the motor end-organs 

 of the reptiles and the higher vertebrates. The lizard shows excellent 

 examples (Fig. 172, A). The end branches of the nerve or telodendria 

 are short and thick and very irregular. They anastomose to form a 

 thick, heavy plexus. The collection of sarcoplasm around the plexus 

 so formed is very large (see also the part on the muscle fiber). (Also 

 read the parts on the nerve-endings on the different electric cells.) 



The efferent processes of the nerve cells also end on gland cells. They 

 thus transmit an impulse to the gland cell to secrete. Whether the im- 

 pulse is necessary to the metabolism of the food materials into the secre- 

 tion or whether it merely excites the cell to discharge or prepare to dis- 

 charge the secretion already prepared by its cytoplasm is not definitely 

 known. The fact that many cells secrete apparently without any nerve 

 supply would point to the latter view in our example. In controlling 

 the metabolism itself the nerve cell would only be doing what it prob- 

 ably does in muscle cells and others. One must also be careful to 

 distinguish such endings as motor in character, because sensory end- 

 ings are found in so many positions on the periphery. 



The manner of ending in gland cells is well shown in the nerve-ending 

 in the tear gland of the rabbit (Fig. 173). Fibers from several sources 

 form plexes around the alveoli of this gland, and their terminal branches 

 enter the glandular epithelium. Here they form motor endings that are 

 pressed against the proximal and middle surfaces of the gland cells. 

 These terminal fibers, which are the motor end-organs, differ from the 

 fiber from which they come only in that they are irregular in contour and 

 have several thickened 

 portions, the varicosi- ~>r~^_^~~- 



ties, of which a num- 

 ber occur somewhat 

 regularly distributed 

 on each branch. The 



variCOSltieS are about FIG I73 ._ stimulatory nerve end-organs in the epithelium 



twice the diameter Of of the lachrymal gland of a rabbit. A, lateral view, with 



the fiber and are nearly Basement membrane (&..); B, superficial view. X 200. 



J (After A. DOGIEL in Arch. f. mik. Anat.) 



spherical in shape. 



These nerves are not the only ones that direct the activities of the gland. 

 Others act indirectly through the medium of the muscle fibers that 

 regulate the blood supply and those that act as compressors of the gland 

 mass itself. 



