9 6 



TEXT-BOOK OF PHYSIOLOGY 



FIG. 46. MOTOR NERVE-ENDINGS 

 or INTERCOSTAL MUSCLE-FIBERS OF 

 A RABBIT. X 150. (St'ohr.) 



roots contain all the efferent fibers, the posterior or dorsal roots all the afferent 

 fibers. 



The Peripheral Endings of Nerves. The efferent nerves as they 

 approach their ultimate terminations lose both the neurilemma and myelin 

 sheaths. The axon or axis-cylinder then divides into a number of branches 

 which become directly and intimately associated with tissue-cells. The 



particular mode of termination varies in 



BHBSBnBBaHHBBMMBHi different situations. These terminations 



are generally spoken of as end-organs, 

 terminal organs, or end-tufts. 



In the skeletal muscle the nerve-fiber 

 loses both neurilemma and myelin sheath 

 at the point where it comes in contact with 

 the muscle-fiber. After penetrating the 

 sarcolemma, the axon or axis-cylinder 

 divides into a number of small branches 

 which appear to be embedded in a rela- 

 tively large mass of sarcoplasm and nuclei, 

 the whole forming the so-called "motor 

 plate." Each muscle-fiber possesses one 

 such plate or end-organ in mammalia, 

 several in the frog. (Fig. 46.) 



In the visceral muscle the terminal nerve-fibers derived from sympathetic 

 or peripheral neurons are primarily non-medullated. The axons divide and 

 subdivide and form plexuses which surround the muscle-cell bundles. Fine 

 fibers from the plexuses are given off which ultimately come into relation 

 with each individual cell, on the surface of which they terminate in the form 

 of one or more granular masses. 



In the glands, taking as an illustration the parotid and mammary glands, 

 the nerve-fibers, also derived from sympathetic or peripheral neurons, pass 

 into the body of the gland and ultimately 

 reach the acini, on the outer surface of 

 which they ramify and form a plexus. 

 From this plexus fine fibers penetrate 

 the acinus wall and end on the gland-cell. 

 The fibers present a varicose appearance 

 (Fig. 47). 



The afferent nerves as they ap- 

 proach their ultimate terminations un- 

 dergo similar changes. The end-tufts 

 become associated, in some situations, 

 with specialized end-organs which are extremely complex. 



In the skin and mucous membranes the mode of termination varies con- 

 siderably. The following are some of the principal modes: 



1. Free endings in the epithelium. 



2. Tactile cells of Merkel. 



3. Tactile corpuscles in -the papillae of the true skin. 



4. Pacinian corpuscles found attached to the nerves of the hands and 



feet, to the intercostal nerves, and to nerves in other situations. 



5. End-bulbs of Krause in the conjunctiva, clitoris, penis, etc. 



6 



FIG. 47. TERMINATIONS OF NERVE- 

 FIBERS IN THE GLAND-CELLS. A. Cell 

 of the parotid gland of a rabbit. B. 

 Cells of the mammary gland of a cat in 

 gestation. (Doyon and Moral.) 



