NERVE ENDINGS IN MUSCLE AND TENDON 



175 



End plates of 'accessory' non-medullated, probably sympathetic, 

 fibers have also been described in striped muscle (Perroncito, Ihibcr ami 

 De Witt, and Boecke). Muscle tonus is believed to depend upon this 

 innervation. 



B. CARDIAC AND SMOOTH MUSCLE 



The nerves (sympathetic) of the heart are distributed to the cardiac 

 ganglia, whence non-medullated fibers pass to all portions of the organ 

 and form a very rich plexus in 

 the intermuscular connective 

 tissue. Fine terminal fibrils 

 are distributed from this plexus 

 to the muscle fibers, upon 



whose surface they end in vari- 



FIG. 194. NERVE ENDINGS IN CARDIAC 

 MUSCLE FROM THE HEART OF A CAT. 



a, muscle cells; b, nerve fiber. Methylene 

 blue. Highly magnified. (After Huber and 

 De Witt.) 



cose swellings and end knobs. 

 While most of these fibrils are 

 probably motor in function, 

 others which end in the inter- 

 muscular connective tissue are 

 more probably afferent (sensory). Occasional endings in cardiac muscle 

 resemble the simpler motor end organs of skeletal muscle. 



In smooth muscle, 

 plexuses of sympa- 

 thetic nerve fibers oc- 

 cur in the intervals 

 between the bundles 

 of muscle fibers. Sec- 

 ondary plexuses of 

 naked fibrils are 



found among the muscle cells, and from this plexus fine lateral fibrils 

 are distributed to the muscle cells, upon whose surface they end in small 

 terminal granules or end knobs. Many of the nerve fibers in smooth 

 muscle are undoubtedly of sensory function. 



The nerve endings and the distribution of the peripheral nerve fibers 

 in the various organs of the body are more fully described in the several 

 chapters devoted to those organs. 



FIG. 195. NERVE ENDINGS IN SMOOTH MUSCLE, FROM 

 THE INTESTINE OF A CAT. 



a, muscle cell; b, nerve fiber. Methylene blue. Highly 

 magnified. (After Huber and De Witt.) 



