730 NEUROLOGY 



they supply. The former are sometimes called their origins or central terminations; 

 the latter their peripheral terminations. 



Origins of Nerves. The origin in some cases is single that is to say, the whole 

 nerve emerges from the nervous center by a single root; in other instances the nerve 

 arises by two or more roots w r hich come off from different parts of the nerve center, 

 sometimes widely apart from each other, and it often happens, when a nerve arises 

 in this way by two roots, that the functions of these two roots are different; as, for 

 example, in the spinal nerves, each of which arises by two roots, the anterior of 

 which is motor, and the posterior sensory. The point where the nerve root or 

 roots emerge from the surface of the nervous center is named the superficial or 

 apparent origin, but the fibers of the nerve can be traced for a certain distance into 

 the substance of the nervous center to some portion of the gray matter, which 

 constitutes the deep or real origin of the nerve. The centrifugal or efferent nerve 

 fibers originate in the nerve cells of the gray substance, the axis-cylinder processes 

 of these cells being prolonged to form the fibers. In the case of the centripetal or 

 afferent nerves the fibers grow inward either from nerve cells in the organs of special 

 sense, e. g., the retina, or from nerve cells in the ganglia. Having entered the nerve 

 center they branch and send their ultimate twigs among the cells, without, however, 

 uniting with them. 



Peripheral Terminations of Nerves. Nerve fibers terminate peripherally in various 

 ways, and these may be conveniently studied in the sensory and motor nerves 

 respectively. The terminations of the sensory nerves are dealt with in the section 

 on Sense Organs. 



Motor nerves can be traced into either unstriped or striped muscular fibers. In 

 the unstriped or involuntary muscles the nerves are derived from the sympathetic, 

 and are composed mainly of non-medullated fibers. Near their terminations they 

 divide into numerous branches, which communicate and form intimate plexuses. 

 At the junction of the branches small triangular nuclear bodies (ganglion cells) are 

 situated. From these plexuses minute branches are given off which divide and 

 break up into the ultimate fibrillae of which the nerves are composed. These 

 fibrillse course between the involuntary muscle cells, and, according to Elischer, 

 terminate on the surfaces of the cells, opposite the nuclei, in minute swellings. 



In the striped or voluntary muscle the nerves supplying the muscular fibers are 

 derived from the cerebrospinal nerves, and are composed main'y of medullated 

 fibers. The nerve, after entering the sheath of the muscle, breaks up into fibers or 

 bundles of fibers, which form plexuses, and gradually divide until, as a rule, a single 

 nerve fiber enters a single muscular fiber. Sometimes, however, if the muscular 

 fiber be long, more than one nerve fiber enters it. Within the muscular fiber the 

 nerve terminates in a special expansion, called by Kiihne, who first accurately 

 described it, a motor end-plate (Fig. 637). The nerve fiber, on approaching the mus- 

 cular fiber, suddenly loses its medullary sheath, the neurolemma becomes continuous 

 with the sarcolemma of the muscle, and only the axis-cylinder enters the muscular 

 fiber. There it at once spreads out, ramifying like the roots of a tree, immediately 

 beneath the sarcolemma, and becomes imbedded in a layer of granular matter, 

 containing a number of clear, oblong nuclei, the whole constituting an end-plate 

 from which the contractile wave of the muscular fiber is said to start. 



Ganglia are small aggregations of nerve cells. They are found on the posterior 

 roots of the spinal nerves; on the sensory roots of the trigeminal, facial, glosso- 

 pharyngeal, and vagus nerves, and on the acoustic nerves. They are also found in 

 connection with the sympathetic nerves. On section they are seen to consist of a 

 reddish-gray substance, traversed by numerous white nerve fibers; they vary con- 

 siderably in form and size; the largest are found in the cavity of the abdomen; 

 the smallest, not visible to the naked eye, exist in considerable numbers upon the 

 nerves distributed to the different viscera. Each ganglion is invested by a smooth 





