CHAPTER XCIV 



EFFECTS OF EXPERIMENTAL LESIONS OF VARIOUS PARTS 

 OF THE NERVOUS SYSTEM 



Having learned the main characteristics of reflex action, we shall now 

 proceed to study the peculiar function of each part of 'the cerebrospinal 

 system by noting the effects which follow destruction or stimulation of 

 its different parts. 



THE ANTERIOR ROOT 



Section of an anterior root produces a limited degree of paralysis in- 

 volving several muscles having no functional relationships to one an- 

 other. If several anterior roots are cut, the paralysis becomes much 

 more extended, and is followed very soon by an evident atrophy of the 

 muscles concerned. Reflex actions from these muscles are of course im- 

 possible. Stimulation of the peripheral end of a cut motor root. causes 

 partial contraction of several muscles, no definite joint movement, how- 

 ever, being the result, because the affected muscles are not functionally re- 

 lated and there is no reciprocal inhibition. Flexor and extensor, adductor 

 and abductor may contract at the same time, thus causing the joint on which 

 th'ey act to become muscle-bound. It is in the plexus that the nerve 

 fibers of the roots become sorted out, according to function, into motor 

 and sensory nerve trunks. The distribution of the anterior root fibers 

 according to segments in man for the cervical and lumbosacral regions 

 is as follows: 



C5 Deltoid, biceps, brachialis, supinators, rhomboids. Occasionally 

 radial extensors. Earely pronator radii teres. 



C6 Pronators, radial extensors, pectoralis major (clavicular libers), 

 serratus anticus. 



C7 Triceps, extensor carpi ulnaris, extensors of fingers, pectoralis 

 major. 



C8 Flexors of wrist and fingers. 



Tl Intrinsic muscles of hand. 



S3, 4 Levator ani, sphincter ani, perineal muscles. 



S2 Glutei, biceps, semitendinosus and semimembranosus, 



SI Intrinsic muscles of foot, tibialis posticus, and muscles of calf. 



L5 Muscles of ventrolateral leg (except tibialis anticus). 



L4 Extensors of leg and tibialis anticus. 



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