EFFERENT PATHS AND REFLEX ARCS 



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lesion may cause a monoplegia, i. e., paralysis of a single part, such as the arm or 

 leg (Fig. 241, A). But in the internal capsule the motor fibers are grouped 

 within a small area and are frequently all destroyed together. This causes 

 paralysis of the opposite half of the body or hemiplegia (Fig. 241, B). Damage 

 to the pyramidal system in the cerebral peduncle, pons, or upper part of the 

 medulla oblongata may also cause hemiplegia; but in such cases those cortico- 



To the arm 



To the leg 

 Fig. 241. Diagram to illustrate the effects of lesions in various parts of the motor path. 



bulbar fibers, which leave the main strand of pyramidal fibers above the level 

 of the lesion, may escape injury and the corresponding cranial nerves need not 

 be involved (Fig. 241, C). Furthermore, in lesions of the brain stem the motor 

 nucleus or emergent fibers of one of the cranial nerves may be destroyed along 

 with the pyramidal fibers, in which case there would result a paralysis of the 

 muscles supplied by that nerve as well as a paralysis of the opposite half of the 

 body below that level a crossed paralysis (Fig. 241, C). While damage to the 



