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Saturday, June 21, 2008
Motor function is hierarchically organized at four arbitrarily identified neuraxial levels, with the spinal cord being the lowest. Motor nuclei of the spinal reflex are the final common pathway for both spinal reflex and cortical projections to muscle fibers. Consequently, the spinal cord is crucial in reflex muscle contractions and voluntary movements. The environmentally triggered reflex responses regulated by the spinal cord include the stretch (myotatic) reflex, withdrawal (flexor) reflex, and crossed extensor reflex. Even though these reflexes are independent of voluntary motor control, intact cortical projections to the spinal cord are important in the regulation of these reflexes. Constantly relayed sensory information, which is vital to coordinated motor activity, is integrated at every level of the nervous system. Spinal lesions that interrupt both cortical and spinal reflex projections to limb muscles result in LMN syndrome. The clinical picture of this syndrome is characterized by flaccid paralysis, absent reflexes, and atrophy of muscle fibers.
運動功能在四個任意且可辦別的軸索的階段neuraxial levels是有分層地組織，而脊髓是最下面的。脊髓反射的運動神經核與皮質支配肌肉纖維Motor nuclei of the spinal reflex are the final common pathway for both spinal reflex and cortical projections to muscle fibers.。之後Consequently = therefore,，脊髓對於肌肉收縮的反射以及自主性的活動voluntary movements是重要的。環境性會引起受到脊髓調節的反射反應The environmentally triggered reflex responses regulated by the spinal cord，這包含了牽張反射、屈肌反射withdrawal (flexor) reflex以及交叉伸肌反射。雖然，這些反射在自主運動神經控制之下是獨立的，完整的皮質對脊髓的支配對於調節這些反射是很重要的。持續性的感覺訊息傳遞is integrated at every level of the nervous system，這對協調運動活動是很重要的，在每一階段的神經系統是完整的。脊髓損傷that interrupt both cortical and spinal reflex projections to limb muscles對於皮質以及脊髓對於肢體肌肉的反射與支配兩者都會受到干擾，因此造成了下運動神經元系統受傷的症狀。這種症狀is characterized by臨床的描寫，有鬆弛性癱瘓、缺乏反射和肌肉的萎縮特徵。