Physiology and biochemistry in modern medicine . ntraction of the external rectus ofthe right eye. This movement, due to the atonicity of the external rec-tus, does not however succeed in causing the eye to rotate beyond themidline of the field of vision. This is an instance of a willed reciprocalinhibition; i. e., a reciprocal inhibition brought about by stimuli coming 814 RECIPROCAL INNERVATION 81f> from the volitional center in the cerebrum. The same result may beobtained by electric stimulation of the center for eye movements on thecerebral cortex. The most important details concerning
Physiology and biochemistry in modern medicine . ntraction of the external rectus ofthe right eye. This movement, due to the atonicity of the external rec-tus, does not however succeed in causing the eye to rotate beyond themidline of the field of vision. This is an instance of a willed reciprocalinhibition; i. e., a reciprocal inhibition brought about by stimuli coming 814 RECIPROCAL INNERVATION 81f> from the volitional center in the cerebrum. The same result may beobtained by electric stimulation of the center for eye movements on thecerebral cortex. The most important details concerning the mechanism of reciprocalinnervation have been obtained by studying the flexion reflex in a spinalanimal which has completely recovered from shock. In such an animalthe tonus of the extensor muscles of the knees is well marked. Thistonus is maintained by afferent impulses transmitted to the spinal cordfrom receptors situated in the muscles, and its degree of intensity canbe estimated by the briskness of the knee-jerk, which, it will be remem-. Fig. 212.—Record from myograph connected with the extensor muscle of the knee. Duringthe time marked by the lower signal, the skin of the opposite foot was stimulated, thus causingthe crossed extension reflex. While still maintaining this stimulation, faradic shocks were ap-plied to the skin of the foot of the same side (as indicated by the upper signal), with the resultthat immediate inhibition of the contracted extensor occurred. (From Sherrington.) bered, is elicited by tapping the patellar tendon, and consists of a sud-den extension movement at the knee joint. By observing the brisknessof the knee-jerk we are therefore enabled to form an estimate of thetonicity of the extensor muscles; and if after doing so we throw theflexors which are their antagonists into activity by eliciting the flexionreflex, the knee-jerk will be found much less active. If we prevent theflexors from acting on the knee joint and the leg is held in an extend
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