Antagonistic Innervation

ANTAGONISTIC INNERVATION, in essence, coincides with the concept of reciprocal inhibition. Excitation (contraction) of agonists corresponds to inhibition (relaxation) of antagonists, and conversely—inhibition (relaxation) of agonists corresponds to excitation (contraction) of antagonists. In general, 'reflex inhibition (relaxation) and reflex excitation (contraction) are parts of the same reflex act; although they are opposite in direction, they represent mutually coordinated factors united in a single reaction' (Sherrington). The phenomenon of reciprocal inhibition consists in the fact that excitation of the agonist, i.e., the main working muscle or group of muscles, leads to inhibition of the antagonist, i.e., the oppositely acting muscle or group of muscles. The fact itself was known for a long time: Descartes in 1649 noted this phenomenon in the eye muscles, and Bell (Ch. Bell) in 1823 described the following illustrative experiment: 'I suspended a weight from the tendon of the extensor, which slightly stretched it, and found that contraction of the flexor was accompanied by the lowering of the weight, which indicated relaxation of the extensor'. In general form, the law of reciprocal inhibition was formulated, however, only by Sherrington (Sherrington, 1893), who discovered a fact of very great fundamental importance, that the phenomena of reciprocal inhibition characterize not only reflexes but also motor reactions arising from direct irritation of the cortex. Faradic irritation of any point in the motor area of the cortex, leading to contraction of a given muscle, at the same time invariably leads to relaxation of its antagonist.