On inhibition as a reflex accompaniment of the tendon jerk and of other forms of active muscular response

Abstract

In the condition of decerebrate rigidity the extensor muscles involved are in a state of tonic contraction, which is accompanied by a series of small action-currents, first demonstrated by Dusser de Barenne (9) and Buytendijk (4). Fulton and Pi-Suñer (12) have recently observed that these action-currents cease during the course of a tendon jerk in the same muscle, and that their reappearance precedes by a constant interval, and therefore is almost certainly the action-current accompaniment of the small mechanical contraction which is usually seen delaying the decline of the decerebrate tendon jerk. This mechanical contraction on the decline of the tendon jerk was known to earlier workers (24) as the tonic after-discharge of the jerk, and was described as the "hump" or "myotatic appendage" of the jerk, by Ballif, Fulton and Liddell (2). It was interpreter by them as a reflex contraction caused by the sudden relaxation of the jerk, a phenomenon of stretch-reflex type caused by the passive lenghening of the muscle during the relaxation. Fulton and Pi-Suñer (12) interpret the absence of action-currents during the jerk as the result of slackening of some receptor organ in the muscle by the mechanical shortening taking place during the tendon jerk, and their reappearance as due to the reflex result of renewal of tension upon that receptor. This receptor, which, ex hypothesi , must react to passive stretch by causing reflex excitation in the same muscle, these latter authors identified with the muscle spindle, since in their opinion that organ, in virtue of lying "in parallel" with the muscle fibres, was likely to be slackened when the muscle substance surrounding it contracted.