THE PROPRIOCEPTIVE REFLEX OF A FLEXOR MUSCLE

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Abstract
1. Quick stretching of tibialis anticus by a sharp pull on its tendon as the muscle lies slack in the decerebrate or spinal preparation (cat) elicits a reflex contraction of the muscle. The reflex is also obtainable in the intact animal under narcosis. It is more marked in the decerebrate than in the spinal preparation.2. The reaction is a proprioceptive reflex, the only afferent nerve required being that belonging to the muscle itself. The tendon of the muscle and the muscular part immediately adjacent to the tendon are not essential for the reflex. It is not therefore a tendon phenomenon, strictly speaking. It may be termed a stretch‐reflex.3. The minimal amount of stretching required to evoke the reaction is very small, a stretch amounting to 1 mm.—that is, less than 1/100th of the total length of the muscle—being sometimes sufficient. A stretch amounting to about 1/13th of the total length of the muscle evoked the reflex in fullest amplitude.4. Rate of stretching is an important factor in the stimulation, a slow stretching, however ample, being apparently unable to evoke the reflex.5. The contraction has often the myographic appearance of a simple twitch, lasting about 1 second; but under certain circumstances it is considerably more prolonged. When well marked, it develops force enough to raise a weight of more than 30 grms.Sometimes the response is multiple, and 2–4 separate twitch‐like contractions succeed each other in quick succession.6. The latent period of the reflex is shorter than that for reflexes evoked from the muscle by other afferent channels.7. When the reflex response of the muscle has been tired out for the ordinary “flexion‐reflex,” this proprioceptive stretch‐reflex persists unaffected by that fatigue.8. Strychnine increases the reflex.

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