SOME OBSERVATIONS ON THE REFLEX ACTIVITY OF A MUSCLE OF THE FORE‐LIMB (M. SUPRASPINATUS)

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Abstract
The reflex activity of M. supraspinatus, a muscle of the fore‐limb, has been examined in decerebrated cats, and points of similarity and dissimilarity with the extensor of the knee have been noted.Points of similarity are:1. In the response to stimulation of a nerve of the contralateral arm the phenomenon of “recruitment” of neurone units is apparent.2. In thalamic and intercollicular decerebrate preparations the muscle responds to stretching of its tendon by a sustained “stretch reflex.”Points of dissimilarity are:3. In some preparations neither the crossed extensor reflex nor the stretch reflex are markedly susceptible to inhibitory stimuli, but may show, when the stimuli are not strong, an augmented contraction within 60 σ.4. On occasion, the recruitment curve may be preceded by a brief abrupt contraction resembling a reaction d‐emblee.5. Even quite strong ipsilateral stimuli may fail to produce marked inhibition. When effective, however, the latent period of inhibition is notably brief (25 σ), as in the hind‐limb. There is clearly evident an exaggerated excitatory tendency in the ipsilateral nerves of the fore‐limb which hinders the inhibitory aspect of the same nerves, giving a nett result of either excitation or inhibition. It has been possible to differentiate the exciting and the inhibitory components by inducing a small heemorrhage which usually favours inhibition.6. Section of the spinal cord in the thoraco‐lumbar region increases to a large degree the postural contraction of M. supraspinatus to a degree which, as measured by the decreased length of the muscle, often amounts to 3–7 per cent.

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