Spread of phasic muscle reflexes in normal and spastic subjects

Abstract

The pathway of indirect'' reflexes in man was studied by means of electromyography in 4 normal subjects and 16 patients with upper motro neuron lesions affecting the limbs. The reflex most commonly examined was the indirect hamstrings jerk. Procaine block experiments indicated that receptors for the indirect reflexes are the spindles in the muscles themselves. Ischemic experiments showed that the latency of the reflex is such that it could not be mediated by small afferent fibers. It was also found that muscle stretch is not essential to the reflex. A comparison of reflex and vibration latencies showed an increase in reflex latency triggered indirectly which closely matched the increase in time required for a vibration wave to arrive at the muscle. It is concluded that an indriect reflex is elicited by percussion of bone or another firm part of limb or trunk which initiates a vibration wave. This vibration wave goes from bone to muscle stimulating the receptors of any sensitive muscle spindles along the path.