Electrical responses of extensor muscles during postural (myotatic) contraction

Abstract

Liddell and Sherrington (22) have observed that an anti-gravity muscle of decerebrate and thalamic animals responds to relatively slow stretches by active contraction, and it has been concluded that these myotatic reflexes are in large measure responsible for the postural tonus of muscles (29). As the behaviour of the electrical responses during such stretch reflexes has not been previously examined, we have obtained simultaneous mechanical and electrical records of the responses of the quadriceps extensor of cats to stretching, and we propose in this communication to describe the results. Method . —A myograph of high natural frequency (1,600 per second) in the same optical system as the galvanometer has been employed as previously described (13, 15, 17). Two silver pins coated with chloride have been used as leads, one inserted into the tendon, the other inserted into the belly of rectus femoris. The falling table described by Liddell and Sherrington (22) has been used for slow stretches. Cats decerebrated under deep anæsthesia by the trephine method and allowed to recover have been used throughout. All muscles (except the one used) of both hind limbs were immobilised by nerve section and resection of tendons. The knee-jerks studied were usually elicited by tapping the tendon with the finger, but sometimes also by tapping the table, which, although heavy and rigid, yielded probably 1/40 mm., thereby stretching the muscle and eliciting the reflex.