The electric response in reflex contractions of spinal and decerebrate preparations

Abstract

In a series of communications Liddell and Sherrington (1) have analysed the mechanical response of a muscle stimulated to reflex contraction by rhythmic shocks to an afferent nerve. In particular they have described characteristic differences between the flexor response of the spinal and the extensor response of the decerebrate preparation ( i. e ., the preparation in which the midbrain is left attached to the spinal cord). During the past year we have attempted an analysis of the electrical response of a reflexly contracting muscle. The investigation was concerned in the main with some other points, but it has involved many comparisons of the electrical response of spinal and decerebrate preparations, and as these supplement and generally confirm, the views of Liddell and Sherrington it seems best to publish them as a separate communication. Method of Experiment . The experiments have been made on cats either decapitated under anæsthesia by Sherrington’s method or decerebrated by removal of all the brain above the anterior colliculi. The limb was fixed by a drill through. the lower end of the femur and shielded stimulating electrodes were applied to the popliteal nerve. The muscles whose action currents were recorded were the tibialis anticus for the flexion reflex and the vastocrureus for the crossed extension reflex. In the earlier experiments the tendon of the muscle was fixed by a clamp; in the later it was attached to a rubber tambour which communicated by a leaden pipe 9 feet long with another tambour which carried a pointer moving in the eyepiece of the string galvanometer. A more direct method could not be used owing to the distance between the animal table and the galvanometer. The movement of this pointer, magnified 40 times, was recorded on the same strip of cinematograph film as the movements of the string. Owing to the length of the pipe there is a lag of some hundredths of a second in the movement of the second tambour, and sudden movements ( e. g ., the single twitch of a muscle) set up waves in the pipe which cause oscillations on the record.