Observations on spinal and decerebrate knee-jerks, with special reference to their inhibition by single break-shocks

Abstract

The present communication deals with certain differences observed in knee-jerk reflexes when elicited from decerebrate animals (i) with intact spinal cord, and (ii) with the spinal cord separated from the higher centres by section in the thoracic region, and further with their different behaviour to inhibition produced by single break-shocks. Sherrington was the first to show that the knee-jerk was inhibitable like other spinal reflexes (32, 35), and the work of Jolly (23), of Snyder (39), of Dodge (9) and of Viets (40a) contributed further to the recognition of the jerk as a true reflex phenomenon. Method .—The isometric myograph of high vibration frequency, previously described (16, 18, 20, 21) has been used throughout with a string galvanometer (new Cambridge pattern) arranged in the same optical system. As before, the reflex has been elicited by a finger tap on the tendon or by tapping the table with the finger or light hammer (Waller, 41). Control records such as that shown in fig. 1, A, have shown that the taps so elicited are constant (in height) within 5 per cent. The animals used have been cats, decerebrated at the inter-collicular level by the trephine method under deep anæsthesia, and allowed to recover. When they are made “ spinal,” the level of transection has been usually between the last thoracic and the first lumbar root. The section was made under anæsthesia sometimes before, sometimes after, decerebration. In some cases the preparations have been used “ decerebrate,” and after some hours have been made spinal. In one case a decapitate preparation was used. In a small number of cases the cord had been severed by aseptic operation a few days previously. For inhibiting the jerk a single break induction shock has been used, delivered in all cases to an ipsilateral afferent nerve. The leads from the muscle for recording the electrical responses were two silver pins, coated with chloride, one in the tendon, the other in the belly of rectus femoris.