Rotation compensating reflexes independent of the labyrinth

Abstract

Pigeons without labyrinths or with sectioned spinal cords continue to show compensatory reflexes to passive body rotations. This paper reports electrophysiological efforts to identify the source of afference controlling these reflexes. A proportion of fibres in lumbosacral spinal dorsal roots were found to respond briskly to body rotations around the longitudinal and the transversal axes and less to rotation around the vertical axis. Their responsiveness to rotation was unaffected by sectioning the spinal cord at a rostral level and by cutting the somatic branch of the spinal nerve corresponding to the relevant dorsal root. It could be demonstrated that movements of the viscera brought about in two different ways were adequate stimuli for these ldquorotationrdquo units. It is surmised that the sense organs responsible are stretch receptors located in the mesenteries. The arrangement of mesenteries is deemed suitable for the detection of visceral movements caused by body rotation. Concordances between the behaviour of the rotation units and responses of muscle units involved in the righting reflexes as described by Biederman-Thorson and Thorson (1973) strongly suggest that the afferences described are those controlling the reflexes of labyrinthless or spinally transected pigeons.