Depolarization of Central Terminals of Group la Muscle Afferent Fibres during Desynchronized Sleep

Abstract

THE stage of deep sleep is characterized by a desynchronized electroencephalogram (EEG), periodic bursts of rapid eye movements and a great reduction of the electro-myographic (EMG) activity of dorsal cervical muscles. There is also a tonic depression of spontaneous EMG activity in both flexor and extensor muscles, and a further phasic reduction of residual muscular activity occurs synchronously with the periodic bursts of rapid eye movements¹. Both the heteronymous^2,3 and the homonymous⁴ monosynaptic reflexes are tonically depressed throughout the desynchronized phase of sleep. A further phasic depression frequently occurs at the time of the bursts of rapid eye movements⁴. This suggests that an abrupt but transient increase of the barrage of descending inhibitory impulses occurs phasically in relation to the rapid eye movements of deep sleep⁴. Muscular twitches have also been found to predominate during the bursts of rapid eye movements¹. These occur, paradoxically, just when the spontaneous muscle activity¹ and the spinal reflexes⁴ are most profoundly depressed.