MUSCLE SPINDLE ACTIVITY AND NATURALSLEEP IN THE CAT

Abstract

Single spike activities of the primary ending of the muscle spindle of ankle flexors and extensors were recorded in the unanesthetized chronic cat, keeping the muscle slightly and constantly stretched, with particular reference to the natural sleep. Three different kinds of influences attributable to the fusimotor neuron activity were differentiated during the para-sleep: tonic depression, phasic depression and phasic facilitation. In awake state the muscle spindle activity changed its rate, continuously, being higher or lower. During ortho-sleep the rate was more regular and relatively lower than in awake state. In the para-sleep state, compared with ortho-sleep, the rate of the spontaneous activity of muscle spindle afferents became irregular and decreased in 12 units out of tested 14 units (tonic depressions). In addition to the tonic depression during para-sleep there was transient burst pattern of the firing with or without muscle twitching (phasic facilitation) and there was the transient depression without co-contractions (phasic depression). The latter often associated with the rapid eye movement phase.