Abstract
Muscle spindles are one of the most popular sensory receptors found in skeletal muscles and their physiological function has long been studied using various muscles. Recent advances in the method recording from spindle afferents in intact animals facilitate understanding of the singnificance of this kind of receptors for motor control. Chronic experiments on spindle behaviour of the masticatory muscles reveal that secondary spindle endings can transmit information on the jaw position while primary spindle activities are more related to the velocity of jaw movement than to the jaw position though their firing patterns are more complex in intact animals than in anesthetized ones. These spindle behaviour seems to be controlled by the co-activation mechanism of alpha and gammamotoneurons, although both activities are not rigidly related with each other. In addition to facilitation of alpha-motoneuron activities during jaw closing phase of a rhythic jaw movement cycle, spindle discharges contribute to stabilize jaw position through the jaw-jerk reflex path.
