Position and velocity sensitivity of muscle spindles in the cat. 3. Static fusimotor single-fibre activation of primary and secondary endings.

Abstract

AbstractDuring the tetanic stimulation of single static fusimotor fibres, primary and secondary endings in ankle extensor and flexor muscles of the cat have been subjected to ‘triangular’ length changes. Position and velocity sensitivities were determined and compared with those obtained in non‐activated endings. Two types of action of static fibre stimulation on the position sensitivity have been observed both in primary and secondary endings: it was either unchanged, or it decreased with increasing rate of stimulation (type I effect); it increased with increasing rate of stimulation (type II effect). The distribution of the two types was different to primary and secondary endings and to extensor and flexor endings. During stimulation of most static fibres, irrespective of their type, the velocity responses of both primary and secondary endings resembled those of non‐activated secondary endings. The ‘quick’ component of the velocity response was usually larger in primary than in secondary endings, while the ‘slow’ components were about the same. Comparisons made in secondary endings between the velocity responses during static activation and in the non‐activated state showed that the ‘quick’ component was reduced and the ‘slow’ component increased by the stimulation. ‘Exceptional’ velocity responses were observed in type I activation of some primary endings.