Position and Velocity Sensitivity of Muscle Spindles in the Cat. I. Primary and Secondary Endings Deprived of Fusimotor Activation

Abstract

AbstractResponses of primary and secondary muscle spindle endings of the ankle extensor and flexor muscles in the cat were studied in the absence of fusimotor activation by applying length changes of triangular form over a large range of velocities. Both position and velocity responses were determined. No differences were obtained in these responses between endings in extensor and flexor muscles or between endings in fast and slow muscles. It was found necessary to subdivide the velocity responses into two different components based on the great difference in time course of their transients. Mathematical expressions for the two components are given in an Appendix. They were denoted the ‘quick’ and the ‘slow’ velocity responses respectively. Primary and secondary endings differed both with respect to the ‘quick’ and the ‘slow’ components of the velocity response. Endings with response characteristics typical of both primary and secondary endings were distinguished as a special group. They have been referred to as endings of intermediate type. Some possible spindle mechanisms responsible for the observed properties of the spindle endings are discussed.