The responses of the primary and secondary endings of muscle spindles with intact motor innervation during applied stretch.

Abstract

The effects of small stretches applied at constant velocities, varying from 8 to 100 mm/sec. on the muscle spindle endings of the cat's soleus were recorded in dorsal root fibres of decerebrate animals with intact motor roots. The primary endings showed a greatly increased and well‐sustained discharge rate during stretch application. They were particularly sensitive to the velocity of stretch and the rates reached were considerably higher than those recorded during the subsequent maintained extensioin of the muscle. The endings often showed some discharge in release of stretch. The secondary endings showed a wide range of thresholds for stretch. The increase of discharge rate during stretch application was very moderate, and might not exceed the steady rate during maintained stretch. On release of stretch impulses were frequently seen. These differences in the behaviour of the two kinds of ending to stretch are considered in relation to the histological structure of a muscle spindle.