THE STATIC SENSITIVITY OF TENDON ORGANS DURING RECOVERY FROM NERVE INJURY

An investigation has been carried out into the physiological propertie s of tendon organs and their interactions with motor units following t wo types of nerve injury: nerve crush and nerve transection followed b y suture repair. Recovery from nerve crush was very successful: 6 week s after the injury 60% of the tendon organ-motor unit interactions (n = 62) evoked normal or near-normal patterns of afferent discharge but with reduced firing rates. After 10 weeks of recovery 81% of the inter actions (n = 43) were normal. The main abnormality observed was a phas ic-only pattern of discharge. The overall reductions in firing rate du ring early recovery may be attributable to the lower contractile force s generated by the reinnervated muscle units, while the phasic-only re sponses may also represent immaturity of the transduction mechanism of the regenerated afferent axons. Following nerve transection the quali ty of recovery was much lower and a range of abnormal, as well as norm al patterns of response were observed. For all the afferents studied, both types of response were recorded, suggesting that although there m ay be changes in the sensitivity of the afferents to muscle contractio n, the abnormal responses more probably reflect changes in the form of the mechanical input rather than abnormalities of the transduction pr ocess.