Regeneration of afferent and efferent fibres to muscle spindles after nerve injury in adults cats.

1. The nerves to cat peroneus longus and tenuissimus muscles were either cut or crushed close to the muscle and the afferent and efferent nerve supply to the muscle spindles was studied electrophysiologically between 2 and 32 weeks later. 2. Recovery was more rapid and complete after crush than section for both afferent and efferent fibres. After recovery from either procedure normal primary and secondary afferents and static and dynamic gamma efferent fibres were found. 3. Some abnormally occurring neurones were found. One group consisted of beta fibres which had a static action on muscle spindles. Static beta fibres are very rarely found in normal muscles. 4. The results indicate that some guidance mechanism exists which after crush injuries of nerves may restore muscle receptor function almost to normal. Even after nerve section some muscle spindles may become correctly reinnervated.