Histological identification of (static) skeletofusimotor innervation to a cat muscle spindle.

Two skeletofusimotor (beta) axons were identified histologically in cat tenuissimus muscle. The axons supplied the distal poles of 3 intrafusal muscle fibers of the nuclear chain type and two extrafusal fibers of the fast twitch type. The observations strengthen the case for the existence of static beta-innervation to cat muscle spindles.