Histophysiological observations on fast skeleto-fusimotor axons.

In three instances, repetitive stimulation of a single fast skeleto-fusimotor axon supplying cat tenuissimus muscle was observed to activate a secondary ending belonging to a precisely located spindle. Prolonged repetitive stimulation of these beta-axons elicited glycogen depletion in the intrafusal muscle fibres of the located spindles and in extrafusal fibres. The intrafusal depletion affected the longest of the chain fibres in two instances, and the bag1 and bag2 fibres in the third instance. In one experiment, the discharge from the primary ending of the located spindle was also recorded. The fast beta-axon (it supplied the longest chain fibre in the spindle) had a static action on the primary ending. The extrafusal muscle fibres of the 3 fast beta-motor units belonged to the fast oxidative-glycolytic type.