Fusimotor Endings Responsible for Chain Fibre ‘Driving’ of Primary Sensory Endings in Cat Muscle Spindles
The effect of stimulation of single static γ axons, in ventral spinal root filaments, on the response of primary sensory endings from tenuissimus muscle spindles in dorsal root filaments was correlated with the ultrastructure of the fusimotor endings of these same axons. Static γ axons causing ‘driving’ of the Ia discharge were stimulated at frequencies from 0 to 150HZ with the spindle at constant length, and when subjected to ramp stretches. Seven spindles were isolated and intrafusal events observed during axon stimulation. The spindles were fixed with glutaraldehyde and reconstructed from serial transverse sections. Ultrathin sections were prepared at several levels of section through all the fusimotor endings.