Structural Features relative to the Function of Intrafusal Muscle Fibres in the Cat

Abstract

Publisher Summary Nuclear bag fibres that are operated electrophysiologically by either static or dynamic γ axons are iontophoretically labelled with dye. Subsequent histology shows that the nuclear bag fibres operated by static γ axons have thick elastic fibres around their polar regions that continue past the end of the fibres into the muscle. The dynamic nuclear bag fibres have fewer and thinner elastic fibres around their polar regions. This difference is used to correlate indirectly other physiological and structural properties of these fibres with their innervation. In this way, it is inferred that the dynamic nuclear bag fibre is more sensitive to direct application of acetylcholine than the static nuclear bag fibre and that the ATPase of the static nuclear bag fibre is stable in both alkaline and acid conditions, whereas the dynamic nuclear bag fibre contains the acid-stable,—alkalinelabile form of ATPase.