Histochemical study of an unusual cat intrafusal muscle fiber

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Abstract
A cat tenuissimus muscle spindle that contained two long chain intrafusal fibers in its distal pole is described. One of the fibers (1 c1) had a histochemical profile (ATPase, NADH-TR, ChE reactions) of the kind which is characteristic for long chain fibers. The other fiber (1 c2) consisted of two separate segments. The inner 1 c2 segment included the sensory equatorial region and was histochemically normal. The outer 1 c2 segment carried a motor plate, and did not stain for NADH-TR in the same way as the inner 1 c2 segment and the 1 c1 fiber. It is suggested that the unusual enzyme staining properties of the outer 1 c2 segment stemmed from its lack of sensory innervation, a situation which may have permitted the full expression of influences mediated by its motor nerve supply.