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neuromuscular spindle

A fusiform end organ in skeletal muscle in which afferent and a few efferent nerve fibres terminate; it contains from 3 to 10 striated muscle fibres (intrafusal fibres) that are much smaller than the ordinary muscle fibres, are separated from them by a capsule that encloses the organ, and are innervated by the thin axon of a gamma motoneuron (gamma motor fibre); the sensory endings that occur on the intrafusal fibres are either annulospiral or flower spray endings; this sensory end organ is particularly sensitive to passive stretch of the muscle in which it is enclosed.

Synonym: kuhne's spindle, muscle spindle.