neuromuscular spindle

Function

• proprioreceptor that provides information about changes in muscle length
• the neuromuscular spindle is especially sensitive to passive stretch of the muscle in which it is encapsulated

Structure

• a fusiform-shaped encapsulated end organ in skeletal muscle in which afferent & a few efferent nerve fibers terminate
• contains 3-10 small* striated muscle fibers (intrafusal fibers) innervated by a thin axon of a gamma motor neuron
• sensory nerve endings are annulospiral or flower-spray endings which terminate on the central region of the muscle spindle that is devoid of contractile proteins

* smaller than ordinary striated muscle fibers

Notes

• gamma motor neurons inducing contraction of intrafusal fibers of muscle spindle are coactivated with alpha motor neurons inducing extrafusal muscle fibers thus synchronizing contraction of both fiber types, keeping the muscle spindle fiber taut & responsive to stimulation by stretch

More general terms

• anatomic structure