neuromuscular spindle, any one of a number of small bundles of delicate muscular fibers enclosed by a capsule, in which sensory nerve fibers terminate. The spindles vary in length from 0.8 to 5 mm, accommodating as many as four large myelinated nerve fibers that pierce the capsule and lose their myelin sheaths. The nerve fibers end as naked axons encircling the intrafusal fibers with flattened expansions or ovoid disks.
