Spiral nerve endings and dapple motor end plates in monkey extra-ocular muscles.

The suggestion that spiral nerve endings in extra-ocular muscles are sensory was tested. Spiral, serpentine and pincer-like endings were identified in extra-ocular muscles of rhesus and cynomolgus monkeys in light and electron microscopic preparations. Spiral and other complex nerve endings each terminated in the motor end plate zone as well separated clusters of boutons applied to various aspects of the muscle fibre, in contrast to the single group of boutons of other endings. They displayed a dappled appearance with acetylcholinesterase stain. Dapple endings had morphological features and staining characteristics consistent with motor end plates. Hence, spiralling of nerve fibre endings is shown to be a device for conveying boutons to dapple motor end plates rather than for monitoring the contraction of muscle fibres.