The palisade endings of cat extraocular muscles: a light and electron microscope study.

The palisade endings (PEs), a particular type of nerve ending found only in extraocular muscles of mammals, have been studied using both silver-stained teased preparations and electron microscope techniques. They have been found, in act, in both the proximal and distal muscle insertions of the four recti and the two oblique mucles. PEs are exclusively associated with some of the mitochondria-poor, multiply-innervated muscle fibres present in the globar layer os these muscles, and consist of a multitude of terminal branches embracing the extremity of the muscle fibre and penetrating the infoldings formed by the muscle fibre at its tendinous attachment. The whole formation is surrounded by a thin capsule. These nerve endings present striking similarities to the developing Golgi tendon organ; the terminal branches lying among the collagen fibrils and occasionally making 'sensory-like' close contacts with the muscle fibre are disposed in such a way that they could easily have a sensory role. It was concluded that PEs present sufficient morphological evidence to be considered as sensory, encapsulated, myotendinous receptors, each related to a single multiply-innervated muscle fibre.