Simple spiral nerve endings in human extraocular muscles.

The goal of this paper is to describe the presence and morphology of simple spiral nerve endings as well as their distribution within the extraocular muscles of the human being. The extraocular muscles of four male subjects were dissected out and stained with several silver impregnation methods. The results obtained showed the presence of nerve endings that surround muscle fibers and correspond to the classification of simple spiral nerve endings by Daniel (1946). However they were found to differ in size from this description. They were distributed throughout the entire body of the muscles, although they appeared to be more abundant in the proximal third. Most of these endings encircled between two and four times the muscles fibers. The nerve fiber forming the spirals were surrounded by a capsule of connective tissue which appears to keep the fibers attached to the muscles. The fact that proprioceptors may adopt different morphological shapes suggests that proprioception may be conformed of different components, one of which may be mediated by simple spiral nerve endings.