RESUMO
The ultrastructures of the fifteen muscle spindles in poliomyelitis were studied especially concerning the structural alterations of intrafusal muscle fibers, sensory and motor nerve endings, though light microscopically previous workers have yielded no significant findings. Simultaneously performed light microscopic study of the same specimens revealed degenerative changes of the capsules in four muscle spindles and less significant changes in the remaining eleven muscle spindles. Ultrastructural findings of intrafusal muscle fibers consist or small vacuoles with irregular loss of myofilaments. Electron density of mitochondria in sensory nerve endings have increased and its cristae have disappeared. Plasma membranes of sensory nerve endings and intrafusal fibers are discontinuous. Mitochondria in motor nerve endings showed same findings, and basal lamina and junctional folds are also discontinuous or partially obscure. These findings seem to be neuropathic alterations of muscle spindles in poliomyelitis.
