Structural and functional rearrangement of muscle spindles in rats under conditions or zero gravity

Electron microscopy of muscle spindles in m. extensor halucis longus of rats 14 days after space mission on board SLS-2 space laboratory (USA) showed structural rearrangement in the receptors. The number of intrafusal fibers increased, but some fibers developed degenerative changes. The changes were also seen in the spindle capsule, but its integrity was not impaired. Vascularization of the spindle capsule was impaired as a result of necrobiotic changes in capillary endotheliocytes. Sensory nerve endings were the most sensitive structures of the receptor. Destructive changes in various structures of the muscle spindles were paralleled by regenerative processes.