ULTRASTRUCTURE OF THE MUSCLE SPINDLE IN DYSTROPHIA MYOTONICA. II. THE SENSORY AND MOTOR NERVE TERMINALS

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Abstract
The normal pattern of innervation was lost in the 4 human dystrophia myotonica muscle spindles examined. There was a proliferation of sensory and motor nerve terminals, and many endings showed varying degrees of structural abnormality. The changes seen in the sensory nerve endings were an incomplete contact relationship between the terminal and the muscle fiber, the association of Schwann cell processes with the nerve ending, abnormal shape of the terminal, multiple sensory endings and changes in the ultrastructural organization of the terminal axoplasm. Remnants of degenerated sensory terminals and isolated sensory endings were also seen. Motor nerve terminals varied in size and shape. They contained a normal complement of vesicles and mitochondria. Junctional folding was often absent or simplified and sarcoplasmic specialization was, at the most, rudimentary. The relationship between these changes and intrafusal muscle fiber fragmentation is discussed.