Normal organization and induced degeneration of the muscle attachment in the crayfish opener muscle

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Abstract
The attachments of muscle fibers to the central tendon were studied in the opener muscle of the crayfish. Muscle fibers are attached to microtubule-containing tendinous cells at desmosomelike junctions and also by means of connective tissue microfibrils. Tendinous cells are anchored to tonofibrillae in the tendon. After tenotomy, microtubules in the tendinous cells lose their usual orientation (parallel to the longitudinal axis of the muscle fiber) and appear to be reduced in number. After transection of the motor nerve the tendinous cells retain their normal appearance for long periods (100 days), but eventually their microtubules show misalignment and reduction. These results suggest that the normal morphology of the muscle attachment region, and in particular the microtubule content of tendinous cells, is determined by passive tension exerted by the opener muscle fibers.