Responses of isolated Golgi tendon organs of the cat.

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Abstract
The responses to stretch were studied in living, isolated Golgi tendon organs (GTO) from tail muscles of cat. Experiments were performed in vitro and consisted of subjecting single GTO to controlled ramp-and-hold stretch while recording the response from their sensory axons raised in oil. The threshold force required for sustained afferent discharge was measured directly, and was between 8-170 dynes at 24.degree. C for 9 GTO tested. Beyond threshold, the discharge frequency was approximately proportional to applied static tension over a wide range. Sensitivity to tension varied among different GTO and appeared to be inversely correlated with mechanical stiffness. With impulse activity blocked by tetrodotoxin, graded receptor potentials were recorded whose amplitude varied in proportion to applied static tension. All GTO examined showed in addition a dynamic response, which became larger with increasing velocity of ramp stretch. This dynamic sensitivity appeared in the receptor potential and was then augmented by an apparent accommodative process at the impulse initiating site. Mechanical models for the sensory transduction mechanism were discussed.