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1 Centro de Investigación y de Estudios Avanzados del I. P. N.
2 Centro de Investigación y de Estudios Avanzados
* To whom correspondence should be addressed. E-mail: jmunoz{at}fisio.cinvestav.mx.
The question on whether or not skin receptors might help in the perception of muscle contraction and body movement has not been settled. The present paper gives direct prove of skin receptor firing in close coincidence with the contraction of vaginal and anal sphincters. The distal stump of the sectioned motor pudendal nerve was stimulated with single shocks. This induced a wave-like increase in the lumen pressure of the distal vagina and the anal canal, as well as constriction of the vaginal introitus and the anus. The constriction pulls on and moves the surrounding skin, which was initially detected visually. In the present experiments, a thin strain gauge that pressed on the skin surface detected its displacement. Single shocks to the motor nerve induced a wave of skin movement with maximal amplitude at 5 mm from the anus and propagated with decrement beyond 35 mm. The peripheral terminals of the sensory pudendal nerve and the posterior femoral nerve supply the skin that moves. Sensory axons from both nerves fired in response to both, tactile stimulation and the skin movement produced by the constriction of the orifices (motor-sensory coupling). In cats with all nerves intact, single shock to the sensory nerves induced reflex waves of skin movement and lumen pressure (sensory-motor coupling). Both couplings provide evidence for a feed-forward action that might help to maintain the female posture during mating, and to the perception of muscle contraction.
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