STRETCH-SENSITIVE AFFERENT NEURONS IN CAT KNEE-JOINT CAPSULE - SENSITIVITY TO AXIAL AND COMPRESSION STRESSES AND STRAINS

1. Experiments were performed to determine whether the response of str etch-sensitive mechanoreceptors to tissue deformation is caused by the axial stretching of the tissue or by the associated transverse compre ssion of the tissue caused by the Poisson effect. 2. Single, stretch-s ensitive mechanoreceptors were recorded in vitro in a preparation of i nnervated, isolated capsule from the cat knee. Afferents were isolated in a ligamentous capsule thickening that has a uniform geometry and p arallel collagen fibers. The tissue was loaded axially while simultane ously stretching it around the surface of a cylinder to produce compre ssion stresses and strains. Axial stresses and strains were measured o r estimated. 3. By altering the diameter of the cylinder, given axial stresses and strains produced different levels of compression stresses and strains. It was possible to compare the neuronal response to pure uniaxial tension with the response when both axial stretching and tra nsverse compression was applied. 4. In 8 of 11 experiments, transverse compression did not significantly change the response (P > 0.05). In one experiment, the response was decreased by compression. In the othe r two experiments, the response was increased but was not a function o f the magnitude of the compressive stress. 5. Compressive strain was n ot significantly correlated with neuron response in any experiment. 6. The data do not sustain the model that the responses of stretch-sensi tive neurons are due to local compression of the afferent ending.