Characteristics of the receptors in the isolated capsule of the hip in the cat.

The properties of the afferent fibres from the capsule of the hip joint have been studied in the cat in situ, in relations to joint rotation, and in an isolated capsule preparation which was opened and stretched directly with an actuator. In situ two types of afferent fibres were found, those having a full range of sensitivity and others having only a limited range in response to the joint rotation. When studied in isolated tissue the afferent fibres of the capsule were uniform in threshold and sensitivities, and no full range receptors were found. We conclude that the full range receptors which enter the articular nerve of the hip are spindle afferents and not capsule receptors. On the basis of these and previous results in animals and man the role of joint receptors in kinaesthesia and position sense is discussed.