Static and dynamic responses of slowly adapting joint receptors

1. (1) A systems analysis approach was used to study slowly adapting knee joint receptors. Transfer functions were obtained from the receptor response to sinusoidal inputs of knee joint angle over a range of frequencies from 0.01 to 7 Hz. 2. (2) The Bode plots obtained in the dynamic studies revealed a high pass filter characteristic with a magnitude slope on the order of 5 dB/decade and a phase lead on the order of 22.5°. The gain of the transfer function was found to be influenced by both the input angle excursion and the static bias angle. 3. (3) The static angle sensitivity curves of the receptors were found to be 'bell shaped' in some cases and to increase or decrease monotonically with joint angle in other cases. 4. (4) The static sensitivity curve produced by a series of positive increments of joint angle was not the same as the static sensitivity curve produced by a series of negative increments of joint angle. Tentatively this finding is attributed to a non-Newtonian viscoelastic effect and is felt to limit the information available from a single, peripheral receptor.