Dynamic analysis of muscle spindle endings in the cat using length changes of different length-time relations.

Primary and secondary muscle spindle endings in the ankle extensors of the cat were studied in response to length changes of ramp, triangular wave, sine wave and parabolic wave form with the intention of finding the most suitable input signal for an extensive dynamic analysis of the spindle during constant fusimotor input. In dynamic tests the spindle endings were not found to obey linear length-response transfer functions; no support for a power function relation could be obtained.Sine wave analysis was therefore not considered suitable for the purpose of determining the transfer functions.Attention was directed towards the use of step changes of velocity and of acceleration of length changes.No evidence for a specific sensitivity to acceleration was found in responses to ‘parabolic’ length changes.Responses interpreted as due to mechanical properties in the spindle elements resembling ‘stiction’ were obtained when ‘ramp’ length changes were applied.These effects were largely avoided when recurring ‘triangular’ length changes of constant velocity were used.It is concluded that the dynamic analysis might be adequately performed by subjecting the musscle spindles to periodically recurring length changes of triangular wave form giving step changes in velocity.