Characteristics of the sensory discharge of the muscle spindle in Xenopus laevis

Single isolated muscle spindles from the toad Xenopus laevis were studied with regard to their response to different levels of steady stretch and to their response to small precisely controlled length variations. The spectral distribution of the applied variations was designed to be essentially uniform in the region between 0.04 Hz and a number of selectable upper limits none exceeding 20 Hz. The results obtained relate to the statistics of receptor discharge intervals, to receptor transfer functions and to the coding and decoding of sensory information. The conclusion is that spectral analysis techniques can be used to clarify many aspects of muscle spindle behavior.