抄録
1. In the toad's sartorius muscle, two receptive fields sensitive to stretch were found to be localized on the pelvic side of the site of nerve entry and on the tibial, and they were supplied by each corresponding branch. Those two receptive zones were verified also to respond to pressure. This holds good in respect to every individual fascicule.
2. The muscle was also clarified to be innervated usually bi-segmentally from DR 9, 10, and the latter mainly innervats the sensitive zone of the tibial side, and rarely trisegmentally, with DR8 innervating the pelvic zone.
3. By separating muscle into fascicules and observing histologically, it was clarified that each fascicule does not correspond to one stretch receptor, but one receptor is encircled by some fascicules.
4. The group of these fascicules innervated by one and the same afferent fibre was called “sensory unit” in this paper, because they have an integrated character. In a whole muscle, there were estimated to exist 5 sensory units either in the pelvic or tibial sides.
5. With the sensory unit, the impulse frequency of a single afferent fibre responding to stretch of a bundle of some fascicules was equal to the mean value of the impulse frequencies obtained by stretch with the same load on each fascicule constituting the bundle. This behaviour of the spindle response was elucidated tentatively with a mechanical interaction between the fascicules.
6. On the basis of these results, the phenomena of facilitation, occlusion and postexcitatory depression of the response of a single afferent nerve fibre were discussed, and a new model for the muscle spindle was depicted.
