HYPOTHESIS FOR A PRESSURE-SENSITIVE MECHANISM IN MUSCLE SPINDLES.

The suggestion is made that the mammalian muscle spindle may serve in part as a pressure sensor. Pressure acting nonuniformly on the spindle would express the intracapsular fluid distad, thus elongating the capsule. "Intracapsular fibers," those intrafusal muscle fibers inserting into the capsule, would be lengthened, whereas "percapsular fibers" passing beyond the capsule would be relatively unaffected. Since "flower-spray" terminals are preferentially associated with the smaller intrafusal fibers, they would chiefly be concerned with the pressure sensing mechanism. Observations in support of this hypothesis are given.