Reflex Reversal Resulting from Active Movements in the Antenna of the Rock Lobster

In the rock lobster, Palinurus vulgaris, study was made of the effect of active flexion of the J3 joint of the flagellum upon the reflex produced by passive movement of this joint. Active flexion was accompanied by activity of motoneurones to musdes assisting the movement. Passive flexion not immediately preceded by active flexion was accompanied by activation of muscles to resist the movement (resistance reflex). When the passive movement followed slow active flexion (7.5°/8), there was some activity to assist the movement. If preceded by an active flexion of high velocity (25 °/s), the assistance reflex predominated. Passive extension produced a resistance reflex that was usually facilitated by preceding active flexion. The functional significance of the reversal is discussed.