A surgical instrument comprises a surgical end effector operable to effect a surgical procedure when actuated, and an actuation assembly operable to actuate the surgical end effector. The actuation assembly has a part (60, 1060, 102) operable to move between a starting position and an actuated position in which the part actuates the surgical end effector, an electrically-powered motor (1520), a transmission mechanically connecting the motor (1520) to the part (60, 1060, 102) and being operable to selectively displace the part (60, 1060, 102) to the starting position, the actuated position, and at least one point between the starting position and the actuated position when the motor (1520) is operated, and a manual release (1800) mechanically coupled to the transmission to selectively interrupt the transmission and, during interruption, displace the part (60, 1060, 102) towards the starting position independent of operation of the motor (1520).