A medical instrument having a proximal control handle and a distal tool that are intercoupled by an elongated instrument shaft that is meant to pass internally of an anatomic body, proximal and distal movable members that respectively intercouple the proximal control handle and the distal tool with the instrument shaft, cable control means disposed between the movable members, an actuation member at the handle for controlling the distal tool through the movable members, and a coupler for selectively engaging or disengaging separable cable segments of the actuation member.