Internal structure of a robotic surgical instrument

A robotic surgical instrument has a shaft, an end effector 701, and an articulation connecting the end effector to a distal end of the shaft. Pairs of driving elements A,B, such as cables, run through the shaft to operate joints in the articulation. At least one additional element E1, such as a power cable or fibre-optic conduit, extends through the shaft to the end effector via the articulation. Both the driving elements and the additional element(s) pass through holes in a resilient barrier 706 inside the distal end of the shaft, the resilient barrier being in resilient contact with the additional element(s) so as to provide an opposing force to movement of the additional element(s) to take up slack. The barrier may be sealed to the interior wall of the shaft to inhibit the passage of insufflation gas.