A modular shaft assembly is disclosed. The modular shaft assembly includes one or more inputs configured to receive input motions from a surgical instrument system, such as a handle, for example. The shaft assembly further includes one or more on-board inputs configured to generate input motions. The input motions received and generated by the shaft assembly are transferrable to an end effector of the shaft assembly to perform various functions at the end effector. The end effector can include a staple cartridge and a firing member which is movable between a proximal position and a distal position to eject staples from the staple cartridge. The end effector can include a plurality of jaw members and the firing member can comprise camming members which are configured to position the jaw members relative to one another.