actuator

noun4

1. •
   Something that actuates something else.

   • The mind is the actuator of the body.
2. •
   A usually electric device that causes a mechanical device (i.e., a mechanism) to be switched on or off. For example; an electric motor that opens and closes a valve.
3. •
   The mechanism that moves the head assembly on a disk drive.
4. •
   A relay that controls the flow of electricity.