An activation button exposed through the top of the assembly is depressed to actuate {HEAD ~ a switch assembly} which, in turn, actuates {TAIL ~ a drive mechanism} 
actuates
An activation button exposed through the top of the assembly is depressed to actuate { HEAD ~ a switch assembly } which , in turn , actuates { TAIL ~ a drive mechanism }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL