A voltage stimulus applied to the drain forces current to flow through the channel coupling {TAIL ~ the drain} to {HEAD ~ the source} 
A voltage stimulus applied to the drain forces current to flow through the channel coupling { TAIL ~ the drain } to { HEAD ~ the source }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD