The trigeminal nerve is considered the largest nerve in the human body, as it is located in the posterior region of the head. The main branches of the nerve meet in the ganglion, a single large sensory root exits the ganglion and enters the brain stem at the level of the bridge, and a motor root of a smaller size exits the bridge in the immediate vicinity of the sensory root. Eyes: it controls the eye, upper eyelid, and forehead. Upper jaw: It affects the top lip, upper gums, cheek, and lower eyelid. Lower jaw: it moves the jaw, lower lip, lower gums, and some muscles that you use to chew.