The trigeminal nerve is the largest cranial nerve and has three main branches - the ophthalmic, maxillary, and mandibular nerves. It arises from the semilunar ganglion and has both sensory and motor components. The ophthalmic nerve innervates the eye and forehead. The maxillary nerve innervates the midface, upper teeth, and sinuses. The mandibular nerve has both anterior and posterior divisions which innervate the lower face, scalp, ear, and lower teeth.