The lacrimal nerve is a branch of the ophthalmic nerve, which is part of the trigeminal nerve (cranial nerve V). It primarily provides sensory innervation to the skin of the upper eyelid and the conjunctiva, which is the membrane covering the eye's surface. Additionally, it carries parasympathetic fibers that help stimulate tear production from the lacrimal gland. This nerve also plays a role in the sensation of the lateral aspect of the forehead and the scalp. It is important for maintaining eye health by ensuring proper moisture levels through tear secretion, which protects the eye from dryness and irritation.