Answer:
The trigeminal nerve is the largest cranial nerve and gives origin to three major branches:
The ophthalmic nerve is sensory. Near its origin it gives off a meningeal branch, soon divides into lacrimal, frontal and nasociliary branches which enter the orbit through the superior orbital fissure. The frontal nerve continues forward between the orbital roof and the levator palpebrae superioris and splits into the supraorbital and supratrochlear nerves, to innervate the forehead and scalp almost to the level of the lambdoid suture. The nasociliary nerve ends by dividing into the anterior ethmoidal and infratrochlear nerves. The lacrimal nerve runs above the upper border of the lateral rectus muscle to supply several branches to the lacrimal gland and adjacent conjunctiva.
The maxillary nerve is also sensory. It also gives off a small meningeal branch, then leaves the skull through the foramen rotundum, enters the pterygopalatine fossa and then the orbit via the inferior orbital fissure. Finally, it traverses the infraorbital groove as the infraorbital nerve and emerges on the face to supply the lower eyelid, nasal alae and upper lip. In the pterygopalatine fossa, the maxillary nerve gives off the zygomatic nerve, and continues to form the superior alveolar nerves which descend in the wall of the maxillary sinus and supply the upper teeth and gums.
The mandibular nerve has a large sensory and a small motor component. The two parts leave the skull through the foramen ovale and then lie between the lateral pterygoid and tensor veli palatini muscles. There is a meningial branch that reenters the skull via the foramen spinosum. The posterior part of the nerve is mainly sensory, and divides into the auriculotemporal, lingual and inferior alveolar nerves. The auriculotemporal nerve supplies the skin and fascia of the temple, temporomandibular joint, external acoustic meatus, tympanic membrane, skin of the tragus and part of the helix. The lingual nerve supplies sensation to the anterior 2/3 tongue and floor of mouth. The inferior alveolar nerve enters the mandibular foramen and canal to supply the lower teeth and gums and continues as the mental nerve exiting through the mental foramen. Just before entering the mandibular canal, the nerves gives off its only motor branch to the mylohyoid muscle and anterior belly of the digastric. The motor root fibers supply the muscles derived from the first branchial (mandibular) arch – the muscles of mastication (medial and lateral pterygoid, masseter, temporal), mylohyoid, anterior belly of the digastric, tensor veli palatini, and tensor tympani (8 muscles).