The Facial Nerve

Key points

• • The facial nerve (the seventh cranial nerve) mainly moves the muscles of facial expression, and it also carries taste from the anterior two-thirds of the tongue and supplies the lacrimal, submandibular and sublingual glands.
• • It leaves the brainstem, passes through the internal acoustic meatus and a bony canal in the temporal bone, and exits the skull at the stylomastoid foramen.
• • After leaving the skull it passes through the parotid gland and splits into five branches to the face (temporal, zygomatic, buccal, mandibular and cervical).
• • Its taste and gland fibres travel with a branch called the chorda tympani, which crosses the eardrum on its way.
• • A lesion of the nerve itself (a lower motor neurone lesion) weakens the whole side of the face, including the forehead, as in Bell's palsy.
• • A lesion above the nerve in the brain (an upper motor neurone lesion) spares the forehead, because the forehead muscles get signals from both sides of the brain.