chapter  5
2 Pages


The facial or seventh cranial nerve (Figure 13) is the motor nerve to the muscles of facial expression. It moves the eyebrows, closes the eyelids and moves the angle of the mouth. The nerve also supplies vestigial muscles behind the ears, the posterior part of the scalp muscle, and the tiny stapedius muscle within the middle ear which is responsible for tightening the ossicular chain in response to loud external sounds. The facial nerve also provides the motor supply to the lacrimal glands, which produce tears, and the submandibular salivary glands, which produce some of the saliva within the mouth. Finally, it has a sensory component mediated through the chorda tympani nerve, which traverses the middle ear. This nerve carries the motor fibres to the submandibular salivary gland but also carries taste fibres from the anterior two-thirds of the tongue so that injury or division of the nerve may produce abnormalities of taste sensation on the same side of the tongue.