CN VII. Facial Nerve

The facial nerve is mixed nerve containing both sensory and motor components. The nerve emanates from the brain stem at the ventral part of the pontomedullary junction. The nerve enters the internal auditory meatus where the sensory part of the nerve forms the geniculate ganglion. In the internal auditory meatus is where the greater petrosal nerve branches from the facial nerve. The facial nerve continues in the facial canal where the chorda tympani branches from it the facial nerve leaves the skull via the styolomastoid foramen. The chorda tympani passes through the petrotympanic fissure before entering the infratemporal fossae. The main body of the facial nerve is somatomotor and supplies the muscles of facial expression. The somatomotor component originates from neurons in the facial motor nucleus located in the ventral pons. The visceral motor or autonomic (parasympathetic) part of the facial nerve is carried by the greater petrosal nerve. The greater petrosal nerve leaves the internal auditory meatus via the hiatus of the greater petrosal nerve which is found on the anterior surface of the petrous part of the temporal bone in the middle cranial fossa. The greater petrosal nerve passes forward across the foramen lacerum where it is joined by the deep petrosal nerve (sympathetic from superior cervical ganglion). Together these two nerves enter the pterygoid canal as the nerve of the pterygoid canal. The greater petrosal nerve exits the canal with the deep petrosal nerve and synapses in the pterygopalatine ganglion in the pterygopalatine fossa. The ganglion then gives of nerve branches which supply the lacrimal gland and the mucous secreting glands of the nasal and oral cavities. The other parasympathetic part of the facial nerve travel with the chorda tympani which joins the lingual nerve in the infratemporal fossa. They travel with lingual nerve prior to synapsing in the submandibular ganglion which is located in the lateral floor of the oral cavity. The submandibular ganglion originates nerve fibers that innervate the submandibular and sublingual glands. The visceral motor components of the facial nerve originate in the lacrimal or superior salivatory nucleus. The nerve fibers exit the brainstem via the nervus intermedius. (The nervus intermedius is so called because of its intermediate location between the eighth cranial nerve and the somatomotor part of the facial nerve just prior to entering the brain). There are two sensory (special and general) components of facial nerve both of which originate from cell bodies in the geniculate ganglion. The special sensory component carries information from the taste buds in the tongue and travel in the chorda tympani. The general sensory component conducts sensation from skin in the external auditory meatus, a small area behind the ear, and external surface of the tympanic membrane. These sensory components are connected with cells in the geniculate ganglion. Both the general and visceral sensory components travel into the brain with nervus intermedius part of the facial nerve. The general sensory component enters the brainstem and eventually synapses in the spinal part of trigeminal nucleus. The special sensory or taste fibers enter the brainstem and terminate in the gustatory nucleus which is a rostral part of the nucleus of the solitary tract.