The facial nerve is the seventh of the Twelve Cranial Nerves. The efferent fibers are either motoric fibers or parasympathetic fibers, while the afferent fibers are sensory fibers. Together these branches innervate the muscles of facial expression. The word afferent means toward the centre, as in from a peripheral area of a limb to the central nervous system. The word efferent is the opposite of afferent, meaning away from the centre and toward the periphery; when the stimulus is carried back to the brain from a peripheral area.
The pathway for the efferent fibers of the main branch of the facial nerve before and after its division is the following (from the initiation in the brain to the termination in the periphery):
- Note: this article will indicate the pathway of the facial nerve and its branches and not where individual fibers run in postganglionic bundles of other nerves!
- The facial nucleus is situated in the vestibular area of the brainstem and contributes the motoric fibers to the facial nerve bundle.
- The superior salivary nucleus sits behind the medullary striae and emits the parasympathetic fibers into the facial nerve via the intermediate nerve.
- The facial nerve and the intermediate nerve run in the internal acoustic meatus and become one at the geniculate ganglion.
- From the geniculate ganglion the greater petrosal nerve runs with only parasympathetic fibers and is joined by the Deep petrosal nerve before it becomes the nerve of the pterygoid canal.
- This nerve synapses on the otic ganglion and from there onwards the facial nerve Fibers run in other nerve bundles.
- The larger bundle which exits the geniculate ganglion continues as the facial nerve with both motoric and parasympathetic fibers.
- The parasympathetic fibers branch off before exiting the stylomastoid foramen and give the stapedius nerve, they connect with the tympanic plexus (to which the glossopharyngeal nerve – CN IX contributes parasympathetic fibers via the tympanic nerve) as well as the caroticotympanic nerve (from the internal carotid plexus), they run into the minor petrosal nerve and synapse on the otic ganglion.
- Meanwhile the main bundle of the facial nerve exits the stylomastoid foramen and gives the following branches: the posterior auricular nerve which branches into the auricular nerve and the occipital nerve, the stylohyoid nerve branch and the digastric nerve branch, the marginal mandibular branch which gives the neck branch, the buccal branch and the zygomatic branch which have an anastomosis and finally the temporal branch.
- In order to clarify this topic, the five main branches of the facial nerve are: auricular, marginal mandibular, buccal, zygomatic and temporal.
- These branches innervates all of the muscles of facial expression collectively listed here from cranial to caudal: the occipitofrontal muscle, the orbicularis oculi muscle, the corrugator supercili muscle, the major and minor zygomatic muscles, the procerus muscle, the levator labii superioris muscle, the alaquae nasi muscle, the levator angulis oris muscle, the nasalis muscle, the depressor septi nasi muscle, the orbicularis oris muscle, the depressor labii inferioris, the mentalis muscle, the buccinator muscle and the platysma muscle.
The pathway for the afferent fibers of the main branch of the facial nerve before and after its division is the following (from the initiation in the periphery to the termination in the brain):
- The sensory afferent fibers course back through the smaller branches from the musculature of the tongue which they innervate in the anterior two thirds and produce a sense of taste, to the lingual nerve.
- Upon passing the submandibular ganglion they then run together in the chorda tympanii with the efferent parasympathetic fibers of the superior salivary nucleus.
- The fibers branch into the main facial nerve and synapse on the geniculate ganglion.
- They then run in the intermediate nerve and terminate in the nucleus of the solitary tract which is situated in the brainstem.