Facial nerve

General characteristics and nuclei

Anatomically, the VII pair is divided into two functional parts: the motor facial nerve and the intermediate nerve (nervus intermedius). The latter carries sensory and parasympathetic fibers.

The entire system relies on three nuclei located in the brainstem:

• Motor nucleus (nucleus nervi facialis). It lies in the central part of the pons, within the reticular formation. When viewed from the rhomboid fossa, the projection of this nucleus corresponds to the region of the facial colliculus (colliculus facialis).
• Parasympathetic nucleus (nucleus salivatorius superior). This is the superior salivatory nucleus, which belongs to the intermediate nerve and performs a secretory function.
• Sensory nucleus (nucleus tractus solitarii). The solitary tract nucleus, which also belongs to the intermediate nerve and is responsible for the perception of taste sensation.

Internal course and exit from the brain

The pathway of nerve fibers inside the brainstem has a complex topography. The roots of the facial and intermediate nerves initially run dorsally. Along their path, they loop around the nucleus of the abducens nerve, forming a characteristic bend — the genu of the facial nerve (genu nervi facialis).

After forming the genu, the fibers run toward the inferior surface of the brain. The site of their exit is located at the posterior border of the pons, lateral to the olive.

Course within the pyramid of the temporal bone

After leaving the brainstem, the facial and intermediate nerves head toward the internal acoustic meatus and enter it. Further, their path runs inside the bony facial canal (canalis nervi facialis).

It is here, within the thickness of the temporal bone, that the sensory ganglion of the intermediate nerve is formed — the geniculate ganglion (ganglion geniculi).

While in the facial canal, three important branches arise from the intermediate part:

1. Greater petrosal nerve (nervus petrosus major) — carries parasympathetic fibers that ensure the secretion of the lacrimal gland.
2. Nerve to the stapedius (nervus stapedius) — innervates the muscle of the same name in the tympanic cavity.
3. Chorda tympani (chorda tympani) — a mixed branch that provides taste sensation to the anterior two-thirds of the tongue, and also delivers parasympathetic fibers to the salivary glands.

Extracranial branches and parotid plexus

The main trunk of the facial nerve leaves the cranial cavity through the stylomastoid foramen (foramen stylomastoideum). Immediately after exiting, even before plunging into the tissue of the parotid salivary gland, it gives off several muscular branches:

• Posterior auricular nerve (nervus auricularis posterior);
• Digastric branch (ramus digastricus);
• Stylohyoid branch (ramus stylohyoideus).

Next, the nerve penetrates the thickness of the parotid gland, where it divides into multiple branches forming the parotid plexus (plexus parotideus). This plexus gives rise to five main groups of branches that diverge in a fan-like manner across the face and innervate the facial muscles of expression:

• Temporal branches (rami temporales);
• Zygomatic branches (rami zygomatici);
• Buccal branches (rami buccales);
• Marginal mandibular branch (ramus marginalis mandibulae);
• Cervical branch (ramus colli).

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Topography of the facial canal in the pyramid of the temporal bone
• Functional anatomy of the intermediate nerve
• Connection of the facial nerve with the parotid salivary gland
• Detailed distribution of the terminal branches of the parotid plexus

Other topics in the "PNS" section

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