Topography and Course
- Origin: Arises near the foramen ovale, at the same level as the inferior alveolar nerve.
- Interpterygoid space: Passes downward and medially between the lateral and medial pterygoid muscles. It lies within or deep to the interpterygoid fascia, anterior to the inferior alveolar nerve.
- Maxillary/Mandibular region: Descends between the inner surface of the mandibular ramus and the medial pterygoid muscle.
- Floor of the mouth: Runs superior to the submandibular gland along the lateral surface of the hyoglossus muscle. It then loops inferiorly and laterally around the submandibular duct before entering the lateral surface of the tongue.
Clinical Note: The nerve lies very superficially in the mylohyoid groove.
Connection with the Chorda Tympani and Autonomic Ganglia
At the upper border of the medial pterygoid muscle, the chorda tympani (chorda tympani), which enters through the petrotympanic fissure, joins the lingual nerve. It contains fibers from the facial nerve:
- Taste fibers — to the taste buds of the anterior 2/3 of the tongue.
- Secretomotor parasympathetic fibers — to the submandibular and sublingual ganglia.
The lingual nerve is connected to the submandibular ganglion (gangl. submandibulare), and its branch, the sublingual nerve, connects to the sublingual ganglion (gangl. sublinguale). Postganglionic parasympathetic secretomotor fibers proceed from these ganglia to the salivary glands.
Branches and Innervation Zones
Within the oral cavity, the nerve gives off the following branches:
- Branches of the isthmus of the fauces — to the mucous membrane of the fauces.
- Sublingual nerve (n. sublingualis) — to the floor of the mouth and the sublingual salivary gland.
- Lingual branches — to the anterior 2/3 of the tongue and the lingual gingiva of the mandibular teeth.
Gustatory Pathway
Afferent impulses from the taste buds of the anterior tongue follow this pathway:
- Travel within the lingual nerve.
- Enter the chorda tympani.
- Cell bodies of the first-order sensory neurons are located in the geniculate ganglion (ganglion geniculi).
- Proceed within the nervus intermedius to the brainstem and terminate in the nucleus of the solitary tract (nucleus tractus solitarii).
Fibers then cross the midline and ascend to the thalamus via the medial lemniscus. Axons of thalamic neurons terminate in the inferior part of the postcentral gyrus and the insula.
Clinical Significance and Anesthesia
The lingual nerve is typically anesthetized during inferior alveolar nerve block (mandibular block).
- Isolated anesthesia: Performed in the mylohyoid groove. The tongue is retracted with a spatula, and the needle is inserted into the mucosa at the level of the middle of the crown of the third mandibular molar. 2 mL of local anesthetic is injected.
- Access from the submandibular region: To block the lingual nerve, the needle is advanced along the medial surface of the mandibular ramus for an additional 1 cm superiorly after an inferior alveolar nerve block.
- Bersche-Dubov subzygomatic approach: The needle is advanced horizontally beneath the zygomatic arch toward the midline for 3–3.5 cm. The target zone lies between the heads of the lateral pterygoid muscle, where the inferior alveolar and lingual nerves lie in close proximity.
- Ageusia: Total loss of taste resulting from cranial nerve lesions is extremely rare because taste fibers are distributed across three cranial nerve pairs: VII, IX, and X.