The lingual nerve is a sensory nerve that is part of the mandibular division (V3) of the trigeminal nerve (cranial nerve V). It primarily provides sensation to the anterior two-thirds of the tongue. It is important for detecting tactile stimuli, pain, and temperature.
Location
The lingual nerve is located in the oral cavity, running along the inner side of the mandible (lower jaw). It descends between the medial pterygoid muscle and the mandible and then passes forward and upward toward the tongue. It lies close to the lower third molar teeth before moving toward the floor of the mouth.
Structure and Anatomy
Origin
The lingual nerve originates from the posterior division of the mandibular nerve, which is the third division (V3) of the trigeminal nerve (cranial nerve V). It is purely sensory and arises within the infratemporal fossa.
Course in the Infratemporal Fossa
After originating from the mandibular nerve, the lingual nerve travels through the infratemporal fossa, located behind the maxilla (upper jaw). In this region, the lingual nerve runs parallel and slightly anterior to the inferior alveolar nerve, another branch of the mandibular nerve.
Relationship with the Chorda Tympani
In its course through the infratemporal fossa, the lingual nerve is joined by the chorda tympani nerve, a branch of the facial nerve (cranial nerve VII). The chorda tympani merges with the lingual nerve and carries special sensory fibers (for taste) and parasympathetic fibers. However, these are not components of the lingual nerve proper, as it remains primarily a sensory nerve.
Medial Pterygoid and Mandibular Relation
The lingual nerve descends along the medial side of the mandible and passes between the medial pterygoid muscle and the ramus of the mandible. Here, it is in close relation to the inferior alveolar nerve, though the lingual nerve takes a more medial path.
Proximity to the Mandibular Third Molar
As it continues anteriorly, the lingual nerve passes near the medial surface of the mandibular third molar. In this region, it lies close to the surface of the oral mucosa and is vulnerable to injury during dental procedures, such as wisdom tooth extractions.
Path in the Oral Cavity
The lingual nerve runs beneath the mucosa of the floor of the mouth, medial to the submandibular gland and lateral to the base of the tongue. As it progresses forward, it lies superficial, just beneath the mucosa, making it accessible during surgical interventions.
Terminal Branches
Toward the anterior portion of the oral cavity, the lingual nerve divides into multiple smaller branches that supply sensation to the anterior two-thirds of the tongue and adjacent structures. These branches travel in the submucosal tissue, distributing themselves across the surface of the tongue and the floor of the mouth.
Function
The lingual nerve plays a crucial role in sensory innervation within the oral cavity, particularly the tongue and surrounding structures. Below are the primary functions of the lingual nerve, categorized into its sensory roles.
General Sensation of the Anterior Two-Thirds of the Tongue
The most prominent function of the lingual nerve is to provide general sensory innervation to the anterior two-thirds of the tongue. This includes the perception of:
- Touch: The nerve transmits tactile stimuli from the surface of the tongue, allowing the sensation of textures and pressure.
- Pain: The lingual nerve is responsible for detecting painful stimuli such as cuts, burns, or injuries within the anterior part of the tongue.
- Temperature: It helps sense variations in temperature, such as when consuming hot or cold food and beverages.
It does not carry taste fibers on its own, but it conveys general sensory input related to touch and pain.
Mucosal Sensation of the Floor of the Mouth
In addition to the tongue, the lingual nerve also innervates the mucosa on the floor of the mouth. This region includes the mucosal tissue that lines the area beneath the tongue, which is crucial for detecting sensations related to foreign bodies or trauma, such as burns or cuts caused by food particles or dental tools.
Mucosal Sensation of the Inner Surface of the Gingiva (Lower Jaw)
The lingual nerve provides sensory input to the inner surface of the gingiva (gums) on the lower jaw. This includes the mucosa around the mandibular teeth, particularly near the molars. This function helps in the detection of irritation or injury to the gums from dental issues, such as gum disease or dental procedures.
Relay of Taste Sensation via the Chorda Tympani
While the lingual nerve does not directly transmit taste sensations, it plays an essential role in carrying fibers from the chorda tympani nerve, a branch of the facial nerve (cranial nerve VII), after they join the lingual nerve in the infratemporal fossa. The chorda tympani fibers provide:
Taste Sensation: These fibers relay taste from the anterior two-thirds of the tongue to the brain. Although this taste function is facilitated by the chorda tympani, the lingual nerve acts as a conduit for these fibers, carrying them through its course before they separate to reach their respective targets.
Parasympathetic Innervation via the Chorda Tympani
The lingual nerve, in conjunction with the chorda tympani, carries parasympathetic fibers that innervate the submandibular and sublingual salivary glands. These fibers do not originate from the lingual nerve itself but are carried along its pathway. The parasympathetic fibers contribute to:
Salivary Gland Secretion: The stimulation of the submandibular and sublingual glands, aiding in the production and release of saliva. The lingual nerve acts as a conduit for these fibers as they traverse to their target organs.
Clinical Significance
The lingual nerve is of considerable clinical importance due to its close anatomical relationship with oral structures, particularly during dental procedures. It is especially vulnerable to injury during surgical interventions such as wisdom tooth extractions, dental implant placements, or mandibular surgeries. Damage to the lingual nerve can lead to lingual nerve injury, resulting in loss or alteration of sensation (numbness, tingling, burning) in the anterior two-thirds of the tongue, floor of the mouth, or inner gums. In severe cases, permanent sensory deficits, including dysesthesia (painful abnormal sensation), may occur.
In addition, since the lingual nerve carries taste fibers from the chorda tympani, injury may also cause loss of taste in the anterior two-thirds of the tongue. Early diagnosis and treatment of lingual nerve injury are crucial to optimize recovery and minimize long-term damage.
