The mandibular nerve is the third branch (V3) of the trigeminal nerve (cranial nerve V). It is a mixed nerve, carrying both sensory and motor fibers. The sensory component provides sensation to the lower face, including the lower lip, chin, and teeth, while the motor component controls the muscles involved in mastication.
Location
The mandibular nerve exits the cranial cavity through the foramen ovale of the sphenoid bone. After emerging from the foramen, it enters the infratemporal fossa, a space beneath the skull, where it divides into multiple branches. These branches extend to various structures in the lower face, including the muscles of mastication, the lower jaw, and the oral cavity. The nerve is positioned between the pterygoid muscles and is closely associated with the mandibular ramus as it descends toward the lower jaw.
Structure and Anatomy
Origin
The mandibular nerve (V3) is the third and largest branch of the trigeminal nerve (cranial nerve V), which has three divisions: ophthalmic (V1), maxillary (V2), and mandibular (V3). The mandibular nerve is a mixed nerve, containing both sensory and motor fibers. It originates in the trigeminal ganglion, located in the middle cranial fossa, where the sensory and motor roots of the trigeminal nerve merge.
Exit from the Skull: Foramen Ovale
The mandibular nerve exits the cranial cavity through the foramen ovale, a large opening in the sphenoid bone. This passage allows the nerve to descend into the infratemporal fossa, where it divides into its various sensory and motor branches.
Division in the Infratemporal Fossa
Once the mandibular nerve passes through the foramen ovale, it enters the infratemporal fossa, a deep space located beneath the skull and medial to the mandible. In this fossa, the mandibular nerve divides into two main divisions:
- Anterior Division: Primarily motor, with one sensory branch.
- Posterior Division: Primarily sensory, with one motor branch.
Branches of the Mandibular Nerve
Anterior Division
The anterior division consists mostly of motor branches that innervate the muscles of mastication, with one sensory branch:
- Masseteric Nerve: This motor branch innervates the masseter muscle, passing through the mandibular notch.
- Deep Temporal Nerves (Anterior and Posterior): These motor nerves supply the temporalis muscle.
- Lateral Pterygoid Nerve: This motor branch innervates the lateral pterygoid muscle, which is involved in jaw movement.
- Buccal Nerve: The only sensory branch of the anterior division, the buccal nerve provides sensory innervation to the skin of the cheek and the mucosa of the inner cheek.
Posterior Division
The posterior division contains primarily sensory fibers, but also has a motor branch:
- Auriculotemporal Nerve: This sensory branch innervates the skin of the temple and the external ear. It also carries parasympathetic fibers to the parotid gland.
- Lingual Nerve: A sensory nerve that provides sensation to the anterior two-thirds of the tongue and the floor of the mouth.
- Inferior Alveolar Nerve: This sensory branch supplies sensation to the lower teeth and gums. Before entering the mandibular foramen, it gives off a motor branch:
- Nerve to Mylohyoid: A motor branch that innervates the mylohyoid muscle and the anterior belly of the digastric muscle.
The inferior alveolar nerve continues through the mandibular canal and exits via the mental foramen as the mental nerve, providing sensation to the chin, lower lip, and anterior gingiva.
Course of the Mandibular Nerve in the Infratemporal Fossa
Within the infratemporal fossa, the mandibular nerve travels between the medial and lateral pterygoid muscles. It is closely related to other important structures in this region, including the maxillary artery and the pterygoid venous plexus. The branches of the nerve fan out to reach their target areas, innervating the muscles of mastication and providing sensory input to the lower face, jaw, and oral cavity.
Motor and Sensory Roots
- Motor Root: The motor fibers of the mandibular nerve originate in the motor nucleus of the trigeminal nerve in the brainstem. These fibers join the sensory root after the nerve passes through the foramen ovale, and they innervate the muscles of mastication (masseter, temporalis, medial pterygoid, lateral pterygoid), as well as the mylohyoid and anterior belly of the digastric muscle.
- Sensory Root: The sensory fibers originate from the trigeminal ganglion and are responsible for conveying sensation from the skin of the lower face, the anterior two-thirds of the tongue, the mucous membranes of the oral cavity, and the teeth.
Terminal Branches
The mandibular nerve’s terminal branches extend to different areas of the lower face and jaw, supplying sensory and motor fibers to various structures:
- Mental Nerve: A terminal branch of the inferior alveolar nerve, it exits through the mental foramen to innervate the skin of the chin and lower lip.
- Lingual Nerve: Extends toward the tongue, innervating its anterior portion.
- Auriculotemporal Nerve: Reaches the side of the face, providing sensory innervation to the scalp, ear, and temple area.
Function
The mandibular nerve (V3), the third branch of the trigeminal nerve (cranial nerve V), serves as a mixed nerve with both motor and sensory functions. Its diverse role involves innervating the muscles of mastication and providing sensory innervation to the lower face, jaw, tongue, and oral cavity. Below are its functions categorized in detail.
Motor Functions
The mandibular nerve’s motor fibers supply muscles primarily involved in mastication (chewing), as well as other accessory muscles in the head and neck region.
Innervation of Muscles of Mastication
The mandibular nerve provides motor innervation to the four muscles responsible for chewing, enabling movements such as jaw elevation, depression, protrusion, and side-to-side grinding. These muscles include:
- Masseter Muscle: The masseteric nerve, a branch of the mandibular nerve, innervates the masseter muscle, which is responsible for elevating the mandible to close the jaw during chewing and biting.
- Temporalis Muscle: The deep temporal nerves, branches of the mandibular nerve, innervate the temporalis muscle. This muscle elevates and retracts the mandible, assisting in closing the mouth and grinding food.
- Medial Pterygoid Muscle: The medial pterygoid nerve innervates this muscle, which assists in elevating the mandible and moving the jaw side-to-side for grinding food.
- Lateral Pterygoid Muscle: The lateral pterygoid nerve innervates this muscle, responsible for depressing the mandible (opening the jaw) and protruding the jaw forward.
Innervation of Accessory Muscles
In addition to the muscles of mastication, the mandibular nerve also supplies motor innervation to the following muscles:
- Mylohyoid Muscle: Via the nerve to the mylohyoid, the mandibular nerve innervates this muscle, which assists in elevating the floor of the mouth and the hyoid bone during swallowing.
- Anterior Belly of the Digastric Muscle: The same nerve that supplies the mylohyoid also innervates the anterior belly of the digastric muscle, which helps in depressing the mandible (opening the mouth) and elevating the hyoid bone.
Sensory Functions
The sensory fibers of the mandibular nerve are responsible for conveying sensation from various regions of the lower face, jaw, and oral cavity, including the teeth, gums, tongue, and skin. This sensory input involves touch, pain, temperature, and proprioception.
Sensation to the Lower Face and Jaw
The mandibular nerve provides sensory innervation to the skin over the lower face, jaw, and chin through its various branches:
- Inferior Alveolar Nerve: This branch supplies the lower teeth, providing sensory input for pain, pressure, and temperature. After passing through the mandibular canal, it emerges as the mental nerve, which innervates the skin of the chin, lower lip, and anterior gingiva.
- Buccal Nerve: This sensory branch supplies the skin and mucosa of the cheek and the buccal gingiva of the lower molars, allowing for sensory feedback from the inside of the mouth and external cheek area.
- Auriculotemporal Nerve: This nerve provides sensory innervation to the skin of the temple, external ear, and scalp. It also conveys sensory input from the temporomandibular joint (TMJ), detecting pain and proprioception in the jaw joint.
Sensation to the Oral Cavity and Tongue
The mandibular nerve supplies sensory input to various structures within the oral cavity:
- Lingual Nerve: This nerve provides general sensory innervation to the anterior two-thirds of the tongue and the floor of the mouth. It transmits sensations of touch, temperature, and pain from the tongue, helping detect food textures and potential oral injuries.
- Teeth and Gums: Through the inferior alveolar nerve and its branches, the mandibular nerve provides sensory feedback from the lower teeth and gums, detecting pain from tooth decay, injury, or dental procedures.
Proprioception of Jaw Movement
The mandibular nerve carries proprioceptive fibers that provide the brain with information about the position of the mandible, helping coordinate the movements of chewing and speaking. This proprioception is essential for maintaining proper bite force, jaw alignment, and movement during mastication.
Reflex Actions
The mandibular nerve plays an important role in two reflex actions:
Jaw-Jerk Reflex
The jaw-jerk reflex is a monosynaptic reflex that involves the masseter muscle and the mandibular nerve. When the mandible is tapped, the proprioceptive fibers in the masseter muscle are activated and the masseter contracts reflexively. This reflex helps protect the jaw and teeth from damage by stabilizing the mandible during sudden movements.
Gag Reflex
The lingual nerve (a branch of the mandibular nerve) contributes to the sensory aspect of the gag reflex by providing sensation to the anterior part of the tongue and floor of the mouth. If something irritates these areas, it can trigger the gag reflex, which is important for preventing choking or the ingestion of harmful substances.
Clinical Significance
The mandibular nerve (V3) is clinically significant due to its motor and sensory functions in the lower face, oral cavity, and muscles of mastication. Injury or compression of the mandibular nerve can result in mandibular nerve neuropathy, leading to symptoms such as weakness in the muscles of mastication, difficulty chewing, and jaw deviations during movement. Sensory disturbances, including numbness, tingling, or pain in the lower lip, chin, and teeth, can also occur, particularly with trauma, dental procedures, or tumors.
Damage to the nerve, especially during surgical procedures like third molar extractions or mandibular surgeries, can result in complications such as lingual nerve injury, leading to sensory loss in the tongue. Additionally, mandibular nerve involvement in temporomandibular joint (TMJ) disorders may contribute to pain and dysfunction of the jaw joint. Understanding its anatomy is crucial in managing conditions like trigeminal neuralgia, where the mandibular nerve can be affected, causing severe facial pain.
