The deep temporal nerves are branches of the anterior division of the mandibular nerve (V3), which is part of the trigeminal nerve (cranial nerve V). These nerves are responsible for supplying the temporalis muscle, which is crucial for the movement of the jaw.
Location
The deep temporal nerves originate from the mandibular nerve in the infratemporal fossa. There are typically two nerves, an anterior deep temporal nerve and a posterior deep temporal nerve, though some people may have a third (middle) branch. These nerves ascend along the infratemporal surface of the skull, running deep to the temporalis muscle. They pass between the temporalis muscle and the periosteum of the temporal bone, providing innervation as they travel upward toward the coronoid process of the mandible.
Structure and Anatomy
Origin
The deep temporal nerves arise from the anterior division of the mandibular nerve (V3), which is the third branch of the trigeminal nerve (cranial nerve V). They originate within the infratemporal fossa, a deep region located below the base of the skull and medial to the mandible.
Classification: Anterior and Posterior Branches
There are typically two main branches of the deep temporal nerves:
- Anterior Deep Temporal Nerve
- Posterior Deep Temporal Nerve
Occasionally, a third branch, the middle deep temporal nerve, may also be present, but this is less common.
Course of the Anterior Deep Temporal Nerve
The anterior deep temporal nerve is the larger of the two branches and takes a more anterior course. After originating from the mandibular nerve, it passes superiorly and laterally, running deep to the temporalis muscle. The nerve travels between the temporalis muscle and the periosteum of the temporal fossa. It innervates the anterior part of the temporalis muscle and travels superiorly toward the coronal suture of the skull, where it supplies additional muscle fibers. The anterior deep temporal nerve may also communicate with branches of the facial nerve.
Course of the Posterior Deep Temporal Nerve
The posterior deep temporal nerve takes a slightly more posterior course compared to the anterior branch. After originating from the mandibular nerve, it also ascends through the infratemporal fossa and passes deep to the temporalis muscle, but in a more posterior direction. It innervates the posterior portion of the temporalis muscle. The posterior deep temporal nerve travels closer to the mandibular condyle and the temporomandibular joint (TMJ) than the anterior branch.
Infratemporal Fossa Pathway
Both the anterior and posterior deep temporal nerves course through the infratemporal fossa, a space bounded by the lateral pterygoid muscle, the mandible, and the maxilla. This region contains several important structures, including the pterygoid muscles, the maxillary artery, and the mandibular nerve branches, all of which are closely related to the deep temporal nerves as they ascend to the temporal region.
Relationship with the Temporalis Muscle
The deep temporal nerves are closely associated with the temporalis muscle, a large fan-shaped muscle involved in elevating the mandible. Both the anterior and posterior deep temporal nerves pass beneath this muscle, running between its muscle fibers and the underlying periosteum of the temporal bone. As they ascend, they innervate the different sections of the temporalis muscle, with the anterior branch supplying the anterior portion and the posterior branch supplying the posterior portion.
Connection to Other Nerves
The deep temporal nerves have connections with other branches of the trigeminal nerve. For instance, the anterior deep temporal nerve may communicate with the zygomaticotemporal nerve, a branch of the maxillary nerve (V2). This communication serves to reinforce the sensory input from the temporal region. Additionally, the deep temporal nerves may connect with smaller branches of the facial nerve as they course toward their target regions.
Terminal Branches
As the deep temporal nerves ascend within the temporal fossa, they terminate by distributing their fibers within the temporalis muscle. These terminal branches extend into the muscle tissue to provide innervation for muscle contraction, though they remain deep to the muscle fibers, ensuring they are not exposed on the surface of the muscle.
Function
The deep temporal nerves are primarily motor nerves that innervate the temporalis muscle, playing a key role in jaw movement. Their function is crucial for mastication (chewing) and other movements involving the elevation and retraction of the mandible. Below is a detailed breakdown of their functions.
Motor Innervation to the Temporalis Muscle
The primary function of the deep temporal nerves is to provide motor innervation to the temporalis muscle, one of the major muscles involved in mastication. The deep temporal nerves ensure coordinated movement of the muscle, which is essential for:
- Elevation of the Mandible: Both the anterior and posterior deep temporal nerves activate different portions of the temporalis muscle to elevate the mandible (jaw), a critical movement for biting and chewing.
- Retraction of the Mandible: The posterior portion of the temporalis muscle, which is innervated by the posterior deep temporal nerve, is primarily responsible for the retraction of the mandible. Retraction involves pulling the jaw backward after protrusion, allowing for finer control of jaw movement during chewing.
- Closing the Jaw: The anterior fibers of the temporalis muscle, innervated by the anterior deep temporal nerve, are responsible for the powerful closure of the jaw during biting. This action is critical for breaking down food into smaller pieces during the initial phases of digestion.
Coordination of Chewing Movements
The deep temporal nerves allow for the temporalis muscle to work in coordination with other muscles of mastication, such as the masseter and pterygoid muscles, ensuring smooth and efficient chewing movements. The combined action of these muscles facilitates:
- Precise Jaw Movement: The anterior and posterior deep temporal nerves ensure that different parts of the temporalis muscle work together to produce precise and controlled movements of the jaw. This coordination is vital for chewing food in a way that avoids excessive force or damage to the teeth or temporomandibular joint (TMJ).
- Bilateral Activation: During mastication, both temporalis muscles on each side of the head must work together. The deep temporal nerves enable this bilateral activation, allowing the jaw to move symmetrically for efficient grinding and chewing.
Sensory Role (Proprioception)
Though the deep temporal nerves are primarily motor, they also contribute to proprioception, the body’s ability to sense the position and movement of muscles and joints. This is crucial for:
- Feedback for Jaw Position: Proprioceptive input from the temporalis muscle, carried by the deep temporal nerves, helps the brain determine the exact position of the mandible during chewing, allowing for adjustments in force and angle to avoid injury to the teeth or TMJ.
- Coordinated Movements during Mastication: The deep temporal nerves provide proprioceptive feedback to ensure the temporalis muscle contracts and relaxes in harmony with other muscles of mastication. This feedback helps maintain the correct pressure on food during chewing and prevents accidental injury.
Clinical Significance
The deep temporal nerves are clinically significant due to their role in jaw movement and mastication, as they innervate the temporalis muscle. Damage to these nerves can occur during surgeries involving the temporalis muscle, the infratemporal fossa, or trauma to the skull. Injury to the deep temporal nerves may result in weakness of the temporalis muscle, leading to difficulties in jaw elevation and retraction, which can impair chewing and biting.
Involvement of the deep temporal nerves in temporomandibular joint (TMJ) disorders is another clinical aspect. Dysfunction of these nerves may contribute to TMJ pain, muscle spasms, and restricted jaw movement. Additionally, these nerves are important during reconstructive surgeries or procedures involving the cranial bones, as inadvertent damage may lead to complications such as muscle atrophy or chewing difficulties. Understanding the anatomy and course of the deep temporal nerves is crucial for preventing nerve injury in surgical procedures involving the face and skull.
