Lateral pterygoid muscle

Origin and insertion

Lateral pterygoid is located deep to the temporalis and masseter muscles, spanning between the sphenoid bone and temporomandibular joint. Its muscle belly is separated by a small horizontal fissure into two heads; superior (upper) and inferior (lower).

The superior head is formed by the most superomedial fibers of the muscle. It consists of muscular slips that originate from the infratemporal crest of the greater wing of sphenoid bone.

The inferior head is much wider than the superior one. It originates from the lateral surface of the lateral pterygoid plate of sphenoid bone.

Fibers from both heads converge to course posterolaterally, in a predominately horizontal plane. The superior fibers insert into the anteromedial part of the articular capsule and articular disc of the temporomandibular joint. Whilst the inferior fibers insert into the pterygoid fovea on the neck of the condyloid process of mandible. The superior attachment onto the temporomandibular joint (TMJ) enables the muscle head to act on the superior compartment of the joint, and to produce the gliding motions of the disc and mandibular condyle. The inferior head acts on the inferior compartment of the TMJ. Facilitating the hinge-like rotation that occurs between the mandibular condyle and the inferior surface of the articular disc.

Relations

The lateral pterygoid muscle comprises the medial wall of the infratemporal fossa and is contained within the masticator space. This space is bounded by the superficial layer of the deep cervical fascia, which, at the level of the mandibular ramus, splits into superficial and deep laminae. The two laminae cover the outer surface of the masseter muscle and the deep surface of the medial pterygoid muscle, respectively. Besides the lateral pterygoid muscle, the masticator space also contains the temporalis tendon, masseter and medial pterygoid muscles and the pterygoid venous plexus, along with several structures anatomically related to the lateral pterygoid muscle.

Within this anatomical space, lateral pterygoid lies deep to the superficial head of the medial pterygoid and the tendon of temporalis muscle. While it is superficial to the deep head of medial pterygoid, sphenomandibular ligament, middle meningeal artery and mandibular nerve (CN V3).

The superior margin of the muscle is crossed by the temporal and masseteric branches of the mandibular nerve, and the lingual and inferior alveolar nerves cross its inferior margin. Of note, the maxillary artery and buccal nerve (branch of mandibular nerve) pass through the split between the superior and inferior heads of the lateral pterygoid muscle.

Innervation

The lateral pterygoid muscle is innervated by the nerve to lateral pterygoid muscle, a branch of the mandibular nerve (CN V3). In fact, there is one nerve for each head. The nerve to the superior head and lateral half of the inferior head receives fibers from the buccal nerve, itself a branch of the mandibular nerve. While the nerve to the medial half of the inferior head gets fibers directly from the mandibular nerve.

Blood supply

Vascular supply to lateral pterygoid comes from the pterygoid branches of the maxillary artery and the ascending palatine branch of the facial artery.

Function

Being a masticatory muscle, the lateral pterygoid aids in chewing and biting actions by controlling the movements of the mandible. The sphenoid attachment of the muscle is always fixed, meaning that the direction of pull is oriented towards it.

Bilateral contraction of the left and right lateral pterygoid muscles results in translation and rotation within both temporomandibular joints. The inferior heads pull the mandibular condyle anteriorly, which results in rotation of the condyle against the inferior surface of the articular disc. At the same time, the superior heads pull the articular capsule and disc in the same direction (anteriorly) to cushion the movements of the condyle. The end result is anterior translation of the disc and condyle, occurring concurrently with rotation of the condyle. Which we see as protrusion and depression of the mandible. Alternate contraction of the digastric and geniohyoid muscles finalizes the movement of opening the jaw.

The retrodiscal fat pad within the TMJ stretches and limits anterior joint translation during protrusion and depression. In fact, its inherent elasticity generates the force that initiates closing of the mouth. In jaw closing, the same translation and rotation movements occur within the TMJ, they just happen in the opposite direction. Here, the inferior heads of the muscle eccentrically contract to smoothen the posterior translation of the articular disc and mandibular condyle, counteracting the net pull of temporal and masseter muscles which draw the mandible posteriorly.

Side-to-side movements of the jaw happen when the inferior head contracts unilaterally, rotating the mandibular condyle anteromedially. The action occurs in synergy with contraction of the ipsilateral medial pterygoid muscle. This combined muscle action swings the jaw to the opposite side, and is seen, for example, when grinding food between the teeth on one side of the mouth.

Don't forget to quiz yourself on the lateral pterygoid and other masticatory muscles to consolidate your knowledge!