Medial Pterygoid Muscle
- The medial and lateral pterygoid muscles are occupants of the infratemporal fossa.
- To see them, it is necessary to remove a portion of the ramus of the mandible.
- The medial pterygoid muscle is almost a mirror image of the masseter muscle. It is rhomboidal and runs practically in the same direction on the inner surface of the mandibular ramus.
- Origin:
- The origin is fleshly from the medial aspect of lateral pterygoid plate of sphenoid bone.
- A few fibers arise from the maxillary tuberosity.
- Insertion:
- The fibers run downward, backward, and slightly laterally to insert into the medial aspect of the mandibular ramus.
- The insertion extends from just below the mylohyoid groove to the inferior border and angle of the mandible.
- Its tendinous insertion joins that of the masseter muscle at the angle of the mandible to form a common sling. The sling allows the masseter on the lateral surface of the mandibular ramus and the medial pterygoid on the medial surface to act in concert as powerful elevators of the jaw.
- Actions:
- Elevation (Bilateral): acts with the masseter muscle as a powerful elevators of the mandible
- Protrusion (Bilateral): The insertion of the muscle is posterior to its origin and, therefore, the right & left muscle aid in protruding the mandible.
- Contralateral excursion (Unilateral): The insertion of the medial pterygoid is lateral to its origin, allowing the muscle fibers to move the mandible to the opposite side in lateral movements.
- Blood Supply:
- Second Branch of maxillary artery
- Nerve Supply:
- Undivided Branch of mandibular nerve of Trigeminal Nerve (V Cranial Nerve)
- Examination:
- Palpated intraorally, lingual to the mandibular ramus
Lateral Pterygoid Muscle
- The lateral pterygoid muscle is almost triangular in shape with two distinct heads, inferior and superior, each with contrasting functions.
- It is the only muscle of the four muscles of mastication to occupy primarily a horizontal position.
- Origin:
- The inferior head: arises as fleshy fibers from the lateral aspect of the lateral pterygoid plate of sphenoid bone.
- The superior head originates as fleshy fibers from the inferior aspect of the greater wing of sphenoid bone, which forms the roof of the infratemporal fossa.
- Insertion:
- The inferior head: passes backward, upward, and slightly laterally to insert into the pterygoid fovea on the anterior aspect of the condylar neck.
- The superior head: passes posteriorly and somewhat laterally to insert into the articular capsule and the articular disc and anterior aspect of the condylar neck.
Most of the inserting fibers blend with the tendon of the inferior head to insert into the pterygoid fovea of the condylar neck.
A smaller number of deeper or more medial fibers insert into the medial aspect of the capsule and disc. - Actions:
- Inferior head:
- Protrusion (Bilateral): The inferior lateral pterygoids acting together are the prime protractors of the mandible.
- Depression (Bilateral)
- Contralateral excurion (Unilateral): The insertion of the lateral pterygoid is lateral to its origin, and thus the lateral pterygoid muscle acting singly moves the mandible to the opposite side.
- Superior head:
- The superior lateral pterygoids are inactive during opening. They are active, however, during mandibular elevation or closing along with the temporalis, masseter, and medial pterygoid muscles.
- The superior heads are particularly active when the teeth, upon closure, encounter resistance such as a bolus of food. Closure on resistance is termed the power stroke, and the superior lateral pterygoid play an active role in the power stroke.
- Superior head of lateral pterygoid is activated during mandibular retrusion (Providing controlled movement)
- Blood Supply:
- Second Branch of maxillary artery
- Nerve Supply:
- Anterior division of mandibular nerve of Trigeminal nerve (V Cranial nerve)
- Examination:
- Lower head:
- By placing a little finger up behind the maxillary tuberosity (The pterygoid sign)
- Examin the lateral pterygoid muscle, which cannot readily be palpated, indirectly by asking the patient to open the jaw against resistant and to move the jaw to one side while applying a gentle resistance force.
Accessory muscles of mastication:
Other muscles that are active in mastication include the suprahyoid and infrahyoid muscles of the neck. Both groups of muscles are active in helping to depress the mandible.
Other muscles that are active in mastication include the suprahyoid and infrahyoid muscles of the neck. Both groups of muscles are active in helping to depress the mandible.
