Medial pterygoid muscle
Medial pterygoid is a thick quadrilateral muscle that connects the mandible with maxilla, sphenoid and palatine bones. It belongs to the group of masticatory muscles, along with the lateral pterygoid, masseter and temporal muscles.
Medial pterygoid muscle consists of two heads; superficial and deep. Although having different origins, both heads insert on the inner surface of mandible, creating an axis for a strong pull of this bone. Unilateral contraction of medial pterygoid causes rotation of mandible, while bilateral contraction elevates and protrudes it. In synergy with other masticatory muscles, these actions facilitate chewing.
Superficial part: Tuberosity of maxilla, Pyramidal process of palatine bone;
Deep part: Medial surface of lateral pterygoid plate of sphenoid bone
|Insertion||Medial surface of ramus and angle of mandible|
Bilateral contraction - Elevates and protrudes mandible
Unilateral contraction - Medial movement (rotation) of mandible
|Innervation||Medial pterygoid nerve (of mandibular nerve (CN V3)|
|Blood supply||Pterygoid branches (maxillary artery, buccal artery, facial artery)|
This article will discuss the anatomy of the medial pterygoid muscle including its attachments, neurovascular supply, relations and functions.
- Origin and insertion
- Blood supply
- Clinical significance
Origin and insertion
Medial pterygoid muscle consists of two heads; superficial and deep, that are separated by the inferior head of lateral pterygoid muscle at their origin.
- The deep part forms the bulk of the muscle and arises from the medial surface of the lateral pterygoid plate of sphenoid bone and from the pyramidal process of the palatine bone.
- The smaller, superficial part arises from the maxillary tuberosity and the grooved surface of the pyramidal process of palatine bone.
As these two sets of fibers descend posterolaterally, they insert to the triangular impression found on the medial surface of the ramus and angle of mandible. The fibers attach via a strong tendinous lamina that extends from the mandibular foramen superiorly, to the mylohyoid groove anteroinferiorly.
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Medial pterygoid muscle is located in the infratemporal fossa lying deep to masseter and temporalis muscles and medial to lateral pterygoid muscle.
The outer surface of the muscle lies against the inner surface of mandible, from which it is separated by the lateral pterygoid muscle, sphenomandibular ligament, maxillary artery, mandibular nerve and its lingual and inferior alveolar branches. Near its insertion, the outer surface of the medial pterygoid muscle is related to the process of the parotid gland.
The inner surface of the muscle is in relation to tensor veli palatini, styloglossus and salpingopharyngeus muscles. The latter two muscles separate the medial pterygoid muscle from the superior pharyngeal constrictor. Near its insertion, the medial pterygoid muscle is medially related to the lateral surface of the submandibular gland, and the facial artery, which descends between these two structures.
Medial pterygoid muscle is innervated by the medial pterygoid branches of mandibular nerve (CN V3), one of the three divisions of trigeminal nerve (CN V).
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Medial pterygoid muscle receives blood supply from pterygoid and buccal branches of maxillary artery. To a lesser extent, ascending palatine artery and muscular branches of facial artery also contribute to the blood supply of this muscle.
Due to its posteroinferior direction and the fact that its mandibular attachment is always mobile, medial pterygoid muscle can exhibit several actions:
- Unilateral contraction slightly medially rotates the mandible. When this action occurs simultaneously with the contraction of the ipsilateral lateral pterygoid, it results with a noticeable movement; same sided part of mandible swings anteriorly and medially. In addition, alternating contraction of the medial pterygoid and lateral pterygoids causes side-to-side movements of the mandible.
- Bilateral contraction elevates the mandible. This action, when combined with bilateral contraction of the lateral pterygoids protrudes the mandible.
Medial pterygoid usually acts together with other masticatory muscles. Therefore, its actions combine with those of other masticators to facilitate chewing and food grinding between the maxillary and mandibular teeth.
The medial pterygoid muscle can sometimes be injured during inferior alveolar nerve block due to it being in close proximity to the nerve. The injury occurs if the anesthetic needle is placed too medially and accidentally injects into the muscle instead of the inferior alveolar nerve. This can cause hemorrhage and the development of medial pterygoid trismus hours to days after the procedure. This manifests with inability to completely open the mouth and significant medial pterygoid muscle pain when attempting to open the mouth beyond the restriction.
Pterygoid muscles functions mnemonic
The mnemonic "La" and "Me" is useful to quickly recall the functions of the pterygoid muscles at any time.
- When you pronounce "La" - your jaw is now open, so the lateral pterygoid muscle opens the mouth.
- When after that you pronounce "Me" - you have to close your jaw first, so the medial pterygoid muscle closes the mouth.
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