Learning Objective: At the end of this session, the learner should be able to identify the muscles of mastication, describe their attachments, actions, and nerve supply, and apply this knowledge to clinical scenarios involving the temporomandibular joint (TMJ).
The muscles of mastication are responsible for the complex movements of the temporomandibular joint (TMJ) that enable chewing and speaking. There are four paired muscles, all derived from the first pharyngeal arch, and therefore innervated by the mandibular nerve (V3), a branch of the trigeminal nerve (CN V).
The four muscles of mastication are:
- Masseter
- Temporalis
- Medial pterygoid
- Lateral pterygoid
All these muscles are bilateral and work in coordination to move the mandible for chewing.
Masseter
The masseter is the most powerful muscle of mastication. It lies superficially, covering the pterygoid and temporalis muscles.
Attachments:
- Superficial part: from the maxillary process of the zygomatic bone
- Deep part: from the zygomatic arch of the temporal bone
- Insertion: Ramus of the mandible
Action: Elevates the mandible (closes the mouth)
Innervation: Mandibular nerve (V3)
Temporalis
The temporalis is a fan-shaped muscle located on the lateral aspect of the skull.
Attachments:
- Origin: Temporal fossa
- Insertion: Coronoid process of the mandible
Actions:
- Elevates the mandible (closes mouth)
- Retracts the mandible (moves jaw backward)
Innervation: Mandibular nerve (V3)
💡 The temporalis fascia is clinically important—it can be used for myringoplasty (repair of perforated tympanic membrane).
Medial Pterygoid
The medial pterygoid is a quadrangular muscle located deep to the masseter and inferior to the lateral pterygoid.
Attachments:
- Deep head: from the medial surface of the lateral pterygoid plate (sphenoid)
- Superficial head: from the maxillary tuberosity and pyramidal process of palatine bone
- Insertion: Inner surface of the ramus and angle of the mandible
Action: Elevates the mandible (closes mouth)
Innervation: Mandibular nerve (V3)
Lateral Pterygoid
The lateral pterygoid is a triangular muscle that lies almost horizontally. It is the major protractor of the mandible.
Attachments:
- Superior head: from the greater wing of the sphenoid
- Inferior head: from the lateral surface of the lateral pterygoid plate
- Insertion: Neck of mandible and articular disc of TMJ
Actions:
- Bilateral: Protracts the mandible and depresses the chin
- Unilateral: Produces side-to-side movements (grinding)
Innervation: Mandibular nerve (V3)
Clinical Correlation
Case: A 32-year-old patient presents with difficulty opening her mouth after a minor jaw injury. On examination, there is a deviation of the mandible to the left side during mouth opening.
Interpretation:
This suggests left lateral pterygoid weakness, since the functional muscle on the right pushes the mandible toward the affected side.
