Featured Muscle(s): The Muscles of Mastication

The four muscles of mastication are the primary muscles that move the jaw when chewing.

The four muscles are:

  1. The Masseter
  2. Medial Pterygoid
  3. Lateral Pterygoid
  4. Temporalis

The four muscles of mastication

The Masseter

This quadrangular shaped muscle is the most powerful of the four mastication muscles and arguably the best known muscle of the jaw. The masseter wins the award for the muscle’s ability to exert the most pressure of all of the body’s muscles.

The Action:
The primary responsibility of this muscle is to close the mouth. The masseter is often referred to as the ‘strongest’ muscle in the body. It is referred to as the strongest based on the exertion of pressure. The secondary function of the masseter is to help stabilize tension of the articular capsule of the temporomandibular joint.

Potential Dysfunction:
This muscle will often present with myofascial pain and muscle hyperactivity. You will often find yourself rubbing your jaw when this muscle is in a state of dysfunction.

Medial Pterygoid

A quadrangular shape muscle with two heads: one deep and one superficial.

The Action:
The primary responsibility of this muscle is also to close the mouth. This muscle is not as strong as the masseter, but equally important when it comes to closing your mouth.

Potential Dysfunction:
Common causes of tension in this muscle is trauma or abnormal occlusion. Tension can also present due to stress and anxiety.

Lateral Pterygoid

This muscle has a triangular shape with two heads: superior and inferior. The lateral pterygoid is horizontally orientated fibers.

The Action:
The muscle serves two primary functions. Bilaterally, it protracts the mandible, therefore pushing the jaw forward. Unilaterally, it creates a side-to-side motion of the jaw. This muscle also differs from the other three because it’s the only one that opens the jaw.

Potential Dysfunction:
The best way to consider dysfunction of this muscle is to look at the function of the jaw. An example would be looking at the tracking of the jaw and assessing if it tracks off to one side or the other when you open your jaw.


This muscle is located in a shallow depression on the outside of the skull, just above the ear. It forms a tendon that inserts into the coronoid process of the mandible. It is covered by tough fascia.

The Action:
The primary responsibility is to close the mouth. It also retracts the mandible and clenches the teeth.

Potential Dysfunction:
It is common to feel pressure in the side of your head and near the joint in your jaw when this muscle is tense. This pressure can feel like a dual headache or a sharp localized pain.

The muscles of mastication are important to understand if you suffer from jaw pain.

Outside of a known physical trauma to the jaw, we need to take into serious consideration the connection between emotional and psychological stress and the manifestation of physical pain in this area.

Check out Don’t Just Grin and Bear It to learn more about TMJ dysfunction and treatment.

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