The muscles of mastication, also known as masticatory muscles, are a group of paired muscles located around the temporomandibular joint (TMJ). They provide movements at the mentioned joint; therefore, these muscles are also responsible for moving the lower jaw. 

The muscles of mastication primarily act during chewing. However, besides the movements associated with eating, they also move the mandible during speaking. Overall, these muscles open and close the mouth. They elevate, depress, protrude (move forward), retract (pull backward) the mandible and provide side-to-side movements.

All muscles of mastication originate from the skull bones and insert onto various features of the mandible. Overall, the masticatory muscles can be subdivided into primary (main) and secondary (accessory) muscles of mastication.

Each side of the head contains four primary or main muscles of mastication:

• Temporalis (Read more!)
• Masseter (Read more!)
• Medial pterygoid (Read more!)
• Lateral pterygoid (Read more!)

In contrast to the primary muscles of mastication, each person has several secondary or accessory muscles of mastication:

• Buccinator (Read more!) - facial muscle;
• Digastric (Read more!) - suprahyoid neck muscle;
• Stylohyoid (Read more!) - suprahyoid neck muscle;
• Mylohyoid (Read more!) - suprahyoid neck muscle;
• Geniohyoid (Read more!) - suprahyoid neck muscle;
• Sternohyoid (Read more!) - infrahyoid neck muscle;
• Sternothyroid (Read more!) - infrahyoid neck muscle;
• Thyrohyoid (Read more!) - infrahyoid neck muscle;
• Omohyoid (Read more!) - infrahyoid neck muscle.

Muscles of mastication and their provided functions

Besides the classification described above, all muscles of mastication can be grouped according to the functions they provide.

Muscles that elevate the mandible (close the mouth) include the following:

• Temporalis
• Masseter
• Medial pterygoid
• Lateral pterygoid (superior head)

Muscles that, along with gravity, depress the mandible (open the mouth) are as follows:

• Lateral pterygoid (inferior head)
• Digastric (anterior belly)
• Mylohyoid
• Geniohyoid

Muscles that protrude the mandible (move it forward) are:

• Masseter
• Medial pterygoid
• Lateral pterygoid (inferior head)
• Digastric
• Temporalis

Muscles that provide retraction of the mandible (pull it backward) include the following muscles:

• Temporalis
• Digastric
• Lateral pterygoid (inferior head)

Muscles that are responsible for side-to-side movements of the lower jaw are:

• Masseter
• Temporalis
• Medial pterygoid
• Lateral pterygoid