Muscles of Mastication

Original Editor - Olajumoke Ogunleye

Top Contributors - Olajumoke Ogunleye, Wendy Walker, Joao Costa, Kim Jackson, Vidya Acharya, Areeba Raja and Ahmed M Diab

Introduction and Overview

• The muscles of mastication are a group of muscles responsible for the chewing movement of the mandible at the temporomandibular (TMJ) joint, they enhance the process of eating, they assist in grinding food, and also function to approximate the teeth.

• The four main muscles of mastication originate from the surface of the skull and they attach onto the rami of the mandible at the TMJ.

• The movement performed by these muscles is elevation, depression, protrusion, retraction, and side to side movement.

• Unlike the muscles of facial expression that are innervated by the facial nerve (CN VII), the muscles of mastication are innervated by motor branches of the mandibular division of the trigeminal nerve (CNV3), while the main arterial supply is derived from branches of the maxillary artery.

Description

The muscles of mastication can be divided into the primary muscles and secondary or accessory muscles. The primary muscles include:

• Masseter
• Temporalis
• Lateral pterygoid
• Medial pterygoid

The secondary or accessory muscles are:

• Buccinator
• Suprahyoid muscles (digastric muscle, mylohyoid muscle, and geniohyoid muscle)
• Infrahyoid muscles (the sternohyoid, sternothyroid, thyrohyoid, and omohyoid muscle)

We will examine the muscles separately.

Masseter

It is a rectangular muscle that covers most of the lateral aspect of the ramus. It consists of three layers which blend anteriorly. They are the superficial layer, intermediate layer, and deep layer.

Origin and Insertion

The fibres of the muscle originate from the inferior zygomatic arch and the anterior two-thirds of the zygomatic arch with a connection to the posterior aspect of the zygomatic bone. The firers converge inferiorly forming a tendon that inserts at the outer surface of the mandibular ramus and the coronoid process of the mandible.

Nerve and blood supply

It is innervated by the masseter muscle from the masseteric nerve which is a branch of the mandibular nerve. Its blood supply is derived from the masseteric artery, which emerges from the maxillary artery.

Function

• The major function of the masseter muscle is to elevate the mandible, approximate the teeth.

• The intermediate and deep muscle fibres of the masseter function to retract the mandible and the superficial fibres function to protrude the mandible.

Resources

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