Muscles of Mastication Overview

Muscles of Mastication

The muscles of mastication are a group of muscles that work together to facilitate chewing and grinding of food. These muscles are associated with movements of the jaw (temporomandibular joint) and are all bilateral structures. They develop from the first pharyngeal arch and are innervated by branches of the trigeminal nerve (CN V), specifically the mandibular nerve. The four main muscles of mastication are:

Masseter

The masseter muscle is the most powerful muscle of mastication. It is quadrangular in shape and has two parts: a deep part and a superficial part. The superficial part originates from the maxillary process of the zygomatic bone, while the deep part originates from the zygomatic arch of the temporal bone. Both parts attach to the ramus of the mandible. The masseter muscle is responsible for elevation of the mandible (closing the mouth) and is innervated by the mandibular nerve (V 3).

Temporalis

The temporalis muscle originates from the temporal fossa, a shallow depression on the lateral aspect of the skull. It is covered by tough fascia and can be harvested surgically to repair a perforated tympanic membrane (myringoplasty). The muscle attaches to the coronoid process of the mandible and is responsible for elevation of the mandible (closing the mouth) and retraction of the mandible (moving the jaw posteriorly). It is also innervated by the mandibular nerve (V 3).

Medial Pterygoid

The medial pterygoid muscle has a quadrangular shape with two heads: superficial and deep. It is located inferiorly to the lateral pterygoid. The superficial head originates from the maxillary tuberosity and the pyramidal process of the palatine bone, while the deep head originates from the medial aspect of the lateral pterygoid plate of the sphenoid bone. Both heads attach to the ramus of the mandible near the angle of the mandible. The medial pterygoid muscle is responsible for elevation of the mandible (closing the mouth) and is innervated by the mandibular nerve (V 3).

Lateral Pterygoid

The lateral pterygoid muscle has a triangular shape with two heads: superior and inferior. It has horizontally orientated muscle fibers, making it the major protractor of the mandible. The superior head originates from the greater wing of the sphenoid, and the inferior head originates from the lateral pterygoid plate of the sphenoid. The two heads converge into a tendon that attaches to the neck of the mandible. The lateral pterygoid muscle is responsible for both bilateral protraction of the mandible and depression of the chin, as well as unilateral 'side to side' movement of the jaw. It is innervated by the mandibular nerve (V 3).

In addition to these four primary muscles, there are secondary or accessory muscles that assist in mastication, including the buccinator, suprahyoid muscles (digastric, mylohyoid, and geniohyoid), and infrahyoid muscles (sternohyoid, sternothyroid, thyrohyoid, and omohyoid). These muscles work together to ensure proper chewing, food grinding, and approximation of the teeth. The muscles of mastication are vital for the process of eating and are essential for maintaining oral health.