Where Are The Four Muscles Of Mastication?

Mastication is the action of chewing on food using the teeth, making it easy to be ingested by the body. It is known to be the first and foremost step of digestion as food can’t be swallowed effectively without it being turned into something that is easily consumable. For the jaw to be able to churn the food repeatedly, it requires muscles to adduct and abduct as well as give it strength to bite on hard food such as tooth-crackers. Muscles of mastication are known to be the most crucial muscles in the head aside from the muscles that are required to show facial expressions. The four muscles of mastication include: • Masseter muscle
• Temporalis muscle
• Medial pterygoid muscle
• Lateral pterygoid muscle Each of which has a
specific function in the action of twisting and stirring up food in the mouth. All the muscles embryologically originate from the first pharyngeal arch are supplied by two nerves: the trigeminal nerve and the mandibular nerve. The masseter muscle is the most dominant muscle of mastication.
It is divided into superficial masseter muscle and deep masseter muscle. The superficial part arises from the maxillary process of the zygomatic bone, although the deep part comes from the zygomatic arch of the temporal bone. Both muscles insert into the lateral surface of the ramus of the mandible. They act by elevating the mandible upwards making it possible to close the mouth. Moreover, they are supplied by the mesenteric
nerves.

Then comes the Temporalis muscle, It originates from the floor of the temporal fossa and inserts into the coronoid process of the mandible. It consists of two different types of fibers that perform different activities. Vertical fibers elevate the mandible, making it easy to close the mouth, whereas horizontal fibers act on retracting the mandible. Ultimately, they are supplied by the temporal nerves.

The third muscle of mastication consists of the medial pterygoid muscle. It is thick and quadrangular in shape. It happens to be made up of 2 heads, the superficial medial pterygoid muscle and deep medial pterygoid muscle. Both of which have two different places to emerge from. Superficial medial pterygoid muscle emerges from the tuberosity of the maxilla while the deep medial pterygoid muscle appears from the medial surface of the lateral pterygoid plate. They attach to the ramus of the mandible near the angle of the mandible. They behave by elevating the mandible and protruding it with the lateral pterygoid muscle. Similar to any other muscle, the medial pterygoid muscle too has a nerve supply which is made up of the branch from the trunk of mandibular nerve.

The fourth and last muscle of mastication is composed of the lateral pterygoid muscle, which also has two heads.
The upper head originates from the greater wing of the sphenoid and the lower end from the lateral surface of the lateral pterygoid plate. Despite the fact that both heads originate from two different places, they then converge into a tendon which attaches to the neck of the mandible. They could either conduct bilateral or unilateral actions. Bilateral actions include protracting the mandible, pushing the jaw forwards using the lateral pterygoids and producing side to side movement of the jaw using the unilateral action. They are inverted by the branch from the anterior division of the mandibular
nerve.

Lateral pterygoid muscle has plenty of structures that are related to it based on the location:

• Deep to the muscles
Branches of the mandibular nerve and the main origin of the medical pterygoid muscle.
• Superficial to the lower head
The maxillary artery.
• Between the two heads
The buccal branch of the mandibular nerve.
• Below the inferior border
Medial pterygoid muscle and the lingual and inferior alveolar nerves.
• Upper border
The deep temporal nerves the vessels.
• Around and within the lateral muscle
The pterygoid venous plexus.