Muscles of mastication: masseter, temporalis and pterygoids, actions and nerve

What are the muscles of mastication?

Clench your back teeth. Two places harden: behind the cheek and at the temple. These are the masseter and temporalis, two of the muscles of mastication.

The muscles of mastication move the lower jaw (mandible) when you chew: the masseter, temporalis, medial pterygoid and lateral pterygoid. They are a separate group from the muscles of facial expression, with different attachments and a different nerve. Some textbooks add the suprahyoid muscles such as the digastric as accessory muscles, since they help open the mouth.

Origins and insertions

With the masseter and temporalis hidden, the two pterygoids are left: the medial runs vertically, the lateral almost horizontally. The masseter and medial pterygoid clasp the angle of the mandible from outside and inside, forming a sling that lifts the jaw.

Three close, one opens

The masseter, temporalis and medial pterygoid close the jaw. The lateral pterygoid runs almost horizontally and pulls the condylar process forward, protruding the jaw and starting wide opening. The posterior fibres of the temporalis pull a protruded jaw back. Grinding comes from the pterygoids of each side working in turn: when the medial and lateral pterygoids of one side contract together, the jaw shifts to the opposite side.

One nerve: the mandibular nerve

All four are supplied by branches of the mandibular nerve, the third division of the trigeminal nerve: the masseteric, deep temporal, and medial and lateral pterygoid nerves. The muscles of facial expression, such as the zygomaticus major and orbicularis oris, are supplied by the facial nerve instead.

Name and terms

Mastication means chewing; the group is also called the masticatory muscles. Pterygoid comes from the Greek for wing-like, after the pterygoid processes of the sphenoid bone they arise from.

See it in the app

The pterygoids lie inside the ramus of the mandible, out of reach of the fingers and hidden behind the masseter in side views. In the 3D anatomy app teamLabBody you can hide the masseter and temporalis, keep only the two pterygoids, and rotate them to compare their directions. The masseter is shown as separate superficial and deep parts. Cross sections are available with the PREMIUM plan.

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