Anatomy mnemonic
How to Remember the Muscles of Mastication
Four muscles that move the jaw. All supplied by V3 (mandibular division of trigeminal). One mnemonic for the actions.
The four muscles of mastication are temporalis, masseter, medial pterygoid, and lateral pterygoid. All four are supplied by V3, the mandibular division of the trigeminal nerve. They collectively move the jaw for chewing.
The four muscles and their primary actions
Each has a signature action beyond simple jaw closure.
- Temporalis — elevation and retraction of the mandible
- Masseter — elevation (the primary jaw-closing muscle)
- Medial pterygoid — elevation and side-to-side grinding
- Lateral pterygoid — jaw opening and protrusion (the only opener)
The mnemonic for lateral pterygoid's unique action
'Lateral Lets you Lower.' Lateral pterygoid is the muscle that opens the jaw — the other three close it. This is a common test question.
Clinical high-yield
Trismus (lockjaw) — spasm of the mastication muscles. TMJ dysfunction — often involves lateral pterygoid. V3 lesions weaken all four muscles ipsilaterally — jaw deviates toward the weak side on opening (because the strong lateral pterygoid on the intact side pushes the jaw across).
Frequently asked questions
What innervates the muscles of mastication?
All four by the mandibular division (V3) of the trigeminal nerve, via branches: masseteric nerve, deep temporal nerves, and pterygoid nerves.
Is buccinator a muscle of mastication?
No — buccinator is a muscle of facial expression, innervated by CN VII (facial). It assists chewing by holding food between teeth but is not a mastication muscle.
Why does the jaw deviate toward the lesion side?
Lateral pterygoid protrudes and deviates the jaw to the opposite side. If one lateral pterygoid is weak, the intact one pushes the jaw to the weak side on opening.
Any Step 1 relevance?
Yes — trigeminal nerve lesions and their motor findings. TMJ syndrome comes up on Step 2.
Is this the same as facial muscles?
No. Facial expression muscles are CN VII (facial nerve). Mastication muscles are CN V3 (trigeminal). Different nerves, different functions.
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