Muscles of Mastication

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Muscles of Mastication

Open with the idea that chewing depends on a small group of paired muscles moving the mandible at the temporomandibular joint.

Learning goal

I can identify the four primary muscles of mastication and explain their main functions and nerve supply.

What words do you associate with chewing muscles?

Use this to surface prior knowledge about jaw movement, chewing, the mandible, the TMJ, and cranial nerves before the named muscles are introduced.

What these muscles do

The muscles of mastication are paired muscles that move the mandible at the temporomandibular joint (TMJ).

They make chewing, biting, grinding, and jaw positioning possible.

Emphasise structure and function: these muscles are defined by the jaw movements they produce.

Shared features

• Originate from the skull

• Insert on the mandible

• Develop from the first pharyngeal arch

• Share motor innervation from CN V3

Students do not need embryological detail beyond recognising that these muscles share a common developmental origin.

The four primary muscles

• Masseter

• Temporalis

• Medial pterygoid

• Lateral pterygoid

Together, they control closing, opening, protruding, retracting, and side-to-side movement of the jaw.

Jaw movement at the TMJ

Different muscles produce different actions at the TMJ:

• elevation

• depression

• protrusion

• retraction

• lateral movement

Link each movement term to a simple meaning: elevation closes the jaw, depression opens it, protrusion moves it forwards, retraction moves it backwards.

Which movement means opening the jaw at the TMJ?

A

Retraction

B

Depression

C

Protrusion

D

Elevation

Checks the movement vocabulary from the TMJ overview. Students may confuse depression with retraction if they only remember that both are not closing movements.

Shared features and movement

The muscles of mastication are paired muscles that move the mandible at the TMJ. They originate from the skull, insert on the mandible, and share motor innervation from CN V3.

mandible

TMJ

CN V3

maxilla

CN V2

sternum

atlas

All three blanks are load-bearing terms from the introductory block: mandible, TMJ, and CN V3.

Masseter

• Function: elevates the mandible

• Role: strongest jaw-closing muscle

• Produces major bite force

The masseter is often the easiest chewing muscle for students to picture because it is superficial and powerful.

Masseter attachments

• Origin: zygomatic arch

• Insertion: ramus and angle of mandible

Its line of pull makes it well suited to raise the mandible during chewing.

Temporalis

• Function: elevates and retracts the mandible

• Shape: fan-shaped

• Helps with precise jaw movements

Contrast with masseter: both elevate the mandible, but temporalis also helps retract it.

Temporalis attachments

• Origin: temporal fossa

• Insertion: coronoid process of mandible

This broad origin and focused insertion support controlled jaw movement.

Which muscle is the strongest jaw-closing muscle?

A

Masseter

B

Temporalis

C

Medial pterygoid

D

Lateral pterygoid

Tests the key distinction from the masseter slides. The other three are plausible because students may remember they also move the mandible.

Masseter and temporalis

The masseter elevates the mandible and produces major bite force. The temporalis also elevates the mandible but can additionally retract it.

masseter

temporalis

retract

protrude

depress

lateral pterygoid

medial pterygoid

This anchors the comparison between masseter and temporalis: shared elevation, but only temporalis retracts.

Medial pterygoid

• Function: elevates the mandible

• Assists in protrusion

• Contributes to side-to-side grinding

This muscle is important for the grinding movements used during chewing, especially with alternating left and right activity.

Medial pterygoid attachments

• Origin: medial surface of lateral pterygoid plate and maxillary tuberosity

• Insertion: medial surface of mandibular ramus

It forms a functional sling with the masseter.

The sling idea helps students remember that medial pterygoid and masseter act together to elevate the mandible from opposite sides.

Lateral pterygoid

• Function: protrudes and depresses the mandible

• Produces lateral movements

• Main muscle assisting in opening the mouth

Highlight the key distinction: among the four primary muscles, lateral pterygoid is the one associated with opening the jaw.

Lateral pterygoid attachments

• Origin: greater wing of sphenoid and lateral pterygoid plate

• Insertion: TMJ capsule and condylar neck

Its attachment to the joint helps explain its role in mandibular movement.

Which muscle mainly helps open the mouth?

A

Masseter

B

Temporalis

C

Lateral pterygoid

D

Medial pterygoid

The key contrast in this block is that lateral pterygoid is the only one associated with jaw opening.

Pterygoid actions

The medial pterygoid helps elevate the mandible and assists in protrusion. The lateral pterygoid protrudes and depresses the mandible and helps with lateral movement.

medial pterygoid

protrusion

lateral pterygoid

retraction

masseter

temporalis

elevation

Reinforces the contrast between the two pterygoids while keeping the shared action of protrusion visible.

Why is masseter + medial pterygoid called a sling?

Expected elements: medial pterygoid and masseter both elevate the mandible; they act from opposite sides of the mandibular ramus like a functional sling; this supports jaw closing during chewing.

One nerve supply

All four primary muscles of mastication are innervated by the mandibular nerve, the V3 branch of the trigeminal nerve (CN V).

This is their shared motor nerve supply.

Keep terminology consistent: mandibular nerve = CN V3 = mandibular branch of the trigeminal nerve.

Why shared innervation matters

Because these muscles share the same motor nerve supply, they are grouped together anatomically and functionally as the muscles of mastication.

You can connect this back to their common first pharyngeal arch origin if useful.

Working together

Masseter + temporalis + medial pterygoid mainly help close the jaw.

Lateral pterygoid is the key muscle that helps open the jaw.

Combined action also allows protrusion, retraction, and grinding.

This synthesis slide helps students organise the four muscles by action rather than memorising isolated facts.

Which nerve supplies all four primary chewing muscles?

A

CN V1

B

CN V2

C

CN V3

D

CN VII

Tests the shared motor innervation. CN V1 and V2 are plausible distractors because they are also trigeminal branches.

Working together

Masseter, temporalis, and medial pterygoid mainly help close the jaw. The lateral pterygoid is the key muscle that helps open the jaw. All four share motor supply from CN V3.

close

lateral pterygoid

open

CN V3

grind

CN V2

masseter

retract

This synthesis item ties action grouping to the common nerve supply.

What is one thing you will remember from this lesson?

Which part of this lesson felt hardest to remember?

Glossary

mandible - the lower jaw bone

temporomandibular joint (TMJ) - the joint where the mandible meets the skull

mastication - chewing

elevation - movement that raises the mandible

depression - movement that lowers the mandible

protrusion - forward movement of the mandible

retraction - backward movement of the mandible

Glossary

masseter - a powerful muscle that elevates the mandible

temporalis - a fan-shaped muscle that elevates and retracts the mandible

medial pterygoid - a muscle that elevates the mandible and assists protrusion

lateral pterygoid - a muscle that protrudes and depresses the mandible

trigeminal nerve - cranial nerve V

mandibular nerve (CN V3) - the branch of the trigeminal nerve that supplies the muscles of mastication