Muscles of mastication

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Head & Neck • Anatomy

MUSCLES OF MASTICATION

The principal muscles of mastication are Masseter, Temporalis, Lateral pterygoid and Medial pterygoid.

01

Notes

The principal muscles of mastication are:

  1. Masseter
  2. Temporalis
  3. Lateral pterygoid
  4. Medial pterygoid
02

Masseter

Muscle 1

General Features

  • Shape: Quadrilateral.
  • Covers the lateral surface of the ramus of mandible.
  • Has three layers.

Origin

Zygomatic arch

a. Superficial Layer — Largest

  • From the anterior 2/3rd of lower border of zygomatic arch.
  • Also from adjoining zygomatic process of maxilla.

b. Middle Layer

  • From the lower border of posterior 1/3rd of zygomatic arch.

c. Deep Layer

  • From the deep surface of zygomatic arch.

Fibres

  • Superficial fibres → pass downwards and backwards at 45°.
  • Middle fibres → pass vertically downwards.
  • Deep fibres → pass vertically downwards.

Insertion

  • Lateral surface of ramus of mandible.
  • Superficial layer → lower part of lateral surface of ramus of mandible.
  • Middle layer → central part of ramus of mandible.
  • Deep layer → rest of the ramus of mandible.

Nerve Supply

Masseteric nerve → branch of anterior division of mandibular nerve.

Actions

  1. Elevates mandible → to close the mouth, to bite.
  2. Superficial fibres → cause protrusion.
03

Temporalis

Muscle 2

General Features

  • Shape: Fan-shaped.
  • Fills the temporal fossa, excluding the zygomatic bone.

Origin

  1. Temporal fossa
  2. Temporal fascia

Fibres

  • Anterior fibres → run vertically.
  • Middle fibres → run obliquely.
  • Posterior fibres → run horizontally.
  • All fibres converge and pass through a gap deep to the zygomatic arch.

Insertion

  1. Margins and deep surface of coronoid process.
  2. Anterior border of ramus of mandible.

Nerve Supply

Two deep temporal branches from the anterior division of mandibular nerve.

Actions

  1. Elevates mandible.
  2. Helps protrude mandible.
  3. Posterior fibres retract the protruded mandible.
04

Lateral Pterygoid

Muscle 3

General Features

  • Shape: Short, conical.
  • Has upper and lower heads.

Origin

a. Upper Head — Small

From:

  • Infratemporal surface.
  • Crest of greater wing of sphenoid bone.

b. Lower Head — Larger

  • From the lateral surface of lateral pterygoid plate.
  • Origin is medial to insertion.

Fibres

  • Fibres run backwards and laterally and converge for insertion.

Insertion

  1. Pterygoid fovea on the anterior surface of neck of mandible.
  2. Anterior margin of articular disc and capsule of temporomandibular joint.

Insertion is posterolateral and at a slightly higher level than origin.

Nerve Supply

A branch from the anterior division of mandibular nerve.

Actions

  1. Depresses mandible to open mouth, with suprahyoid muscles.
    • It is indispensable for actively opening the mouth.
  2. Protrudes mandible.
  3. Right lateral pterygoid turns the chin to the left side.
05

Medial Pterygoid

Muscle 4

General Features

  • Shape: Quadrilateral.
  • Has a small superficial head.
  • Has a large deep head.

Origin

a. Superficial Head — Small Slip

  • From tuberosity of maxilla and adjoining bone.

b. Deep Head — Quite Large

  • From the medial surface of lateral pterygoid plate.
  • Also from adjoining process of palatine bone.

Fibres

  • Fibres run downwards, backwards and laterally.
  • The two heads embrace part of the lower head of lateral pterygoid.

Insertion

  • Roughened area on the medial surface of angle and adjoining ramus of mandible.
  • Located below and behind the mandibular foramen and mylohyoid groove.

Nerve Supply

Nerve to medial pterygoid → branch of the main trunk of mandibular nerve.

Actions

  1. Elevates mandible.
  2. Helps protrude mandible.
  3. Right medial pterygoid with right lateral pterygoid turns the chin to the left side as part of grinding movements.
06

Peculiarities of Muscles of Mastication

  1. They move the mandible during mastication and speech.
  2. They develop from the mesoderm of the 1st branchial arch.
  3. They are supplied by the mandibular nerve, which is the nerve of the 1st arch.
07

Clinical Anatomy

  • Temporalis and masseter muscles are palpated by requesting the person to clench the teeth.
  • Medial and lateral pterygoid muscles can be tested by requesting the person to move the lower jaw from one side to the other side.
08

Relations of Lateral Pterygoid

The lateral pterygoid may be regarded as the key muscle of this region because its relations provide a fair idea about the layout of structures in the infratemporal fossa.

Superficial Relations

  1. Masseter
  2. Ramus of mandible
  3. Tendon of temporalis
  4. Maxillary artery

Deep Relations

  1. Mandibular nerve
  2. Middle meningeal artery
  3. Sphenomandibular ligament
  4. Deep head of medial pterygoid

Structures Emerging at the Upper Border

  1. Deep temporal nerves
  2. Masseteric nerve

Structures Emerging at the Lower Border

  1. Lingual nerve
  2. Inferior alveolar nerve and artery
  3. Middle meningeal and accessory meningeal arteries pass upwards deep to it.

Structures Passing Through the Gap Between the Two Heads

  1. Maxillary artery enters the gap.
  2. Buccal branch of mandibular nerve with buccal artery comes out through the gap.

Pterygoid plexus of veins surrounds the lateral pterygoid.

09

Relations of Medial Pterygoid

The superficial and deep heads of medial pterygoid enclose the lower head of lateral pterygoid muscle.

Superficial Relations

Upper Part of the Muscle

The upper part is separated from the lateral pterygoid muscle by:

  1. Lateral pterygoid plate
  2. Lingual nerve
  3. Inferior alveolar nerve

Lower Part of the Muscle

The lower part is separated from the ramus of mandible by:

  1. Lingual nerve
  2. Inferior alveolar nerve
  3. Maxillary artery
  4. Sphenomandibular ligament

Deep Relations

  1. Tensor veli palatini
  2. Superior constrictor of pharynx
  3. Styloglossus
  4. Stylopharyngeus attached to the styloid process.
MUSCLES OF MASTICATION
Head & Neck Anatomy Study Notes