Muscles of Mastication

Masseter

• Quadrilateral muscle

• covers the lateral surface of ramus of mandible

Origin

1. Superficial Layer: anterior 2/3 of lower border of zygomatic arch

2. Deep layer: deep surface of zygomatic arch

3. Middle Layer: posterior 1/3 of lower border of zygomatic arch

Insertion

Superficial layer into lower part of lateral surface of ramus of mandible

Deep Layer into rest of the ramus Middle layer into central part of ramus

Nerve supply: Masseteric Nerve, branch of anterior division of mandibular Nerve

Action:

• Elevation of mandible
• Superficial fibres cause protrusion

Temporalis

• fan shaped muscle
• fills the temporal fossa

Origin:

• temporal fossa including zygomatic bone
• temporal fascia

Insertion:

• Margins & deep surface of coronoid process of mandible
• anterior border of ramus of mandible

Nerve Supply: Two deep temporal nerve from anterior division of mandibular nerve

Action:

• elevate the mandible
• helps in side to side grinding movements 
• retracts the protruded mandible 

Lateral Pterygoid

Origin:
Upper head - from infra temporal surface and crest of greater wing of sphenoid

Lower head - from lateral surface of lateral pterygoid plate

Insertion:

• pterygoid fovea on the anterior surface of neck of the mandible
• anterior margin of the articular disc & capsule of temporomandibular joint

Nerve supply: branch from anterior division of mandibular nerve

Action:

• depression of mandible
• lateral & medial pterygoids protrudes the mandible
• right lateral & medial pterygoids turn the chin to left side, as a part of grinding movement 

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.
The relations are as follows:
Superficial
1. Masseter
2. Ramus of the mandible
3. Tendon of the temporalis
4. The maxillary artery

Deep
1. Mandibular nerve
2. Middle meningeal artery.
3. Sphenomandibular ligament
4. Deep head of the 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
3. The middle meningeal artery passes upwards deep to it

Structures Passing through the Gap Between the Two Heads
1. The maxillary artery enters the gap
2. The buccal branch of the mandibular nerve comes out through the gap
✦The pterygoid plexus of veins surrounds the lateral pterygoid. 

Medial Pterygoid Origin

Superficial head: from tuberosity of maxilla & adjoining bone

Deep head: from medial surface of lateral pterygoid plate & adjoining process of palatine bone

Insertion: roughened area on the medial surface of the angle & adjoining ramus of mandible

Nerve Supply: Nerve to medial pterygoid, a branch from the main trunk of mandibular nerve

Action:

• elevation of mandible protrusion of mandible
• right medial & right lateral pterygoid moves the chin to left side 

RELATIONS OF MEDIAL PTERYGOID

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

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

• 1. The lateral pterygoid plate
• 2. The lingual nerve
• 3. The inferior alveolar nerve.

Lower down the muscle is separated from the ramus of the mandible by

• 1. the lingual and inferior alveolar nerves,
• 2. the maxillary artery, and
• 3. the sphenomandibular ligament.

Deep Relations
The relations are:

• 1. Tensor veli palatini
• 2. Superior constrictor of pharynx
• 3. Styloglossus
• 4. Stylopharyngeus attached to the styloid process 

Watch lectures on YouTube:

Muscles of Mastication - Masseter Muscle | Origin | Insertion | Nerve Supply | Action | AA

Temporalis Muscle | Origin | Insertion | Nerve Supply | Action

Lateral Pterygoid muscle | Origin | Insertion | Nerve Supply | Actions | Relations

Medial Pterygoid Muscle | Origin | Insertion | Nerve Supply | Actions | Relations