Muscles Of Mastication

Question 1

Structure of TMJ

Answer 1

A modified hinge synovial joint

Between the mandibular fossa of temporal bone and condylar process of mandible

The articular surfaces of bone are covered with fibrocartilage

The fibrocartilaginous articulated disc is separating the joint into superior and inferior articular cavities

Question 2

Ligaments of TMJ

Answer 2

Connect mandible to cranium

Sphenomandibular ligament (extrinsic)
- originates from sphenoid spine to attach to mandible
- primary passive support of mandible

Stylomandibular ligament (extrinsic)
- originates from styloid process to mandible
- supports weight of jaw

Lateral ligament (intrinsic)
- originates from beginning of articular tubule to mandibular neck
- strengthen TMJ laterally
- with postglenoid tubercle prevents posterior dislocation

Question 3

TMJ gliding movements

Answer 3

• between temporal bone and articular disc
• includes

protrusion (forward) by lateral pterygoid

retraction (backward) by posterior fibres of temporalis, masseter, geniohyoid and digastric

Question 4

TMJ hinge and rotational movements

Answer 4

• between head of mandible and articular disc
• includes

Elevation (upwards) by temporalis, masseter and medial pterygoid

Depression (downwards) by digastric, geniohyoid, mylohyoid, lateral pterygoid and GRAVITY

Question 5

TMJ lateral movements

Answer 5

• grinding and chewing side to side movements

By lateral and medial pterygoid

Question 6

Anterior dislocation of TMJ

Answer 6

Most common dislocation on tmj

Where head of mandible has moved outwards and has popped out of mandibular fossa and becomes locked due to anatomical relations of skull

Unlike posterior dislocation where postglenoid tubercle prevents it

Question 7

CN V branches

Answer 7

V1 - ophthalamic via supraorbital foramen
- frontal
- lacrimal
- nasociliary

V2 - maxillary via infraorbital foramen
- infraorbital
- lesser palatine
- greater palatine
- nasopalatine

V3 - mandibular via mental foramen
- lingual
- inferior alveolar

Question 8

Muscles of mastication and their nerve supply

Answer 8

Temporalis
Masseter
Medial pterygoid
Lateral pterygoid

All supplied via CN V3

Question 9

Temporalis

Answer 9

Origin: temporal fossa and fascia

Inserts: coronoid process of mandible and anterior border of ramus of mandible

Action: elevates and retracts mandible

Innervation: deep temporal nerves from anterior trunk of CN V3

Question 10

Masseter

Answer 10

Origin: maxillary process of zygomatic bone and anterior 2/3 of inferior border of zygomatic arch

Inserts: angle and lateral surface of ramus of mandible

Action: elevates mandible

Innervation: masseteric nevre by anterior trunk of CN V3

Question 11

Medial pterygoid

Answer 11

Orgin: medial surface of lateral pterygoid plate (deep) and maxillary tuberosity (superficial)

Inserts; medial surface of ramus and angle of mandible

Action: elevates the mandible and assists in lateral movement

Innervation: nerve to medial pterygoid by main trunk of CN V3

Question 12

Lateral pterygoid

Answer 12

Origin: infratemporal surface of greater wing of sphenoid (superior) and lateral surface of lateral pterygoid plate (inferior’

Inserts: joint capsule of TMJ and pterygoid fovea

Action:
Protrudes and depresses mandible and lateral movement

Innervation: nerve to lateral pterygoid and buccal nerve from anterior trunk of CN. 3

Question 13

Phases of swallowing

Answer 13

1. Oral voluntary phase

Food bolus formed by chewing
Elevated mandible and retracted tongue
Food bolus pushed to oropharynx by tongue

2. Pharyngeal involuntary phase

Superior pharyngeal constriction and soft plate elevation
Pharyngeal elevation to receive bolus (pharyngeal elevators)
Bolus pushed towards oesophageal (pharyngeal constrictors)
Epiglottis close laryngeal inlet to protect airway

3. Oesophageal phase

As inferior pharyngeal constrictor contacts upper oesophageal sphincter relaxes so bolus passes into oesophagus. Peristaltic movement for food to go to stomach

Question 14

Infratemporal fossa contents

Answer 14

Muscles: lateral pterygoid, medial pterygoid, temporal jaw

Vessels: maxillary artery, inferior alveolar artery, buccal artery

Nerves: mandibular, inferior alveolar, lingual, buccal, chorda tympani, otic ganglion

Question 15

Aurciotemporal nerve

Answer 15

Encircles the middle meningeal artery

Gives sensory fibres to auricle and temporal region and TMJ

Gives secretomotor fibres to parotid gland via otic ganglion

Question 16

Inferior alveolar nerve

Answer 16

Branches

• nerve to mylohyoid (branches off before the IAN enters the mandibular foramen)

Nerve terminates around 2nd premolar to give

• mental nerve (comes out through mental foramen)
• incisive nerve (continues in mandibular incisive canal)

Question 17

Lingual nerve

Answer 17

Sensory Innervation to anterior 1/3 of tongue, floor of mouth and gingivae

Passes medial and inferior to 3rd molar tooth

Joined by chorda tympani nerve within infratemporal fossa

Question 18

Maxillary artery branches

Answer 18

3 parts

Mandibular
- middle meningeal artery
- inferior alveolar artery

Pterygoid
- masseteric
- deep temporal branches
- buccal branch
- descending palatine

Prerygopalatine
- infraorbital
- superior alveolar