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AN33.1-5 | Temporal and Infratemporal regions — Self-Directed Learning

Temporal and Infratemporal Fossae — Boundaries and Contents (AN33.1)

Temporal Fossa
- Boundaries: Superiorly/anteriorly — superior + inferior temporal lines; Anteriorly — frontal and zygomatic bones; Posteriorly — temporal bone; Inferiorly — zygomatic arch (roof of infratemporal fossa)
- Contents: Temporalis muscle, deep temporal vessels (from maxillary artery), deep temporal nerves (from CN V3), small amount of fat
- Floor: Formed by parts of the frontal, parietal, temporal, and sphenoid bones — this meeting point is called the pterion (weakest part of the skull; overlies the anterior branch of the middle meningeal artery — vulnerable in head trauma)

Infratemporal Fossa (ITF)
- Location: Deep to the ramus of mandible; below and medial to the zygomatic arch; behind the maxilla
- Boundaries:
- Lateral — ramus and coronoid process of mandible
- Medial — lateral pterygoid plate (sphenoid)
- Anterior — posterior surface of maxilla
- Superior — inferior surface of greater wing of sphenoid + squamous temporal bone (infratemporal surface)
- Posterior — open (communicates with the parapharyngeal space)
- No floor (opens inferiorly into the neck)

• Communications:
• With the temporal fossa — through the gap between zygomatic arch and skull (deep to masseter)
• With the pterygopalatine fossa — through the pterygomaxillary fissure (medially)
• With the middle cranial fossa — through foramen ovale (CN V3), foramen spinosum (middle meningeal vessels)

Contents of the ITF (the densely packed space):
1. Muscles: Lower head of lateral pterygoid + medial pterygoid (+ lower parts of temporalis)
2. Vessels: Maxillary artery (and its branches) + pterygoid venous plexus
3. Nerves: Mandibular nerve (CN V3) and its branches; chorda tympani (CN VII); otic ganglion

Muscles of Mastication — Attachments, Actions, and Nerve Supply (AN33.2)

All four muscles of mastication are supplied by the anterior division of CN V3 (mandibular nerve) — specifically by the nerve to masseter, deep temporal nerves, and nerve to pterygoids.

1. Temporalis
- Origin: Temporal fossa (floor and walls) + temporal fascia
- Insertion: Coronoid process + anterior border of ramus of mandible
- Nerve: Deep temporal nerves (anterior division, CN V3)
- Action: Elevation (closing jaw) + Retraction of mandible (posterior fibres); anterior fibres also assist in protraction
- Clinical: Wasting of temporalis visible as hollowing of the temple in malnutrition and motor neuron disease; trismus (inability to open jaw) from temporalis spasm or invasion

2. Masseter
- Origin: Superficial head — lower border of zygomatic arch (anterior 2/3); Deep head — medial surface of zygomatic arch
- Insertion: Lateral surface of ramus and coronoid process of mandible
- Nerve: Masseteric nerve (anterior division, CN V3); enters through the mandibular notch
- Action: Elevation (main biting muscle) + some protraction (superficial head)
- Clinical: Hypertrophy with bruxism (teeth grinding — common in stressed students); parotid gland overlies the masseter

3. Medial Pterygoid
- Origin: Deep head — medial surface of lateral pterygoid plate; Superficial head — tuberosity of maxilla and pyramidal process of palatine bone
- Insertion: Medial surface of angle of mandible (pterygoid fossa)
- Nerve: Medial pterygoid nerve (main trunk, CN V3)
- Action: Elevation + protraction + medial excursion (side-to-side grinding)
- Note: Acts as a medial sling with masseter to suspend the mandible — together they form a "pterygomasseter sling"

4. Lateral Pterygoid
- Origin: Upper head — infratemporal surface and crest of greater wing of sphenoid; Lower head — lateral surface of lateral pterygoid plate
- Insertion: Pterygoid fovea on the neck of mandibular condyle; articular disc of TMJ (upper head)
- Nerve: Lateral pterygoid nerve (anterior division, CN V3)
- Action: Protraction + depression (opening jaw) — bilateral: opens mouth + protrudes; unilateral: side-to-side movement (lateral excursion to opposite side)
- Critical point: The lateral pterygoid is the ONLY muscle of mastication that opens the mouth — all others close it. If both lateral pterygoids contract simultaneously, the jaw protrudes and opens.

Memory Summary:

Muscle	Elevation	Depression	Protraction	Retraction
Temporalis	✓ (all)			✓ (posterior)
Masseter	✓		✓ (superficial)
Medial pterygoid	✓		✓
Lateral pterygoid		✓	✓

Temporomandibular Joint (TMJ) (AN33.3)

Type: Synovial condylar joint (modified hinge); bicondylar joint

Articulating Surfaces:
- Above: Articular tubercle (anterior part of mandibular fossa) + mandibular fossa (glenoid fossa) of the temporal bone — lined with fibrocartilage (NOT hyaline cartilage — important distinction)
- Below: Head (condyle) of the mandible — also covered with fibrocartilage

Articular Disc:
A fibrocartilaginous biconcave disc that divides the joint into two compartments:
- Upper (temporodiscal) compartment — gliding movements (protraction/retraction)
- Lower (discoidal) compartment — hinge/rotation movements (elevation/depression)

The disc is attached anteriorly to the upper head of the lateral pterygoid muscle, accounting for anterior disc displacement in TMJ disorders.

Ligaments:
1. Temporomandibular (lateral) ligament — thickening of the joint capsule; strongest ligament; limits posterior movement of the condyle
2. Sphenomandibular ligament — medial accessory ligament; from spine of sphenoid → lingula of mandibular foramen; not part of the capsule
3. Stylomandibular ligament — from styloid process → angle of mandible; separates parotid from submandibular gland

Movements:
1. Depression (opening): Rotation in lower compartment + translation (gliding forward) in upper compartment. Lateral pterygoid initiates opening; digastric + mylohyoid + geniohyoid assist.
2. Elevation (closing): Reverse; masseter, medial pterygoid, temporalis.
3. Protraction: Both lateral pterygoids; upper compartment gliding.
4. Retraction: Posterior fibres of temporalis + digastric.
5. Lateral excursion (chewing): Unilateral lateral pterygoid of the opposite side + ipsilateral masseter/temporalis.

Blood supply: Superficial temporal + maxillary arteries (branches of ECA)
Nerve supply: Auriculotemporal nerve + masseteric nerve (both from CN V3)

Pterygoid Venous Plexus and TMJ Dislocation (AN33.4 & AN33.5)

Pterygoid Venous Plexus (AN33.4)

The pterygoid venous plexus is a dense network of veins lying in the infratemporal fossa, surrounding the pterygoid muscles.

Tributaries: Middle meningeal veins, deep temporal veins, masseteric vein, infraorbital vein, greater palatine vein, sphenopalatine vein, inferior ophthalmic vein.

Drainage: → Maxillary vein → joins the superficial temporal vein to form the retromandibular vein → ultimately drains into the internal and external jugular veins.

Clinical significance:
1. Route for infection spread: Dental infections (especially upper molar teeth → pterygopalatine fossa → pterygoid plexus) can spread to the cavernous sinus via emissary veins (including a connection through foramen ovale and foramen of Vesalius). This is a potentially fatal complication.
2. Dangerous injections: Aspiration is mandatory before inferior alveolar nerve block — inadvertent injection into the pterygoid plexus causes a haematoma in the ITF.
3. Anastomosis with the cavernous sinus: Via the deep facial vein (from angular vein → pterygoid plexus), emissary veins through foramen ovale and foramen spinosum.

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Dislocation of the TMJ (AN33.5)

Definition: Anterior dislocation — the condyle moves forward, over the articular tubercle, and becomes locked in front of it. It cannot return on its own because the elevator muscles (masseter, temporalis, medial pterygoid) hold it in spasm.

Why does it happen?
- Excessive mouth opening (wide yawning, prolonged dental procedures, general anaesthesia intubation)
- Laxity of the temporomandibular + capsular ligaments
- Shallow articular fossa or low articular tubercle

Clinical features:
- Mouth fixed open (cannot close)
- Jaw deviated toward the unaffected side (if unilateral)
- Pre-auricular hollow (condyle no longer palpable in the fossa)
- Pain and muscle spasm

Reduction — Hippocratic manoeuvre:
1. Stand facing the seated patient
2. Place thumbs (wrapped in gauze) on the lower molar teeth bilaterally
3. Fingers grip the lower border of the mandible
4. Apply firm downward and backward pressure: thumbs push molars down (clearing the articular tubercle), fingers lift the chin up
5. The condyle slides back into the mandibular fossa — a "clunk" is felt

Post-reduction: Bandage the jaw for 2–4 weeks; avoid wide opening; treat underlying hypermobility.