Motor Supply of Mandibular Nerve — Muscles of Mastication
Overview
The motor root of V3 (special visceral efferent — derived from branchial arch musculature) supplies:
- 4 muscles of mastication (primary group)
- 4 additional muscles (secondary group)
All muscles supplied by V3 are derivatives of the 1st pharyngeal (branchial) arch.
Muscles of Mastication
| Muscle | Origin | Insertion | Nerve | Action |
|---|---|---|---|---|
| Masseter | Zygomatic arch (superficial head: lower border; deep head: medial surface) | Lateral surface of ramus and angle of mandible | Masseteric nerve (anterior division V3) | Elevation of mandible (jaw closure); some protrusion |
| Temporalis | Floor of temporal fossa (temporal surface of greater wing of sphenoid, temporal bone, parietal bone) | Coronoid process and anterior border of ramus of mandible | Deep temporal nerves, anterior and posterior (anterior division V3) | Elevation (vertical fibres); retraction (horizontal/posterior fibres) |
| Medial pterygoid | Deep head: medial surface of lateral pterygoid plate; Superficial head: pyramidal process of palatine and maxillary tuberosity | Medial surface of ramus and angle of mandible (pterygoid fossa) | Nerve to medial pterygoid (from undivided trunk V3) | Elevation; protrusion; side-to-side (chewing) movement |
| Lateral pterygoid | Upper head: infratemporal surface of greater wing of sphenoid; Lower head: lateral surface of lateral pterygoid plate | Neck of mandible (condyle) and articular disc of TMJ | Nerve to lateral pterygoid (anterior division V3) | Protrusion; depression of mandible (with digastric); side-to-side movement; opens mouth |
Mnemonic: Muscles that close the jaw = Masseter, Medial pterygoid, Temporalis (M.M.T. — “Munch Munch Temporalis”). Muscle that opens the jaw primarily = Lateral pterygoid (with digastric and gravity).
Other Muscles Supplied by V3
| Muscle | Nerve | Action |
|---|---|---|
| Mylohyoid | Nerve to mylohyoid (from inferior alveolar, posterior division) | Elevates floor of mouth and tongue during swallowing; depresses mandible |
| Anterior belly of digastric | Nerve to mylohyoid | Depresses mandible; elevates hyoid |
| Tensor veli palatini | Nerve to medial pterygoid (branch) | Tenses soft palate; opens auditory tube during swallowing/yawning |
| Tensor tympani | Nerve to medial pterygoid (branch) | Tenses tympanic membrane; dampens loud sounds |
Embryological Basis
All muscles supplied by the mandibular nerve are derivatives of the mesoderm of the 1st pharyngeal arch (Meckel’s cartilage arch), consistent with the general rule: nerve of an arch supplies all muscles derived from that arch.
Applied
- Trismus (lockjaw): Spasm of muscles of mastication — causes include tetanus, pericoronitis, TMJ disorders, fracture of mandible, parotid abscess
- Jaw jerk reflex: Afferent and efferent via V3; tests upper motor neurone integrity for CN V; exaggerated in pseudobulbar palsy
- TMJ dysfunction: Lateral pterygoid spasm is a common cause of clicking and pain at TMJ