Anatomy chapters
Muscles of facial expression and mastication
The muscles that move the face (facial nerve) and the muscles that chew (mandibular nerve), their actions, and how Bell's palsy and nerve injuries show up.
- Facial expression muscles come from the second pharyngeal arch and are supplied by the facial nerve (VII).
- Mastication muscles come from the first arch and are supplied by the mandibular nerve (V3).
- The lateral pterygoid is the only chewing muscle that opens the mouth.
On this page
Overview
The face has two groups of skeletal muscles with different nerve supplies.
- Muscles of facial expression: thin muscles in the superficial fascia that move the skin. Supplied by the facial nerve (VII).
- Muscles of mastication: four strong muscles that move the mandible. Supplied by the mandibular division of the trigeminal nerve (V3).
Muscles of facial expression
These muscles develop from the second pharyngeal arch, so they share its nerve, the facial nerve.
Most arise from bone and insert into skin. They act as sphincters and dilators around the eyes, nose and mouth.
Around the eye
Orbicularis oculi closes the eyelids.
- The palpebral part closes the lids gently, as in blinking and sleep.
- The orbital part closes the eye tightly.
Corrugator supercilii draws the eyebrows together (frowning).
Paralysis of orbicularis oculi means the patient cannot close the eye. The cornea dries and may ulcerate.
Around the mouth
Orbicularis oris closes and purses the lips.
Buccinator lies in the cheek. It presses the cheek against the teeth, keeps food between the teeth while chewing, and helps blowing and whistling. The parotid duct pierces it opposite the upper second molar.
Other muscles pull the lips in different directions: zygomaticus major (smiling), levator labii superioris, depressor anguli oris, and others.
Buccinator helps chewing but is a muscle of facial expression, supplied by the facial nerve. The buccal nerve from V3 is sensory to the cheek only.
Scalp, nose and neck
- Occipitofrontalis: raises the eyebrows and wrinkles the forehead. Its two bellies are joined by the epicranial aponeurosis.
- Nasalis and procerus: move the nose.
- Platysma: a thin sheet in the neck that tenses the skin and pulls down the corner of the mouth.
The facial nerve to the face
The facial nerve leaves the skull through the stylomastoid foramen, enters the parotid gland and divides into five branches.
| Branch | Main muscles |
|---|---|
| Temporal | Frontalis, upper orbicularis oculi |
| Zygomatic | Orbicularis oculi |
| Buccal | Buccinator, muscles of the upper lip |
| Marginal mandibular | Muscles of the lower lip and chin |
| Cervical | Platysma |
"To Zanzibar By Motor Car": temporal, zygomatic, buccal, marginal mandibular, cervical.
Muscles of mastication
These four muscles develop from the first pharyngeal arch and are supplied by V3.
| Muscle | Origin | Insertion | Main action |
|---|---|---|---|
| Masseter | Zygomatic arch | Lateral surface of ramus and angle of mandible | Elevates (closes) the jaw |
| Temporalis | Temporal fossa | Coronoid process and front of ramus | Elevates; posterior fibres retract the jaw |
| Medial pterygoid | Medial surface of lateral pterygoid plate (deep head) and maxillary tuberosity | Medial surface of ramus and angle | Elevates; helps side-to-side grinding |
| Lateral pterygoid | Infratemporal surface of greater wing of sphenoid, lateral surface of lateral pterygoid plate | Neck of mandible, articular disc and capsule of TMJ | Depresses (opens) and protrudes the jaw |
The lateral pterygoid is the only muscle of mastication that opens the mouth. It pulls the condyle and disc forward.
The medial pterygoid closes the mouth. Do not mix up the two pterygoids.
Side-to-side grinding happens when the pterygoids of one side act alone.
Other muscles from the first arch, also supplied by V3, are the anterior belly of digastric, mylohyoid, tensor tympani and tensor veli palatini.
Clinical relevance
Bell's palsy (facial nerve palsy)
How it happens: inflammation of the facial nerve in its bony canal, often without a known cause.
What you see: weakness of the whole of one side of the face: the forehead cannot wrinkle, the eye cannot close, the mouth droops and food collects between the cheek and teeth (buccinator weakness).
Upper motor neuron facial palsy
How it happens: a stroke affecting the motor cortex or its pathway.
What you see: weakness of the lower face only. The forehead is spared, because the upper face gets fibres from both sides of the brain.
Forehead spared = upper motor neuron lesion (stroke). Forehead involved = lower motor neuron lesion (Bell's palsy).
Parotid surgery and tumours
How it happens: the facial nerve branches run through the parotid gland.
What you see: facial weakness if the nerve is damaged or invaded by a malignant tumour.
Trigeminal (V3) lesion
How it happens: injury or tumour affecting the mandibular nerve.
What you see: weak chewing on that side, and the jaw deviates towards the weak side on opening, because the healthy lateral pterygoid pushes it across.
Questions test the nerve supply of each group, the embryological arch, the muscle that opens the mouth, the nerve to buccinator, and the difference between upper and lower motor neuron facial palsy.
Quick revision
- Facial expression: second arch, facial nerve.
- Mastication: first arch, mandibular nerve (V3).
- Facial nerve branches in the parotid: temporal, zygomatic, buccal, marginal mandibular, cervical.
- Buccinator: facial nerve. Parotid duct pierces it opposite the upper second molar.
- Lateral pterygoid opens and protrudes; the others close.
- Bell's palsy: whole half of the face. Stroke: forehead spared.
Written by The House Job from standard anatomy references (Snell's Clinical Anatomy by Regions is the book named in the UHS PGET syllabus).
FAQ
Which nerve supplies the muscles of facial expression?
The facial nerve (VII).
Which muscle of mastication opens the mouth?
The lateral pterygoid.
What is the nerve supply of buccinator?
The buccal branch of the facial nerve. The buccal nerve from the mandibular nerve is only sensory.
Why is the forehead spared in a stroke?
The part of the facial nucleus supplying the forehead receives fibres from both sides of the brain.