Muscles of Facial Expression and Mastication: Structure and Function

Muscles of the Face and Neck

Overview

The muscles of the face and neck are responsible for facial expression, mastication (chewing), and certain movements of the head and neck. These muscles are categorized as superficial or deep based on their anatomical location. Understanding their names, locations, and functions is essential for students of anatomy and physiology.

Superficial Muscles of the Face

• Epicranius (Occipitofrontalis): A broad muscle covering the top of the skull, consisting of the frontal and occipital bellies connected by the epicranial aponeurosis. Function: Raises eyebrows and wrinkles the forehead.

• Frontal belly of occipitofrontalis: The anterior part of the epicranius. Function: Elevates the eyebrows and draws the scalp forward.

• Orbicularis oculi: Circular muscle surrounding the eye. Function: Closes the eyelids (blinking, squinting).

• Levator labii superioris: Runs from the upper lip to the infraorbital margin. Function: Elevates the upper lip.

• Zygomaticus minor and major: Extend from the zygomatic bone to the corners of the mouth. Function: Raise the corners of the mouth (smiling).

• Risorius: Extends from the fascia over the parotid gland to the angle of the mouth. Function: Draws the angle of the mouth laterally (grinning).

• Depressor anguli oris: Runs from the mandible to the angle of the mouth. Function: Depresses the corner of the mouth (frowning).

• Depressor labii inferioris: Runs from the mandible to the lower lip. Function: Depresses the lower lip.

• Platysma: Thin, superficial muscle covering the anterior neck. Function: Tenses the skin of the neck and helps depress the mandible.

Deep Muscles of the Face

• Corrugator supercilii: Small muscle located deep to the eyebrows. Function: Draws eyebrows medially and downward (frowning).

• Levator palpebrae superioris: Located in the upper eyelid. Function: Elevates the upper eyelid (opens the eye).

• Nasalis: Covers the nose. Function: Compresses the bridge and depresses the tip of the nose; flares nostrils.

• Levator anguli oris: Runs from the maxilla to the angle of the mouth. Function: Elevates the angle of the mouth (smiling).

• Masseter: Thick muscle at the angle of the jaw. Function: Elevates the mandible (closes the jaw); primary muscle of mastication.

• Buccinator: Forms the muscular portion of the cheek. Function: Compresses the cheek (as in blowing or sucking); assists in mastication.

• Orbicularis oris: Encircles the mouth. Function: Closes and protrudes the lips (kissing, speaking).

• Mentalis: Located at the tip of the chin. Function: Elevates and protrudes the lower lip (pouting).

Muscles of the Neck

• Sternocleidomastoid: Prominent muscle running from the sternum and clavicle to the mastoid process of the temporal bone. Function: Flexes the neck, rotates the head to the opposite side.

Table: Major Muscles of Facial Expression and Mastication

Muscle	Location	Primary Action
Frontal belly of occipitofrontalis	Forehead	Raises eyebrows, wrinkles forehead
Orbicularis oculi	Around eyes	Closes eyelids
Zygomaticus major/minor	Cheek to mouth corner	Elevates mouth corners (smiling)
Risorius	Cheek	Draws mouth laterally
Depressor anguli oris	Lower jaw to mouth corner	Depresses mouth corner (frowning)
Platysma	Neck	Tenses neck skin, depresses mandible
Masseter	Jaw	Elevates mandible (chewing)
Buccinator	Cheek	Compresses cheek
Orbicularis oris	Around mouth	Closes/protrudes lips
Sternocleidomastoid	Neck	Flexes/rotates head

Key Terms and Definitions

• Aponeurosis: A broad, flat tendon connecting muscles to each other or to bone.

• Facial expression: Movements of facial muscles that convey emotions.

• Mastication: The process of chewing food, involving muscles such as the masseter and buccinator.

Clinical Relevance

• Facial nerve (Cranial Nerve VII): Innervates most muscles of facial expression. Damage can result in facial paralysis (e.g., Bell's palsy).

• Trigeminal nerve (Cranial Nerve V): Innervates muscles of mastication (e.g., masseter, temporalis).

Example

• Smiling: Involves coordinated contraction of the zygomaticus major and minor, risorius, and orbicularis oculi.

• Frowning: Involves contraction of the corrugator supercilii and depressor anguli oris.

Additional info: The above notes synthesize the labeled muscles from the provided diagram and expand with standard anatomical context for clarity and completeness.