Detailed Study Notes on Facial Muscles

Chapter 3: Muscles of the Face

Characteristics of Facial Muscles

  • Thin, flat sheets of muscles.

  • Located in the subcutaneous tissue primarily around the orifices of the face.

  • Inserted into the dermis layer of the skin.

  • Innervated by the facial nerve (cranial nerve VII), originating from the 2nd pharyngeal (branchial) arch.

  • Common functions include guarding facial orifices and facilitating facial expressions.

Classification of Facial Muscles

I. Muscles of the Eyelids

  • Closure: Responsible for closing the eyelids.

    • Example: Orbicularis oculi.

  • Opening: Responsible for opening the eyelids.

    • Example: Levator palpebrae superioris.

II. Muscles of the Nose

  • Closure: Muscles that close the nostrils.

  • Opening: Muscles that open the nostrils.

  • Others: Additional musculoskeletal functions in the nasal region.

    • Examples: Compressor naris, dilator naris, procerus.

III. Muscles of the Lips and Cheeks

  • Closure: Muscles that close the mouth.

    • Example: Orbicularis oris.

  • Opening: Muscles that open the mouth.

Orbicularis Oris

  • Origin: Midline of the upper jaw (incisive slips) and lower jaw (mental slips).

  • The muscle fibers curve around the mouth at the angles of the mouth; the decussating fibers lateral to the mouth are referred to as the modiolus.

  • Nerve Supply: Supplied by the facial nerve through its buccal branches.

  • Actions:

    1. Narrows the mouth opening, important for functions such as whistling and blowing.

    2. Essential for speech.

Orbicularis Oculi

  • Consists of three parts:

    1. Palpebral Part:

    • Forms a complete ellipse around the eyelids.

    • Origin: Medial palpebral ligament.

    • Insertion: Lateral palpebral ligament (raphe).

    • Action: Blinking of the eyelids.

    1. Orbital Part:

    • Origin: Anterior lacrimal crest and frontal process of the maxilla.

    • Action: Forcible closure of the eyelids.

    1. Lacrimal Part:

    • Origin: Posterior lacrimal crest (part of the lacrimal bone).

    • Insertion: Into the lacrimal sac.

    • Action: Creates negative pressure in the lacrimal sac to suck tears into the sac.

  • Nerve Supply: Supplied by the facial nerve.

Buccinator

  • Origin: Outer surface of the maxilla above the last three molar teeth, pterygomandibular raphe, oblique line of the mandible.

  • Insertion:

    • Upper fibers: into the upper lip.

    • Lower fibers: into the lower lip.

    • Middle fibers: decussate at the modiolus (where upper and lower fibers exchange).

  • Nerve Supply: Supplied by the facial nerve through its buccal branches.

  • Actions:

    1. Prevents accumulation of food in the vestibule of the mouth (region between the cheeks, teeth, and gums).

    2. Expels air from the mouth cavity (important for whistling).

Nerve Supply of the Face

  • Sensory Supply:

    • The skin of the face is primarily innervated by the trigeminal nerve (cranial nerve V), except for a small area covering the angle of the mandible which is supplied by the great auricular nerve (C2, 3).

    • Divisions of the Trigeminal Nerve:

    • Ophthalmic Division:

      • Branches:

      • Frontal nerve (gives rise to supraorbital and supratrochlear nerves).

      • Lacrimal nerve.

      • Nasociliary nerve (branches include the infratrochlear nerve and external nasal nerve).

    • Maxillary Division:

      • Branches:

      • Infraorbital nerve (gives rise to palpebral, nasal, and labial branches).

      • Zygomaticofacial nerve.

    • Mandibular Division:

      • Branches:

      • Buccal nerve (supplies skin over buccinator).

      • Mental nerve (supplies skin of the lower lip).

  • Motor Supply:

    • The facial nerve (VII) is responsible for motor innervation of facial muscles, exiting the skull via the stylomastoid foramen. It gives off several branches:

    1. Posterior auricular nerve (supplies occipitalis and auricularis posterior).

    2. Branch to posterior belly of digastric and stylohyoid muscles.

    • Inside the parotid gland, it splits into five terminal branches:

    • Temporal branches: Supply frontalis and upper orbicularis oculi.

    • Zygomatic branches: Supply eyefrontalis and orbicularis oculi; paralysis leads to inability to blink.

    • Buccal branches: Supply buccinator and muscles surrounding the upper lip.

    • Mandibular branch: Supplies muscles of the lower lip.

    • Cervical branch: Supplies the platysma muscle.

Arterial Supply of the Face

I. Arteries from the Internal Carotid Artery:

  • Ophthalmic Artery: Provides branches for the face including:

    1. Supraorbital artery.

    2. Supratrochlear artery.

    3. Dorsal nasal artery.

    4. Medial and lateral palpebral arteries.

    5. Zygomaticofacial artery.

II. Arteries from the External Carotid Artery:

  • Facial Artery:

    • Course: Pierces deep fascia at the mandibular border moving upwards, curving anterior to anterior facial vein, ending at the eye's medial angle.

    • Branches include:

    1. Inferior labial artery (supplies lower lip).

    2. Superior labial artery (supplies upper lip).

    3. Lateral nasal artery (becomes angular artery).

  • Superficial Temporal Artery: Emerges from the parotid gland; gives rise to:

    • Transverse facial artery.

    • Zygomatico-orbital artery.

  • Maxillary Artery: Also branches from the external carotid artery, contributing:

    1. Mental artery (supplies chin, traverses mental foramen).

    2. Buccal artery (passes between lateral pterygoid heads).

    3. Infraorbital artery (continuation passing through infraorbital foramen).

Venous Drainage of the Face and Scalp

  1. Anterior Facial Vein: Begins at the medial eye angle, drains into the internal jugular vein via the common facial vein.

  2. Retro-mandibular Vein: Formed in the parotid gland, splits into anterior (joining facial vein) and posterior divisions (joining posterior auricular vein).

  3. Occipital Vein: Drains posterior scalp into the suboccipital plexus.

Clinical Relevance

  • Dangerous Area of the Face:

    • Region potentially susceptible to infections connecting to the cavernous sinus, includes:

    • Medial angle of the eye.

    • Dorsum and sides of nose.

    • Upper lip and median part of cheeks.

  • Facial Paralysis (Bell's Palsy):

    • Manifestations:

    1. Loss of skin creases on the affected side.

    2. Inability to close the eye firmly due to orbicularis oculi paralysis.

    3. Deviation of the mouth toward the healthy side.

    4. Inability to whistle due to orbicularis oris paralysis.

    5. Accumulation of food in the vestibule due to buccinator paralysis.

    • Cause: Trauma to the facial nerve as it emerges from stereomastoid foramen.

Note: This document encompasses a comprehensive breakdown of the facial muscles, their anatomy, nerve supplies, vascularization, and clinical significance.