Facial Anatomy: Apertures, Muscles & Nerves

• The face is the front part of the head, located between the ears and from the chin to the hairline.
• The facial skeleton includes the front part of the skull and the mandible.
• Major openings in the facial skeleton are the orbits, piriform aperture, and oral aperture.
• The supraorbital, infraorbital, and mental foramina are aligned vertically.

Skin of the Face

• Tension lines in facial skin run in an 'onion skin' pattern from mouth to ear.
• Senile facial wrinkles are perpendicular to the pull of underlying muscles.
• Horizontal wrinkles on the brow, crow's feet at the lateral canthus, and vertical lip wrinkles are examples of senile wrinkles.
• Incisions along these wrinkles result in minimal scarring.

Muscles of the Face

• Facial expression muscles develop from the mesoderm of the second pharyngeal arch.
• These muscles migrate to their adult positions and are supplied by the facial nerve (seventh cranial nerve).
• They are specialized parts of the panniculus carnosus, which attaches to the dermis, causing wrinkles or dimples.
• The face lacks a deep fascia.
• Functionally, facial muscles form groups around the orifices of the orbit, nose, and mouth.
• Each orifice has a sphincter and dilator arrangement.
• The purpose of the facial muscles is to control these orifices.
• Varying expressions are side effects, and humans are sensitive to minor changes in these expressions.
• Some muscles supplied by the facial nerve do not affect facial expression.
• Facial expressions are also produced by muscles not supplied by the facial nerve.
• Facial appearances are determined by the contour of connective tissues and their connections to muscles, influenced by genetic expression.
• Facial expression muscles are best understood by their functional arrangement around the orbits, nose, and mouth.

Muscles of the Eyelids

• The palpebral fissure is surrounded by the orbicularis oculi (sphincter) and dilated by the levator palpebrae superioris and occipitofrontalis.
• Orbicularis oculi has two parts: palpebral (confined to the lids) and orbital (extending beyond the orbital margins).
• The palpebral part arises from the medial palpebral ligament and inserts into the lateral palpebral raphe.
• Some lower fibers attach to the posterior lacrimal crest and lacrimal sac.
• The orbital arises from the anterior lacrimal crest and the frontal process of the maxilla, encircling the orbital margin.
• Temporal and zygomatic branches of the facial nerve supply the orbicularis oculi.
• Contraction of the palpebral fibers gently closes the eyelids and stretches the lacrimal sac without diminishing the conjunctival sac volume.
• The orbital part lowers the eyebrow to shade the eye.
• Contraction together closes the eyelids forcibly, diminishing the conjunctival sac volume and causing tears to spill out.
• In normal eye closure, the lateral upper lid comes down first, spreading lacrimal secretion from the gland side towards the nose.
• Levator palpebrae superioris opposes the palpebral fibers of orbicularis oculi.
• Occipitofrontalis is associated with the scalp.

Muscles of the Nostrils

• The transverse part of nasalis (compressor naris) acts as the sphincter muscle of the nostril, embracing the alar cartilages.
• The alar part of nasalis (dilator naris) is the opponent, inserting into the lateral part of the ala.
• Both arise from the maxilla.
• Procerus and levator labii superioris alaeque nasi elevate the nose.
• Depressor septi depresses the nose, assisted by elastic recoil of nasal cartilages.
• Zygomatic and buccal branches of the facial nerve supply these muscles.

Muscles of the Lips and Cheeks

• Orbicularis oris acts as the sphincter.
• The remaining facial muscles act as the dilator mechanism, radiating outwards from the lips.
• Orbicularis oris consists of intrinsic fibers attached near the midline to the jaws and extrinsic fibers from the dilator muscles.
• Incisive and mental slips curve around the angle of the mouth, forming a loop.
• These are the deepest orbicularis fibers, and the mucous membrane of the lips is firmly attached to them.
• Most extrinsic fibers come from the buccinator.
• Buccinator fibers converge towards the modiolus, forming a chiasma.
• The uppermost and lowermost fibers pass into their respective lips, while the middle fibers decussate.
• Buccal and marginal mandibular branches of the facial nerve supply the orbicularis oris.
• Damage to the marginal mandibular branch causes drooping of the corner of the mouth.
• Contraction of the orbicularis oris narrows the mouth, pursing the lips.
• Buccinator originates from both jaws opposite the molar teeth and from the pterygomandibular raphe.
• It arises just beyond the buccogingival fold, away from the gum margin.
• The origin line passes horizontally backwards, skirts the root of the zygomatic process, and curves downwards to the tuberosity of the maxilla.
• A fibrous band (pterygomaxillary ligament) connects the hamulus tip to the nearest part of the tuberosity of the maxilla.
• The tendon of tensor palati hooks around the base of the hamulus through a gap above this band.
• The pterygomandibular raphe extends from the hamulus tip to the mandible above the mylohyoid line.
• Buccinator arises from the entire raphe length, interdigitating with the superior constrictor fibers.
• The raphe passively elongates when the mouth is open.
• The mandibular attachment of the raphe is separated from the posterior attachment of mylohyoid; the lingual nerve rests on the mandible.
• Buccinator converges on the modiolus, where fibers decussate.
• The outer surface is pierced by the parotid duct opposite the third upper molar tooth.
• The buccal fat pad lies on the outer surface of buccinator and is prominent in infants.
• Molar glands (four or five nodules) lie beneath the fat, piercing the muscle to open on the cheek's mucous membrane.
• Buccal branches of the facial nerve supply the buccinator.
• Filaments from the buccal branch of the mandibular nerve are proprioceptive only.
• Buccinator is an accessory muscle of mastication, returning the bolus from the cheek pouch to the molars.
• Does not move the jaw.
• Buccinator helps keep food out of the vestibule of the mouth and between the teeth.
• When cheeks are puffed out, the muscle is relaxed, contracting only in forcible expulsion of air.
• Contraction obliterates the vestibule cavity and pulls the closed lips tightly back against the teeth.

Dilator Muscles of Lips

• Dilator muscles radiate from orbicularis oris, inserting into the lips or modiolus and opening the lips into a wide circle.
• Upper and lower lips have elevator and depressor muscles.
• Muscles converge towards the angle of the mouth, building up the modiolus with decussating fibers.
• Fibrous tissue binds intersecting fibers in the modiolus, allowing it (and the angle of the mouth) to be moved about.
• The modiolus lies lateral to the mouth's angle, opposite the second upper premolar tooth, and is important in prosthetic dentistry.
• Levator labii superioris alaeque nasi arises from the frontal process of the maxilla and elevates the alar cartilage and upper lip.
• Levator labii superioris arises from the inferior orbital margin and elevates the upper lip.
• Levator anguli oris arises from the canine fossa below the infraorbital margin, with the infraorbital nerve sandwiched between it and levator labii superioris, converging to the modiolus.
• Zygomaticus minor from the zygomaticomaxillary suture and zygomaticus major on the zygomatic bone converge to the modiolus.
• Risorius is a variable muscle extending from the platysma, converging on the modiolus.
• Depressor anguli oris arises from the oblique line of the mandible, passing through the modiolus.
• Depressor labii inferioris arises deep to depressor anguli oris, inserting into the lower lip.
• Mentalis arises from the symphysis menti, passing through depressor labii inferioris to reach the skin, elevating the skin of the chin and centre of the lower lip.

Nerve Supply of Face Muscles

• All described muscles receive motor supply from the facial nerve.
• The facial nerve contains no sensory fibers on the face.
• Proprioceptive impulses from facial muscles are conveyed centrally by the trigeminal nerve.
• Cutaneous branches of the trigeminal nerve intermingle with facial nerve branches.
• Muscles supplied by the facial nerve receive proprioceptive innervation from branches of the sensory nerve supplying the skin over the muscle.
• Branches of the trigeminal nerve provide afferent innervation for all facial muscles.
• The transverse cervical nerve supplies platysma, lying beyond the trigeminal nerve's cutaneous distribution.

Facial Nerve Branches

• The facial nerve emerges from the stylomastoid foramen, giving off the posterior auricular nerve.
• A muscular branch supplies the posterior belly of digastric and stylohyoid.
• The nerve divides into temporozygomatic and cervicofacial branches before entering the parotid gland.
• Within the parotid gland, each divides and rejoins to divide again, emerging in five main groups of branches (pes anserinus).
• Pes anserinus lies superficial to the retromandibular vein and external carotid artery. -The five digits indicate the five branches of the nerve
• Temporal branches emerge from the upper border of the gland, cross the zygomatic arch, and supply auricularis anterior and superior, and part of frontalis, important for wrinkling the forehead.
• Zygomatic branches consist of upper and lower parts, proceeding above and below the eye.
• Upper branches supply frontalis and the upper half of orbicularis oculi.
• Lower branches supply the lower half of orbicularis oculi and muscles below the orbit.
• Paralysis prevents blinking, leading to corneal ulceration and impaired vision.
• Buccal branches supply buccinator and upper lip muscle fibers (orbicularis oris and lower fibers of the elevators).
• Paralysis prevents emptying of the cheek pouch, affecting chewing.
• The marginal mandibular branch supplies the lower lip muscles.
• It emerges from the lower border of the parotid gland and may pass into the neck below the angle of the mandible.
• It crosses the inferior border of the mandible to reach the face beyond the anterior border of the masseter muscle, crossing the facial artery and vein.
• Incision of an abscess near the nerve can result in permanent paralysis of the lower lip.
• The cervical branch passes vertically downwards from the lower border of the parotid gland behind the mandible and supplies platysma.
• The marginal mandibular branch occasionally arises from it below the parotid gland.

Explore the facial skeleton's primary apertures including orbits to oral fissure. Understand facial tension lines influencing wrinkle formation and scarring. Learn about the facial muscles' origin from the first pharyngeal arch mesoderm and the facial nerve's exclusive innervation.