Learning objectives
- Identify the major facial muscle groups by region, origin, insertion, and action
- Describe the superficial musculoaponeurotic system (SMAS) and its clinical significance
- Explain the relationship between facial musculature and the overlying soft tissue compartments
- Recognise anatomical danger zones relevant to injectable and energy-based treatments
- Apply anatomical knowledge to treatment planning and adverse event prevention
Section 01
Overview of facial musculature
The facial muscles — collectively termed the muscles of facial expression or mimetic muscles — are unique in that the majority insert directly into the dermis rather than into bone. This direct dermal attachment is what enables the skin to move and form the full range of human expression. It is also what makes these muscles highly relevant to aesthetic practitioners: both their contractile function and their atrophy determine the texture, volume distribution, and dynamic line formation that underpin the ageing face.
Unlike the muscles of the limbs, most facial muscles are derived from the second pharyngeal arch and are innervated by the facial nerve (cranial nerve VII). Understanding the branching anatomy of CN VII is inseparable from understanding facial muscle anatomy — injury to any branch, whether from trauma, surgical dissection, or a misplaced injection, produces predictable functional deficit.
The facial muscles are broadly organised by region: the forehead and scalp, the periorbital region, the nose, the cheeks and midface, the perioral region, and the neck. Each region is covered in detail below.
Foundation note
The facial muscles are generally thin, flat, and difficult to palpate in isolation. In clinical practice, their position is inferred through movement: asking a patient to raise their brows, squint, smile, or pucker will reliably activate specific muscle groups. This dynamic assessment is the foundation of injectable treatment planning.
Advanced note
The concept of agonist–antagonist muscle balance is central to advanced neuromodulator practice. Weakening a depressor muscle (e.g. depressor anguli oris) without considering the pull of its antagonist elevator (e.g. zygomaticus major) can produce asymmetry. Comprehensive anatomical knowledge allows the practitioner to predict and correct these imbalances.
Section 02
The SMAS — superficial musculoaponeurotic system
The SMAS is a fibromuscular layer that envelops the muscles of facial expression, connecting them to the overlying dermis and the underlying deep facial fascia. First described by Mitz and Peyronie in 1974, it represents one of the most clinically significant anatomical concepts in aesthetic medicine.
The SMAS is continuous with the platysma inferiorly, the temporoparietal fascia superiorly, and the galea aponeurotica of the scalp. It acts as a mechanical coupling between muscle contraction and skin movement — the reason a smile produces cheek elevation rather than simply wrinkling the overlying skin in isolation.
In the midface, the SMAS is intimately associated with the retaining ligaments (osteocutaneous and fibromuscular ligaments) that anchor the soft tissue to the underlying skeleton. As these ligaments weaken with age, the SMAS and attached soft tissue descend — producing the characteristic features of facial ageing: deepening nasolabial folds, jowling, and loss of the acute cervicomental angle.
Advanced note — injectable relevance
Filler placement relative to the SMAS determines both the aesthetic result and the safety profile of an injection. Supraperiosteal placement (deep to muscle) is generally the safest plane for high-volume structural augmentation. Subdermal placement above the SMAS carries a higher vascular risk in areas where named vessels run within or immediately superficial to this layer. A clear mental model of the SMAS plane is therefore essential for safe deep-plane work.
| Structure |
Continuity |
Clinical significance |
| SMAS proper |
Platysma (inferior), temporoparietal fascia (superior) |
Primary surgical plane in rhytidectomy; injectable reference layer |
| Galea aponeurotica |
SMAS (via frontalis) |
Transmits frontalis contraction across scalp |
| Platysma |
SMAS (superior), pectoral fascia (inferior) |
Neck banding; neuromodulator target for Nefertiti lift |
| Retaining ligaments |
Anchor SMAS to periosteum / dermis |
Laxity contributes to ptosis; injection release technique described |
Section 03
Forehead and scalp musculature
The forehead region contains the frontalis muscle, the primary brow elevator, alongside the corrugator supercilii and procerus — the primary brow depressors responsible for glabellar rhytids.
Frontalis
M. frontalis
OriginGalea aponeurotica at the coronal suture level
InsertionSkin and subcutaneous tissue of the forehead; blends with orbicularis oculi and corrugator at brow level
ActionElevates the brow and forehead skin; produces horizontal forehead lines
InnervationTemporal branch of CN VII
Clinical noteThe only brow elevator. Over-treatment with neuromodulators can cause brow ptosis. Medial–lateral pattern variation is significant: some individuals have a central gap in frontalis fibres, requiring tailored injection patterns.
Corrugator supercilii
M. corrugator supercilii
OriginMedial supraorbital ridge (superciliary arch)
InsertionSkin of the medial eyebrow (deep and superficial heads)
ActionDraws the brow medially and inferiorly; produces vertical glabellar lines ("11 lines")
InnervationTemporal branch of CN VII
Clinical noteHas two heads (transverse and oblique). The transverse head runs in a deeper plane. Accurate injection requires appreciation of depth variation across the muscle's course.
Procerus
M. procerus
OriginFascia covering the lower nasal bones and upper lateral cartilages
InsertionSkin between the eyebrows; blends with frontalis
ActionPulls the medial brow inferiorly; produces horizontal nasal root lines ("bunny lines" when over-recruited)
InnervationTemporal and buccal branches of CN VII
Clinical noteTreated as a single midline injection point in standard glabellar protocols. Often under-treated in isolation, leading to residual horizontal lines at the nasal root.
Depressor supercilii
M. depressor supercilii
OriginMedial orbital rim (frontal process of maxilla)
InsertionMedial aspect of brow skin
ActionDepresses the medial brow; contributes to glabellar complex activity
InnervationTemporal branch of CN VII
Clinical noteOften functionally integrated with the corrugator supercilii. Some anatomists classify it as a component of the orbicularis oculi. Frequently targeted alongside corrugator in comprehensive glabellar treatment.
Clinical application
The glabellar complex (frontalis, corrugator supercilii, procerus, depressor supercilii) is the most commonly treated region with neuromodulators in aesthetic practice. Understanding the relative contributions of each muscle is essential for avoiding the characteristic complications of over- or under-treatment: lateral brow elevation ("Spock brow") from selective frontalis weakening, medial brow ptosis, or residual oblique lines from incomplete corrugator treatment.
Section 04
Periorbital musculature
The periorbital region contains the orbicularis oculi — the muscle responsible for eyelid closure, and a central player in crow's feet formation and lower eyelid aesthetics. The periorbital region also contains the levator palpebrae superioris (a skeletal muscle of extraocular origin) and the smaller muscles of the medial and lateral canthi.
Orbicularis oculi
M. orbicularis oculi
OriginMedial palpebral ligament, frontal process of maxilla, lacrimal bone
InsertionEncircles the orbit; fibres interdigitate laterally to form the lateral palpebral raphe
ActionOrbital part: forceful eye closure (blinking and squinting). Palpebral part: gentle eyelid closure. Lacrimal part: dilates lacrimal sac during blinking
InnervationTemporal and zygomatic branches of CN VII
Clinical noteThe lateral orbital fibres (orbital part) are the primary target for crow's feet neuromodulator treatment. The palpebral part lies within 1–2 mm of the orbital rim — injection here risks diffusion to the levator palpebrae, causing eyelid ptosis. Injections lateral to the orbital rim reduce this risk substantially.
Levator palpebrae superioris
M. levator palpebrae superioris
OriginLesser wing of sphenoid, above optic canal
InsertionSuperior tarsal plate and skin of upper eyelid
ActionElevates the upper eyelid
InnervationOculomotor nerve (CN III) — NOT CN VII
Clinical noteThough not a target of aesthetic treatment, the levator palpebrae is the muscle implicated in the most feared complication of periorbital neuromodulator injection: upper eyelid ptosis. Diffusion through the orbital septum from glabellar or brow injections can transiently paralyse this muscle.
Advanced note — eyelid ptosis mechanism
Upper eyelid ptosis following neuromodulator injection occurs via diffusion of toxin through the orbital septum to the levator palpebrae superioris. The risk is higher with injections placed medially and close to the orbital rim, particularly below the brow. The 1 cm above orbital rim rule for glabellar injections is based on the thickness and integrity of the septum at various positions. Apraclonidine 0.5% eye drops (an alpha-2 adrenergic agonist) can partially ameliorate the ptosis by stimulating Müller's muscle (superior tarsal muscle), an accessory elevator innervated by the sympathetic nervous system.
Section 05
Nasal musculature
The nasal muscles are small, often overlooked, and clinically relevant in both neuromodulator practice (nasal tip elevation, bunny lines, nostril flare reduction) and in understanding the dynamics of the upper lip complex.
| Muscle |
Action |
Clinical relevance |
| Nasalis (transverse) |
Compresses the nostril (nose flaring, reversed) |
Target for nostril flare reduction; blends with procerus superiorly |
| Nasalis (alar) |
Dilates the nostril |
Treatment here risks compromising nasal patency; rarely indicated |
| Depressor septi nasi |
Depresses the nasal tip and columella; animates the upper lip downward during smiling |
Primary target for nasal tip elevation (injection at the nasal spine); relevant in gummy smile treatment |
| Procerus |
Pulls medial brow inferiorly; horizontal nasal root lines |
Treated with corrugator/glabellar complex; also target for bunny lines at nasal root |
| Levator labii superioris alaeque nasi |
Elevates the upper lip and dilates the nostril |
Contributes to nasal flare and gummy smile; longest named muscle in the body |
Clinical application — depressor septi nasi
The depressor septi nasi (DSN) pulls the nasal tip inferiorly during animation — a feature particularly noticeable during smiling. Treatment of the DSN with 2–4 units of botulinum toxin at the nasal spine (columellar base) is a well-described technique for nasal tip elevation. The same injection often contributes to improvement in a dynamic gummy smile. The key injection point is in the midline, at the base of the columella — superficial, subcutaneous, with the needle bevel up.
Section 06
Cheek and midface musculature
The midface contains the largest and most complex grouping of facial muscles, including the zygomaticus major — the primary smile muscle — and the buccinator, masseter, and several lip elevators. This region is also traversed by the parotid duct and facial artery, making thorough anatomical knowledge critical for safe treatment.
Zygomaticus major
M. zygomaticus major
OriginZygomatic bone (anterior to zygomaticotemporal suture)
InsertionModiolus (fibromuscular node at the oral commissure) and skin of the upper lip
ActionDraws the oral commissure superiorly and laterally — primary muscle of smiling
InnervationBuccal and zygomatic branches of CN VII
Clinical noteBifid zygomaticus major (double zygomaticus) occurs in a significant proportion of patients and is associated with cheek dimples. Understanding its pathway is important when treating the nasolabial fold with filler — inadvertent injection into or around this muscle can impair smile symmetry.
Zygomaticus minor
M. zygomaticus minor
OriginZygomatic bone (medial to zygomaticus major)
InsertionUpper lip (lateral to levator labii superioris)
ActionElevates the upper lip; contributes to the nasolabial fold deepening during smiling
InnervationBuccal branch of CN VII
Clinical noteWhen present (anatomical variant in ~40% of individuals), the zygomaticus minor contributes to the dynamics of the nasolabial fold and medial cheek. Appreciation of this variation is relevant in surgical and filler midface work.
Levator labii superioris
M. levator labii superioris
OriginInfraorbital margin (maxilla)
InsertionUpper lip (skin and muscle)
ActionElevates and everts the upper lip; deepens the nasolabial fold
InnervationBuccal branch of CN VII
Clinical noteOne of the muscles implicated in gummy smile (class II). Treatment with neuromodulator in the infraorbital region targets this muscle. Careful dosing is required to avoid undue lip ptosis or asymmetry.
Masseter
M. masseter
OriginZygomatic arch (superficial head) and deep surface of zygomatic arch (deep head)
InsertionLateral surface of ramus and angle of mandible
ActionPrimary jaw closer; elevates the mandible for chewing
InnervationMasseteric nerve (branch of CN V3 — mandibular trigeminal)
Clinical noteA primary target for jaw slimming and bruxism treatment with neuromodulators. The masseteric hypertrophy treatment requires injection into the lower third of the muscle bulk, palpated at the angle of the mandible. High injections risk weakening the zygomaticus, buccinator, or risorius.
Buccinator
M. buccinator
OriginAlveolar processes of maxilla and mandible (opposite molar teeth); pterygomandibular raphe posteriorly
InsertionModiolus; blends with orbicularis oris
ActionCompresses cheeks against teeth; involved in blowing, chewing, sucking
InnervationBuccal branch of CN VII; sensory supply from buccal branch of CN V3
Clinical noteThe parotid duct (Stensen's duct) pierces the buccinator at the level of the upper second molar. Filler injections in the mid-buccal region carry a risk of duct injury — rare but described. The buccal fat pad lies immediately lateral to the buccinator and is a key volumetric structure in midface aesthetics.
Risorius
M. risorius
OriginParotid fascia
InsertionModiolus; skin at the corner of the mouth
ActionRetracts the commissure laterally (produces a "grimace" smile)
InnervationBuccal and mandibular branches of CN VII
Clinical noteA variable muscle with significant individual anatomy. When over-dominant relative to the zygomaticus, the risorius contributes to a wide, flat smile. Rarely a direct injection target but relevant in understanding smile mechanics and commissure position.
Section 07
Perioral musculature
The perioral region is dominated by the orbicularis oris — the sphincter of the mouth — and surrounded by multiple depressor and elevator muscles that converge at the modiolus. This complex is central to lip aesthetics, gummy smile treatment, and marionette line formation.
Orbicularis oris
M. orbicularis oris
OriginNo bony origin; formed by interdigitation of surrounding muscles converging at the modiolus
InsertionSkin and mucosa of the lips
ActionCloses and purses the lips; involved in speech, kissing, whistling
InnervationBuccal and mandibular branches of CN VII
Clinical noteThe peri-oral vertical lines ("lipstick lines") are caused by repeated contraction of the orbicularis oris in combination with age-related volume loss and dermal thinning. Neuromodulator treatment of this muscle requires low doses and careful placement to preserve lip function. Filler is generally the preferred treatment for lip lines.
Depressor anguli oris
M. depressor anguli oris (DAO)
OriginOblique line of the mandible
InsertionModiolus and skin at the oral commissure
ActionPulls the oral commissure inferiorly; contributes to the downturned mouth appearance and marionette lines
InnervationMarginal mandibular branch of CN VII
Clinical noteA primary neuromodulator target for the downturned commissure. The DAO runs in a fairly consistent pathway from the mandibular body laterally upwards to the modiolus. Injection is typically 1–1.5 cm lateral to the commissure and 1 cm above the mandibular border. Medial placement risks the depressor labii inferioris and can impair speech and oral competence.
Depressor labii inferioris
M. depressor labii inferioris (DLI)
OriginAnterior mandible (oblique line, between mental foramen and symphysis)
InsertionSkin and muscle of the lower lip
ActionPulls the lower lip inferiorly and laterally; contributes to lower lip eversion and lower dental show
InnervationMarginal mandibular branch of CN VII
Clinical noteTreated for smile asymmetry (where one side shows excessive lower lip depression) and as part of lip flip refinement. The marginal mandibular nerve runs close to the DLI — inadvertent blockade causes lower lip asymmetry and drooping.
Mentalis
M. mentalis
OriginIncisive fossa of the mandible (below lower incisors)
InsertionSkin of the chin
ActionRaises and wrinkles the chin skin; protrudes the lower lip
InnervationMarginal mandibular branch of CN VII
Clinical noteHyperactive mentalis produces the characteristic "cobblestone" or "pebbly" chin — a common neuromodulator target. Over-treatment can soften the chin pad excessively, reducing projection. The mental nerve exits the mental foramen just lateral to the midline — a key anatomical landmark during chin filler injection.
Section 08
Neck musculature
The platysma is the primary aesthetic muscle of the neck and the inferior continuation of the SMAS. The sternocleidomastoid (SCM) and posterior cervical muscles are generally not aesthetic injection targets, but their relationship to neck anatomy and key vascular structures is clinically important.
Platysma
M. platysma
OriginFascia of the pectoralis major and deltoid (infraclavicular region)
InsertionInferior border of the mandible; blends with muscles of the lower face and SMAS superiorly; skin of the lower face and neck
ActionTenses neck skin; pulls the mandible and lower lip inferiorly; assists in depressing the commissures
InnervationCervical branch of CN VII
Clinical notePlatysmal banding — visible vertical cords in the neck — is a primary indication for neuromodulator treatment (the "Nefertiti lift"). Bands are treated with multiple injections of 2–4 units along each visible band. The medial bands are the most prominent. Injection depth is subcutaneous to superficial platysma — care is taken to avoid the external jugular vein and carotid vessels, which lie deep to the platysma in the lateral neck.
Sternocleidomastoid
M. sternocleidomastoid (SCM)
OriginSternal head: manubrium sterni. Clavicular head: medial third of clavicle
InsertionMastoid process and lateral superior nuchal line of occipital bone
ActionIpsilateral neck flexion; contralateral rotation; bilateral: neck flexion, assists respiration
InnervationAccessory nerve (CN XI) and C2–C3 cervical plexus
Clinical noteRarely a direct aesthetic target (except in specialist spasticity or torticollis practice). Its anterior border defines the posterior triangle of the neck — a key landmark for identifying the external jugular vein and cervical plexus branches.
Section 09
Anatomical danger zones
Certain regions of the face carry elevated risk for vascular injury, nerve compromise, or inadvertent muscle effects during injectable and energy-based treatments. The following is not a comprehensive vascular anatomy reference — it is a muscle-anatomy-informed summary of clinically critical zones. A dedicated vascular anatomy module is recommended in conjunction with this content.
High-risk injection zones
Advanced — vascular and nerve awareness
- Glabellar complex: Supratrochlear and supraorbital arteries run in predictable pathways lateral to midline at the brow. Deep injections medial to the midpupillary line at brow level risk inadvertent intravascular injection with documented cases of retinal artery embolism.
- Nasal region: The dorsal nasal artery and angular artery converge at the nasal tip. This is one of the highest-risk filler zones in the face. Muscle anatomy (nasalis, depressor septi) provides surface landmarks but vascular awareness is paramount.
- Infraorbital / tear trough: The infraorbital foramen, with its emerging neurovascular bundle, lies at the midpupillary line approximately 8–10 mm below the infraorbital rim. Filler injection in this zone risks vascular occlusion with potential orbital sequelae.
- Temporal region: The middle temporal vein ("danger vein") and superficial temporal artery traverse this region. The temporal fat pad is a high-risk filler zone — intravascular injection in the temporal artery has a retrograde pathway to the ophthalmic circulation.
- Perioral: The superior and inferior labial arteries run within the orbicularis oris muscle, not at the vermilion border. Intramuscular injection with filler in the lip body carries a higher risk of intravascular injection than submucosal or subcutaneous placement.
- Mandibular border (DAO region): The facial artery crosses the inferior mandibular border at approximately the anterior border of the masseter. It then runs superiorly toward the oral commissure in a variable but generally subdermal course. Awareness of this pathway is essential during commissure filler and DAO neuromodulator treatment.
Advanced note — vascular risk stratification
Not all facial regions carry equal vascular risk. Risk is highest in zones that supply the ophthalmic circulation via anastomoses: the glabella, nose, and temporal region. Risk is lower (but not absent) in zones with terminal vessel supply without ophthalmic connection: the lips and chin. All practitioners performing injectable treatments should have a current understanding of arterial anatomy, an emergency hyaluronidase protocol (for HA fillers), and the ability to recognise the early signs of vascular compromise: blanching, pain disproportionate to the procedure, livedo reticularis pattern, and vision changes.
Reference index
All anatomical and clinical statements in this module are drawn from or consistent with the following peer-reviewed and authoritative sources. This index is maintained as a living document and updated on each module review cycle.
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[1]
Standring S, ed. Gray's Anatomy: The Anatomical Basis of Clinical Practice. 42nd ed. Elsevier; 2020. Chapters 29–31: Head and Neck Musculature. [Primary anatomical reference for all muscle origin, insertion, action, and innervation data in this module.]
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[2]
Mitz V, Peyronie M. The superficial musculo-aponeurotic system (SMAS) in the parotid and cheek area. Plast Reconstr Surg. 1974;58(1):80–88. doi:10.1097/00006534-197607000-00013. [Original description of the SMAS layer.]
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Rohrich RJ, Pessa JE. The fat compartments of the face: anatomy and clinical implications for cosmetic surgery. Plast Reconstr Surg. 2007;119(7):2219–2227. doi:10.1097/01.prs.0000265403.66886.54. [Facial fat compartments and their relationship to SMAS and muscle planes.]
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[4]
de Maio M, Rzany B. Botulinum Toxin in Aesthetic Medicine. 2nd ed. Springer; 2014. [Comprehensive reference for neuromodulator injection anatomy and technique.]
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[5]
Braz AV, Humphrey S, Weinkle S, et al. Individual approach to the glabellar region. J Drugs Dermatol. 2013;12(12):1283–1294. [Glabellar complex anatomy and injection pattern individualisation.]
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[6]
Pessa JE, Rohrich RJ. Facial Topography: Clinical Anatomy of the Face. Quality Medical Publishing; 2012. [Regional facial anatomy with surgical and injectable clinical correlation.]
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[7]
Carruthers J, Carruthers A. Botulinum Toxin. 4th ed. Elsevier Saunders; 2013. Procedures in Cosmetic Dermatology Series. [Standard clinical reference for neuromodulator anatomy and technique in aesthetic practice.]
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[8]
Cotofana S, Lachman N. Arteries of the face and their relevance for minimally invasive facial procedures: an anatomical review. Plast Reconstr Surg. 2019;143(2):416–426. doi:10.1097/PRS.0000000000005201. [Vascular anatomy in the context of aesthetic injectable treatments; danger zone reference.]
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[9]
Scheuer JF III, Sieber DA, Pezeshk RA, Campbell CF, Gassman AA, Rohrich RJ. Anatomy of the facial danger zones: maximising safety during soft-tissue filler injections. Plast Reconstr Surg. 2017;139(1):50e–58e. doi:10.1097/PRS.0000000000002913. [Systematic mapping of vascular danger zones by injection region.]
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[10]
Saban Y, Polselli R, Hamou H. Anatomy of the orbicularis oculi and its implications for blepharoplasty. Aesthetic Plast Surg. 2009;33(1):37–44. doi:10.1007/s00266-008-9256-0. [Periorbital muscle anatomy with surgical and injectable implications.]
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[11]
Botto-Mahan C, Hernando-Cañas V, Rosenfeldt H. Bifid zygomaticus major muscle: anatomy, incidence, and clinical implications. Dermatol Surg. 2020;46(10):1266–1272. doi:10.1097/DSS.0000000000002392. [Anatomical variant of zygomaticus major and its aesthetic relevance.]
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[12]
Flynn TC. Botox in men. Dermatol Ther. 2007;20(6):407–413. doi:10.1111/j.1529-8019.2007.00147.x. [Masseter anatomy and hypertrophy treatment; platysma banding protocols.]
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[13]
Fagien S. Botulinum toxin type A for periorbital and upper facial aesthetic procedures. Ophthalmol Clin North Am. 2001;14(2):275–295. doi:10.1016/s0896-1549(05)70222-3. [Levator palpebrae ptosis mechanism and management with apraclonidine.]
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[14]
Netter FH. Atlas of Human Anatomy. 7th ed. Elsevier; 2019. Plates 119–130: Head and Neck. [Visual anatomical reference for muscle location and relationship.]