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»	Dermatologic Surgery
»	Surgical Anatomy
	»	Anatomy of Head and Neck Muscles
	»	Sensory Innervation of Head and Neck
	»	Motor Innervation of Head and Neck
	»	Arterial Supply of Head and Neck
	»	Lymph Nodes of the Head and Neck

Anatomy of Head and Neck Muscles

Figure 6.1
Muscles of the head and neck
(Reprint from Nouri, K. Complications in
Dermatologic Surgery. Philadelphia,
PA: Mosby Elsevier; 2008)

(Figure 6.1)

Know function of specific function and innervation of head/neck muscles (Table 6-1)
Location-specific layers:
- Scalp has five layers: epidermis/dermis, subcutaneous tissue, musculoaponeurotic layer, loose subaponeurotic tissue and periosteum
- Facial layers: epidermis, dermis, subcutaneous fat, SMAS and periosteum
Superficial musculoaponeurotic system (SMAS)
- Superficial fibromuscular layer enclosing facial muscles of face/neck; extends from frontalis muscle superiorly to platysma muscle inferiorly, temporalis muscle laterally
- Allows organized movement of regional muscles during contraction and contributes to appearance of skin tension lines
- Protective anatomic plane as sensory nerves and axial blood vessels typically located within or between SMAS and subcutaneous fat; motor nerves usually deep to SMAS
- During facelift, SMAS plicated or pulled to draw skin tight
- Equivalent of SMAS on scalp is galea aponeurotica, which is a thick inelastic membrane and ideal plane to undermine as it is relatively avascular, separates easily, and results in decreased trauma to neurovascular structures
Dissection planes (Table 6-2)
- Undermining should always take place above SMAS with few exceptions

Table 6-1 Muscles of Head and Neck
	Muscle	Function	Innervation
	Occipitalis	Pulls scalp posteriorly	Posterior auricular br. of facial nerve (CN VII) {Do not confuse with postauricular branch of trigeminal nerve (CNV)}
	Frontalis muscle	Elevates eyebrows and wrinkles forehead (horizontal forehead lines)	Temporal br. of CN VII
	Orbicularis oculi	Blinking and tight closure of eyelids (“crow’s feet”), lesser role as brow depressor (depressor supercilii)	Temporal br. of CN VII (upper portion), zygomatic branch of CN VII (lower portion)
	Corrugator supercilii	Pulls eyebrows medially and downward (vertical glabellar lines)	Temporal br. of CN VII
	Procerus	Pulls medial portion of eyebrows and glabellar skin downward (horizontal glabellar lines over root of nose)	Zygomatic and buccal br. of CN VII per Bolognia (rare sources say temporal br.)
	Nasalis	Alar flaring and compression (“bunny lines” over upper bridge of nose)	Zygomatic and buccal br. of CN VII
	Levator labii superioris	Elevates upper lip	Buccal br. of CN VII
	Levator labii superioris alaeque nasi	Lifts upper lip, dilates nostrils	Buccal br. of CN VII
	Levator anguli oris	Lifts corners of the mouth	Buccal br. of CN VII
	Risorius	Produces smile by drawing back corners of mouth	Marginal mandibular br. of CN VII per Bolognia (other sources say buccal br.)
	Zygomaticus major	Main contributor to smile: elevates and draws corner of mouth laterally	Buccal br. of CN VII
	Zygomaticus minor	Elevates upper lip	Buccal br. of CN VII
	Modiolus	Accounts for cheek dimples in some patients
	Orbicularis oris	Closes and purses lips (vertical perioral lip lines)	Buccal or marginal mandibular br. of CN VII
	Buccinator	Presses cheek against teeth, allows blowing of cheeks	Buccal br. of CN VII
	Depressor anguli oris	Pulls corner of mouth downward (marionette lines → vertical lines at oral commissure)	Marginal mandibular (MM) br. per Bolognia (most other sources say both MM and buccal br.)
	Depressor labii inferioris	Depresses lower lip	Marginal mandibular br. CN VII
	Mentalis	Protrudes lower lip	Marginal mandibular br. CN VII
	Platysma	Pulls corner of mouth inferiorly, tenses neck (horizontal neck lines)	Marginal mandibular br (upper portion) and cervical br. CN VII

Table 6-2 Dissection Planes in Head and Neck
	Location	Plane of Dissection
	Face	Superficial to SMAS: superficial to mid fat (more superficial in high-risk areas like zygomatic arch, temporal fossa, etc.)
	Nose	Deep to SMAS: superficial to periosteum or perichondrium (below nasalis muscle)
	Scalp	Subgaleal plane: superficial to periosteum (below galea aponeurotica), relatively avascular space
	Trunk/limbs	Deep fat if small excision; just above deep fascia if larger excision