Auriculotemporal N.

Cranial N.

VII,IX and X

Great auricular N.

Summary: Muscles of Facial Expression

•Muscles of facial expression enable human beings to communicate nonverbally and aid in functions such as lacrimation, mastication, and speech.

•Muscles of facial expression are encased by an interconnected, unified layer of fascia, forming the superficial musculoaponeurotic system (SMAS) which allows them to work synergistically or antagonistically with one another.

Fig. 30.8 Innervation of the auricle

level of the vertex. The third occipital nerve, a branch of C3, supplies the midline occipital scalp [8].

30.2.3 Innervation of the Ear

Extrinsic muscles of the ear include the anterior, superior, and posterior auricular muscles. They are innervated by branches of the facial nerve but possess little functional importance. The sensory innervation of the external ear is quite complex and comprised of contributions from several different nerves including the trigeminal, facial, glossopharyngeal, and vagus nerves as well as the cervical plexus (C2 and C3). Anteriorly, the auriculotemporal nerve, a branch of V3, supplies sensation to the skin overlying the tragus, anterior helix, anterior and superior external auditory canal, and a portion of the external surface of the tympanic membrane. A majority of the anterior auricle as well as the posterolateral auricle is innervated by the great auricular nerve, a branch of C2 and C3. The lesser occipital nerve also provides sensory innervation to the skin overlying the mastoid process. The conchal bowl, posterior external auditory meatus, posterior tympanic membrane, and the posterior auricular sulcus are supplied by the sensory fibers from the seventh, ninth, and tenth cranial nerves (Fig. 30.8) [4, 9, 10]. Adequate local anesthesia of the auricle, with the exception of the conchal bowl, may be obtained by injecting a ring of anesthesia circumferentially around the base of the ear including the posterior auricular sulcus. The conchal bowl and external auditory canal must be anesthetized separately.

30.3Muscles of Facial Expression

Muscles of facial expression enable human beings to communicate nonverbally. In addition, they aid in functions such as lacrimation, mastication, speech, and protection of vital structures such as the mouth and eye (Fig. 30.9a, b). Injury to the motor nerves that supply these muscles can lead to devastating consequences, and knowledge of these structures is of utmost importance to the cutaneous surgeon. Unlike muscles of the body, which originate and insert on the bony structures which they act upon, the muscles of facial expression may originate on bone but insert directly onto the skin, other soft tissue structures, or adjoining muscles [1, 4]. This unique characteristic allows for the formation of skin tension lines. Muscles of facial expression are encased by an interconnected, unified layer of fascia, forming the superficial musculoaponeurotic system (SMAS) which allows them to work synergistically or antagonistically with one another.

30.3.1 Muscles of the Forehead

The muscles of the forehead include the frontalis, the corrugator supercilii, and the procerus muscles. The frontalis muscle originates at the frontal hairline where it is directly connected to the galea aponeurotica, a fibrous band of connective tissue that spans across the length of the scalp, connecting to the occipitalis muscle posteriorly. Collectively, this muscle may be termed the “occipitofrontalis” muscle. The frontalis muscle serves to raise the forehead and eyebrows and contributes to horizontal wrinkling of the forehead (Table 30.1).

a

Superficial temporalis fascia

Depressor supercilii M.

Orbicularis oculi M.

Orbital portion

Pars palpebrarum

Preseptal portion

Pretarsal portion

Zygomaticus minor M.

Zygomaticus major M. Levator labii superioris M.

Levator labii superioris alaeque nasi M.

Risorius M.

Modiolus

Depressor anguli oris M. Platysma M.

b

Orbicularis oculi M.

Orbital portion

Palpebral portion

Levator labii superioris alaeque nasi M.

Nasalis M.

Levator labii superioris M.

Levator angularis oris M.

Orbicularis oris M.

Mentalis M.

Depressor labii inferioris M.

Galea aponeurotica

Frontalis M.

Procerus M.

Corrugator Supercilii M.

Orbital Septum

Temporalis M.

Levator angularis oris M.

Nasalis M.

Masseter M.

Buccinator M.

Orbicularis oris M.

Depressor labii inferioris M.

Mentalis M.

Occipitofrontalis M.

Galea aponeurotica Frontalis M. Occipitalis M.

Temporalis M. Zygomaticus minor M.

Zygomaticus major M.

Buccinator M.

Risorius M.

Masseter M.

It is divided into left and right bellies, which insert into the skin of the forehead as well as the corrugator, procerus, and orbicularis oculi muscles. Motor innervation of the frontalis muscle is provided by the temporal branch of the facial nerve [6].

The corrugator supercilii is a “V”-shaped muscle that originates on the frontal bone medial to the eyebrows. It travels superior to the brow, running deep to the frontalis, procerus, and orbicularis muscles and eventually inserts into the skin of the medial brow. It is responsible for pulling the brows medially and downward and creates a scowl and vertical rhytides overlying the glabella. The procerus muscle is a solitary muscle, originating from the superior nasal bones and lateral cartilage and inserting into the skin overlying the nasal root as well as the aponeurosis of the nasalis muscle [4]. It pulls the medial brows and forehead skin downward, creating horizontal furrows overlying the nasal root and bridge [6].

30.3.2 Muscles of the Periorbital Region

The orbicularis oculi muscle is the most important muscle governing eyelid function. It is subdivided into orbital, preseptal, and pretarsal segments based on their relationship to the orbit, septum, and tarsal plates. The pretarsal and preseptal components collectively comprise the pars palpebrarum, which is involved in involuntary blinking and voluntary gentle closure of the eyelid (Fig. 30.10). When tight closure of the eyelid is necessary, the orbital component of the muscle may be elicited voluntarily.

The preseptal and pretarsal portions of the orbicularis oculi muscle arise from two heads. The superficial heads converge to form the medial canthal tendon, and the deep heads pass posterior to the lacrimal sac, attaching to the lacrimal diaphragm and lacrimal crest, respectively. Contraction of these muscles with blinking augments the pumping mechanism and tear flow in the lacrimal apparatus. Both the pretarsal and preseptal

segments insert into the ligamentous attachments at the lateral canthus [11]. The orbital portion of the orbicularis oculi muscle originates from the medial orbital margin and medial canthal tendon. Superiorly, this muscle intertwines with the procerus, frontalis, and corrugator supercilii muscles. Laterally, it connects to the superficial temporalis fascia, and it extends variable distances inferiorly on the cheek [4, 12].The levator palpebrae superioris, although not considered a muscle of facial expression, is vital to proper eyelid function. This muscle originates within the inner orbit and serves to open the eyelid. It receives its motor innervations from the oculomotor or third cranial nerve. If the motor innervation to the orbicularis oculi muscle is disrupted, the levator palpebrae superioris muscle acts unopposed leading to chronic lid elevation [1].

30.3.3 Muscles of the Nose

The muscles of the nose are highly variable in their development among different individuals. The procerus muscle, as discussed previously, extends inferiorly from the paired frontalis muscle to insert in the skin overlying the nasal root and the aponeurosis of the nasalis muscle. Upon contraction, it shortens the nose and creates horizontal “bunny lines” overlying the nasal root. The nasalis muscle is the deepest muscle of the nose, originating on the maxillary bone. This muscle consists of a transverse and alar component. The transverse component travels over the nasal bridge where it inserts into an aponeurosis, decussating with fibers from the contralateral side. It serves to tense the skin over the dorsal nose. The alar portion of the nasalis muscle inserts into the lateral crus of the alar cartilage and assists in flaring the nostril [4]. The depressor septi muscle inserts at the septal cartilage and lies deep to the orbicularis oris muscle. It is thought to displace the nasal septum inferiorly upon deep inspiration as well as draw the columella downwards [13].