Craniofacial Muscles

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15 Facial Nerve Innervation and Facial Palsies267two-thirds of the tongue), the taste fi bers from the soft palate via the palatine andgreater petrosal nerves, and the preganglionic parasympathetic innervation to thelacrimal, submandibular, and sublingual glands. The lesser petrosal nerve carriessecretomotor fi bers to the parotid gland. There is also a small cutaneous sensorycomponent arising from the posterior auricular area.The facial nerve has the longest bony course of any nerve as it traverses thefacial canal of the petrous temporal bone and then the lateral canal of the mastoidbone, some 20–30 mm in all. This extended encased section is vulnerable to bothswelling through edema or in fl ammation, and fractures. The labyrinthine segmentin particular is especially narrow and lacks arterial cascades making it susceptibleto ischemia. Between the labyrinthine and tympanic segments lies the geniculateganglion where the petrosal branches are given off. Lesions prior to the geniculate ganglionresult in more severe ocular complications due to the lack of lacrimalsecretions (Mavrikakis 2008 ) . In the tympanic segment, the nerve passes behind thecochleariform process against the medial wall of the cavum tympani, above andposterior to the oval window. The bony wall is commonly thin or dehiscent here,and the nerve may lie directly against the middle ear mucosa making it particularlyvulnerable to iatrogenic injury and middle ear infections. Between the externalauditory meatus and the horizontal semicircular canal the nerve makes a secondturn into the lateral canal of the mastoid bone. Three branches exit in this segment:the chorda tympani, the nerve to stapedius, and the nerve from the auricular branchof the vagus nerve (CNX).Base of skull fractures can result in a facial palsy as a result of transection ortension accompanied by entrapment of the nerve in its bony course. The presence ofa facial palsy in the setting of head and neck trauma is an indication that urgentfurther assessment is essential with CT and MRI scans.The facial nerve exits the skull through the stylomastoid foramen, supplies abranch to the posterior auricular muscle, passes between and innervates the posteriorbelly of digastric and the stylohyoid muscle before entering the parotid gland. In thesubstance of the parotid, it divides into upper and lower trunks, which subdivideinto fi ve main branches: temporal, zygomatic, buccal, marginal mandibular, andcervical.The temporal branch innervates the upper eyelid and forehead. Paralysis resultsin a ptosis of the brow and upper lid that in the elderly can be severe enough toobscure vision. In addition, the upper eyelid is responsible for blinking and distributingthe watery tear fi lm that protects the cornea. Ulceration of an unprotectedcornea is a serious risk, and assessment of an adequate Bell’s re fl ex is an essentialpart of any examination. Xeropthalmia (i.e., dry eye syndrome) is extremely uncomfortablefor patients and a dry eye can paradoxically elicit excessive tear productionthat overwhelms the lacrimal duct resulting in epiphora.The zygomatic and buccal branches innervate the muscles of the midface andexperience signi fi cant cross-innervation. Paralysis results in ptosis of the lowereyelid and increased scleral show, exacerbating the eye problems alluded to above.In combination with the two inferior branches, they control the movements of themouth and are responsible for oral continence, smiling, and speech.
268 A.O. Grobbelaar and A.C.S. WoollardTable 15.1 Distribution and function of the facial nerve (CNVII)Branch of CN VII Muscle ActionPosterior auricular Posterior auricular Pulls ear backOccipitofrontalis Moves scalp backDirect branch Stylohyoid Retracts and elevates fl oor of mouthDirect branch Posterior belly digastric Raises hyoid bone in swallowingTemporal Anterior auricular Pulls ear forwardSuperior auricular Raises earFrontalisRaises browCorrugator supercilli Pulls eyebrows medially and downProcerusPulls medial eyebrow downTemporal and zygomatic Orbicularis oculi Closes eyelidsZygomatic and buccal Zygomaticus major Elevates corners of mouthBuccal Zygomaticus minor Elevates upper lipLevator labii superioris Elevates upper lip and mid nasolabial foldLevator labii superioris Elevates nasolabial fold and nasal alaalaeque nasiRisoriusAssists lateral vector of smileBuccinatorDe fl ates cheeksLevator anguli oris Pulls corners of mouth up and mediallyOrbicularis orisPurses lipsNasalis, dilator naris Flares nostrilsNasalis, compressor naris Closes nostrilsBuccal and marginal Depressor anguli oris Depresses corner of mouthmandibularDepressor labii inferioris Depresses lower lipMarginal mandibular Mentalis Pulls skin of chin upCervical Platysma Tightens skin of neck and depressescorner of mouthThe marginal mandibular and cervical branches innervate the platysma and thedepressor anguli oris. Paralysis of the lower lip depressors impairs depression of thelower lip on the affected, giving a snarl-like appearance especially during crying(Tulley et al. 2000 ) . See Table 15.1 for a complete list of the muscles innervated byeach branch.15.3 EtiologyEvidence for facial palsy dates back as far as 4000 BCE with an Egyptian statueexhibiting a left-sided facial palsy (Resende and Weber 2008 ) . Avicenna (979–1037CE) identi fi ed the difference between a central lesion affecting the body and face,and an isolated nerve lesion affecting only the face (Kataye 1975 ) . Freidrich was thefi rst to describe three cases of idiopathic facial palsy in 1797 in Germany (Bird andNicolaus 1979 ) . However, it was Charles Bell (later knighted) who demonstrated
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Craniofacial Muscles
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EditorsLinda K. McLoonDepartment of
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viContents8 Masticatory Muscle Resp
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viiiContributorsMark Lewis School o
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Chapter 1The Craniofacial Muscles:
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1 The Craniofacial Muscles: Argumen
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1 The Craniofacial Muscles: Argumen
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Chapter 2Head Muscle DevelopmentIta
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2 Head Muscle Development132.3 Head
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2 Head Muscle Development15Fig. 2.3
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2 Head Muscle Development17normal h
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2 Head Muscle Development19to specu
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2 Head Muscle Development21as Islet
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2 Head Muscle Development232.10 Sum
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2 Head Muscle Development25Hirsinge
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2 Head Muscle Development27Rudnicki
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Part IIIExtraocular Muscles
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32 L.K. McLoon et al.Fig. 3.1 Diagr
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34 L.K. McLoon et al.Fig. 3.4 Speci
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36 L.K. McLoon et al.3.4 Unusual Ch
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38 L.K. McLoon et al.Fig. 3.7 Longi
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40 L.K. McLoon et al.Fig. 3.8 Co-ex
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42 L.K. McLoon et al.Fig. 3.9 An ex
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44 L.K. McLoon et al.Fig. 3.10 Use
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46 L.K. McLoon et al.3.9 SummaryIn
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48 L.K. McLoon et al.Fuchs AF, Bind
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50 L.K. McLoon et al.Tajbakhsh S, R
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52 V.E. DasFig. 4.1 Initial studies
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54 V.E. DasFig. 4.2 Schematic view
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56 V.E. DasFig. 4.3 Top panel —co
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58 V.E. Das4.3 Motor Control of Con
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60 V.E. DasFig. 4.6 Schematic showi
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62 V.E. DasFR: fi ring rateD t : ne
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64 V.E. Dasresponses of abducens ne
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66 V.E. Dasend (Buttner-Ennever et
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68 V.E. Dascontrolled by appropriat
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70 V.E. Das4.6 SummaryThe oculomoto
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72 V.E. DasHoerantner R, Kaltofen T
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74 V.E. DasTweed DB, Haslwanter TP,
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76 F. Pedrosa Domellöfcompletely d
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78 F. Pedrosa DomellöfFig. 5.2 NMJ
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80 F. Pedrosa DomellöfHowever, bec
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82 F. Pedrosa Domellöfadhesions be
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84 F. Pedrosa Domellöfshown that (
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86 F. Pedrosa DomellöfReferencesAg
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88 F. Pedrosa DomellöfMori M, Kuwa
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Chapter 6Masticatory Muscle Structu
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6 Masticatory Muscle Structure and
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112 B.J. Sessle et al.zygomaticus m
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114 B.J. Sessle et al.Fig. 7.1 ( a
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116 B.J. Sessle et al.Most of the m
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118 B.J. Sessle et al.lie immediate
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120 B.J. Sessle et al.(Dubner et al
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122 B.J. Sessle et al.Fig. 7.3 An e
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124 B.J. Sessle et al.that each out
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126 B.J. Sessle et al.2010 ; Plowma
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128 B.J. Sessle et al.activities. S
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130 B.J. Sessle et al.Moayedi M, We
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132 S.L. Hebert et al.type 3 and cr
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134 S.L. Hebert et al.This early de
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136 S.L. Hebert et al.that EMG valu
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138 S.L. Hebert et al.Newton JP, Ab
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Chapter 9Structure and Function of
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9 Structure and Function of the Lar
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Chapter 10Motor Control and Biomech
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10 Motor Control and Biomechanics o
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186 J.C. Stemple et al.established
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188 J.C. Stemple et al.of protein d
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190 J.C. Stemple et al.the depictio
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192 J.C. Stemple et al.Fig. 11.2 Ul
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194 J.C. Stemple et al.11.6 Larynge
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196 J.C. Stemple et al.Neurapraxia,
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198 J.C. Stemple et al.of the preci
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200 J.C. Stemple et al.Gardner GM,
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202 J.C. Stemple et al.Rhee HS, Luc
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Part VITongue Musculature
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208 A. Sokoloff and T. BurkholderTh
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210 A. Sokoloff and T. BurkholderFi
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212 A. Sokoloff and T. Burkholder12
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318 J. Park et al.Grandas F, Elston
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320 J. Park et al.McCord CD Jr (198
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Part VIIISummary and Conclusions
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326 L.K. McLoon and F.H. Andrade17.
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332 L.K. McLoon and F.H. AndradeDie
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334 L.K. McLoon and F.H. AndradeSam
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IndexAAbducens nucleusvs. lateral r
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Index339Embryonic myosin heavy chai
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IndexLLagophthalmos , 304, 308Lamin
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Indexmuscular dystrophy , 187-190my
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Index345hydrostat mass reduction ,
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