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Motor Innervation of Head and Neck

   
 Mnemonic for CN VII branches: To Zanzibar by Motor Car 
   
  • Facial nerve exits skull via stylomastoid foramen, enters parotid gland, and then divides into five branches: temporal, zygomatic, buccal, marginal mandibular, and cervical
  • Facial nerve innervates muscles of facial expression (motor) and small component sensory innervation (external auditory meatus, anterior tongue)
  • All motor nerves innervate respective muscles on muscle’s underside with few exceptions
  • Three danger zones areas in head/neck for motor nerve injury (Table 6-4)
   
 
Table 6-4 Danger Zones for Motor Nerve Injury
 Nerve Location Function Deficiency
 Spinal accessory
nerve (CN XI)		 Nerve courses within posterior triangle of neck in superficial plane, emerges posterior to sternocleidomastoid (SCM) within 2 cm of Erb’s point Innervates
trapezius muscle		 Shoulder drooping, winged scapula, inability to abduct arm
   
     
     
  Erb’s point: midpoint of posterior border of SCM (point where cervical plexus emerges  
     
     
 Temporal branch of
facial nerve (CN VII)		 Nerve courses from a point located 0.5 cm inferior to the tragus to a point 2 cm superior and lateral to tail of eyebrow before diving beneath frontalis muscle Innervates
frontalis muscle		 Inability to raise eyebrow, drooping of ipsilateral eyebrow, inability to close eye completely
 
     
     
  Danger zone between following two lines: ear lobe to lateral edge of eyebrow and tragus to lateral highest forehead crease – nerve most superficial over bony prominence  
     
     
  
 Marginal mandibular
branch of facial nerve
(CN VII)		 Most susceptible to injury anterior to angle of mandible during undermining due to superficial location over bony prominence Innervates lip
depressors		 Asymmetry with resultant crooked smile and drooling on affected side
        
 
   


 

 

 

 

 

 

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