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Overview of Cranial Nerves

 
Snapshot
  • A 66-year-old woman presents with worsening double vision and a mild headache. She denies any head injury, vision loss, or jaw claudications. Medical history is significant for hypertension, hyperlipidemia, and type II diabetes mellitus. On physical exam, she has right-sided ptosis, conjugate gaze, and impaired extraocular movement of the right eye except with right lateral gaze. The pupils are round and reactive to light. (Ischemic injury leading to a third-nerve palsy with sparing of the pupils)
Muscles Innervated by Cranial Nerves
Cranial Nerve
Muscle(s)
Lesion(s)
Oculomotor nerve (CN III) 
  • Extraocular muscles innervated by CN III are
    • superior rectus (SR)
    • infecrior rectus (IR)
    • medial rectus (MR)
    • inferior oblique (IO)
  • Levator palpebrae
    superioris
  • Ciliary muscle
  • Sphincter pupillae
  • Diplopia
  • Ptosis
  • Loss of accomodation
  • Pupillary involvement
    • in compressive lesions the pupil becomes dilated and non-reactive
    • in ischemic lesions (e.g., diabetes mellitus) the pupil is spared
Trochlear nerve (CN IV)
  • Superior oblique
  • Difficulty looking down
  • Head tilt away from the side of the lesion
Mandibular branch of the trigeminal nerve (CN V3)
  • Muscles of mastication include
    • masseter
    • temporalis
    • lateral and medial pterygoid
  • Anterior belly of the diagstric muscle
  • Mylohyoid muscle
  • Tensor palati
  • Tensor tympani
  • Jaw deviation towards the side of the lesion
Abducens nerve (CN VI)
  • Lateral rectus
  • Horizontal diplopia
Facial nerve (CN VII)
  • Muscles of facial expression
  • Posterior belly of digastric muscle
  • Stylohyoid muscle
  • Stapedius muscle

 

  • Bell's palsy
  • Loss of blink reflex
  • Hyperacusis (when the stapedius is involved)

 

 

Glossopharyngeal nerve (CN IX)
  • Stylopharyngeus muscle
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Vagus nerve (CN X)
  • Muscles of the palate and pharynx except
    • tensor palati muscle (CN V3)
    • Stylopharyngeus muscle (CN IX)
  • All muscles of the larynx
  • Palate droop
  • Dysphagia
  • Deviation of the uvula away from the side of the lesion
  • Loss of gag reflex (the sensory component of this reflex is mostly via CN IX)
Accessory nerve (CN XI)
  • Sternocleidomastoid muscle
  • Trapezius muscle
  • Weakness with turning of the head
  • Shoulder droop
Hypoglossal nerve (CN XII)
  • Muscles of the tongue except for the
    • palatoglossus muscles
  • Tongue deviation towards the side of the lesion
   
 

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