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Cranial Nerve Palsies

Topic updated on 06/24/17 9:21pm

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
-
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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Qbank (1 Questions)

TAG
(M2.NE.79) A 75-year-old man with a history of diabetes and hypertension presents to his ophthalmologist with blurry vision. He notes that his vision is clearest when looking down and to his right. His blood pressure is 155/98 mmHg, heart rate is 89 beats per minute, respiratory rate is 12 breaths per minute, and he is afebrile. On exam, his right eye is fixed in a "down and out" position, while his left eye maintains full range of motion. Which of the following additional findings would be an indication for urgent neurosurgical evaluation? Topic Review Topic

1. Dilated, nonreactive right pupil
2. Bilateral mydriasis
3. Isolated, right-sided ptosis
4. Isolated, left-sided ptosis
5. Bilateral ptosis

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