Cranial nerve abnormalities

Eye movements by extra-ocular muscles and cranial nerve innervation

(A) Schematic diagram of the motor innervation of the facial nerve. (B) Schematic diagram of the parasympathetic innervation of the facial nerve.

Bilateral course of facial nerve. Note that the forehead muscles receive innervation from both hemispheres of the brain, which is why there is forehead sparing for stroke but not Bell's palsy (or other peripheral facial nerve injury).

Cranial nerves

Tongue deviation from unilateral hypoglossal nerve injury (CN XII).

• CN I (Olfactory)
  • Anosmia + perceived change in taste of food
  • Deficit caused by shearing of the nerve ending passing through the cribriform plate usually by closed head trauma
• CN II (Optic)
  • Monocular and binocular visual field defects
  • Monocular: Giant cell arteritis, anterior ischemic optic neuropathy, glaucoma, optic neuritis, trauma, increased ICP, emboli/arteritis/stenosis leading to retinal ischemia, ophthalmic artery or vein occlusion
  • Binocular - Hemianopsia due to bilateral optic nerve disease.
• CN III (Oculomotor) –See Third Nerve Palsy
• CN IV (Trochlear)- See Trochlear nerve palsy
• CN VI (Abducens)- See Abducens nerve palsy
• Internuclear ophthalmoplegia - Lesion in medial longitudinal fasciculus, cannot adduct in horizontal lateral gaze, but normal convergence. Caused by multiple sclerosis or stroke
• CN V (Trigeminal)
  • Jaw weakness and spasm. Jaw closure may be weak and/or asymmetric. +/- Trismus if irritative lesion to motor root.
  • See trigeminal neuralgia
• CN VII (Facial)
  • Upper motor neuron deficit – See Stroke, Hemorrhagic stroke, Multiple sclerosis, Amyotrophic Lateral Sclerosis (Upper and lower motor neuron disease)
    • Sudden-onset of weakness: forehead sparing, facial droop
  • Lower motor neuron deficit – See Bell's palsy
    • Ipsilateral to defect: Inability to raise eyebrows, drooping of angle of mouth, incomplete closure of eyelid. No forehead sparing.
• CN VIII (Vestibular)
  • Dysfunction may be characterized by: tinnitus, deafness, nausea, vertigo, balance issues
  • See vertigo
• CN IX (Glossopharyngeal)
  • Dysfunction may be characterized by: dysarthria, dysphagia
• CN X (Vagus)
  • Dysfunction may be characterized by: hoarseness (unilateral vocal cord paralysis), dyspnea and inspiratory stridor (bilateral). Dysarthria, dysphagia.
• CN XI (Accessory)
  • Dysfunction may be characterized by: Sternocleidomastoid and trapezius weakness leads to weak head rotation and shoulder shrug
• CN XII (Hypoglossal)
  • Dysfunction may be characterized by: tongue deviation and wasting

See Also

• Neurologic Exam
• Stroke
• Ocular palsy