Cranial nerve abnormalities

Nerves

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.

• CN I – Olfactory
• CN II – Optic
• CN III – Oculomotor
  • Third Nerve Palsy
• CN IV – Trochlear
• CN V – Trigeminal
• CN VI – Abducens
  • Abducens nerve palsy
• CN VII – Facial
  • Bell's Palsy
• CN VIII – Vestibulocochlear
  • Vertigo
• CN IX – Glossopharyngeal
• CN X – Vagus
• CN XI – Accessory
• CN XII – Hypoglossal

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