Overview
This lecture outlines how to assess the function of each cranial nerve during a neurologic examination and how findings can help localize neurologic pathology.
Importance of Cranial Nerve Assessment
- Cranial nerves originate in the brainstem and abnormalities suggest issues in the brainstem or along nerve pathways.
- Focal cranial nerve signs strongly localize the problem to the brainstem or its vicinity.
- Specific combinations of cranial nerve signs can further pinpoint lesion locations at the skull base.
Cranial Nerve Examination Techniques
1st (Olfactory) Nerve
- Smell is tested after trauma, suspected anterior fossa lesions, or reported smell/taste changes.
- Patient identifies odors with one nostril occluded at a time.
2nd (Optic) Nerve
- Test visual acuity with a Snellen chart, each eye individually.
- Color vision is checked using Ishihara or Hardy-Rand-Ritter plates.
- Assess visual fields by confrontation in all quadrants.
- Direct and consensual pupillary responses and funduscopic examination are performed.
3rd, 4th, 6th (Oculomotor, Trochlear, Abducens) Nerves
- Observe eye movement symmetry, globe position, ptosis, and nystagmus.
- Test extraocular movements by following a target through all gaze directions.
- Pupillary size and light response are assessed.
5th (Trigeminal) Nerve
- Facial sensation tested by pinprick; corneal reflex tested with cotton wisp.
- Masseter muscle palpation during teeth clenching and mouth opening against resistance for motor function.
- Jaw deviation indicates pterygoid weakness.
7th (Facial) Nerve
- Check for hemifacial weakness and asymmetry during spontaneous facial movements.
- Test taste on the anterior two-thirds of the tongue with basic solutions.
- Hyperacusis detected via tuning fork.
8th (Vestibulocochlear) Nerve
- Hearing screened by whisper test; Rinne and Weber tests may differentiate hearing loss type.
- Vestibular function evaluated by presence, direction, and type of nystagmus during vertigo.
- Central vs. peripheral vertigo differentiated by associated findings and maneuvers (e.g., head thrust, Frenzel lenses, Dix-Hallpike).
9th & 10th (Glossopharyngeal & Vagus) Nerves
- Palate elevation symmetry and gag reflex checked.
- Observe for uvula deviation and isolated hoarseness.
11th (Spinal Accessory) Nerve
- Test sternocleidomastoid by head turn against resistance.
- Test trapezius by shoulder elevation against resistance.
12th (Hypoglossal) Nerve
- Ask patient to protrude tongue; check for deviation, atrophy, or fasciculations.
Key Terms & Definitions
- Nystagmus — Involuntary eye movement, often indicating vestibular disorder.
- Palsies — Weakness/paralysis of cranial nerve-controlled muscles.
- Anisocoria — Unequal pupil sizes.
- Vestibular Ocular Reflex — Reflex for maintaining gaze stability during head movement.
- Frenzel Lenses — Special lenses to prevent visual fixation and reveal nystagmus.
Action Items / Next Steps
- Review and practice cranial nerve examination techniques.
- Study the differences between central and peripheral causes of vertigo.
- Familiarize yourself with maneuvers such as Dix-Hallpike and Epley for vestibular testing.