Learning the 12 cranial nerves can be challenging so a good mnemonic can be a lifesaver.
Cranial Nerves can be difficult to learn and many nursing students struggle to learn them. This useful mnemonic can help you memorize them.
The nerves in the human body are divided into two parts. The cranial nerves and the spinal nerves. Cranial nerves originate in the brain and brain stem. Spinal nerves originate from various locations in the spinal cord.
There are 12 Paris of cranial nerves. Gustav Fritsch discovered cranial nerve Zero, in shark brains. There has been some controversy about this nerve in humans. Some of the human nerves are Sensory, some are motor and others are both motor. Only the first two sensory nerves originate in the cerebrum. The other cranial nerves originate in the brain stem.
Assessment of Cranial Nerves
Patient sitting over edge of bed.
CN I: Olfactory
- Usually not tested.
- Rash, deformity of nose.
- Test each nostril with essence bottles of coffee, vanilla, peppermint.
CN II: Optic
- With patient wearing glasses, test each eye separately on eye chart/ card using an eye cover.
- Examine visual fields by confrontation by wiggling fingers 1 foot from pt’s ears, asking which they see move.
- Keep examiner’s head level with patient’s head.
- If poor visual acuity, map fields using fingers and a quadrant-covering card.
- Look into fundi.
CN III, IV, VI: Oculomotor, Trochlear, Abducens
- Look at pupils: shape, relative size, ptosis.
- Shine light in from the side to gauge pupil’s light reaction.
- Assess both direct and consensual responses.
- Assess afferent pupillary defect by moving light in arc from pupil to pupil. unne). Optionally: as do arc test, have pt place a flat hand extending vertically from his face, between his eyes, to act as a blinder so light can only go into one eye at a time.
- “Follow finger with eyes without moving head”: test the 6 cardinal points in an H pattern.
- Look for failure of movement, nystagmus [pause to check it during upward/ lateral gaze].
- Convergence by moving finger towards bridge of pt’s nose.
- Test accommodation by pt looking into distance, then a hat pin 30cm from nose.
- If MG suspected: pt. gazes upward at Dr’s finger to show worsening ptosis.
CN V: Trigeminal
- Corneal reflex: patient looks up and away.
- Touch cotton wool to other side.
- Look for blink in both eyes, ask if can sense it.
- Repeat other side [tests V sensory, VII motor].
- Facial sensation: sterile sharp item on forehead, cheek, jaw.
- Repeat with dull object. Ask to report sharp or dull.
- If abnormal, then temperature [heated/ water-cooled tuning fork], light touch [cotton].
- Motor: pt opens mouth, clenches teeth (pterygoids).
- Palpate temporal, masseter muscles as they clench.
- Test jaw jerk:
- Dr’s finger on tip of jaw.
- Grip patellar hammer halfway up shaft and tap Dr’s finger lightly.
- Usually nothing happens, or just a slight closure.
- If increased closure, think UMNL, esp pseudobulbar palsy.
CN VII: Facial
- Inspect facial droop or asymmetry.
- Facial expression muscles: pt looks up and wrinkles forehead.
- Examine wrinkling loss.
- Feel muscle strength by pushing down on each side [UMNL preserved because of bilateral innervation].
- Pt shuts eyes tightly: compare each side.
- Pt grins: compare nasolabial grooves.
- Also: frown, show teeth, puff out cheeks.
- Corneal reflex already done. See CN V.
CN VIII: Vestibulocochlear (Hearing, Vestibular rarely)
Dr’s hands arms length by each ear of pt.
- Rub one hand’s fingers with noise on one side, other hand noiselessly.
- Ask pt. which ear they hear you rubbing.
- Repeat with louder intensity, watching for abnormality.
Weber’s test: Lateralization
- 512/ 1024 Hz [256 if deaf] vibrating fork on top of patients head/ forehead.
- “Where do you hear sound coming from?”
- Normal reply is midline.
Rinne’s test: Air vs. Bone Conduction
- 512/ 1024 Hz [256 if deaf] vibrating fork on mastoid behind ear. Ask when stop hearing it.
- When stop hearing it, move to the patients ear so can hear it.
- Normal: air conduction [ear] better than bone conduction [mastoid].
If indicated, look at external auditory canals, eardrums.
CN IX, X: Glossopharyngeal, Vagus
- Voice: hoarse or nasal.
- Pt. swallows, coughs (bovine cough: recurrent laryngeal).
- Examine palate for uvular displacement. (unilateral lesion: uvula drawn to normal side).
- Pt says “Ah”: symmetrical soft palate movement.
- Gag reflex [sensory IX, motor X]:
- Stimulate back of throat each side.
- Normal to gag each time.
CN XI: Accessory
- From behind, examine for trapezius atrophy, asymmetry.
- shrugs shoulders (trapezius).
- turns head against resistance: watch, palpate SCM on opposite side.
CN XII: Hypoglossal
- Listen to articulation.
- Inspect tongue in mouth for wasting, fasciculations.
- Protrude tongue: unilateral deviates to affected side.