Flashcards

Cranial nerve I

Olfactory — sensory. Smell. Tested with coffee or vanilla, one nostril at a time; never ammonia (that is a pain test).

Cranial nerve II

Optic — sensory. Vision. Snellen chart, visual fields; afferent limb of the pupillary light reflex.

Cranial nerve III

Oculomotor — motor. Most eye movement, eyelid lift, and parasympathetic pupil constriction. Palsy: down-and-out eye, ptosis, dilated pupil.

Cranial nerve IV

Trochlear — motor. Superior oblique: intorts and abducts the eye and depresses it most effectively when adducted. SO4.

Cranial nerve V

Trigeminal — both. Facial sensation in three divisions (V1 forehead, V2 cheek, V3 jaw) plus muscles of chewing.

Cranial nerve VI

Abducens — motor. Lateral rectus: eye abduction. LR6. Stretched by raised intracranial pressure.

Cranial nerve VII

Facial — both. Facial expression, taste on the anterior two-thirds of the tongue, lacrimal and salivary secretion.

Cranial nerve VIII

Vestibulocochlear — sensory. Hearing and balance. Whisper test screens hearing; vertigo and nystagmus point to the vestibular branch.

Cranial nerve IX

Glossopharyngeal — both. Taste on the posterior one-third of the tongue, the afferent arm of the gag reflex, parotid saliva.

Cranial nerve X

Vagus — both. Voice (recurrent laryngeal), swallowing and palate lift, parasympathetic supply to heart, lungs, and gut.

Cranial nerve XI

Accessory — motor. Trapezius and sternocleidomastoid: shoulder shrug and head turn against resistance.

Cranial nerve XII

Hypoglossal — motor. Tongue movement. On protrusion a unilateral LMN/CN XII lesion makes the tongue deviate toward the affected side; corticobulbar lesions require separate localization.

Sensory-only cranial nerves

I, II, and VIII — the special senses: smell, vision, hearing and balance.

Motor-only cranial nerves

III, IV, VI, XI, XII — eye movers, shoulder girdle, tongue.

Mixed (both) cranial nerves

V, VII, IX, X — the big face-and-throat nerves with autonomic riders.

Names mnemonic in order

Oh, Oh, Oh, To Touch And Feel Very Good Velvet, Ah Heaven.

Types mnemonic in order

Some Say Marry Money But My Brother Says Big Brains Matter Most — S S M M B B M B S B B M.

The eye-movement rule

SO4, LR6, all the rest 3: superior oblique is IV, lateral rectus is VI, every other mover plus lid and pupil is III.

The CN III palsy triad

Down-and-out eye, ptosis, dilated fixed pupil — with a blown pupil think compression (herniation, aneurysm): an emergency.

CN IV failure picture

Vertical diplopia, worst looking down and inward — reading or descending stairs.

CN VI failure picture

Cannot abduct the eye; it drifts inward, diplopia worst on lateral gaze toward the lesion.

Corneal reflex arc

V1 afferent (senses the touch) to VII efferent (blinks the eye).

Pupillary light reflex arc

II afferent (sees the light) to III efferent (constricts the pupil).

Gag reflex arc

IX afferent (throat sensation) to X efferent (the gag motor).

The forehead rule

Whole-face weakness, including the forehead, suggests a peripheral/LMN VII pattern; forehead sparing suggests a supranuclear/UMN pattern. Bell's palsy and stroke are important causes, but the forehead sign localizes imperfectly and does not establish the diagnosis.

Tongue deviation rule

With a unilateral LMN/CN XII lesion, the tongue deviates toward the affected side: the weak side is slack, the strong side pushes it across the midline.

Uvula deviation rule

The uvula deviates away from the lesion: the intact palate lifts and pulls it to the strong side.

Trigeminal sensory divisions

V1 ophthalmic (forehead), V2 maxillary (cheek), V3 mandibular (jaw) — test all three bands.

Taste map of the tongue

Anterior two-thirds: VII facial. Posterior one-third: IX glossopharyngeal.

The sixty-second screen order

I smell, II read, III-IV-VI follow the H, V face and jaw, VII smile, VIII whisper, IX-X say ah and voice, XI shrug, XII tongue.

Quiz

1. Which cranial nerve is responsible for the sense of smell?

   • II — Optic
   • VII — Facial
   • VIII — Vestibulocochlear
   • I — Olfactory (answer)

   CN I is pure smell. VII carries taste from the front of the tongue, not smell; II is vision; VIII is hearing and balance.

2. The trochlear nerve (IV) controls which eye muscle?

   • Lateral rectus
   • Medial rectus
   • Superior oblique (answer)
   • Inferior oblique

   SO4: CN IV drives the superior oblique — intorsion and abduction, with depression strongest when the eye is adducted. Lateral rectus is VI (LR6); the rest are III.

3. A patient cannot abduct the right eye, and diplopia is worst on right gaze. Which nerve is failing?

   • CN III
   • CN VI (answer)
   • CN IV
   • CN VII

   Abduction is the lateral rectus, CN VI — the abducens. III and IV move the eye in other directions; VII is the face.

4. Which cranial nerves are PURELY sensory?

   • I, II, VIII (answer)
   • V, VII, IX
   • III, IV, VI
   • XI, XII

   The special-senses trio: smell (I), vision (II), hearing and balance (VIII). III/IV/VI/XI/XII are motor-only; V/VII/IX/X are mixed.

5. A patient cannot shrug the shoulders or turn the head against resistance. Which nerve is damaged?

   • CN X — Vagus
   • CN XII — Hypoglossal
   • CN XI — Accessory (answer)
   • CN IX — Glossopharyngeal

   CN XI drives trapezius (shrug) and sternocleidomastoid (head turn). XII is the tongue; X and IX are the throat pair.

6. On tongue protrusion, the tongue deviates right with right-sided atrophy and fasciculations. Where is the lesion?

   • Right CN VII
   • Left CN XII
   • Left CN X
   • Right CN XII (answer)

   For a unilateral LMN/CN XII lesion, the tongue deviates toward the weak side because the intact side pushes it across the midline. Corticobulbar lesions follow different localization logic.

7. The corneal reflex tests which arc?

   • V1 afferent to VII efferent (answer)
   • IX afferent to X efferent
   • II afferent to III efferent
   • VII afferent to X efferent

   The trigeminal eye division (V1) senses the touch; the facial nerve (VII) blinks. II-to-III is the pupillary light reflex; IX-to-X is gag.

8. The pupillary light reflex arc is:

   • II afferent to III efferent (answer)
   • III afferent to II efferent
   • V1 afferent to VII efferent
   • VIII afferent to III efferent

   The optic nerve (II) carries light in; the oculomotor parasympathetics (III) constrict the pupil out.

9. A head-injury patient has a fixed, dilated right pupil, a drooping lid, and an eye resting down and out. This is:

   • CN VI palsy
   • CN III compression — an emergency (answer)
   • CN IV palsy
   • A normal finding under sedation

   III carries the eye movers, the lid lifter, and the pupil constrictor. Down-and-out plus a blown pupil means compression (uncal herniation, aneurysm) — escalate immediately.

10. Taste on the ANTERIOR two-thirds of the tongue travels in:

    • CN VII (answer)
    • CN X
    • CN IX
    • CN V

    Facial (VII) serves the front two-thirds; glossopharyngeal (IX) serves the posterior one-third.

11. The sensory arm (afferent limb) of the gag reflex is:

    • CN X
    • CN VII
    • CN IX (answer)
    • CN XII

    IX senses the pharynx; X provides the motor gag and palate lift. Afferent IX, efferent X.

12. The muscles of mastication (chewing) are driven by:

    • CN V motor fibers (answer)
    • CN XII
    • CN XI
    • CN VII motor fibers

    The trigeminal (V) motor arm chews; VII is facial expression. Test: clench and open the jaw against resistance.

13. Light touch is tested on the forehead, cheek, and jaw separately. These bands are:

    • The glossopharyngeal map
    • The three facial branches
    • Cervical dermatomes
    • The three trigeminal divisions (answer)

    V1 ophthalmic (forehead), V2 maxillary (cheek), V3 mandibular (jaw) — the trigeminal sensory divisions.

14. A patient's hearing is screened by whispering behind one ear with the other masked. This tests:

    • CN VII
    • CN V
    • CN II
    • CN VIII (answer)

    The vestibulocochlear nerve (VIII) carries hearing and balance; the whisper test is its bedside screen.

15. Parasympathetic fibers to the heart, lungs, and much of the gut travel in:

    • CN IX
    • CN XI
    • CN X — the vagus (answer)
    • CN III

    The vagus is the wanderer: voice, swallowing, and the long parasympathetic ride to the thorax and abdomen.

16. When the patient says “ah,” the uvula deviates to the LEFT. The lesion is:

    • Left CN X
    • Right CN X (answer)
    • Right CN XII
    • Left CN IX

    The intact left palate lifts and pulls the uvula away from the weak right side. Rule: uvula away from the lesion.

17. A patient cannot raise the left eyebrow or close the left eye, and the whole left face droops. The most likely diagnosis is:

    • Bell's palsy — a peripheral CN VII lesion (answer)
    • Stroke with upper motor neuron facial weakness
    • CN V neuralgia
    • CN VI palsy

    Whole-face weakness suggests a peripheral/LMN VII pattern, while a typical hemispheric supranuclear pattern spares the forehead because the upper face has bilateral cortical input. This is a localization clue, not proof of Bell's palsy or exclusion of stroke.

18. Which finding points to a CENTRAL (upper motor neuron) cause of facial droop?

    • Inability to close the eye on the weak side
    • Inability to raise the eyebrow on the weak side
    • Forehead sparing with a flat smile (answer)
    • Loss of taste on the front of the tongue

    Forehead sparing with lower facial weakness suggests a supranuclear/UMN pattern, while impaired eye closure or brow movement suggests peripheral VII involvement. These findings localize imperfectly and do not by themselves prove or exclude stroke.

19. Vertical diplopia that is worst when reading or walking downstairs suggests:

    • CN VI palsy
    • CN IV palsy (answer)
    • CN III palsy
    • CN II lesion

    The superior oblique (CN IV, SO4) depresses the adducted eye and also intorts and abducts it; this is why reading or descending stairs may provoke vertical diplopia.

20. Testing smell with ammonia is incorrect because:

    • Ammonia is too weak to register
    • Ammonia tests CN VIII
    • Patients cannot smell irritants at all
    • Ammonia stimulates trigeminal pain fibers, not olfactory receptors (answer)

    Irritant chemicals recruit the V pain pathway, so a patient with total anosmia can still “pass.” Use coffee or vanilla, one nostril at a time.

21. A patient develops horizontal double vision that worsens when looking toward the LEFT, and the left eye cannot move outward. Which nerve is compressed?

    • Left CN VI (answer)
    • Left CN III
    • Right CN IV
    • Left CN II

    Abduction failure is the lateral rectus — CN VI, the abducens. It has a long course and is famously stretched by raised intracranial pressure.

22. Sharp, electric, one-sided facial pain triggered by chewing is the classic presentation of:

    • Bell's palsy
    • Glossopharyngeal neuralgia
    • Trigeminal neuralgia (CN V) (answer)
    • Vestibular neuritis

    The trigeminal sensory divisions cover the face; neuralgia of V is lightning-pain in those bands. Bell's is motor weakness, not pain.

23. Which nerve pair is tested together when the patient says “ah” and the voice is evaluated?

    • XI and XII
    • VII and VIII
    • III and IV
    • IX and X (answer)

    The throat pair: glossopharyngeal sensation with vagus motor — palate lift, uvula position, swallow, and voice quality.

24. The motor-only cranial nerves are:

    • I, II, VIII
    • III, IV, VI, XI, XII (answer)
    • V, VII, IX, X
    • III, V, VII, X

    The eye movers (III, IV, VI), the shoulder nerve (XI), and the tongue nerve (XII). I/II/VIII are sensory; V/VII/IX/X are mixed.

25. A hoarse voice and difficulty swallowing after neck surgery most directly implicate:

    • CN VII
    • CN X — recurrent laryngeal branch (answer)
    • CN II
    • CN V

    The vagus supplies the vocal cords through the recurrent laryngeal nerve and drives palatal swallowing — both at risk in neck and carotid surgery.

Formula Sheet

• I Olfactory — sensory — smell — coffee or vanilla, one nostril at a time
• II Optic — sensory — vision — Snellen chart and fields
• III Oculomotor — motor — eye movement, lid lift, pupil constriction — cardinal fields, PERRLA
• IV Trochlear — motor — superior oblique (intorts/abducts; depresses the adducted eye) — SO4
• V Trigeminal — both — face sensation (V1/V2/V3) plus chewing — touch bands, clench jaw, corneal reflex
• VI Abducens — motor — lateral rectus (abduction) — LR6
• VII Facial — both — expression, anterior 2/3 taste, tears and saliva — smile, brows, eye squeeze
• VIII Vestibulocochlear — sensory — hearing and balance — whisper test
• IX Glossopharyngeal — both — posterior 1/3 taste, gag afferent, parotid saliva — gag reflex
• X Vagus — both — voice, swallow, organ parasympathetics — say ah, uvula, voice quality
• XI Accessory — motor — trapezius and sternocleidomastoid — shrug, head turn
• XII Hypoglossal — motor — tongue movement — protrude at midline
• Sensory-only: I, II, VIII | Motor-only: III, IV, VI, XI, XII | Both: V, VII, IX, X
• Names mnemonic: Oh Oh Oh To Touch And Feel Very Good Velvet Ah Heaven
• Eye rule: SO4, LR6, all the rest 3
• CN III palsy: down-and-out eye + ptosis + blown pupil = compression, emergency
• Corneal reflex: V1 in, VII out
• Gag reflex: classically IX in, X out; absence alone does not diagnose dysphagia
• Pupillary light reflex: II in, III out
• Tongue deviates TOWARD a unilateral LMN/CN XII lesion
• Uvula deviates AWAY from the lesion (X)
• Jaw deviates toward the lesion (V motor)
• Forehead rule: involved = Bell's (peripheral VII); spared = stroke (central)
• Taste map: VII anterior 2/3, IX posterior 1/3
• VI is stretched by raised intracranial pressure — false-localizing diplopia
• Screen in nerve order: smell, read, follow the H, face, smile, whisper, ah, shrug, tongue

MindMap

• The Cranial Nerves (I-XII)
  • Sensory three
    • I Olfactory — smell
    • II Optic — vision
    • VIII Vestibulocochlear — hearing, balance
    • Never test smell with ammonia
  • Eye movers
    • SO4 — superior oblique
    • LR6 — lateral rectus
    • III — the rest, plus lid and pupil
    • Down-and-out + blown pupil = emergency
    • Cardinal fields H test
  • Mixed four
    • V: face sensation V1/V2/V3 + chewing
    • VII: expression + front 2/3 taste
    • IX: back 1/3 taste + gag afferent
    • X: voice, swallow, parasympathetics
    • Trigeminal neuralgia
  • Motor tail
    • XI: shrug, head turn
    • XII: tongue protrusion
    • Tongue toward unilateral LMN/CN XII lesion
  • Reflex arcs
    • Corneal: V1 in, VII out
    • Gag: IX in, X out
    • Light: II in, III out
  • Exam rules
    • Forehead sign: localization clue, not diagnosis
    • Uvula away from lesion
    • VI false localizer under ICP
    • Sixty-second screen in nerve order

Comparison

Peripheral VII pattern versus central/UMN facial weakness