Cranial nerves Flashcards
(17 cards)
Cranial Nerve Overview (I–XII)
Mnemonic for names:
“Oh Oh Oh, To Touch And Feel Very Green Vegetables, AH!”
Mnemonic for function (Sensory/Motor/Both):
“Some Say Marry Money But My Brother Says Big Brains Matter Most”
Cranial nerves
CN
Name
Function Summary
I
Olfactory
Smell
II
Optic
Vision
III
Oculomotor
Eye movement (most), pupil constriction
IV
Trochlear
Eye movement (superior oblique)
V
Trigeminal
Facial sensation, mastication
VI
Abducens
Eye movement (lateral rectus)
VII
Facial
Facial expression, taste (anterior 2/3 tongue), lacrimation, salivation
VIII
Vestibulocochlear
Hearing, balance
IX
Glossopharyngeal
Taste (posterior 1/3), salivation (parotid), carotid body/sinus
X
Vagus
Swallowing, speech, parasympathetics
XI
Accessory
Head turning, shoulder shrug
XII
Hypoglossal
Tongue movement
CN I (Olfactory)
• Lesion: Anosmia
• Clinical context: Head trauma, Parkinson’s, Kallmann syndrome
CN II (Optic)
Lesion: Visual field defects
• Test: Visual acuity, pupillary reflex (afferent limb), visual fields
• Classic lesion: Optic chiasm → bitemporal hemianopia (e.g., pituitary adenoma)
CN III (Oculomotor)
Lesion: Eye down and out, ptosis, dilated pupil
• Causes: Posterior communicating artery aneurysm (pupil involvement)
• Pupillary reflex: Efferent limb
CN IV (Trochlear)
Lesion: Eye can’t look down and in → vertical diplopia (worse on stairs)
• Test: Look in and down
CN V (Trigeminal)
Lesion: Loss of facial sensation, jaw weakness, impaired corneal reflex (afferent limb)
• Divisions: V1 (ophthalmic), V2 (maxillary), V3 (mandibular - motor)
CN VI (Abducens)
Lesion: Eye can’t abduct → horizontal diplopia
• Vulnerable: In increased ICP (long intracranial course)
CN VII (Facial)
Lesion:
• Upper motor neuron (UMN): Contralateral lower face weakness (forehead spared)
• Lower motor neuron (LMN): Ipsilateral full-face weakness (Bell palsy)
• Other functions: Lacrimation, salivation (submandibular), taste (anterior 2/3)
CN VIII (Vestibulocochlear)
Lesion: Hearing loss, vertigo, nystagmus
• Tumor association: Schwannoma (at cerebellopontine angle)
CN IX (Glossopharyngeal)
Lesion: Loss of taste (posterior 1/3), impaired gag reflex (afferent)
• Carotid body/sinus afferents
CN X (Vagus)
Lesion: Hoarseness, dysphagia, uvula deviates away from lesion
• Gag reflex: Efferent limb
• Parasympathetics: To thoracoabdominal viscera
CN XI (Accessory)
Lesion: Weakness turning head to opposite side (SCM) or shoulder droop (trapezius)
CN XII (Hypoglossal)
Lesion: Tongue deviates toward lesion (LMN)
• Test: Stick out tongue
Brainstem Localization
Midbrain: CN III, IV
• Pons: CN V, VI, VII, VIII
• Medulla: CN IX, X, XI, XII
Step 1 Tip:
Crossed findings (e.g., ipsilateral CN + contralateral body weakness) = brainstem lesion
High-Yield Syndromes
Weber syndrome: Midbrain stroke → CN III palsy + contralateral hemiparesis (cerebral peduncle)
• Wallenberg syndrome (lateral medullary): CN IX, X → hoarseness, ↓ gag + contralateral body pain/temp loss
• Millard-Gubler syndrome: CN VI & VII + corticospinal tract → facial droop + abduction weakness + contralateral hemiparesis
• Vestibular schwannoma: CN VIII → hearing loss + vertigo; may involve CN VII, V
USMLE Step 1 Tips
Identify side of CN lesion using tongue, uvula, eye movement
• Corneal reflex: V1 (afferent), VII (efferent)
• Gag reflex: IX (afferent), X (efferent)
• Pupillary reflex: II (afferent), III (efferent)
• Be able to match cranial nerves to foramen:
• CN I: cribriform plate
• CN II: optic canal
• CN III, IV, V1, VI: superior orbital fissure
• CN V2: foramen rotundum
• CN V3: foramen ovale
• CN VII, VIII: internal acoustic meatus
• CN IX, X, XI: jugular foramen
• CN XII: hypoglossal canal
