11/03/2026
🟣 Cranial Nerves I–XII: Short Notes
🟣 Core Overview
➟ Cranial nerves are 12 pairs arising from the brain/brainstem
➟ Classified as Sensory, Motor, or Both
➟ Essential for neurological localization in exams and clinics
🟣 Pure Sensory Cranial Nerves
➟ CN I – Olfactory
→ Smell
→ Lesion: anosmia
➟ CN II – Optic
→ Vision (visual acuity & visual fields)
→ Lesion: visual field defects
➟ CN VIII – Vestibulocochlear
→ Hearing & balance
→ Lesion: hearing loss, vertigo
🟣 Pure Motor Cranial Nerves
➟ CN III – Oculomotor
→ Most eye movements, eyelid elevation, pupillary constriction
→ Lesion: ptosis, “down & out” eye, dilated pupil
➟ CN IV – Trochlear
→ Superior oblique muscle (downward & inward gaze)
→ Lesion: difficulty looking down (stairs)
➟ CN VI – Abducens
→ Lateral re**us muscle (eye abduction)
→ Lesion: medial deviation of eye
➟ CN XI – Accessory
→ Sternocleidomastoid & trapezius
→ Lesion: weak head rotation, shoulder droop
➟ CN XII – Hypoglossal
→ Tongue movement
→ Lesion: tongue deviates toward side of lesion
🟣 Mixed (Sensory + Motor) Cranial Nerves
➟ CN V – Trigeminal
→ Facial sensation (V1, V2, V3)
→ Muscles of mastication
➟ CN VII – Facial
→ Facial expression
→ Taste (anterior 2/3 of tongue)
→ Lacrimation & salivation
→ Lesion: Bell palsy
➟ CN IX – Glossopharyngeal
→ Taste (posterior 1/3 of tongue)
→ Swallowing, carotid body & sinus
➟ CN X – Vagus
→ Parasympathetic control of heart, lungs, GI tract
→ Voice & swallowing
→ Lesion: hoarseness, uvula deviation away from lesion
🟣 Exam Pearls
➟ Motor CN lesions → ipsilateral weakness
➟ Optic chiasm lesion → bitemporal hemianopia
➟ Tongue deviation toward lesion = hypoglossal nerve damage
➟ Facial droop + forehead involvement = LMN facial nerve lesion
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