Cranial nerves (ocular and smell)

Summary of functions of I, II, III, IV and VI, clinical testing, and pathology

 cranial nerves  anatomy  Neurology

I (olfactory)II (optic)III (oculomotor)IV (trochlear)VI (abducens)
functionsmellvisionraising eye lid, constricting pupil and most eye movementssuperior oblique muscle (moves eye downwards)lateral rectus (abducts eye)
defectloss of sense of smellloss of visionptosis, dilated pupil, eye deviated 'down and out'vertical diplopia on looking down (especially on looking 'in', adducted)inability to abduct the eye (move it 'out' laterally)
clinical testUsually just ask or test each nostril with pungent odour.Test visual acuity and fields. Exclude retinal causes.inspection of pupil (including light reflex) and eyelids, eye movementseye movementseye movements
important causeshead injury, meningitis, frontal lobe lesionsstroke affecting visual fields, demyelinating diseasevascular (diabetes, PICA aneurysm, certain strokes), trauma, tumours, cavernous sinus thrombosistraumaraised intracranial pressure, vascular (diabetes, hypertension)
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Cranial nerves (V, VII, VIII) | Motor defects | Cerebral lobe signs | Loss of consciousness | Brain stem strokes |