Nerve	Nucleus Location	Branches	Anatomy
I. Olfactory	Above Brainstem	No major branches	Olfactory bulbs lie on the cribriform plate; olfactory nerve fibers pass through the plate to the nasal cavity.
II. Optic	Above Brainstem; synapses with lateral geniculate nucleus of the thalamus	No major branches	Optic nerve arises from the retina, passes through the optic canal, and forms the optic chiasm where fibers decussate.
III. Oculomotor	Midbrain; Oculomotor nucleus at the level of the superior colliculus	No major branches	Innervates medial rectus, superior rectus, inferior rectus, and inferior oblique muscles. Exits the midbrain between the posterior cerebral artery and superior cerebellar artery. Susceptible to compression by aneurysms.
IV. Trochlear	Midbrain; Trochlear nucleus at the level of the lower colliculus	No major branches	Innervates the superior oblique muscle. Exits posteriorly, crosses the midline, wraps around the midbrain, and enters the orbit via the superior orbital fissure.
V. Trigeminal	Pons; multiple nuclei: Mesencephalic, Chief Sensory, Descending Spinal, and Motor Nuclei	Ophthalmic (V1) Maxillary (V2) Mandibular (V3)	Large trunks exit anteriorly from the pons, and then split into the three branches. Controls sensation in the face and muscles of mastication.
VI. Abducent	Pons	No major branches	Controls the lateral rectus muscle, which abducts the eye. Exits from the pons and passes through the cavernous sinus to enter the orbit via the superior orbital fissure.
VII. Facial	Pons	Temporal Zygomatic Buccal Mandibular Cervical	Controls muscles of facial expression. The upper face receives bilateral input, while the lower face receives contralateral input. It also supplies taste to the anterior two-thirds of the tongue.
IX. Glossopharyngeal	Medulla	No major branches	Supplies the posterior third of the tongue (taste), and is involved in the gag reflex and swallowing.
X. Vagus	Medulla	No major branches	Controls muscles for voice and swallowing, parasympathetic innervation to thoracic and abdominal organs.
XI. Spinal Accessory	Medulla and cervical spinal cord	No major branches	Innervates sternocleidomastoid and trapezius muscles. Controls head turning and shoulder shrugging.
XII. Hypoglossal	Medulla	No major branches	Controls tongue movements. Exits between the pyramid and olive of the medulla and enters the tongue muscles.

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Examination of Cranial Nerves

Cranial Nerve	Name	How to Examine
I	Olfactory	Ask the patient to close their eyes and identify familiar smells (e.g., coffee, vanilla) using one nostril at a time.
II	Optic	Test visual acuity using a Snellen chart. Examine visual fields by confrontation and check for pupillary light reflex.
III	Oculomotor	Check eye movements (up, down, and in) and pupillary constriction to light and accommodation. Look for ptosis.
IV	Trochlear	Ask the patient to follow an object as it moves downward and inward. Assess for double vision or difficulty with downward gaze.
V	Trigeminal	Test sensation on the face in three areas (ophthalmic, maxillary, and mandibular) and palpate the masseter muscles while the patient clenches their teeth.
VI	Abducent	Assess lateral eye movement by asking the patient to follow an object with their eyes moving side to side.
VII	Facial	Ask the patient to raise eyebrows, smile, puff out cheeks, and close their eyes tightly. Check for asymmetry in facial movements.
VIII	Vestibulocochlear	Perform a Rinne and Weber test with a tuning fork. Test hearing with whispered words and assess balance if needed.
IX	Glossopharyngeal	Ask the patient to say "Ah" and observe the movement of the uvula. Test the gag reflex by stimulating the posterior pharynx.
X	Vagus	Check for hoarseness of the voice and ask the patient to swallow. Test the gag reflex along with CN IX.
XI	Accessory	Ask the patient to shrug their shoulders against resistance and turn their head side to side against resistance.
XII	Hypoglossal	Ask the patient to stick out their tongue and move it from side to side. Check for tongue deviation or atrophy.

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OSCE Cranial nerves and examination

Brain Stem Anatomy / Cranial Nerves

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Examination of Cranial Nerves

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