Makindo Medical Notes"One small step for man, one large step for Makindo" |
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Related Subjects: |Cortical functions |Motor System |Sensory System |Mental state Examination |Speech and Language Exam |Cranial nerves and examination |Assessing Cognition
The Brainstem contains all the cranial nerves other than Olfactory and optic nerves
Nerve | Nucleus Location | Branches | Anatomy |
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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 |
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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 |
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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. |
Cranial Nerve | Name | How to Examine |
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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 | Abducens | 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. |