The table below lists the major characteristics of the 12 cranial nerves:
| Nerve | Functions | Clinical | Pathway/foramen |
|---|---|---|---|
| I (Olfactory) | Smell | Cribriform plate | |
| II (Optic) | Sight | Optic canal | |
| III (Oculomotor) | Eye movement (MR, IO, SR, IR)Pupil constrictionAccommodationEyelid opening | Palsy results in | |
| • ptosis | |||
| • 'down and out' eye | |||
| • dilated, fixed pupil | Superior orbital fissure (SOF) | ||
| IV (Trochlear) | Eye movement (SO) | Palsy results in defective downward gaze → vertical diplopia | SOF |
| V (Trigeminal) | Facial sensationMastication | Lesions may cause: | |
| • trigeminal neuralgia | |||
| • loss of corneal reflex (afferent) | |||
| • loss of facial sensation | |||
| • paralysis of mastication muscles | |||
| • deviation of jaw to weak side | V1: SOF, V2: Foramen rotundum,V3: Foramen ovale | ||
| VI (Abducens) | Eye movement (LR) | Palsy results in defective abduction → horizontal diplopia | SOF |
| VII (Facial) | Facial movementTaste (anterior 2/3rds of tongue)LacrimationSalivation | Lesions may result in: | |
| • flaccid paralysis of upper + lower face | |||
| • loss of corneal reflex (efferent) | |||
| • loss of taste | |||
| • hyperacusis | Internal auditory meatus | ||
| VIII (Vestibulocochlear) | Hearing, balance | Hearing lossVertigo, nystagmusAcoustic neuromas are Schwann cell tumours of the cochlear nerve | Internal auditory meatus |
| IX (Glossopharyngeal) | Taste (posterior 1/3rd of tongue)SalivationSwallowingMediates input from carotid body & sinus | Lesions may result in; | |
| • hypersensitive carotid sinus reflex | |||
| • loss of gag reflex (afferent) | Jugular foramen | ||
| X (Vagus) | PhonationSwallowingInnervates viscera | Lesions may result in; | |
| • uvula deviates away from site of lesion | |||
| • loss of gag reflex (efferent) | Jugular foramen | ||
| XI (Accessory) | Head and shoulder movement | Lesions may result in; | |
| • weakness turning head to contralateral side | Jugular foramen | ||
| XII (Hypoglossal) | Tongue movement | Tongue deviates towards side of lesion | Hypoglossal canal |
Some cranial nerves are motor, some sensory and some are both. The most useful mnemonic is given below.
CN I ----------------------------------------------------------------------→XII
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(S= Sensory, M= Motor, B= Both)
Image sourced from Wikipedia
View from the inferior surface of the brain showing the emergence of the cranial nerves
Image sourced from Wikipedia
Diagram showing the nuclei of the cranial nerves in the brainstem
| Reflex | Afferent limb | Efferent limb |
|---|---|---|
| Corneal | Ophthalmic nerve (V1) | Facial nerve (VII) |
| Jaw jerk | Mandibular nerve (V3) | Mandibular nerve (V3) |
| Gag | Glossopharyngeal nerve (IX) | Vagal nerve (X) |
| Carotid sinus | Glossopharyngeal nerve (IX) | Vagal nerve (X) |
| Pupillary light | Optic nerve (II) | Oculomotor nerve (III) |
| Lacrimation | Ophthalmic nerve (V1) | Facial nerve (VII) |
Branches of trigeminal nerve CN V come out from
"Superior Room Only"
Superior orbital fissure => V1 ophthalmic
Foramen Rotundum => V2 maxillary
Foramen Ovale => V3 mandibular