Cranial nerves
32 named structures.
Draft — not yet clinically reviewed. The structure of this map is checked automatically, but its wording has not been fact-checked against a textbook. Do not rely on it for an exam answer yet.
Hover or tab a structure to trace what it connects to. Some structures reveal further branches.
Clinical detail
- Forebrain (telencephalon and diencephalon)CN I CN IIOlfactory groove (subfrontal) meningioma compressing the olfactory tract and then the optic nerve4 questions
- MidbrainCN III CN IVVentral midbrain infarct (branch of the posterior cerebral artery) involving the III fascicle and cerebral peduncle (Weber syndrome)1 question
- PonsCN V CN VI CN VII CN VIIIVentral pontine infarct or tumour involving the VI and VII fascicles and the corticospinal tract (Millard–Gubler syndrome)1 question
- Medulla oblongataCN IX CN X CN XI CN XIILateral medullary infarct from vertebral or posterior inferior cerebellar artery occlusion (Wallenberg syndrome)1 question
- Olfactory nerve (CN I)CN I SensoryHead injury with acceleration–deceleration shearing the olfactory filaments at the cribriform plate4 questions
- Optic nerve (CN II)CN II SensoryOptic neuritis (demyelination, often the first attack of multiple sclerosis)4 questions
- Oculomotor nerve (CN III)CN III Motor ParasympatheticPosterior communicating artery aneurysm expanding against the nerve (surgical, pupil-involving third nerve palsy)1 question
- Trochlear nerve (CN IV)CN IV MotorFourth nerve palsy from head injury (commonest acquired cause, often bilateral because the nerves cross at the velum), microvascular ischaemia or a decompensated congenital palsy1 question
- Trigeminal nerve (CN V)CN V MixedTrigeminal neuralgia from a loop of the superior cerebellar artery compressing the root entry zone (or a demyelinating plaque in a young patient with multiple sclerosis)1 question
- Abducens nerve (CN VI)CN VI MotorRaised intracranial pressure from any cause (tumour, idiopathic intracranial hypertension, hydrocephalus) stretching the nerve over the petrous ridge1 question
- Facial nerve (CN VII)CN VII MixedBell's palsy: acute idiopathic lower motor neurone palsy, probably herpes simplex reactivation with oedema of the nerve inside the narrow facial canal2 questions
- Vestibulocochlear nerve (CN VIII)CN VIII SensoryVestibular schwannoma (acoustic neuroma) growing from the vestibular division in the internal acoustic meatus and cerebellopontine angle; bilateral in neurofibromatosis type 21 question
- Glossopharyngeal nerve (CN IX)CN IX Mixed ParasympatheticJugular foramen lesion involving IX (almost never an isolated palsy)4 questions
- Vagus nerve (CN X)CN X Mixed ParasympatheticUnilateral vagal or nucleus ambiguus lesion (jugular foramen tumour, lateral medullary infarct, skull base fracture)1 question
- Accessory nerve (CN XI)CN XI MotorIatrogenic injury during lymph node biopsy or neck dissection in the posterior triangle, where the nerve lies superficially4 questions
- Hypoglossal nerve (CN XII)CN XII MotorLower motor neurone lesion: skull base tumour or fracture, carotid endarterectomy, submandibular or carotid body surgery, jugular foramen extension (Collet–Sicard), motor neurone disease4 questions
- Cribriform plate of the ethmoidCN IAnterior skull base fracture through the cribriform plate4 questions
- Optic canalCN IIFrontal head injury transmitting force to the fixed intracanalicular nerve (traumatic optic neuropathy)4 questions
- Superior orbital fissureCN III CN IV CN V1 CN VISuperior orbital fissure syndrome from a lateral orbital wall fracture, tumour or inflammation (Tolosa–Hunt)1 question
- Foramen rotundumCN V2Perineural spread of a palatal or maxillary carcinoma back along V2 through the foramen1 question
- Foramen ovaleCN V3Percutaneous treatment of trigeminal neuralgia (radiofrequency rhizotomy, glycerol injection, balloon compression) passing a needle through the foramen ovale to the trigeminal ganglion1 question
- Internal acoustic meatusCN VII CN VIIIVestibular schwannoma arising inside the meatus and expanding it4 questions
- Stylomastoid foramenCN VIIForceps delivery or pressure on the undeveloped mastoid of a newborn2 questions
- Jugular foramenCN IX CN X CN XIJugular foramen syndrome (Vernet syndrome) from a glomus jugulare paraganglioma, schwannoma, meningioma, nasopharyngeal carcinoma, skull base metastasis, osteomyelitis or fracture4 questions
- Hypoglossal canalCN XIIOccipital condyle fracture, clival chordoma, skull base metastasis or nasopharyngeal carcinoma involving the canal4 questions
- Ophthalmic division of the trigeminal nerve (V1)CN V1 SensoryHerpes zoster ophthalmicus: varicella zoster reactivation in the V1 territory1 question
- Maxillary division of the trigeminal nerve (V2)CN V2 SensoryOrbital floor blow-out fracture crushing the infraorbital nerve in its canal1 question
- Mandibular division of the trigeminal nerve (V3)CN V3 MixedLower motor neurone lesion of the motor root (skull base tumour, perineural spread from a facial cancer)1 question
- Chorda tympaniCN VII Sensory ParasympatheticBell's palsy, Ramsay Hunt syndrome or a temporal bone fracture affecting the facial nerve proximal to the chorda tympani2 questions
- Terminal branches of the facial nerve (parotid plexus)CN VII MotorParotid malignancy (adenoid cystic or mucoepidermoid carcinoma) infiltrating the nerve within the gland2 questions
- Recurrent laryngeal nerveCN X MixedThyroidectomy or parathyroidectomy injuring one recurrent laryngeal nerve near the inferior thyroid artery1 question
- Superior laryngeal nerveCN X MixedExternal branch injured while ligating the superior thyroid artery at thyroidectomy1 question
Common questions
Which cranial nerves pass through the superior orbital fissure, and how does that differ from the cavernous sinus?
The superior orbital fissure transmits III, IV, V1 (lacrimal, frontal and nasociliary branches) and VI with the superior ophthalmic vein. The cavernous sinus immediately behind it contains the same nerves plus V2, with III, IV, V1 and V2 in its lateral wall and VI running free beside the internal carotid artery. A cavernous sinus lesion therefore adds V2 numbness of the cheek and upper lip and tends to hit VI first; an orbital apex lesion adds optic nerve involvement with visual loss.
How do you tell an upper from a lower motor neurone facial palsy, and where is the lesion in Bell's palsy?
The forehead has bilateral cortical input, so a stroke or tumour above the facial nucleus weakens only the contralateral lower face and the patient can still raise both eyebrows. A lesion of the nucleus or nerve weakens the whole hemiface including the forehead. Bell's palsy is a lower motor neurone lesion in the facial canal of the temporal bone, which is why it is commonly accompanied by hyperacusis (nerve to stapedius), loss of taste on the anterior tongue (chorda tympani) and sometimes a dry eye (greater petrosal), whereas a parotid lesion at the stylomastoid foramen causes weakness alone.
Why does a compressive third nerve palsy involve the pupil while a diabetic one usually spares it?
The parasympathetic pupillomotor fibres run on the outer dorsomedial surface of the nerve and are fed by pial vessels, so an expanding posterior communicating artery aneurysm or a herniating uncus compresses them first, giving a painful palsy with a dilated unreactive pupil. Microvascular ischaemia in diabetes or hypertension infarcts the vasa nervorum in the core of the nerve, sparing the surface fibres, so ptosis and a down-and-out eye occur with a normal pupil. A pupil-involving palsy is an aneurysm until CT angiography proves otherwise; a pupil-sparing palsy in an older vasculopath can be observed but must be imaged if the pupil becomes involved or it fails to recover.
Which way do the tongue, jaw and uvula deviate with a lower motor neurone lesion?
Tongue and jaw deviate towards the lesion; the uvula deviates away. Genioglossus pushes the tongue forward and across, so the healthy side pushes the tongue towards the weak side (XII). The lateral pterygoid pulls the jaw forward and across, so the healthy side pushes the jaw towards the weak side (V3). The palate is lifted by levator veli palatini, so the healthy side pulls the uvula away from the weak side (X). Fasciculation and wasting confirm the lesion is lower motor neurone; an upper motor neurone lesion deviates the tongue away from the lesion without wasting.
What is jugular foramen syndrome and what causes it?
Vernet syndrome is a unilateral palsy of IX, X and XI where they pass through the jugular foramen: absent gag reflex and loss of posterior-tongue taste, palatal weakness with the uvula deviating away, hoarseness and dysphagia, and weakness of sternocleidomastoid and trapezius. Adding XII from the neighbouring hypoglossal canal, with the tongue deviating towards the lesion, makes it Collet–Sicard syndrome. Causes are glomus jugulare paraganglioma (with pulsatile tinnitus), schwannoma, meningioma, nasopharyngeal carcinoma or metastasis at the skull base, skull base osteomyelitis and fractures.