Cranial Nerves (CN I–XII) — Question Bank

Score — click each question to reveal the answer

CN I (Olfactory nerve) is unique among cranial nerves because it:
TMU Cranial Nerves Slide 17

A. Does NOT synapse in the thalamus before reaching cortex

B. Passes through the internal acoustic meatus

C. Is a motor nerve only

D. Arises from the pons

✓ Answer: A — No thalamic relay

CN I is the only cranial nerve whose afferent fibres project directly to the cerebral cortex (olfactory bulb → pyriform cortex) without first synapsing in the thalamus. All other sensory cranial nerves relay in the thalamus (dorsal thalamus / lateral geniculate body / medial geniculate body) before reaching cortex.

⚠ CN I fibres pass through the cribriform foramina of the ethmoid bone (not the internal acoustic meatus = CN VII + VIII). It arises from olfactory mucosa → olfactory bulb, which is part of telencephalon, not pons. Cribriform plate fracture → anosmia + CSF rhinorrhoea.

CN II (Optic nerve) is correctly described as:
TMU Cranial Nerves Slide 23

A. A true peripheral nerve that exits via the superior orbital fissure

B. A CNS tract covered by meninges, passing through the optic canal

C. A mixed nerve carrying motor fibres to the ciliary muscle

D. Arising from the midbrain at the level of the superior colliculus

✓ Answer: B — CNS tract; optic canal

CN II is developmentally a tract of the diencephalon, not a true peripheral nerve. It is covered by all three meningeal layers (dura, arachnoid, pia) and has a subarachnoid space around it — hence raised intracranial pressure causes papilloedema. It exits the skull through the optic canal (not the superior orbital fissure). Fibres arise from ganglion cells of the retina → lateral geniculate body (diencephalon).

⚠ Superior orbital fissure carries CN III, IV, V1, VI. The optic canal carries CN II + ophthalmic artery. Because CN II is a CNS tract, demyelinating disease (multiple sclerosis) causes optic neuritis with central scotoma — not possible in true peripheral nerves.

CN III (Oculomotor nerve) supplies all of the following extraocular muscles EXCEPT:
TMU Cranial Nerves Slide 29

A. Levator palpebrae superioris

B. Superior rectus

C. Superior oblique

D. Inferior oblique

✓ Answer: C — Superior oblique (= CN IV)

CN III supplies five muscles: levator palpebrae superioris (superior branch) + superior rectus (superior branch) + inferior rectus, medial rectus, inferior oblique (inferior branch). It also carries parasympathetic fibres (Edinger-Westphal nucleus) via the ciliary ganglion to sphincter pupillae (miosis) and ciliary muscle (accommodation). Superior oblique = CN IV; lateral rectus = CN VI.

⚠ Mnemonic: LR₆SO₄(rest)₃ — Lateral Rectus = CN VI; Superior Oblique = CN IV; all others = CN III. CN III palsy → ptosis + eye “down and out” + fixed dilated pupil (surgical third nerve palsy e.g. posterior communicating artery aneurysm).

Which statement about CN IV (Trochlear nerve) is CORRECT?
TMU Cranial Nerves Slide 38

A. It supplies the inferior oblique muscle

B. It exits the brainstem ventrally from the midbrain

C. It passes through the jugular foramen

D. It is the only CN to exit dorsally; it has the longest intracranial course

✓ Answer: D — Only CN to exit dorsally; longest intracranial course

CN IV is unique in two ways: (1) the only cranial nerve to exit from the dorsal surface of the brainstem (inferior to the inferior colliculus); (2) it has the longest intracranial course before entering the cavernous sinus. It supplies superior oblique (not inferior oblique = CN III). It exits the skull via the superior orbital fissure (not jugular foramen).

⚠ CN IV palsy → weakness of superior oblique → patient cannot look down and in; compensates by head-tilting to the opposite shoulder. A trochlear palsy is easily missed; always test by asking patient to look at their nose-tip.

The three divisions of CN V (Trigeminal nerve) exit the skull through which foramina respectively?
TMU Cranial Nerves Slides 52,57,61

A. V1: superior orbital fissure; V2: foramen rotundum; V3: foramen ovale

B. V1: foramen rotundum; V2: foramen ovale; V3: superior orbital fissure

C. V1: optic canal; V2: foramen ovale; V3: foramen rotundum

D. V1: foramen ovale; V2: superior orbital fissure; V3: foramen rotundum

✓ Answer: A — SOF / Rotundum / Ovale

CN V is the largest cranial nerve (mixed). Its three divisions: V1 (Ophthalmic) → superior orbital fissure; V2 (Maxillary) → foramen rotundum → pterygopalatine fossa; V3 (Mandibular) → foramen ovale → infratemporal fossa. V1 and V2 are purely sensory; V3 is mixed (sensory + motor).

⚠ Mnemonic for foramen assignment: Standing Room Only → Superior orbital fissure (V1), Rotundum (V2), Ovale (V3). Foramen spinosum carries the middle meningeal artery, not a CN. The optic canal carries CN II + ophthalmic artery only.

CN V3 (Mandibular nerve) is the ONLY division of CN V that carries motor fibres. Which muscles does it supply?
TMU Cranial Nerves Slides 65, 67

A. Muscles of facial expression + buccinator

B. Muscles of mastication + mylohyoid + anterior belly of digastric + tensor veli palatini

C. All tongue muscles via the lingual nerve

D. Levator veli palatini + palatoglossus

✓ Answer: B — Mastication + mylohyoid + ant. digastric + tensor veli palatini

V3 motor distribution (all muscles of pharyngeal arch 1 origin): (1) Muscles of mastication — masseter, temporalis, medial pterygoid, lateral pterygoid; (2) Mylohyoid (floor of mouth); (3) Anterior belly of digastric; (4) Tensor veli palatini; (5) Tensor tympani. V3 does NOT supply tongue muscles (CN XII) or muscles of facial expression (CN VII).

⚠ The lingual nerve (branch of V3) carries only sensory fibres (general sensation anterior 2/3 tongue); taste anterior 2/3 tongue is carried by the chorda tympani (branch CN VII) which hitches a ride with the lingual nerve. Palatoglossus = CN X.

CN VI (Abducens nerve) is the most commonly affected cranial nerve by raised intracranial pressure because:
TMU Cranial Nerves Slide 41

A. It is the thinnest nerve and most susceptible to ischaemia

B. It passes through the foramen ovale where pressure rises first

C. It has the longest intracranial course and runs along the clivus, making it prone to stretching

D. It lies in the cavernous sinus adjacent to the internal carotid artery

✓ Answer: C — Long course along clivus; prone to stretching

CN VI has a long course along the dorsum sellae and clivus of the skull base before entering Dorello's canal and then the cavernous sinus. Raised ICP causes downward herniation of the brainstem, which stretches CN VI over the petrous apex — producing a false localising sign (bilateral CN VI palsy does not mean a pontine lesion). It supplies only the lateral rectus; palsy → medial squint (convergent strabismus) and diplopia on lateral gaze.

⚠ CN IV actually has the longest intracranial course but is less clinically notorious for raised ICP. CN VI palsy as a false localising sign is a classic neurological teaching point: bilateral medial squint in a patient with papilloedema = raised ICP until proven otherwise.

CN VII (Facial nerve) exits the skull at the:
TMU Cranial Nerves Slide 80

A. Foramen ovale, then enters the parotid gland

B. Jugular foramen, alongside CN IX and X

C. Superior orbital fissure

D. Internal acoustic meatus → facial canal → stylomastoid foramen, then enters parotid

✓ Answer: D — Internal acoustic meatus → facial canal → stylomastoid foramen

CN VII course: bulbopontine sulcus → internal acoustic meatus (alongside CN VIII) → facial canal in petrous temporal bone (gives off greater petrosal nerve, nerve to stapedius, chorda tympani) → stylomastoid foramen → parotid gland (divides into temporal, zygomatic, buccal, marginal mandibular, cervical branches supplying muscles of facial expression).

⚠ The facial nerve has a complex intrapetrous course. Branches given off INSIDE the facial canal: (1) Greater petrosal nerve (secretomotor lacrimal + nasal glands); (2) Nerve to stapedius (dampens ossicular chain); (3) Chorda tympani (taste anterior 2/3 tongue + secretomotor submandibular/sublingual glands). Injury proximal to geniculate ganglion affects all of these.

The chorda tympani (branch of CN VII intermediate nerve) carries:
TMU Cranial Nerves Slide 84

A. Taste from anterior 2/3 of tongue + secretomotor to submandibular and sublingual glands

B. Motor fibres to the tensor tympani muscle

C. Taste from posterior 1/3 of tongue + secretomotor to parotid gland

D. Sensory innervation to the middle ear mucosa

✓ Answer: A — Taste ant. 2/3 tongue + secretomotor submandibular/sublingual

Chorda tympani (from CN VII): (1) Special visceral afferent (taste) → anterior 2/3 of tongue via the lingual nerve (V3); (2) General visceral efferent (parasympathetic secretomotor) → synapse in submandibular ganglion → submandibular and sublingual salivary glands. It traverses the middle ear, hence the name. NOT for parotid (parotid = lesser petrosal nerve of CN IX → otic ganglion) and NOT posterior 1/3 tongue (= CN IX).

⚠ Tympanic nerve (CN IX) carries secretomotor to parotid via the lesser petrosal nerve → otic ganglion → auriculotemporal nerve (V3). Tensor tympani = V3 motor. Mucosa of middle ear = tympanic plexus (CN IX).

Q10

CN VIII (Vestibulocochlear nerve) enters the internal acoustic meatus with CN VII. Injury to CN VIII causes:
TMU Cranial Nerves Slide 104

A. Ipsilateral facial paralysis and hyperacusis only

B. Sensorineural deafness and loss of balance (vertigo/nystagmus)

C. Conductive deafness and loss of taste anterior 2/3 tongue

D. Loss of gag reflex and dysphagia

✓ Answer: B — Sensorineural deafness + loss of balance

CN VIII has two divisions: Cochlear nerve (receptors = spiral organ of Corti → hearing; injury → sensorineural deafness) and Vestibular nerve (receptors = ampullary crests of semicircular canals + macula utriculi + macula sacculi → balance; injury → vertigo, nystagmus, ataxia). Acoustic neuroma (vestibular schwannoma) at the cerebellopontine angle commonly compresses both CN VII and CN VIII together.

⚠ Sensorineural deafness: Weber test → lateralises to good ear; Rinne test → AC>BC in affected ear (but reduced overall). Conductive deafness (ossicle/middle ear pathology) is not a CN VIII lesion. Gag reflex = CN IX/X.

Q11

CN IX (Glossopharyngeal nerve) carries taste and common sensation from:
TMU Cranial Nerves Slides 107–108

A. Anterior 2/3 of tongue only

B. Posterior 1/3 of tongue + lacrimal gland secretion

C. Posterior 1/3 of tongue + carotid body/sinus + pharyngeal mucosa

D. Entire tongue + uvula

✓ Answer: C — Posterior 1/3 tongue + carotid body/sinus + pharyngeal mucosa

CN IX is a mixed nerve (5 components). Key functions: (1) Taste + common sensation posterior 1/3 tongue (lingual branches); (2) Carotid body (peripheral chemoreceptor for O2/CO2/pH) and carotid sinus (baroreceptor for blood pressure) via the carotid sinus branch; (3) Mucosa of pharynx, middle ear, auditory tube; (4) Motor to stylopharyngeus (only muscle); (5) Secretomotor parotid via lesser petrosal → otic ganglion. Exits via jugular foramen.

⚠ Carotid sinus hypersensitivity (e.g. tight collar) → CN IX-mediated bradycardia and hypotension. Gag reflex: afferent = CN IX (posterior pharyngeal wall); efferent = CN X (pharyngeal muscles via pharyngeal plexus). Lacrimal gland = CN VII via greater petrosal nerve.

Q12

CN X (Vagus nerve) is the longest cranial nerve. Its abdominal distribution extends as far as the:
TMU Cranial Nerves Slides 119–121

A. Rectum (supplies entire large bowel)

B. Terminal ileum only

C. Duodenum only (jejunum supplied by sacral parasympathetics)

D. Left colic (splenic) flexure

✓ Answer: D — Left colic (splenic) flexure

The vagus exits the jugular foramen and descends in the carotid sheath. In the abdomen it supplies: anterior gastric wall, posterior gastric wall, duodenum, small intestine, ascending colon, and transverse colon as far as the left colic flexure via the coeliac and superior mesenteric plexuses. Bowel from the left colic flexure to the rectum = pelvic splanchnic nerves (S2–S4, sacral parasympathetics). Clinical: vagotomy for peptic ulcer disease aimed to reduce gastric acid.

⚠ Left (splenic) flexure is also the SMA/IMA vascular watershed — important in ischaemic colitis. The vagus is the afferent limb of the Hering-Breuer reflex (lung inflation) and the efferent limb of the vago-vagal (baroreceptor) reflex.

Q13

The recurrent laryngeal nerve (branch of CN X) supplies all intrinsic laryngeal muscles EXCEPT:
TMU Cranial Nerves Slides 115–117

A. Cricothyroid

B. Posterior cricoarytenoid

C. Lateral cricoarytenoid

D. Thyroarytenoid

✓ Answer: A — Cricothyroid (= external branch of superior laryngeal nerve)

The recurrent laryngeal nerve supplies ALL intrinsic laryngeal muscles except the cricothyroid. The cricothyroid is supplied by the external branch of the superior laryngeal nerve (also from CN X). Left RLN loops under the aortic arch; right RLN loops under the subclavian artery. RLN injury (thyroid surgery, lung/oesophageal cancer, aortic arch aneurysm) → hoarse voice; bilateral injury → aphonia or airway obstruction.

⚠ Superior laryngeal nerve (CN X): internal branch = sensory above vocal folds; external branch = motor to cricothyroid (which tenses the vocal cord to alter pitch). Unilateral RLN injury in thyroid surgery: the external branch of the SLN is at risk when ligating the superior thyroid artery close to the gland — 2020 Past Paper MCQ Q7.

Q14

CN XI (Accessory nerve) supplies which two muscles?
TMU Cranial Nerves Slides 124–126

A. Sternocleidomastoid and platysma

B. Sternocleidomastoid and trapezius

C. Trapezius and levator scapulae

D. SCM and infrahyoid muscles

✓ Answer: B — Sternocleidomastoid + trapezius

CN XI (spinal accessory) lateral branch supplies sternocleidomastoid (turns head to opposite side + flexes neck) and trapezius (shrugs shoulder + stabilises scapula). It exits via the jugular foramen. CN XI injury: (1) SCM paralysis → weakness turning head to contralateral side; (2) Trapezius paralysis → shoulder drop + weakness raising arm above horizontal + winging of scapula (lower fibres). CN XI is tested by asking patient to shrug against resistance.

⚠ Platysma = CN VII. Levator scapulae = C3, C4, dorsal scapular nerve. Infrahyoid muscles = ansa cervicalis (C1–C3). Jugular foramen syndrome = simultaneous CN IX + X + XI palsies (e.g. glomus jugulare tumour).

Q15

CN XII (Hypoglossal nerve) supplies ALL tongue muscles EXCEPT:
TMU Cranial Nerves Slides 130–131

A. Hyoglossus

B. Genioglossus

C. Palatoglossus

D. Styloglossus

✓ Answer: C — Palatoglossus (= CN X / pharyngeal plexus)

CN XII supplies ALL intrinsic tongue muscles (longitudinal, transverse, vertical) and ALL extrinsic tongue muscles (genioglossus, hyoglossus, styloglossus, chondroglossus) except palatoglossus. Palatoglossus is innervated by CN X via the pharyngeal plexus (because it elevates the tongue towards the palate, acting with other palatal muscles). CN XII exits via the hypoglossal canal and travels between the internal carotid artery and internal jugular vein.

⚠ CN XII unilateral lesion: tongue deviates towards the side of the lesion on protrusion (genioglossus pushes tongue forward; the normal side pushes harder). UMN lesion (contralateral corticobulbar tract) → tongue deviates away from lesion side. Key: LMN palsy = tongue deviates TOWARD lesion (medullary syndrome, hypoglossal canal tumour).

Q16

Bell's palsy is a lower motor neuron (LMN) lesion of CN VII. Which finding DISTINGUISHES it from an upper motor neuron (UMN) facial palsy?
TMU Cranial Nerves Slides 93–95

A. Drooping of the angle of the mouth

B. Inability to close the eye (lagophthalmos)

C. Deviation of the mouth to the affected side

D. Paralysis of ALL ipsilateral facial muscles INCLUDING the forehead

✓ Answer: D — ALL muscles paralysed including forehead (LMN Bell's)

In Bell's palsy (LMN CN VII lesion), the entire ipsilateral face is paralysed: forehead wrinkles absent, eye cannot close (Bell's phenomenon = eye rolls up), nasolabial fold flattened, mouth droops to unaffected side. Forehead sparing distinguishes UMN palsy: the frontalis muscle receives bilateral cortical representation, so a unilateral cortical or internal capsule lesion only weakens the contralateral lower face (nasolabial fold + mouth) while the forehead is partially spared. Bell's palsy = idiopathic, often post-viral (HSV-1 reactivation).

⚠ Quick test: ask patient to raise their eyebrows and wrinkle forehead. LMN palsy → forehead also affected. UMN palsy → forehead relatively spared. Other Bell's features: hyperacusis (stapedius paralysis), loss of taste ant. 2/3 tongue, reduced lacrimation if lesion is proximal to geniculate ganglion.

Q17

In an UMN facial palsy (e.g. after a stroke affecting the internal capsule), which part of the face is RELATIVELY SPARED and why?
2023 Review Slide 22; Gray's 4e

A. The lower face is spared because it has bilateral cortical representation

B. The forehead (frontalis) is relatively spared because the frontalis motor nucleus receives input from BOTH cerebral hemispheres

C. The orbicularis oculi is spared because it is supplied by CN III

D. The forehead is spared because it is supplied by CN V3 not CN VII

✓ Answer: B — Frontalis spared; bilateral cortical representation of upper face

The upper facial motor nucleus (which controls frontalis and orbicularis oculi) receives bilateral corticobulbar input (from both hemispheres). A unilateral UMN lesion (e.g. left internal capsule stroke) therefore preserves some function in the contralateral frontalis, producing forehead sparing. The lower facial nucleus receives predominantly contralateral cortical input only, so the lower face (nasolabial fold, mouth) is markedly weak.

⚠ Clinical clue: stroke → contralateral lower facial weakness + forehead sparing. Bell's palsy → ipsilateral complete facial weakness including forehead. Never mistake a stroke for Bell's palsy — look for other UMN signs (arm/leg weakness, brisk reflexes, Babinski) to distinguish.

Q18

Horner's syndrome (ptosis, miosis, anhidrosis) results from interruption of the sympathetic pathway. Which cranial nerve is DIRECTLY responsible for the pupillary findings?

A. CN II (optic nerve)

B. No cranial nerve; Horner's is due to loss of sympathetic supply to the eye

C. CN III (oculomotor nerve) parasympathetic fibres

D. CN V1 ophthalmic division

✓ Answer: B — Sympathetic chain lesion; no CN directly involved

Horner's syndrome is caused by disruption of the oculosympathetic pathway (hypothalamus → ciliospinal centre of Budge C8–T2 → superior cervical ganglion → internal carotid artery → dilator pupillae, superior tarsal muscle, sweat glands). This pathway does NOT run in any cranial nerve. The results: miosis (dilator pupillae denervated; unopposed sphincter via CN III parasympathetics), ptosis (superior tarsal/Müller's muscle), anhidrosis (ipsilateral face). The pupil responds normally to light (CN II afferent + CN III efferent intact).

⚠ Contrast Horner's (sympathetic loss → miosis + ptosis) with CN III palsy (parasympathetic loss → mydriasis + complete ptosis + “down and out” eye). Causes of Horner's: Pancoast tumour (apex lung), carotid artery dissection, lateral medullary (Wallenberg) syndrome, cervical rib, neck surgery.

Q19

Anosmia following a head injury most likely indicates fracture of:
TMU Cranial Nerves Slide 21

A. The petrous part of the temporal bone

B. The foramen rotundum

C. The cribriform plate of the ethmoid bone

D. The sphenoid sinus

✓ Answer: C — Cribriform plate of the ethmoid

The olfactory nerve fibres (CN I) are thin unmyelinated axons that pass through the cribriform foramina of the ethmoid bone to reach the olfactory bulb. An anterior cranial fossa fracture shears these delicate fibres → anosmia. The same fracture tears the dural sleeves around the olfactory nerves → CSF rhinorrhoea (cerebrospinal fluid leaks from the nose). The patient may notice a salty taste and anosmia after a forehead impact.

⚠ Petrous temporal fracture → CN VII and CN VIII injury (facial palsy + sensorineural deafness + haemotympanum). Cribriform plate fracture is a common exam pairing: anosmia + CSF rhinorrhoea. "Halo sign" on linen (CSF forms a clear outer ring around blood) confirms CSF leak.

Q20

Which cranial nerves pass through the cavernous sinus?
2020 Past Paper Definition; 2023 Review Slide 30

A. CN III, V3, VI, VII only

B. CN II, III, IV, V1, VI

C. CN IX, X, XI pass through it before the jugular foramen

D. CN III, IV, V1, V2, VI (and the internal carotid artery)

✓ Answer: D — CN III, IV, V1, V2, VI + internal carotid artery

The cavernous sinus is a dural venous sinus lateral to the pituitary fossa. It transmits: in the lateral wall (superior to inferior) — CN III, CN IV, CN V1 (ophthalmic), CN V2 (maxillary); within the sinus itself — CN VI (lateral to the ICA) + the internal carotid artery with its sympathetic plexus. Cavernous sinus thrombosis (e.g. from facial furuncle spreading via ophthalmic veins) → palsies of CN III, IV, V1, V2, VI + proptosis + chemosis + pain.

⚠ CN V3 does NOT pass through the cavernous sinus (it exits via foramen ovale below the sinus). CN II passes through the optic canal, not the cavernous sinus. CN IX, X, XI exit through the jugular foramen. Mnemonic for lateral wall content (top to bottom): Oh Oh To Touch And Feel → Oculomotor (III), Trochlear (IV), Ophthalmic (V1), Maxillary (V2) — and CN VI is free inside the sinus near the ICA.

D1 Foramen Ovale — contents (CN V3 + lesser petrosal nerve) +

Foramen ovale is an oval aperture in the greater wing of the sphenoid bone, transmitting: (1) CN V3 (Mandibular nerve) — the largest and only mixed division of the trigeminal nerve, carrying general somatic sensory fibres and special visceral motor fibres to muscles of mastication; (2) Lesser petrosal nerve — a parasympathetic secretomotor fibre derived from the tympanic branch of CN IX (glossopharyngeal), which relays in the otic ganglion and then travels with the auriculotemporal nerve (V3) to supply the parotid gland; (3) Accessory meningeal artery; (4) Emissary vein (connecting cavernous sinus to pterygoid plexus). Clinical: mandibular nerve block is achieved by injecting at the foramen ovale.

Gray's Anatomy 4e · TMU Cranial Nerves Slide 61

D2 Jugular Foramen — contents (CN IX, X, XI) +

The jugular foramen lies between the petrous part of the temporal bone and the occipital bone. It transmits: (1) CN IX (Glossopharyngeal) — passes through the anterior compartment; (2) CN X (Vagus) — passes through the middle compartment with its superior (jugular) ganglion; (3) CN XI (Accessory) — passes through the posterior compartment; (4) Internal jugular vein (the primary content by volume) — the continuation of the sigmoid sinus. Clinical: Jugular foramen syndrome (Vernet's syndrome) — simultaneous lesions of CN IX, X, XI (e.g. glomus jugulare tumour, metastasis) producing dysphagia, hoarseness, loss of gag reflex, and trapezius/SCM weakness. The slide question “which CN is EXCEPT from the jugular foramen” = Answer D: CN XII (Hypoglossal) — it exits via the hypoglossal canal.

TMU Cranial Nerves Slides 7–8, 124, 129

D3 Cavernous Sinus +

A paired trabeculated dural venous sinus lying on either side of the body of the sphenoid bone (lateral to the sella turcica / pituitary fossa), at the base of the skull. Contents: Lateral wall (superior to inferior): CN III (oculomotor), CN IV (trochlear), CN V1 (ophthalmic), CN V2 (maxillary). Within the sinus lumen: CN VI (abducens, free-floating, lateral to the ICA) and the internal carotid artery with its pericarotid sympathetic plexus. Tributaries: superior and inferior ophthalmic veins, sphenoparietal sinus, intercavernous sinuses. Drains via: superior and inferior petrosal sinuses → internal jugular vein. Clinical: Cavernous sinus thrombosis — painful ophthalmoplegia, proptosis, chemosis, fever; may cause multiple CN palsies. Carotico-cavernous fistula (post-trauma) → pulsatile proptosis + bruit.

Gray's Anatomy 4e · 2023 Review Slide 30 · TMU Cranial Nerves Slides 27, 38

D4 Bell's Palsy vs UMN Facial Palsy +

Bell's palsy is an acute idiopathic lower motor neuron (LMN) lesion of CN VII, most commonly due to HSV-1 reactivation in the geniculate ganglion causing oedema within the facial canal. Features: sudden unilateral complete facial weakness (ALL muscles on affected side including frontalis — wrinkles absent), lagophthalmos (cannot close eye; Bell's phenomenon = eye rolls up), nasolabial fold flattened, mouth pulled to unaffected side. If lesion is proximal to the geniculate ganglion: additionally hyperacusis (stapedius palsy), loss of taste anterior 2/3 tongue (chorda tympani), reduced lacrimation.

UMN facial palsy (e.g. internal capsule stroke) causes contralateral lower facial weakness with forehead sparing — the frontalis motor nucleus receives bilateral corticobulbar fibres, so a unilateral cortical/capsular lesion does not fully denervate it. The nasolabial fold is flattened and the mouth droops contralateral to the lesion, but the patient can still raise the eyebrow. Look for ipsilateral hemiplegia (arm/leg), brisk reflexes, and upgoing plantar (Babinski) to confirm UMN aetiology.

TMU Cranial Nerves Slides 93–95 · 2023 Review Slides 22, 26

D5 Chorda Tympani +

A branch of CN VII (facial nerve) given off inside the facial canal before the stylomastoid foramen. It traverses the middle ear (crossing the medial surface of the tympanic membrane and the handle of the malleus) to exit through the petrotympanic fissure, then joins the lingual nerve (V3) in the infratemporal fossa. Two components: (1) Special visceral afferent — carries taste from the anterior 2/3 of the tongue (cell bodies in geniculate ganglion; central fibres to solitary nucleus); (2) General visceral efferent (parasympathetic) — preganglionic fibres synapse in the submandibular ganglion; postganglionic fibres supply the submandibular and sublingual salivary glands. Clinical: Sectioning chorda tympani during middle ear surgery → loss of taste anterior 2/3 tongue (ipsilateral) + reduced saliva from submandibular/sublingual glands. Not to be confused with lesser petrosal nerve (CN IX → parotid) or greater petrosal nerve (CN VII → lacrimal gland).

TMU Cranial Nerves Slides 84–85

D6 Recurrent Laryngeal Nerve +

A branch of CN X (Vagus nerve) given off in the thorax. Course: Left RLN loops under the aortic arch (at the level of the ligamentum arteriosum) and ascends in the tracheo-oesophageal groove. Right RLN loops under the right subclavian artery and ascends similarly. Both nerves enter the larynx under the inferior constrictor. Supply: ALL intrinsic laryngeal muscles except the cricothyroid (cricothyroid = external branch of superior laryngeal nerve). Also supplies sensory below the vocal folds. Clinical consequences of injury: Unilateral → hoarse or breathy voice (vocal cord immobile in paramedian position). Bilateral → bilateral adduction of vocal cords → stridor and respiratory obstruction (emergency tracheostomy). Common causes: thyroid surgery, carcinoma of lung/oesophagus (especially left-sided, due to long mediastinal course of left RLN), aortic arch aneurysm, neck dissection. The left RLN is more vulnerable than the right due to its longer intrathoracic course.

TMU Cranial Nerves Slides 115–117 · 2020 Past Paper MCQ Q7

Essay 1

Name the 12 cranial nerves in order. For each, state the functional type (sensory / motor / mixed), its exit foramen from the skull, and two key functions or clinical facts.

10 marks

Classification: sensory / motor / mixed

Pure sensory: I (Olfactory), II (Optic), VIII (Vestibulocochlear)

Pure motor: III (Oculomotor), IV (Trochlear), VI (Abducens), XI (Accessory), XII (Hypoglossal)

Mixed (sensory + motor): V (Trigeminal), VII (Facial), IX (Glossopharyngeal), X (Vagus)

CN I–XII table

I Olfactory — Sensory | Cribriform foramina (ethmoid) | Smell; only CN without thalamic relay; cribriform plate fracture → anosmia + CSF rhinorrhoea
II Optic — Sensory (CNS tract) | Optic canal | Vision; covered by meninges → papilloedema with raised ICP; demyelination → optic neuritis
III Oculomotor — Motor | Superior orbital fissure | 5 extraocular muscles + levator; parasympathetic → pupil constriction via ciliary ganglion; CN III palsy → ptosis + down-and-out + dilated pupil
IV Trochlear — Motor | Superior orbital fissure | Superior oblique; only CN to exit dorsally; longest intracranial course; palsy → cannot look down-and-in, head tilt
V Trigeminal — Mixed (largest CN) | V1: SOF; V2: foramen rotundum; V3: foramen ovale | Sensory: entire face/scalp/dura; Motor (V3): mastication; trigeminal neuralgia = paroxysmal facial pain
VI Abducens — Motor | Superior orbital fissure | Lateral rectus only; most common CN affected by raised ICP (false localising sign); palsy → medial squint
VII Facial — Mixed | Internal acoustic meatus → stylomastoid foramen | Facial expression muscles; taste anterior 2/3 (chorda tympani); secretomotor lacrimal/salivary; Bell's palsy LMN vs UMN palsy
VIII Vestibulocochlear — Sensory | Internal acoustic meatus | Hearing (cochlear) + balance (vestibular); acoustic neuroma at CP angle compresses CN VII + VIII
IX Glossopharyngeal — Mixed | Jugular foramen | Taste + sensation posterior 1/3 tongue; carotid body/sinus; secretomotor parotid; gag reflex afferent; stylopharyngeus motor
X Vagus — Mixed | Jugular foramen | Longest CN; parasympathetics to thorax + abdomen to left colic flexure; RLN → all intrinsic laryngeal muscles except cricothyroid; hoarseness if RLN damaged
XI Accessory — Motor | Jugular foramen | SCM + trapezius; shoulder shrug; jugular foramen syndrome involves IX + X + XI together
XII Hypoglossal — Motor | Hypoglossal canal | All intrinsic + extrinsic tongue muscles except palatoglossus (CN X); lesion → tongue deviates toward side of LMN lesion

Marking (10 marks): Correct name + order (2) · Sensory/motor/mixed classification (2) · Correct foramen for each (3) · Two clinical/function points per nerve (3)

Essay 2

Describe CN V (Trigeminal nerve): its three divisions, their sensory territories on the face and head, the motor branch (V3) and its muscles, the foramina, and the clinical features of trigeminal neuralgia.

8 marks

Overview

CN V is the largest cranial nerve and the principal sensory nerve of the face. It is a mixed nerve (general somatic afferent + special visceral efferent). Cell bodies in the trigeminal (Gasserian) ganglion on the apex of the petrous temporal bone.

Three divisions

V1 Ophthalmic (sensory only) — exits via superior orbital fissure. Sensory territory: skin above the eye + forehead + scalp (to vertex) + dorsum of nose + cornea. Branches: frontal (supratrochlear + supraorbital), lacrimal, nasociliary. Important: corneal reflex afferent = V1; loss = anaesthetic eye.
V2 Maxillary (sensory only) — exits via foramen rotundum → pterygopalatine fossa → inferior orbital fissure. Sensory territory: skin between eye and mouth (cheek, upper lip, side of nose, anterior temple). Branches: infraorbital, zygomatic, superior alveolar (maxillary teeth + gum), pterygopalatine nerves.
V3 Mandibular (mixed: sensory + motor) — exits via foramen ovale → infratemporal fossa. Sensory territory: skin below the mouth + chin + auricle + temple + lower lip + anterior external ear. Sensory branches: auriculotemporal, lingual (general sensation anterior 2/3 tongue), inferior alveolar (mandibular teeth), buccal, mental.

V3 motor supply (muscles of first branchial arch)

Muscles of mastication: masseter (closes jaw) + temporalis (closes + retracts jaw) + medial pterygoid (closes jaw) + lateral pterygoid (opens jaw, protrudes, side-to-side)
Other: mylohyoid + anterior belly of digastric (open jaw + elevate hyoid) + tensor veli palatini (opens Eustachian tube) + tensor tympani (dampens ossicles)

Clinical: Trigeminal neuralgia (Tic douloureux)

Paroxysmal, sudden, severe, stabbing pain in the distribution of CN V (usually V2 or V3)
Triggered by light touch (eating, talking, cold air)
Most common cause: vascular compression of CN V root at the pons (superior cerebellar artery)
Treatment: carbamazepine (first-line), or microvascular decompression surgery

Marking (8 marks): Three divisions named + foramina (2) · Sensory territories described (2) · V3 motor muscles listed (2) · Trigeminal neuralgia: definition + trigger + treatment (2)

Essay 3

Describe CN VII (Facial nerve): its course from brainstem to face, branches given within the facial canal, branches at the face, and the clinical distinction between LMN (Bell's) and UMN facial palsy, including the role of chorda tympani.

8 marks

Course

Arises from the bulbopontine sulcus (pons) as two roots: larger motor root + smaller intermediate nerve (nervus intermedius)
→ Internal acoustic meatus (alongside CN VIII)
→ Facial canal (petrous temporal bone): turns at geniculate ganglion (site of cell bodies for taste/general sensation)
→ Stylomastoid foramen (exits skull)
→ enters parotid gland (but does not supply it), divides into terminal branches

Branches inside the facial canal

Greater petrosal nerve (at geniculate ganglion): preganglionic parasympathetics → pterygopalatine ganglion → lacrimal gland + nasal/palatal glands. Taste from soft palate.
Nerve to stapedius: motor to stapedius muscle (dampens ossicular vibration); loss → hyperacusis
Chorda tympani: taste anterior 2/3 tongue + secretomotor submandibular/sublingual glands (via submandibular ganglion)

Terminal branches (outside parotid)

Mnemonic Two Zebras Bit My Cat (Temporal, Zygomatic, Buccal, Marginal mandibular, Cervical) — all supply muscles of facial expression + platysma. Also: posterior auricular nerve + nerve to posterior belly of digastric + stylohyoid.

Bell's palsy (LMN) vs UMN facial palsy

LMN (Bell's palsy): ipsilateral ALL muscles paralysed including frontalis (forehead smooth, cannot wrinkle) + lagophthalmos (cannot close eye, Bell's phenomenon) + nasolabial fold flattened + mouth droops toward intact side. If lesion proximal to geniculate: + hyperacusis + ageusia anterior 2/3 tongue + reduced lacrimation. Cause: HSV-1 reactivation.
UMN (stroke/capsule lesion): contralateral lower face weakness only; forehead relatively SPARED (bilateral cortical supply to upper facial nucleus). Look for hemiplegia.

Marking (8 marks): Course: 4 key points (2) · Three intracanalicular branches with function (2) · Five terminal branches at face named (1) · Bell's vs UMN: forehead distinction + reason (2) · Chorda tympani function (1)

Essay 4

Describe CN X (Vagus nerve): its exit from the skull, main branches in the neck and thorax (including the recurrent laryngeal nerve), abdominal branches, and the clinical consequences of unilateral and bilateral recurrent laryngeal nerve injury.

8 marks

Origin and exit

CN X is the longest cranial nerve. It arises from the lateral medulla (behind the olive) → exits the skull via the jugular foramen with CN IX and CN XI. Its superior (jugular) ganglion and inferior (nodose) ganglion lie here. It descends within the carotid sheath between the internal carotid artery and the internal jugular vein.

Branches in the neck

Pharyngeal branches: join the pharyngeal plexus with CN IX → motor to all pharyngeal constrictor muscles (except stylopharyngeus = CN IX) and all palatal muscles (except tensor veli palatini = CN V3)
Superior laryngeal nerve: internal branch (sensory above vocal folds) + external branch (motor to cricothyroid, at risk during ligation of superior thyroid artery)
Cervical cardiac branches: to cardiac plexus (parasympathetic slowing of heart rate)

Branches in the thorax

Recurrent laryngeal nerve (RLN): Left RLN loops under the aortic arch at the ligamentum arteriosum; Right RLN loops under the right subclavian artery. Both ascend in the tracheo-oesophageal groove → supply ALL intrinsic laryngeal muscles EXCEPT cricothyroid + sensory below vocal folds
Bronchial branches → bronchial tree; oesophageal branches → oesophageal plexus

Abdominal branches

Anterior gastric branch (anterior wall of stomach + duodenum); posterior gastric branch (posterior wall)
Hepatic branch (via lesser omentum), coeliac branch (via coeliac plexus → small intestine + ascending and transverse colon)
Distal limit: left colic (splenic) flexure; beyond this = sacral parasympathetics (S2–S4)

Clinical: RLN injury

Unilateral RLN: hoarse breathy voice; affected cord paralysed in paramedian position; compensated by contralateral cord crossing midline; no airway compromise
Bilateral RLN: both cords adducted → severe stridor and respiratory obstruction → emergency tracheostomy
Common causes: thyroid surgery, carcinoma of thyroid/lung/oesophagus, aortic arch aneurysm

Marking (8 marks): Exit via jugular foramen (1) · Neck branches: pharyngeal plexus + SLN (1) · RLN course: left under aorta, right under subclavian (1) · RLN supply: all intrinsic except cricothyroid (1) · Abdominal distribution to left colic flexure (1) · Unilateral vs bilateral RLN injury + causes (3)

Essay 5

Describe the cranial nerve supply to the extraocular muscles (CN III, IV, VI). For each, state the nerve, the muscles supplied, and the clinical signs of an isolated lesion (ptosis, diplopia, squint).

8 marks

Overview: 6 extraocular muscles + levator palpebrae

Mnemonic: LR₆SO₄(rest)₃ — Lateral Rectus = CN VI; Superior Oblique = CN IV; all remaining 4 recti + inferior oblique + levator palpebrae superioris = CN III.

CN III (Oculomotor)

Muscles: Superior branch: levator palpebrae superioris (eyelid elevation) + superior rectus (up + in). Inferior branch: medial rectus (adduction) + inferior rectus (down + in) + inferior oblique (up + out).
Parasympathetic: Edinger-Westphal nucleus → ciliary ganglion → sphincter pupillae (miosis) + ciliary muscle (accommodation). These fibres run on the SURFACE of CN III (vulnerable to aneurysm compression).
CN III palsy signs: Complete ptosis (levator paralysed) + eye deviates down and out (unopposed superior oblique + lateral rectus) + fixed dilated pupil (mydriasis, pupil-involving = surgical palsy from PCoA aneurysm); diplopia. Medical CN III palsy (diabetes, hypertension) spares the pupil (ischaemia affects central motor fibres more than peripheral parasympathetics).

CN IV (Trochlear)

Muscle: Superior oblique — depresses the adducted eye (look down-and-in); also intorts (inward rotation).
Course unique: Only CN to exit from the dorsal brainstem; decussates before emerging.
CN IV palsy signs: Vertical diplopia (worse on looking down), inability to look inferomedially, compensatory head tilt to the opposite side (Parks-Bielschowsky three-step test). Often missed; most commonly caused by head trauma (CN IV most vulnerable to shearing at its dorsal exit).

CN VI (Abducens)

Muscle: Lateral rectus only — abducts the eye.
CN VI palsy signs: Horizontal diplopia (worse on lateral gaze to affected side) + eye cannot abduct → convergent squint (medial strabismus) at rest. Most common CN affected by raised ICP (false localising sign — long intracranial course over clivus; stretched by brainstem herniation).

Differentiating the palsies: summary

CN III: ptosis + down-and-out eye + dilated pupil (complete) or preserved pupil (partial/medical)
CN IV: vertical diplopia + head tilt; no ptosis; no squint at rest
CN VI: convergent squint + horizontal diplopia; no ptosis

Marking (8 marks): CN III: correct muscles (1) + parasympathetic pupil (1) + palsy signs including ptosis/down-out/mydriasis (1) · CN IV: superior oblique (1) + palsy signs (vertical diplopia + head tilt) (1) · CN VI: lateral rectus (1) + medial squint + false localising sign (1) · LR6SO4 mnemonic or equivalent clarity (1)

Cranial Nerves CN I–XII · Question Bank

Classification: sensory / motor / mixed

CN I–XII table

Overview

Three divisions

V3 motor supply (muscles of first branchial arch)

Clinical: Trigeminal neuralgia (Tic douloureux)

Course

Branches inside the facial canal

Terminal branches (outside parotid)

Bell's palsy (LMN) vs UMN facial palsy

Origin and exit

Branches in the neck

Branches in the thorax

Abdominal branches

Clinical: RLN injury

Overview: 6 extraocular muscles + levator palpebrae

CN III (Oculomotor)

CN IV (Trochlear)

CN VI (Abducens)

Differentiating the palsies: summary