Cranial nerves

• Cranial nerves I and II are extensions of the forebrain
• Cranial nerves III - XII originate in and emerge from brainstem
• Pure sensory cranial nerves - I, II, VIII
• Pure motor cranial nerves - III, IV, VI, XI, XII
• Mixed motor and sensory cranial nerves - V, VII, IX, X
• Circle of Willis is central and roundabout with optic chiasma in centre
• Temporal lobe epilepsy can cause olfactory hallucinations as part of aura
• Anosmia can be due to trauma or coronavirus
• • olfactory receptors via cribriform plate of ethmoid and synapse with dendrites in olfactory bulb
  • axons from here go to uncus via olfactory tract
• Unilateral anosmia - frontal lobe tumour/uncinate fit with olfactory hallucinations
• Bilateral anosmia - nerves interrupted after head injury, ACF fractures and CSF leakage via cribriform plate as rhinorrhoea
• CSF rhinorrhoea

  • leakage of CSF from the nose due to fractured cribriform plate of ethmoid bone, generally with Le Frt 2 and 3 fractures
  • tram line effect
  • patient complains of salty taste in throat - post nasal leak of CSF
  • warn patient not to blow nose vigorously (traumatic aerocele) and raise head (will increease ICCP)
• Olfactory nerve assessment

  • Q any change in sense of smell
  • assess with formally scented bottles
• Optic nerve assessment

  • visual acuity - clarity
  • visual fields - spatial
  • pupillary reflexes - light
  • fundi - opthalmoscopy - brain, ICP, pathology
• Optic nerve - brain tract drawn out of cerebrum, no myelin sheath and like brain, unable to regenerate after division
• Visual acuity test

  • snellen chart
  • test each eye individually
  • normal is 6/6 (20/20)
• Retinal or optic nerve lesions = ipsilateral blindness
• Optic chiasm (pituitary tumour) = bitemporal hemianopia (tunnel vision)
• Once the optic nerve fibres reach the optic chiasm, nerves from each eye are shared
• Oculomotor nerve

  • main nucleus = extrinsic ocular muscles
  • superior rectus muscle and levator palpebrae superioris (upper eyelid)
  • medial, inferior rectus and inferior oblique
• Oculomotor nerve runs in lateral wall of cavernous sinus to superior orbital fissure
• Oculomotor nerve assessment

  • H (vertical, horizontal and diagonal)
  • ask if any diplopia
• Trochlear nerve innervates superior oblique muscle only
• Trochlear nerve via lateral wall of cavernous sinus and into superior orbital fissure
• Superior oblique paralysis leads to diplopia when patient tries to look down
• Abducens nerve innervates lateral rectus muscle
• Abducens nerve enters cavernous sinus. Long intracranial course so injured in skull base fractures.
• Abducens nerve damage leads to diplopia and convergent squint (patient cannot deviate eye laterally)
• Cranial nerve III, IV,VI assessment

  • nystagmus/diplopia
  • accomodation/pupillary reflexes/convergence
• Cranial nerve VII

  • taste for anterior 2/3 of tongue
  • smile
• Facial nerve

  • facial muscles (motor)
  • taste to anterior 2/3 of tongue (sensory)
  • parasympathetic
  • crying (lachrymal gland)
  • salivating (sublingual and submandibular)
  • chorda tympanitaste
  • c
• Ramsay Hunt syndrome

  • herpes zoster oticus occurs when a shingles outbreak affects the facial nerve involving the geniculate ganglion of 7th cranial nerve
  • painful shingles rash, with facial paralysis and hearing loss in affected ear
  • steroids and antivirals within 3 days full recovery in 75% cases
• Ramsay Hunt syndrome patients may complain of altered taste perception, saliva and tear production as well as hearing loss and vertigo.
• Ramsay Hunt syndrome - triad of acute unilateral facial nerve palsy with ipsilateral otalgia and an erythematous vesicular rash of auricle or oral mucosa.
• Facial paralysis associated with Ramsay Hunt syndrome is usually more severe than that of Bell's palsy and has worse prognosis
• Facial nerve assessment

  • observe for asymmetry or tics
  • screw up eyes tightly, clench teeth, puff out cheeks, smile, whistle, elevate eyebrows - resist these and asses power
• Raising eyebrows - temporal
• Scrunch eyes - zygomatic
• Blow out cheeks - buccal
• Show teeth/whistle - mandibular