Flashcards in Cranial Nerves Deck (16):
What are some causes for oculomotor palsy?
Complete: motor to muscles and parasympathetic to pupil
Surgical lesions, painful, :
Aneyrusm, ipsilateral posterior communicating artery,
Incomplete: pupil spared and ptosis partial
Nerve trunk infraction, midbrain lesion, diabetes, vascular/ demyelination,
Inv: blood flucose, CT/MRI brain, carotid arteriography.
CN III lesion- what happens?
Oculomotor nerve palsy- the tramps pupil.
Eye- DOWN + OUT
Ptosis, acuity + fields normal but limited by ptosis.
Pupils: dilated if complete,mspeead if partial
Movements: nerve VI working (abducencs) so eye moves laterally
Nerve IV works, (trochlear) so eye intorts on trying to look down and in
Fundi: normal, papiloedema if space occupying lesion
Absucens nerve palsy- what happens?
Can be i jured anywhere along its course- vasculopathy common of Vaso nervorum (mononeuritis multiplex eg DM/ sarcoid/vasculitis or exteinsic compression.
Normal: acuity, fields, pupils, obesrvation.
Divergent squint at rest
No abduction ❌ or ⬇️ abduction beyond midline
Diplopia, worsen when looking to the side of the lesion.
Mononeuritis: DM, sarcoid, rheumatoid,
Raised ICP, Brainstem vascular D, MS, UMN? Plaque in pons? Assc w/ 7th
Myasthania? Not typical. Look for fatiguability, worsening diplopia with prolonged lateral gaze
Facial Nerve 7th palsy
Unable to: close eyes, eyeball rolls- Bells phenomenon
Raise eyebrows- spread in unilateral UMN lesions
Blow out cheeks/whistle
Although 7th- 2/3 of taste, but pts rarely notice.
Unilateral facial nerve palsies- complete- LMN, or incomplee UMN.
LMN: All muscles of facial expression are weak
Nerve damaged b/w nucleus (brainstem) and face
Hyperacusis- sensitivity to loud noise - nerve to stapedius
Loss of taste- chorda tympani- lesion is above or below the facial canal (both obserbed below)
Causes: Bells palsy (idiopathic) , Ramsay -Hunt syndrome (herpes zoster at the external auditory meatus/ soft palate)
Mononeuritis - sarcoid/diabetes , paeotid tumor, vascular, demyelinating.
UMN: fibers are damaged b/w cortex and nucleus .
As there is input from both hemispheres to upper facial muscles a lesion of one cortex or its tracts will not cause weakness of the forehead. UMN lesions spare the upper face.
Bilateral: DDx is diff, rare. Causes: nuclear: vasculitis/demyelinating.
Muscular: Myasthania Gravis/ myotonia
Infranuclear: GBS/ sarcoidosis.
What CNs are originating in the midbrain?
What CNs oroginate from the pons?
What CNs originte in the medulla?
7+8 nuclei both pons and medulla.
Commonest- anosmia- nasal congestion
Neuro: tumours on floor of anterior fossa and head injury
What is the pathway of the Optic nerve?
Enter through optic foramina- unite at chiasm-> tracts-> visual cortex via lateral geniculate body+ 3rd nerve N for pupillary reflexes.
How do we asses for the optic nerve?
Snellen test chart- acuity, colour vision + fisual fields, + fundi exam.
+ pupillary reflexes- III,
What are some visual field defects?
Monocular- eye or nerve damage.
Bitemporal hemianopia: chiasm lesions- pituitary adenoma, compress nasal fibres. Craniopharyngioma.
Homonymous hemianopia: lesions in tract, radiation, visual cortex.
OPtic nerve lesions
Unilateral visual loss- starting as a scotoma ie hole in vision.
Complete- blindness + loss of pup reflex - direct + consensual.
Due to demyelination (MS), nerve compression, rerinal artery occlusion(Giant cell arteritis) .
Trauma,mpapilloedema, seve anaemia, drugs, toxins, - ethambutol, quinine, tobacco, methyl alcohol.
What happens in pupillary light reflexes?
1. Retinal image generates action potential
2. Travel via axons, some decussate ot chiasm and pas to L geniculate bodies.
3. Synapse at each pretectal N
4. AP the pass to Edinger Westphal nucleus of III
5. Then to Ciliary gangliom via 3rd nerve
6. Leading to pupil constriction when illuminated (direct) and consensual.
What happens in defects of the occipital cortex?
Homonymous hemianopic defects- unilateral posterio cerebral artery infraction.
What pathologica features can be seen on ophtalmoscopy and what does each mean?
Pale- optic trophy
Papiloedema- oedema- enlargement of the blind spor and vision blurring. Exception: optin neuritis: early and severe visual loss.