Cranial Nerves Flashcards
What are some causes for oculomotor palsy?
Complete: motor to muscles and parasympathetic to pupil
Surgical lesions, painful, :
Aneyrusm, ipsilateral posterior communicating artery,
Tumour
Incomplete: pupil spared and ptosis partial
Nerve trunk infraction, midbrain lesion, diabetes, vascular/ demyelination,
Encephalitis
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.
Movements:
Divergent squint at rest
No abduction ❌ or ⬇️ abduction beyond midline
Diplopia, worsen when looking to the side of the lesion.
Causes:
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
Show teeth
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.
Causes:
CVAs,
Bilateral: DDx is diff, rare. Causes: nuclear: vasculitis/demyelinating.
Muscular: Myasthania Gravis/ myotonia
Infranuclear: GBS/ sarcoidosis.
What CNs are originating in the midbrain?
1
2
3
4
What CNs oroginate from the pons?
5, 6,7,8
What CNs originte in the medulla?
5,6,7,8,9,10,11,12
7+8 nuclei both pons and medulla.
Olfactory probs
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.
Tumour, vascular
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?
Afferent pathway:
- Retinal image generates action potential
- Travel via axons, some decussate ot chiasm and pas to L geniculate bodies.
- Synapse at each pretectal N
Efferent pathway
- AP the pass to Edinger Westphal nucleus of III
- Then to Ciliary gangliom via 3rd nerve
- 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?
Swelling- papilloedema
Pale- optic trophy
Papiloedema- oedema- enlargement of the blind spor and vision blurring. Exception: optin neuritis: early and severe visual loss.
