s4 cranial nerves Flashcards
cranial nerves are part of which nervous system?
peripheral nervous system
where are cranial nerve nuclei located?
brainstem (apart from CN1 and 2)
name CN 1-6
CN 1- olfactory CN 2- optic CN 3- oculomotor CN 4- trochlear CN 5- trigeminal CN 6- abducens
medical term for absence or reduced sense of smell
common cause of this?
anosmia or hyposmia
upper respiratory tract infection/ common cold> inside nasal cavity is lined with mucosa. this becomes swollen and interferes with the odors being able to reach olfactory CN 1.
other causes for absent / reduced sense of smell
head/ facial injury> anterior to posterior displacement of brain can cause shearing injury to CN1.
anterior cranial fossa tumour
association with Parkinsons Disease, Alzheimers
what is the olfactory tract?
carries info to temporal lobe from olfactory bulb
clinical signs of damage to optic nerve?
- abnormalities in pupil size/ doesn’t respond to light in same way
- poor visual acuity (test using snellen chart)
what is papilloedema? which CN affected?
squashed optic nerve CN2
due to rise in intra-cranial pressure
optic disc appears swollen on ophthalmoscopy
capillaries engorged
what is optic neuritis?
inflammation affecting optic nerve
what is anterior ischaemic optic neuropathy?
starve optic nerve of blood supply
> temporal arteritis (inflammation of artery)
> affects branches of internal carotid artery and therefore ophthalmic artery
distinguish between: optic nerve, optic chiasm and optic tract
optic nerve- carries sensory fibres from the one eye
optic chiasm- mixing of sensory fibres from R and L optic nerves
optic tract- contains sensory info from part of the R and L eye
how do pituitary tumours cause visual symptoms?
compress optic chasm
causing bilateral visual symptoms
> bitemporal hemianopia
what is dipoplia
double vision
what is ptosis
drooping of upper eyelid
clinical signs seen when damage to CN 3 oculomotor?
report double vision
ptosis
abnormal position of eye (down and out)
pupil may or may not be dilated (depending on cause)
CN 3 supplies muscles which do what?
extra ocular muscles
levator palpebrae superiors
> controls eyelid
sphincter pupillae
> muscle in iris surrounding pupil
causes of CN 3 damage? key clinical sign diff between the two?
most common= microvascular ischaemia common in >50yrs, diabetics, hypertension > pupil spared!!
compressive e,.g. aneurysm or head injury or tentorial herniation
> pupil involving
why is pupil spared in microvascular ischaemia?
peripheral nerves have blood supply from pial blood vessels AND vasa nevorum
central nerves are vulnerable as vasa nervorum is commonly affected
> backup supply therefore pupil spared
CONTRAST to compression where it affects all
CN 4 trochlear supplies
motor info to superior oblique muscle
clinical signs to damage to CN 4
+ causes
report double vision
abnormal eye position (upwards and inwards)
head tilt as patients compensate by tilting head
causes
- congenital or
- microvascular ischaemia
- trauma
- tumour
which CN found in midbrain?
CN 3 oculomotor
CN 4 trochlear
which CN found in pons?
CN 5 trigeminal
CN 6 abducens
CN 6 abducens supplies? movement of this muscle?
lateral rectus> moves pupil laterally (abduction)
clinical signs of CN 6 damage?causes?
double vision
abnormal eye position
difficulty to move affected eye laterally
causes:
microvascular ischaemia
head injury
raised ICP (most common nerve affected)- false localising sign
