s4 cranial nerves

Question 1

cranial nerves are part of which nervous system?

Answer 1

peripheral nervous system

Question 2

where are cranial nerve nuclei located?

Answer 2

brainstem (apart from CN1 and 2)

Question 3

name CN 1-6

Answer 3

CN 1- olfactory
CN 2- optic
CN 3- oculomotor
CN 4- trochlear
CN 5- trigeminal
CN 6- abducens

Question 4

medical term for absence or reduced sense of smell

common cause of this?

Answer 4

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.

Question 5

other causes for absent / reduced sense of smell

Answer 5

head/ facial injury> anterior to posterior displacement of brain can cause shearing injury to CN1.

anterior cranial fossa tumour

association with Parkinsons Disease, Alzheimers

Question 6

what is the olfactory tract?

Answer 6

carries info to temporal lobe from olfactory bulb

Question 7

clinical signs of damage to optic nerve?

Answer 7

• abnormalities in pupil size/ doesn’t respond to light in same way
• poor visual acuity (test using snellen chart)

Question 8

what is papilloedema? which CN affected?

Answer 8

squashed optic nerve CN2

due to rise in intra-cranial pressure

optic disc appears swollen on ophthalmoscopy
capillaries engorged

Question 9

what is optic neuritis?

Answer 9

inflammation affecting optic nerve

Question 10

what is anterior ischaemic optic neuropathy?

Answer 10

starve optic nerve of blood supply
> temporal arteritis (inflammation of artery)
> affects branches of internal carotid artery and therefore ophthalmic artery

Question 11

distinguish between: optic nerve, optic chiasm and optic tract

Answer 11

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

Question 12

how do pituitary tumours cause visual symptoms?

Answer 12

compress optic chasm
causing bilateral visual symptoms
> bitemporal hemianopia

Question 13

what is dipoplia

Answer 13

double vision

Question 14

what is ptosis

Answer 14

drooping of upper eyelid

Question 15

clinical signs seen when damage to CN 3 oculomotor?

Answer 15

report double vision
ptosis
abnormal position of eye (down and out)
pupil may or may not be dilated (depending on cause)

Question 16

CN 3 supplies muscles which do what?

Answer 16

extra ocular muscles
levator palpebrae superiors
> controls eyelid

sphincter pupillae
> muscle in iris surrounding pupil

Question 17

causes of CN 3 damage? key clinical sign diff between the two?

Answer 17

most common= microvascular ischaemia common in >50yrs, diabetics, hypertension > pupil spared!!

compressive e,.g. aneurysm or head injury or tentorial herniation
> pupil involving

Question 18

why is pupil spared in microvascular ischaemia?

Answer 18

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

Question 19

CN 4 trochlear supplies

Answer 19

motor info to superior oblique muscle

Question 20

clinical signs to damage to CN 4

+ causes

Answer 20

report double vision
abnormal eye position (upwards and inwards)
head tilt as patients compensate by tilting head

causes

• congenital or
• microvascular ischaemia
• trauma
• tumour

Question 21

which CN found in midbrain?

Answer 21

CN 3 oculomotor

CN 4 trochlear

Question 22

which CN found in pons?

Answer 22

CN 5 trigeminal

CN 6 abducens

Question 23

CN 6 abducens supplies? movement of this muscle?

Answer 23

lateral rectus> moves pupil laterally (abduction)

Question 24

clinical signs of CN 6 damage?causes?

Answer 24

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

Question 25

which cranial nerves supply eye muscles? which is most vulnerable?

Answer 25

oculomotor 3
trochlear 4
abducens 6

all pass through cavernous sinus
enter into the orbit via the superior orbital fissure

abducens is most vulnerable as running freely in middle of cavernous sinus

Question 26

3 divisions of CN 5 trigeminal nerve

Answer 26

ophthalmic division
maxillary
mandibular

Question 27

motor element of trigeminal nerve? sensory?

Answer 27

motor- muscles of mastication

sensory- info from eye/ mouth/ anterior 2/3rd of tongue

Question 28

what’s corneal reflex?

Answer 28

touch front of eye
causes both eyes to blink
via obicularis oculi muscle by facial nerve

> tests sensory arm of trigeminal nerve and motor arm of facial nerve

Question 29

clinical conditions affecting trigeminal nerve

Answer 29

• trigeminal herpes zoster e.g. ophthalmic shingles
• trigeminal neuralgia (compression from an aberrant blood vessel)
• orbital and mandibular fractures
• posterior cranial fossa tumours

Question 30

what is ophthalmic shingles?

Answer 30

affects trigeminal nerve
reactivation of Varicella Zoster virus in trigeminal ganglion

• happens in older patients or immunocompromised

Question 31

where does each division of trigeminal nerve pass through?

Answer 31

ophthalmic- (cavernous sinus) superior orbital fissure

maxillary (cavernous sinus) foramen refundum

mandibular - foramen ovale
does NOT pass through CS