Cranial Nerves Flashcards
Cranial nerves are part of which NS?
Peripheral
How many pairs of cranial nerves do we have?
12
Where is the brain stem?
Attaching the brain to the spinal cord
What are the 3 parts of the brainstem?
Midbrain
Pons
Medulla
Define nerve nuclei
Collections of cell bodies of nerve fibres that make up the whole cranial nerve
How many cranial nerves come from each section?
2 forebrain
2 midbrain
4 pons
4 medulla
What is CNI and where does it come from?
Olfactory nerve
Forebrain
What type of nerve is CNI?
Special sensory only
Sense of smell
Describe the route of CNI
Olfactory tract comes from forebrain
To olfactory bulb on top of cribriform plate
Olfactory nerves dangle through cribriform foramina
Sense of smell to very top of nasal cavity
How do we test CNI?
Smelling salts under one nostril at a time
Not commonly tested
What is the clinical term for loss of sense of smell?
Anosmia
What is the commonest cause of anosmia?
A cold
URTI
What is CNII and where does it come from?
Optic nerve
Forebrain
What type of nerve fibres at in CNII?
Special sensory only
Eyesight
Describe the route of CNII from retina
Optic nerves run back from eyes to meet at the optic chiasm
Optic tracts take signals from chiasm to forebrain
What is the danger close to the optic chiasm?
Very close to pituitary gland
Tumours etc can squash chiasm
Present with problem in both eyes most likely
What is CNIII and where does it come from?
Oculomotor
Midbrain
Describe the route of CNIII
Midbrain - through cavernous sinus
Through the superior orbital fissure into the orbit
What nerve fibres are carried for CNIII?
Motor (mainly) Some autonomics (PNS) - to muscles controlling the pupil
What does the motor part of CNIII innervate?
4 out of the 6 extra-ocular muscles
And levator palpebrae superioris of the eyelid
How do we test CNIII?
Inspection of eyelids and pupils
Eye movements
Pupillary light reflexes
What will an eye look like with a CNIII lesion?
Down and out
Severe ptosis
Pupil dilation
Give some causes of CNIII lesions
Raised ICP
Aneurysms
Cavernous sinus thrombosis
Diabetes/hypertension
Why are the autonomics on CNIII easily damaged?
PNS fibres run on the periphery of the nerve
Therefore any squashing of the nerve damages these fibres first
Dilated pupils
What is CNIV and where does it come from?
Trochlear nerve
Dorsal aspect of midbrain
Which CN has the longest intracranial route?
Trochlear
Which hole does CNIV pass through?
Superior orbital fissure
What type of fibres are on CNIV?
Motor only
What does CNIV supply?
One extra-ocular muscle: superior oblique
Which direction does superior oblique muscle make you look?
Down and out
Why can CNIV lesions be easy to miss?
Patient can compensate with a slight tilt to their head
With a CNIV palsy, when will the double vision be worst?
When looking down