Midbrain CNs Flashcards
Which 2 CNs arise from the midbrain?
Occulomotor and trochlear
What is the route of the occulomotor nerve?
Arises in the midbrain, passes through SOF into orbit
What nerve fibres does the occulomotor nerve carry?
M and AN-parasymp
What does the occulomotor nerve do?
MOTOR: Innervates sup and inf rectus, med rectus, inf oblique and levator palpebrae superioris (raises upper eyelid).
ANS: sphincter pupillae (constricts pupil), ciliary muscles constrict (lens more spehrical for short range vision)
How do you test the occulomotor nerve?
Eye movements, pupillary light reflect, inspect eyelids and pupils
What are the afferent and efferent limbs of the pupillary light reflex? Which nuclei are in between?
Optic (sensory), occulomotor (motor).
Pre-tectal and Edinger Westphal nuceli
What is diplopia?
Double vision
What are the 4 causes of occulomotor nerve lesions?
Raised ICP (tumour, haemorrhage), aneurysms, cavernous sinus thrombosis, diabetes/hypertension
What would be the position of the eye in an OM nerve palsy?
Down and out- levator palpebrae superioris paralysed, everything paralysed except lat.rectus and sup.oblique (SO4 LR6)
What is the route of the trochlear nerve? What fires does it carry? What is its function?
Longest route of all CNs, only one to arise from dorsal aspect of brainstem, exits in SOF.
M.
SO4- sup oblique (test eye movements)
Why can trochlear nerve palsy be hard to pick up? What other features are seen? What are the most common causes?
Rare, often corrected with slight tilt of head. Diplopia worse on downward gaze. Head injury or raise ICP most common cause (stretch nerve)
Which nerves pass through the SOF?
Occulomotor, trochlear, opthalmic, abducens- all supply structures/ muscles in/ around eye and orbit
