CN3 Oculomotor nerve Flashcards
What is cranial nerve 3?
Oculomotor nerve
What are the functions of the CN3 oculomotor nerve?
Motor - most of extra-ocular muscles
including levator palpabrae superioris
Autonomic parasympathetic - sphincter papillae muscle, ciliary muscle
What is the action of the extra-ocular muscles?
Move the eye
What is the action of the levator palpabrae superioris muscle?
Retracts the eyelid
What is the action of the sphincter papillae muscle?
Constricts the pupil
What is the action of the ciliary muscle?
Changes the thickness of the lens of the eye
What is the organisation of the motor and autonomic parasympathetic fibres in the CN3 oculomotor nerve?
Autonomic parasympathetic fibres are more external
Motor fibres are more internal
What is the route of the CN3 oculomotor nerve from its origin?
Runs through cavernous sinus
through superior orbital fissure
into orbit
How is the oculomotor nerve most commonly damaged?
Compression
What can cause compression of the oculomotor nerve?
Raised intracranial pressure by tumour or haemorrhage
Aneurysms
Cavernous sinus thrombosis
What function is lost by compression to the oculomotor nerve first? Why?
Autonomic parasympathetic functions lost first
because the fibres are more external, compressed first
How does loss of function of the oculomotor nerve present?
Autonomic parasympathetic - pupillary dilation
diplopia
Motor - down and out position of eye
ptosis
What is diplopia?
Double vision
Why does loss of function of the CN3 oculomotor nerve give a down and out position of the eye?
Unopposed pull of superior oblique and lateral rectus muscles
move eye inferiorly and laterally
because these muscles are innervated by CN4 trochlear nerve and CN6 abducens nerve respectively
