Oculomotor nerve Flashcards
Which is the largest of the extraocular nerves?
oculomotor
Which EOMs are supplied by the CNIII?
all apart from lateral rectus and superior oblique:
- superior rectus
- medial rectus
- inferior rectus
- inferior oblique
What are the two types of oculomotor nerve nuclei?
- Somatic efferent nuclei (5 motor nuclei)
- General visceral efferent nucleus (Edinger Westphal nucleus)
What do the somatic efferent CNIII nuclei consist of?
complex of 5 individual motor nuclei containing cell bodies of the multipolar somatic motor neurones whose axos directly innervate their respectiev EOMs
What is contained within the motor (somatic efferent) nuclei of CNIII?
cell bodies of multipolar somatic motor neurones whose axons directly innervate their respective EOMs
What are the 5 individual motor (somatic efferent) nuclei of CNIII, and which muscle does each supply?
- Dorsal nucleus - inferior rectus
- Intermeediate nucleus - inferior oblique
- Medial nuclei - superior rectus
- Central caudal nucleus - levator palpebrae superioris
- Ventral nucleus - medial rectus
What is the name of the general visceral efferent nucleus of CNIII?
Edinger-Westphal nucleus
What does the Edinger Westphal nucleus contain?
small spindle-shaped preganglionic (first-order) parasympathetic neurones
What type of neurones are contained in a) the somatic efferent nuclei and b) the general visceral efferent nucleus?
- a) motor neurones
- b) preganglionic parasympathetic neurones
What what level and part of the brainstem do the oculomotor nuclei lie?
level of superior colliculus in the midbrain, ventral to the cerebral aqueduct in the periaqueductal grey matter
extends cranially for short distance into floor of third ventricle
How far cranially does the oculomotor nucleus extend?
for short distance into third ventricle
Where is the medial longitudinal fasciculus in relation to the oculomotor nuclei?
lies ventrolateral to the nucleus
What is contained within the medial longitudinal fasciculus?
axons of internuclear neurones that pass vertically between the brainstem nuclei of the oculomotor, trochlear and abducens nerves (see image - MLF)
Where do fibres from the oculomotor nuclei travel intra-cerebrally?
- emerge from oculomotor nuclei
- pass anteriorly through tegmentum of midbrain and red nucleus, medial to substantia nigra
- emerge on medial aspect of cerebral peduncle at upper border of pons in interpeduncular cistern
What are 5 stages of the intracranial oculomotor nerve course (once in the interpeduncular fossa) before it reaches the cavernous sinus?
- CNIII passes forwards, laterally and slightly downwards in the interpeduncular fossa, lateral to posterior communicating artery
- passes between posterior cerebral artery (dorsal) and superior cerebellar artery (ventral)
- grooves posterior clinoid process
- courses forwards
- passes through dural roof of cavernous sinus
What is the interpeduncular fossa an example of?
one of the enlargements of the subarachnoid space or cisterns
What vessel is CNIII lateral to whilst traversing the interpeduncular fossa?
posterior communicating artery
How does CNIII enter the cavernous sinus and what is its course once inside?
passes through dural roof
runs forward in upper part of lateral wall of the cavernous sinus
enters intraconal space of orbit through the superior orbital fissure
How does CNIII enter the orbit?
enters the intraconal space of the orbit from the cavernous sinus through the superior orbital fissure within the tendinous ring
At what point does the CNIII divide into superior and inferior divisions?
once it has entered the intraconal space of the orbit from the cavernous sinus
What are 4 pathological states that can affect CNIII due to its course through the cavernous sinus?
- venous thrombosis
- aneurysms of the internal carotid artery
- pituitary enlargement
- meningioma / expanding lesios in region of superior orbital fissure
Which nerves are more commonly affeted by pituitary enlargement in the cavernous sinus and why?
oculomotor and trochlear nerves, more commonly than the abducent
abducent nerve is protected by the internal carotid artery
What nerve is interposed between the two divisions of the oculomotor nerve in the orbit?
nasociliary nerve
Which 2 muscles are supplied by the superior division of CNIII?
superior rectus + levator palpebrae superioris
