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ANATOMY4: Cranial nerves > Oculomotor nerve > Flashcards

Oculomotor nerve Flashcards

1
Q

Which is the largest of the extraocular nerves?

A

oculomotor

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2
Q

Which EOMs are supplied by the CNIII?

A

all apart from lateral rectus and superior oblique:

  1. superior rectus
  2. medial rectus
  3. inferior rectus
  4. inferior oblique
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3
Q

What are the two types of oculomotor nerve nuclei?

A
  1. Somatic efferent nuclei (5 motor nuclei)
  2. General visceral efferent nucleus (Edinger Westphal nucleus)
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4
Q

What do the somatic efferent CNIII nuclei consist of?

A

complex of 5 individual motor nuclei containing cell bodies of the multipolar somatic motor neurones whose axos directly innervate their respectiev EOMs

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5
Q

What is contained within the motor (somatic efferent) nuclei of CNIII?

A

cell bodies of multipolar somatic motor neurones whose axons directly innervate their respective EOMs

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6
Q

What are the 5 individual motor (somatic efferent) nuclei of CNIII, and which muscle does each supply?

A
  1. Dorsal nucleus - inferior rectus
  2. Intermeediate nucleus - inferior oblique
  3. Medial nuclei - superior rectus
  4. Central caudal nucleus - levator palpebrae superioris
  5. Ventral nucleus - medial rectus
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7
Q

What is the name of the general visceral efferent nucleus of CNIII?

A

Edinger-Westphal nucleus

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8
Q

What does the Edinger Westphal nucleus contain?

A

small spindle-shaped preganglionic (first-order) parasympathetic neurones

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9
Q

What type of neurones are contained in a) the somatic efferent nuclei and b) the general visceral efferent nucleus?

A
  • a) motor neurones
  • b) preganglionic parasympathetic neurones
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10
Q

What what level and part of the brainstem do the oculomotor nuclei lie?

A

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

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11
Q

How far cranially does the oculomotor nucleus extend?

A

for short distance into third ventricle

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12
Q

Where is the medial longitudinal fasciculus in relation to the oculomotor nuclei?

A

lies ventrolateral to the nucleus

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13
Q

What is contained within the medial longitudinal fasciculus?

A

axons of internuclear neurones that pass vertically between the brainstem nuclei of the oculomotor, trochlear and abducens nerves (see image - MLF)

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14
Q

Where do fibres from the oculomotor nuclei travel intra-cerebrally?

A
  1. emerge from oculomotor nuclei
  2. pass anteriorly through tegmentum of midbrain and red nucleus, medial to substantia nigra
  3. emerge on medial aspect of cerebral peduncle at upper border of pons in interpeduncular cistern
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15
Q

What are 5 stages of the intracranial oculomotor nerve course (once in the interpeduncular fossa) before it reaches the cavernous sinus?

A
  1. CNIII passes forwards, laterally and slightly downwards in the interpeduncular fossa, lateral to posterior communicating artery
  2. passes between posterior cerebral artery (dorsal) and superior cerebellar artery (ventral)
  3. grooves posterior clinoid process
  4. courses forwards
  5. passes through dural roof of cavernous sinus
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16
Q

What is the interpeduncular fossa an example of?

A

one of the enlargements of the subarachnoid space or cisterns

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17
Q

What vessel is CNIII lateral to whilst traversing the interpeduncular fossa?

A

posterior communicating artery

18
Q

How does CNIII enter the cavernous sinus and what is its course once inside?

A

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

19
Q

How does CNIII enter the orbit?

A

enters the intraconal space of the orbit from the cavernous sinus through the superior orbital fissure within the tendinous ring

20
Q

At what point does the CNIII divide into superior and inferior divisions?

A

once it has entered the intraconal space of the orbit from the cavernous sinus

21
Q

What are 4 pathological states that can affect CNIII due to its course through the cavernous sinus?

A
  1. venous thrombosis
  2. aneurysms of the internal carotid artery
  3. pituitary enlargement
  4. meningioma / expanding lesios in region of superior orbital fissure
22
Q

Which nerves are more commonly affeted by pituitary enlargement in the cavernous sinus and why?

A

oculomotor and trochlear nerves, more commonly than the abducent

abducent nerve is protected by the internal carotid artery

23
Q

What nerve is interposed between the two divisions of the oculomotor nerve in the orbit?

A

nasociliary nerve

24
Q

Which 2 muscles are supplied by the superior division of CNIII?

A

superior rectus + levator palpebrae superioris

25
Q

How does the superior division of CNIII reach the levator palpebrae superioris?

A

pierces the superior rectus muscle to reach it

26
Q

Which 3 muscles are supplied by the inferior division of CNIII?

A
  1. inferior rectus
  2. inferior oblique
  3. medial rectus
27
Q

How does the inferior division reach its target muscles?

A

splits into several branches that supply the medial rectus and inferior rectus and a long branch passes forwards on the lateral aspect of the inferior rectus to reach inferior oblique

28
Q

Which branch of the inferior division of the oculomotor nerve does the stout motor root containing preganglionic parasympathetic fibres pass to the ciliary ganglion?

A

long branch passes forward to reach the inferior oblique muscle - stout root passes from here to the ciliary ganglion

29
Q

What is the course of the parasympathetic neurones from CNIII nuclei?

A

travel in CNIII then in inferior division, then preganglionic fibres travel from long branch of this supplying inferior oblique to the ciliary ganglion

this is the site of postanglionic parasympathetic (second-order) neurones

axons from postganglionic neurones travel in the short ciliary nerves to supply the choroid, sphincter pupillae of iris and ciliary muscle

30
Q

What are the end nerves of the parasympathetic CNIII fibres?

A

short ciliary nerves

31
Q

What are 3 things supplied by parasympathetic CNIII fibres?

A
  1. choroid
  2. sphincter pupillae of iris
  3. ciliary muscle
32
Q

Where do nerves supplying the EOMs generally pierce them?

A

one third of the way along the muscle belly on the bulbar aspect

33
Q

What are 5 types of lesions which can affect CNIII?

A
  1. complete lesions
  2. incomplete lesions
  3. internal ophthalmoplegia
  4. external ophthalmoplegia
  5. intracranial lesions
34
Q

What is an example of a cause of a complete lesion of CNIII?

A

trauma

35
Q

What are 6 symptoms of complete lesions of CNIII?

A
  1. inability to look upwards, downwards or medially
  2. lateral or external strabismus due to unopposed action of lateral rectus
  3. diplopia
  4. complete ptosis (paralysis of levator palpebrae superioris and unopposed orbicularis oculi)
  5. dilated non-reactive pupils (unoposed dilator pupillae)
  6. lack of accommodation
36
Q

What may be the symptoms of incomplete lesions of CNIII?

A

some of the symptoms of complete lesions may be present (diplopia, lateral/external strabismus, ptosis, dilated pupil, lack of accommodation)

37
Q

What is internal ophthalmoplegia?

A

loss of parasympathetic components of CNIII only - may be first sign of CNIII nerve palsy

38
Q

Why may internal ophthalmoplegia be the first sign of nerve palsy?

A

parasympathetic fibres are located superficially in the nerve and may be damaged first in intracranial lesions

39
Q

Why is pupil dilation a crucial sign of compression within the cranial cavity following head injury?

A

suggests internal ophthalmoplegia - loss of sympathetic component of CNIII as these fibres are located superficially in nerve, first to be damaged

40
Q

What is external ophthalmoplegia?

A

loss of extraocular muscle supply

41
Q

What are 2 types of intracranial pathology that can affect the oculomotor nerve?

A
  1. aneurysms of adjacent arteries around brainstem - compression of nerve
  2. meningitis - can involve nerve along course in subarachnoid space
42
Q

Which part of the brainstem is the oculomotor nucleus located in?

A

midbrain (level of superior colliculus)

ANATOMY4: Cranial nerves (6 decks)

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