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ANATOMY SEM 3 > extraocular muscels and cranial nerves III, IV and VI > Flashcards

extraocular muscels and cranial nerves III, IV and VI Flashcards

1
Q

how many extraocular muscles are there and what are they?

A

6 extraocular muscles — 4 rectus and 2 oblique

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2
Q

what 7 bones is the bony orbit made from?

A
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3
Q

what is the attachment site for the 4 rectus muscles?

A

annulus of zinn

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4
Q

what is the annulus of zinn?

A

oval shaped thickening of the periosteum at the orbital apex

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5
Q

what does the annulus of zinn enclose?

A

optic canal and part of the superior orbital fissure

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6
Q

where do all the rectus muscles insert?

A

the sclera anteriorly

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7
Q

label

A
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8
Q

origin and insertion of the muscles

A
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9
Q

what is intorsion?

A

inward rolling (of superior sclera) around sagittal axis

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10
Q

what is extorsion?

A

outward rolling (of superior sclera) aroudn sagittal axis

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11
Q

what is the primary action of lateral rectus?

A

abduction

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12
Q

what is the primary action of medial rectus?

A

adduction

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13
Q

what are the primary and secondary actions of inferior rectus?

A

primary = depression
secondary = extortion, adduction

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14
Q

what are the primary and secondary actions of superior rectus?

A

primary = elevation
secondary = intorsion, adduction

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15
Q

what are the primary and secondary actions of inferior oblique?

A

primary = extorsion
secondary = abduction, elevation

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16
Q

what are the primary and secondary actions of superior oblique?

A

primary = intorsion
secondary = abduction, depression

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17
Q

what is the function of levator palpebrae superioris?

A

elevates superior eyelid

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18
Q

label with muscles

A
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19
Q

in what direction to all recti muscles pull?

A

medially

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20
Q

medial and lateral recti produce rotation around what axis?

A

the vertical axis — yawing (adduction and abduction respectively)

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21
Q

superior and inferior recti produce rotation around what axis?

A

transverse axis — pitching (elevation and depression respectively)

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22
Q

why do the superior and inferior recti cause rolling (rotation around the sagittal axis)? what is this called for each?

A

because they insert above and below the centre of rotation

  • extortion (inferior rectus)
  • intorsion (superior rectus)
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23
Q

describe the actions of the superior oblique

A
  • produces rotation around the sagittal axis = INTORSION
  • pulls anteriorly around the transverse axis = DEPRESSION
  • also causes ABDUCTION around the vertical axis
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24
Q

describe the actions of the inferior oblique

A
  • produces rotation around the sagittal axis = EXTORSION
  • pulls anteriorly around transverse axis = ELEVATION
  • also causes ABDUCTION around vertical axis
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25
Q

what happens when the eye is ABducted to 23 degrees?

A

superior and inferior rectus pull eye vertically

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26
Q

what happens when the eye is ADducted to 51-55 degrees?

A

superior and inferior oblique pull eye vertically

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27
Q

if the eye cannot abduct, what is there an issue with?

A

lateral rectus

28
Q

if the eye cannot adduct, what is there an issue with?

A

medial rectus

29
Q

place eyes into ____ positions to test muscles that produce vertical movements

A

secondary positions

30
Q

label

A
31
Q

label

A
32
Q

what is each extraocular muscle innervated by?

A

1) OCULOMOTOR (III) = inferior oblique, levator palpebrae superioris, superior/medial/inferior rectus

2) TROCHLEAR (IV) = superior oblique

3) ABDUCENS (VI) = lateral rectus

33
Q

label and where are each of the nerves?

A

oculomotor = between midbrain and pons

trochlear = between temporal lobe and pons

abducens = between pons and medulla

34
Q

where is the optic canal?

A

apex of orbit

35
Q

superior oblique origin

A

lesser wing of sphenoid

36
Q

the insertions of the 4 rectus muscles are all ______

A

anterior to centre of rotation

37
Q

what attaches to sclera posterior to centre of rotation?

A

superior and inferior oblique

38
Q

what are the 3 axis of rotation of the eye ball, which all intersect at the centre of rotation and are at right angles to each other?

A
  • vertical
  • sagittal
  • transverse
39
Q

what 3 types of rotations can occur?

A
  • yawing = around vertical axis
  • sagittal = around sagittal axis
  • pitching = around transverse axis
40
Q

lateral vs medial rotation about vertical axis?

A

lateral = abduction

medial = adduction

41
Q

__duct eyes to test rectus muscles as when eye is __ducted to ___ degrees the rectus muscles pull the eye vertically

A

abduct
abducted
23

42
Q

__dyct eyes to test oblique muscles as when the eye is __ducted to __ degrees the oblique muscles pull the eye vertically

A

adduct
adducted
51-55

43
Q

where is the main oculomotor nuclei?

A

superior colliculus

44
Q

each sub nucleus of the oculomotor nucleus is responsible for what?

A

contracting one of the muscles it innervates

45
Q

the left and right oculomotor nuclei receive fibres from where?

A
  • superior colliculus — therefore supplied by information from visual cortex
  • also receives fibres (internuclear neurones) from medial longitudinal fasciculus — therefore connected to nuclei of Iv, Vi and VIII ( 4 and 6 innervate other extraocular muscles, 8 for vestibulo ocular reflex (position of head in space))
46
Q

the oculomotor passes through what sinus and where does it leave the cranial cavity?

A
  • cavernous sinus
  • leaves through superior orbital fissure
47
Q

what does the oculomotor nerve split into inside the cranial cavity?

A

superior and inferior divisions

48
Q

what does the superior branch of the oculomotor nerve innervate?

A
  • superior rectus (CONTRALATERAL)
  • levator palpebrae superioris (BOTH)
49
Q

what does the inferior branch of the oculomotor nerve innervate?

A
  • medial rectus (IPSILATERAL)
  • inferior rectus (IPSILATERAL)
  • inferior oblique (IPSILTERAL)

also has parasympathetic fibres — ciliary muscle for accommodation, smooth muscles of the iris from pupil constriction
(PS fibres from E-W nucleus, all others from main nuclei)

50
Q

where is the Edinburg-Westphal nucleus?

A

posterior to main oculomotor nucleus

51
Q

what kind of nucleus is the EW nucleus?

A

visceral motor (as it has parasympathetic fibres leaving it)

52
Q

the E-W nucleus receives corticonuclear fibres for what?

A

accomodation reflex

53
Q

the E-W nucleus receives fibres from where for direct and consensual light reflexes?

A

pretectal nucleus

54
Q

where do the parasympathetic fibres of the oculomotor nerve synapse?

A

ciliary ganglion

55
Q

where are the postganglionic fibres of the oculomotor nerve?

A

short ciliary nerves

56
Q

what are the autonomic functions of CN III?

A
  • lens accomodation by innervating ciliary muscles
  • innervate the constrictor pupillae

(both part of accomodation reflex, as wells as convergence)

57
Q

what happens in the eye to see near objects?

A
  • ciliary muscle contracts
  • tension removed from suspensory ligaments
  • tension removed from lens
  • lens bulges antero-posteriorly (bends light waves more and focuses them on to retina)
58
Q

what happens in the accommodation reflex?

A
  • contraction of ciliary muscle
  • convergence of visual field (contraction of medial rectus muscles)
  • pupillary sphincter contraction (pupils constrict)
59
Q

where are the neuronal cell bodies of the trochlear nerve?

A

at the border of the pons and midbrain, located in grey matter surrounding the cerebral aqueduct

60
Q

what do the trochlear nerve nuclei receive fibres from?

A
  • from superior colliculus — therefore supplied by information from visual cortex
  • from medial longitudinal fasciculus — therefore connected to nuclei of III, VI and VIII
  • receives corticonuclear fibres from both cerebral hemispheres
61
Q

what does the trochlear nerve do?

A

innervates superior oblique only (CONTRALATERAL)

62
Q

what does the abducens nerve originate from?

A

neuronal cell bodies beneath the floor of the 4th ventricle

63
Q

where do the CN VI nuclei receive fibres from?

A
  • superior colliculus — therefore supplied by information from visual cortex
  • medial longitudinal fasciculus — therefore connected to nuclei of III, IV and VIII
  • corticonuclear fibres from both cerebral hemispheres
  • internuclear neurones to contralateral main oculomotor nucleus via MLF IMPORTANT
64
Q

abducens nerve function

A

innervates lateral rectus only

65
Q

what is diplopia and what may it indicate?

A

= double vision — occurs when we are not overlapping our visual fields appropriately for the object we are looking at

may indicate:
- fatigue
- CN dysfunction (eg. lesions)
- raised intracranial pressure (cerebrum starts to herniate out through tentorial notch, and the temporal lobe would herniate out through the tentorial notch and put pressure on the oculomotor nerve — impaired CN III function — nothing to resist abduction — get lateral deviation of one or both eyes)
- cerebellar dysfunction (skeletal muscles are coordinated by cerebellum. eg. excessive alcohol consumption or injury)
- blow-out fractures of the orbit (lateral wall of orbit is very thick. medial wall, floor and roof are thin — these walls can be fractured (inferior - into maxillary sinus, medial - into nasal cavity)

ANATOMY SEM 3 (22 decks)

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