extraocular muscels and cranial nerves III, IV and VI Flashcards
how many extraocular muscles are there and what are they?
6 extraocular muscles — 4 rectus and 2 oblique
what 7 bones is the bony orbit made from?
what is the attachment site for the 4 rectus muscles?
annulus of zinn
what is the annulus of zinn?
oval shaped thickening of the periosteum at the orbital apex
what does the annulus of zinn enclose?
optic canal and part of the superior orbital fissure
where do all the rectus muscles insert?
the sclera anteriorly
label
origin and insertion of the muscles
what is intorsion?
inward rolling (of superior sclera) around sagittal axis
what is extorsion?
outward rolling (of superior sclera) aroudn sagittal axis
what is the primary action of lateral rectus?
abduction
what is the primary action of medial rectus?
adduction
what are the primary and secondary actions of inferior rectus?
primary = depression
secondary = extortion, adduction
what are the primary and secondary actions of superior rectus?
primary = elevation
secondary = intorsion, adduction
what are the primary and secondary actions of inferior oblique?
primary = extorsion
secondary = abduction, elevation
what are the primary and secondary actions of superior oblique?
primary = intorsion
secondary = abduction, depression
what is the function of levator palpebrae superioris?
elevates superior eyelid
label with muscles
in what direction to all recti muscles pull?
medially
medial and lateral recti produce rotation around what axis?
the vertical axis — yawing (adduction and abduction respectively)
superior and inferior recti produce rotation around what axis?
transverse axis — pitching (elevation and depression respectively)
why do the superior and inferior recti cause rolling (rotation around the sagittal axis)? what is this called for each?
because they insert above and below the centre of rotation
- extortion (inferior rectus)
- intorsion (superior rectus)
describe the actions of the superior oblique
- produces rotation around the sagittal axis = INTORSION
- pulls anteriorly around the transverse axis = DEPRESSION
- also causes ABDUCTION around the vertical axis
describe the actions of the inferior oblique
- produces rotation around the sagittal axis = EXTORSION
- pulls anteriorly around transverse axis = ELEVATION
- also causes ABDUCTION around vertical axis
what happens when the eye is ABducted to 23 degrees?
superior and inferior rectus pull eye vertically
what happens when the eye is ADducted to 51-55 degrees?
superior and inferior oblique pull eye vertically
if the eye cannot abduct, what is there an issue with?
lateral rectus
if the eye cannot adduct, what is there an issue with?
medial rectus
place eyes into ____ positions to test muscles that produce vertical movements
secondary positions
label
label
what is each extraocular muscle innervated by?
1) OCULOMOTOR (III) = inferior oblique, levator palpebrae superioris, superior/medial/inferior rectus
2) TROCHLEAR (IV) = superior oblique
3) ABDUCENS (VI) = lateral rectus
label and where are each of the nerves?
oculomotor = between midbrain and pons
trochlear = between temporal lobe and pons
abducens = between pons and medulla
where is the optic canal?
apex of orbit
superior oblique origin
lesser wing of sphenoid
the insertions of the 4 rectus muscles are all ______
anterior to centre of rotation
what attaches to sclera posterior to centre of rotation?
superior and inferior oblique
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?
- vertical
- sagittal
- transverse
what 3 types of rotations can occur?
- yawing = around vertical axis
- sagittal = around sagittal axis
- pitching = around transverse axis
lateral vs medial rotation about vertical axis?
lateral = abduction
medial = adduction
__duct eyes to test rectus muscles as when eye is __ducted to ___ degrees the rectus muscles pull the eye vertically
abduct
abducted
23
__dyct eyes to test oblique muscles as when the eye is __ducted to __ degrees the oblique muscles pull the eye vertically
adduct
adducted
51-55
where is the main oculomotor nuclei?
superior colliculus
each sub nucleus of the oculomotor nucleus is responsible for what?
contracting one of the muscles it innervates
the left and right oculomotor nuclei receive fibres from where?
- 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))
the oculomotor passes through what sinus and where does it leave the cranial cavity?
- cavernous sinus
- leaves through superior orbital fissure
what does the oculomotor nerve split into inside the cranial cavity?
superior and inferior divisions
what does the superior branch of the oculomotor nerve innervate?
- superior rectus (CONTRALATERAL)
- levator palpebrae superioris (BOTH)
what does the inferior branch of the oculomotor nerve innervate?
- 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)
where is the Edinburg-Westphal nucleus?
posterior to main oculomotor nucleus
what kind of nucleus is the EW nucleus?
visceral motor (as it has parasympathetic fibres leaving it)
the E-W nucleus receives corticonuclear fibres for what?
accomodation reflex
the E-W nucleus receives fibres from where for direct and consensual light reflexes?
pretectal nucleus
where do the parasympathetic fibres of the oculomotor nerve synapse?
ciliary ganglion
where are the postganglionic fibres of the oculomotor nerve?
short ciliary nerves
what are the autonomic functions of CN III?
- lens accomodation by innervating ciliary muscles
- innervate the constrictor pupillae
(both part of accomodation reflex, as wells as convergence)
what happens in the eye to see near objects?
- 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)
what happens in the accommodation reflex?
- contraction of ciliary muscle
- convergence of visual field (contraction of medial rectus muscles)
- pupillary sphincter contraction (pupils constrict)
where are the neuronal cell bodies of the trochlear nerve?
at the border of the pons and midbrain, located in grey matter surrounding the cerebral aqueduct
what do the trochlear nerve nuclei receive fibres from?
- 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
what does the trochlear nerve do?
innervates superior oblique only (CONTRALATERAL)
what does the abducens nerve originate from?
neuronal cell bodies beneath the floor of the 4th ventricle
where do the CN VI nuclei receive fibres from?
- 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
abducens nerve function
innervates lateral rectus only
what is diplopia and what may it indicate?
= 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)
