Visual System Flashcards
Which cranial nerves are involved in the visual system?
- CN II, optic
- CN III, oculomotor
- CN IV, trochlear
- CN VI, abducens
Which cranial nerves are responsible for somatic motor movement in the visual system?
- CN III, oculomotor
- CN IV, trochlear
- CN VI, abducens
Which cranial nerve is responsible for special sensory in the visual system?
CN II, optic
Which cranial nerve is responsible for parasympathetic responses in the visual system?
CN III, oculomotor
How many extraocular muscles are there?
6
What are the extraocular muscles?
4 straight muscles: inferior, superior, medial, lateral rectus muscles
2 oblique muscles: superior, inferior oblique muscles
Which cranial nerve innervates majority of the extraocular muscles? Which muscles are theres?
- CN III, oculomotor
- superior, inferior, medial rectus mm + inferior oblique mm
Which extraocular muscles are not innervated by CN III? Which cranial nerves are they innervated by instead?
- lateral rectus muscle; CN VI, abducens
- superior oblique muscle; CN IV, trochlear
(hint: LR6SO4)
Which muscle opens and moves the eyes? Which cranial nerve is it innervated by?
levator palpebrae superioris, CN III (oculomotor)
Through which bone structure does the oculomotor nerve (CN III) leave the cranial cavity?
superior orbital fissure
Through which bone structure does CN IV, trochlear nerve leave the cranial cavity?
superior orbital fissure
Through which bone structure does CN VI, abducens nerve, leave the cranial cavity?
superior orbital fissure
Which extraocular muscles would you have to contract to move your gaze to the left?
right medial rectus and left lateral rectus
Which extraocular muscle would you have to contract to cause intorsion of the eye?
superior oblique mm
Which extraocular muscle would you have to contract to cause extorsion of the eye?
inferior oblique mm
What is the effect of a lesion to the abducens nerve to the right eye? Which way would the eye deviate towards?
paralysis of lateral rectum muscle on right eye –> eye will deviate to the left
What is the function of the cornea?
focus light
What is the function of the aqueous humour?
maintain pressure inside the eye
What is the function of the iris?
dilation/constriction –> control light input
What is the function of the ciliary muscles?
change the lens shape to focus light
Where are neural tissues found in the eye?
retina
What is the macula in the eye?
high concentration of photoreceptors; fovea at the center
What is the function of the choroid in the eye?
- supplies oxygen and nutrients to outer retina
- connective tissue between sclera and outer retina
What the is the schlera?
whites of the eyes
Where is the blind spot on the eyeball?
optic nerve
Are there more rods or cones in the eye?
rods
Through which bone cavity does the optic nerve (CN II) exit from the cranial cavity?
optic canal
Describe the visual pathway
lateral geniculate nucleus –> primary visual cortex –> visual association cortex
Which axons in the visual pathway cross the optic chiasm?
nasal RGC axons
Which axons in the visual pathway stay ipsilateral?
temporal axons
TRUE or FALSE: each optic nerve contains only visual information from the opposite visual field.
FALSE –> each optic TRACT contains only visual info from the opposite visual field
What happens if there is lesion in your right optic nerve?
BLINDNESS IN RIGHT EYE b/c no visual info from the right eye is getting to the primary visual cortices
What happens if there is lesion at the optic chiasm?
TUNNEL VISION b/c only receive info from temporal retina
What happens if there is lesion in the left optic tract?
ONLY SEE LEFT VISUAL FIELD
What is the meyer’s loop? In which lobe is it located?
- fibers that carry info from contralateral upper quadrant visual field
- temporal lobe
Which visual field (left/right) projects on the left LGN? right LGN?
- left visual field on right LGN
- right visual field on left LGN
What is anopsia? What kind of lesion causes it?
blindness in one eye; lesion to ipsilateral optic nerve
What is bitemporal hemianopsia? What kind of lesion causes it?
blindness in temporal visual field (both eyes); lesion to optic chiasm
What is left homonymous hemianopsia? What kind of lesion causes it?
left visual field impaired in both eyes; lesion to right optic tract
What is the dorsal pathway of the visual system responsible for?
spatial relationships of objects
What is the ventral pathway of the visual system responsible for?
object recognition
How does damage to the temporal cortex affect the visual system? What is this condition known as?
poor object recognition; visual agnosia
What are the parasympathetic responses of CN III?
- pupillary light reflex
- near (accomodation) reflex
Describe the parasympathetic innervation pathway of CN III, oculomotor.
CN III –> ciliary ganglion –> short ciliary nerves –> sphincter pupillae muscle OR ciliary muscle
What occurs during the pupillary light reflex?
when light is shined into one eye, both pupils constrict
Describe the pupillary light reflex pathway, starting from when light is shined in the right eye.
- light shined in right eye
- AP from right eye reach both RIGHT and LEFT PRETECTAL NUCLEI
- pretectal nuclei stimulate BOTH SIDES of the EDDINGER-WESTPHAL nucleus
- both sides of eddinger-westphal nuclei generate AP through RIGHT AND LEFT CN III’s
- BOTH PUPILS constrict
direct pupil dilation is __________ to light.
ipsilateral
consensual pupil dilation is ___________ to light.
contralateral
WHere does the optic tract synapse in the pupillary light reflex pathway?
pretectal area
Where does the oculomotor nerve (CN III) synapse in the pupillary light refelx pathway?
ciliary ganglion
TRUE or FALSE: the cortex is involed in the pupillary light reflex.
FALSE
TRUE or FALSE: the cortex is involved in the near (accommodation) reflex
TRUE
What does the near (accommodation) reflex do?
- constrict ciliary muscle (accommodation)
- pupillary constriction
- convergence of the 2 eyes
Which extraocular muscles are responsible for the convergence of the two eyes?
medial rectus
Describe the near reflex pathway, starting from when visual info reaches the optic tract.
- optic tract (CN II)
- primary visual cortex
- visual association cortex
- oculomotor nucleus –> oculomotor nerve –> contract medial rectus muscle (converge 2 eyes)
- EW nucleus –> ciliary ganglion –> contract ciliary muscle and pupillary sphincter (accommodate lens and constrict pupil)
