L32 - visual pathways Flashcards
optic radiations
fibres which relay information between the thalamus to the primary visual cortex
location of primary visual cortex
occipital lobe
origin of optic nerve
retina
travels to optic chiasma
travels along optic tracts
reaches lateral geniculate body in the thalamus
visual area of the thalamus
lateral geniculate body
cornea
transparent layer
area od refraction
layers of the ye
conea and sclera
choroid
retina
optic disk
blind spot
fovea
highest visual acuity (only cones)
where does the optic nerve exit the eye
optic disk
sclera
white of the eye
choroid
vascular middle layer
nourishes the cornea and retina
iris
- pigmented
- vascular
- middle layer
- muscles of the iris control the amount of light entering the eye by determining the diameter of the pupil
ciliary body
controls the shape of the lens by pulling on the suspensory ligaments
lens
biconvex, avascular structure
light passes through after passing through the pupil
how does the shape of the lens change
ciliary body pulls on the suspensory ligamnts
inner layer of the eye
retina
what is the retina an extension of
diencephalon
layers of the retina
neuronal and non-neuronal layer
neuronal layer of the retina
ganglion cell axons form the optic nerve
- photoreceptors
- bipolar cells
- ganglion cells
non-neuronal layer of the retina
pigmented epithelium
- sits against choroid
- light absorbing
- provides nutrients and capillaries to photoreceptors
bipolar neurones
connect photoreceptors to the ganglion cells
ganglion cells
give of an axon which becomes the ottos nerve
why is the optic disk a blind spot
contains no photoreceptors
interneurones connection photoreceptors, bipolar and ganglion cells
horizontal neurones
amacrine neurones
horizontal neurone location
level of photoreceptor and bipolar cells
amacrine neurone location
level of bipolar cells and ganglionic cells
role of interneurones in the retina
modulate transmission
energy change in retina
light energy is transferred to electrical energy
types of photoreceptor
rods
cones
which photoreceptor is more common
rods
20x more common
rods
- sensitive to light
- vision in dim light
- high level of convergence
cones
- colour vision
- high visual acuity
- lower level of convergence
how does papilloedema occur
- optic nerve has meninges surrounding it to the eyeball
- increase in CSF (in subarachnoid space) can swell the optic nerve
- increase in pressure compresses the central retinal vein
- prevents venous drainage from the eye
symptoms of papilloedema
headaches
drowsiness
blurred vision
vomiting
calcarine sulcus
primary visual cortex lies above and below this
where does the information from the upper vision field travel
lower bank of calcarine sulcus
where does information from the lower visual field travel
upper bank of the calcarine sulcus
where does information from the left half of the visual field travel
right hemisphere
where does information from the right of the visual field travel
left hemisphere
how does the 3rd order neurone travel in the visual pathway
optic radiations
1st order neurones
bipolar cells
2nd order neurones
ganglion cells
where do bipolar cells travel from and to
photoreceptors to ganglion cells
where do ganglion cells travel to
to lateral geniculate body in thalamus
images from visual field onto retinal fields
upside down and mirror reversed
fibres travelling in the visual pathway
nasal fibres
temporal fibres
where do temporal fibres originate
laterally (further from nose)
where for nasal fibres originate
medially (closer to nose)
which fibres cross the optic chiasma
nasal fibres
optic radiations - types
Meyer's loop (inferior) Superior trajectory (superior)
where does the upper left quadrant of the visual field reach on left eye
- nasal fibres travels down on RHS
- crosses optic chiasma
- travels down optic tract to tract the LGN
- optic radiations carry this info to the lower bank of the right calcarine sulcus
where does the upper left quadrant of the visual field reach on right eye
- temporal fibres travel down on RHS
- does not cross the optic chiasma
- travels down optic tract to tract the LGN
- optic radiations carry this info to the lower bank of the right calcarine sulcus
which trajectory carries lower visual field fibres and to where?
superior trajectory carries lower visual field fibres to the upper bank of the calcarine sulcus
which trajectory carries upper visual field fibres and to where?
Meyer’s loop / inferior trajectory carries upper visual field fibres to the lower bank
location of information from the macula in the primary visual cortex
posteriorly (towards tip of occipital lobe)
location of information from the peripheral fields in the primary visual cortex
anteriorly
scotoma
localised patch of blindness
anopia
loss of one or more quadrants of the visual field
hemianopia
half of the visual field is lost
quadrantanopia
quarter of the visual field is lost
homonymous
visual field losses are similar for both sides
heteronymous
visual field losses are different on each side
what visual defect is the patient likely to have if they have a pituitary tumour impinging on the optic chiasma?
Bitemporal hemianopia
bitemporal hemianopia
RHS of vision on left eye is gone and LHS of vision on right eye is gone
where is the lesion in monocular blindness
optic nerve
where is the lesion in bitemporal hemianopia
optic chiasma - interrups nasal fibres
where is the lesion in homonymous hemianopia
optic tract
pupillary light reflect
ability of both pupils to respond (constrict or dilate) defence on the level of light the retina recieves
which CN does the pupillary light reflex use
oculomotor (CN3)
optic (CN2)
what % of neurones do not travel to the LGN - where do they go?
10% travel to the pretectal area
Edinger-Westphal nucleus
oculomotor nerve nucleus by the pretectal area
how does info travel from the pretectal area to reach the sphincter papillae muscle
ciliary ganglion
pen is shone into subjects right eye: normal
both pupils constrict
pen is shone into subjects right eye: CN3 lesion
left eye will not constrict
- loss of consensual pupillary light reflex
- info from light is reaching CNS however CN3 is not intact on one side
pen is shone into subjects right eye: CN2 lesion
neither eye will constrict
- loss of direct pupillary reflex
- no light has reached CNS
accommodation reflex
A series of changes that occur when the gaze is transferred from a distant to near object
ciliary muscles in accommodation reflex
contract
what do ciliary muscles do when they contract
- lens becomes thicker and more rounded
- allow for refraction / bending of light rays to reach the retina
sphincter pupillae in accommodation reflex
constrict
medial rectus muscle in accommodation reflex
contract
- ocular convergence
afferents in accommodation reflex
Carry visual input to visual cortex then to visual association nerve
- Optic nerve and tract
- LGN to visual cortex
efferents in accommodation reflex
run within CN3
- Parasympathetic to sphincter pupillae & ciliary muscles
- Motor to medial rectus
