Visual pathways Flashcards
What are the reflex pathways in the eye? (2)
- pupillary light reflex
2. accommodation reflex
NOTE
be able to label a diagram of the eye
What are the 2 layers of the retina? (2)
- non-neuronal - pigmented
2. neuronal - photoreceptors
NOTE - know the components of the retina
- optic nerve
- secondary ganglion cells
- primary bipolar cells - link photoreceptors to G.cells
- photo receptors
- pigmented epithelium
- interneuron - horizontal
- interneuron - amacrine
What does the amacrine interneurone do in the retina?
modulates ganglion cells activity
What does a horizontal interneuron do in the retina?
modulates transmission
Why does light have to pass through an array of cells before it reaches the retina?
to help reduce the intensity of the light passing towards the retina
Where does the visual pathway run from?
retina to cortex
How many neurons are in the chain in the visual pathway?
3
like all the others
What are the primary and secondary neurons in the retina outgrowths of?
outgrowth of the diencephalon
What cells are in the retina in a visual pathway?
- photoreceptor
- bipolar cells
- ganglion cells
Where do the axons of the ganglion cells run over and where to?
run over - retina
to - optic disk/blind spot
What does the secondary ganglion cells form?
optic nerve
Where does the optic nerve travel to in the visual pathway?
to lateral geniculate nucleus (LGN) in thalamus
then via optic radiation to primary visual cortex (occipital lobe)
What cranial nerve number is the optic nerve?
CN II
What is the optic nerve an outgrowth of and hence what nervous system is it a part of and what surrounds it?
diencephalon
CNS
surrounded by meninges which goes up to the eyeball
What is the blood supply to the eye?
central retinal artery and vein
What is papilloedema?
rise in CSF pressure
Which foramen does the optic nerve pass through?
optic canal
What does the optic nerve take with it and what does it form in the eyeball?
takes a layer of dura
forms the sclera
What is the CNS an extension of which meninges?
extension of pia mater
What are the symptoms of papilloedema? (4)
- headaches
- drowsiness
- blurred vision
- vomitting
What does the increase pressure in papilloedema compress and what does this prevent and cause?
compress - central retinal vein
prevents - venous drainage from the eye
cause - swelling of the optic disk
NOTE - learn the components of the visual pathway - retina to cortex (7)
- optic nerve
- retina
- optic chiasma
- lateral geniculate nucleus of the thalamus
- optic radiation
- primary visual cortex
- optic tract
NOTE- know the cerebral topography
Lateral aspect of brain
- visual cortex
- visual association
Medial aspect of the brain
- calcarine sulcus
- visual association
Where does the striate cortex lie in relation to the calcimine sulcus?
- above and below the calcarine sulcus
Does the nasal part of the retina send information contra laterally or ipsilaterally?
contralaterally
Does the temporal part of the retina send information contra laterally or ipsilaterally?
ipsilaterally
Where does information from the nasal part and the temporal part first get sent to?
LGN - lateral geniculate nucleus
NOTE
draw out visual pathway
Where does the left half of the visual field go?
right hemisphere
Where does the right half of the visual field go?
left hemisphere
Where does the upper visual field go?
lower bank of the calcarine sulcus
Where does the lower visual field go?
upper bank of the calcarine sulcus
Where does the centre of visual axis (macula) go to?
occipital pole
In terms of optic radiation, how do fibres of the LGN pass to the upper and lower banks of the calcimine sulcus and what can this allow - give an example?
via different pathways
allows prediction of deficits of vision
e.g. Meyers loop
What is scotoma?
localised patch of blindness
What is anopia?
refers to the loss of one or more quadrants of the visual field
What is hemianopia?
half of the visual field is lost
What is quadrantanopia?
quarter of the visual field is lost
What is homonymous?
visual field losses are similar for both sides
What does it mean by heteronymous?
visual field losses are different sides
Do all optic tracts go to the LGN?
no - 10% take a medial root to the pre-tactal area - midbrain
What is the pupillary light reflex?
ability of both pupils to respond (constrict or dilate) dependent on the level of light the retina receives
What 2 cranial nerves does the pupillary light reflex use and star whether they are afferent or efferent?
- optic nerve - afferent root
2. oculomotor nerve - efferent root
What are the 2 components of the pupillary light reflex?
- direct component - light in on eye and the same pupil constricts
- consensual component - light in one eye other pupil constricts
What nucleus does the pupillary light reflex concern?
Edinger- Westphal nucleus
NOTE
understand the pupillary light reflex
NOTE
understand visual defects
