structure and function of the eye

draw and label the eye ( include 9 labels )

briefly describe retinal development

retinal neurons are born in a sequential order then move into their proper positions and connect, forming synapses for vision.

(can also use model organisms to watch it happen) - dont memorise this bit

draw the retina

• highlight each neuron type and support cell types

• further label the layers and the direction of light

structure of photorecptor

• what are the two types of photoreceptor

• what do they do

• what are each of their functions

rid and cone ( light sensitive cells of retina )

• rod = low light ( dark ) ( so rods more snesitive )

• cones = high light (bright) and colour

• light enters through the inner segment of the cells

what type of synapse do retinal neurons use

ribbon synapse

= so neurotransmitters can be released easily ← dont memorise

what is the role of the disks in photoreceptors

active photoreceptors burn up disks throughout the day and they regenerate in the evening

bipolar cells

• what does it mean by they can be on or off

• what does it connect to

• connect retina inner and outer layers

• transmit signals from photoreceptor to retinal ganglion cells

• classed as ON or OFF

• ON = depolarised ( activated) with light

• OFF = depolarise in dark

retinal ganglion cells ( 3 little points)

• what is it located to etc

• output neurons of retina

• synapses with bipolar and amacrine cells

• axons form optic nerve to brain

amacrine and horizontal cells

• what do they do

• excitatory or inhibitoy

• what do they synapse with

• modulate and integrate visual info

• inhibitory neurons

• horizontal cells between photoreceptor and bipolar cells ( outer retina)

• amacrine cells between bipolar and ganglion cells ( inner retina)

why do we have muller glia ?

• what demand is it for filling

lots of energy needed for visual processing → lots of input and waste

→ glial cells helps clean up waste by recycling neurotransmitters

what is the role of muller glia ( 4 points)

• span entire retina (photoreceptors → ganglion cells)

• part of tripartite synapses

• convert glutamate → glutamine (detox + recycling)

• return glutamine to presynaptic neurons

where is the region for high acuity vision

• which photoreceptor do we associate with this area

fovea

• ( cones are here mostly rods in periphery)

• means cones = high acuity vision

after activation do rods or cones hyperpolarise faster

cones

what is a receptive field

small area of retina affects one neuron’s firing

Example:
One Retinal ganglion cells might respond to light falling on 5–10 nearby photoreceptors.

Because many cells are close together, their receptive fields overlap

^^^ context dont memorise

what happens when receptive field overlap? ( 3 key things)

• convergent excitation

Signals from multiple photoreceptors combine → signal stronger

• surround inhibition

receptive field = centre + surround

centre excites

surround inhibits

• lateral inhibtion

strongly activated photoreceptors inhibit nearby ones

this exaggerates differences between light and dark

why does it look like there's a white line between different shades of grey

slight overlap in lateral inhibition at those exact points so can't tell exactly the end point of each shade

^^ dont reallyyy need to memorise

all photoreceptors …. in responser to light

hyperpolarise

more about cones

• how many types and what are they

• what does this mean cones can do

• 3 types of cones , each more receptive to a specific wavelength of light

• L ( long wavelength cones), M ( medium wavelength cones), S (short wavelength cones)

• means they can tell colours

why do the l/m/s photoreceptors respond maximally to different wavelengths of light

they all have the same chromophore but opsins have slightly different amino acid sequences

what is the chromophore in photoreceptors

11 cis retinal ( -> all trans retinal)

( basically changes cis to trans when light is absorbed in eye) ←- dont need to memorise

explain the main cascade that leads to hyperpolarisation in photoreceptors.

good luck babe

to memorise:

Light activates rhodopsin → activates transducin → activates PDE → cGMP decreases → CNG Na⁺/Ca²⁺ channels close → reduced Na⁺ influx → hyperpolarisation

concept behind it explained:

• Photoreceptors naturally depolarised because CNG (cyclic nucleotide-gated) channel open allows Na+ and Ca2+

• This is kept open by cGMP

 

Now light comes in…

•  activates rhodopsin ( because goes from cis-trans) -> activates transductin

-> this decreases cGMP so now it cant keep CNG Na+ and Ca2+ channels open :(

• The reduction of Na+ and Ca+ make photoreceptor more negative = HYPERPOLARIZE

explain the mini cascade that keeps the CNG channel open

Ca2+ inhibits GCAP which activates GC which activates cGMP

which types of bipolar cell so rods and cones synapse with

rods - on only
cones - both