Visual System Flashcards
What is the visual system designed to recognise and localise?
Food
Predators
Mates
The morphology of sensory neurons is largely defined by its ________
Function
What is the superior colliculus responsible for?
Attentional vision (turning to focus on something)
The retina consists of __ layers of neurons and __ layers of synapses
3
2
Feedforward neurons are…
Photoreceptors
Bipolar cells
Ganglion cells
Feedback neurons are…
Horizontal cells
Amacrine cells
Layers of synapses
Inner and outer plexiform layers
Rods are active at ___ light
Dim
Cones are active at ____ light
Bright
ON bipolar cells _____ in response to light
Depolarise
OFF bipolar cells _____ in response to light
Hyperpolarise
What is the receptive field?
An area in the retina which when illuminated activates a visual neuron
The optic nerve is the information…
Bottleneck
Right visual field activates the _____ side of the brain and vice versa
Left
What is the main function of the retina?
Image acquisition
What does the lateral geniculate nucleus do?
Sends information to the primary visual cortex
Preprocesses visual information
What is the superior colliculus responsible for?
Attentional
Focusing on the visual field
Two main visual pathways
Ventral
Dorsal
Ventral pathway
What pathway
Object feature stream
Jennifer Anniston neurones
Dorsal pathway
Where pathway
Space related stream
Useful for sport to position ourselves to catch a ball etc
Where is the ventral pathway?
Inferior temporal lobe
Where is the dorsal pathway?
Posterior parietal lobe
What does the pupil do?
Regulates the amount of light falling on the retina
What does the lens do?
Focuses the image on the fovea
What is the fovea?
Part of the retina with highest visual acuity
The rest of the retina has _____ acuity and contains primarily _____
Smaller
Rods
Light travels through ____ cells
Muller
Horizontal cells
Feedback to photoreceptors
Feedforward to bipolar cells
Amacrine cells
Most diverse type of cell in retina
Inhibitory
Send feedback to bipolar cell (inhibit bipolar cells)
Feedforward to ganglion cells
Phototransduction happens in the _____ segment
Outer
Photoreceptors respond to light flashes by…
Hyperpolarisation
In darkness, the sodium calcium channel is ____ and the membrane is _____
Open
Depolarised
(influx of sodium and calcium ions makes the membrane less negative)
Why are photoreceptor synapses special?
They have ribbon synapses
Can release vesicle constantly
Do not spike, have graded potentials
Release glutamate
When light goes up, the release rate of glutamate goes _____ and vice versa
Down
ON cells ____ when you apply glutamate
Hyperpolarise
What is centre surround organisation of the receptive field?
Illumination of the centre leads to an opposite response to illumination of the surround
Centre depolarises
Surround hyperpolarises
Mechanism of centre-surround organisation
Many photoreceptors coverage to 1 bipolar cell
Photoreceptors in the centre, directly synapsed to bipolar cells
Peripheral photoreceptors synapse to the horizontal cell and therefore cause bipolar cell to depolarise
Centre mechanism
Light
Hyperpolarises photoreeptor
Transmitter (glutamate) stops being released
Bipolar cell hyperpolarises
Surround mechanism
Light Hyperpolarises photoreceptor Hyperpolarises horizontal cell Stops hyperpolarising photoreceptor Bipolar cell depolarises
Do ganglion cells spike?
Yes
What happens when you stimulate the centre of an off-centre ganglion cell?
They stop spiking
What happens when you stimulate the surround of an off-centre ganglion cell?
They spike more frequently
What happens when you stimulate the surround of an on-centre ganglion cell?
They stop spiking
What happens when you stimulate the centre of an on-centre ganglion cell?
They spike more frequently
It appears that ganglion cells are designed to respond to ______ in illumination that occur within the receptive field
Differences
If you have an illumination which covers the whole receptive field evenly, _____ of cells _____ spike.
The majority
Would not
Two major classes of ganglion cells
Parvocellular (80%)
Magnocellular (10%)
P cells have ____ dendrites than M cells
Smaller but more densely packed
P cells have ____ receptive fields than M cells
Smaller
P cells are known as
Sustain cells
M cells are known as
Transient cells
