Visual system Flashcards
- What happens at the LGN?
Information is pre-processed before going to the primary visual cortex
- What pathway deals with object identity?
Ventral pathway – (sometimes called the what pathway
- What does the dorsal pathway do?
Detects object speed (spatial location)
- What is the function of Muller cells and why are they needed?
They focus the light on to the photoreceptor cells because light has to travel through a lot of tissue before reaching the rod and cone cells
- How many layers of neurons are there in the retina?
3
- How many layers of synapses are there?
2
- What are the 3 types of feedforward (activation) neurons?
Photoreceptopr cells, ganglion cells, bipolar cells
- What are the 2 kinds of feedback (inhibitory) neurons?
Amacrine cells and horizontal cells
- What are the 2 layers of synapses?
Inner plexiform layer and outer plexiform layer
- What happens in the outer segment of the photoreceptor cell?
Phototransduction
- How do photoreceptors respond to light flashes? (depolarisation or hyperpolarisation
Hyperpolarisation
- What does cyclic GMP do?
Activates channels on the photoreceptor membrane
Signalling pathway for opsins?
Opsins change conformation ==> ACtivates GPCR ==> Activate PDE ==> Cyclic GMP down regulated ==> Channels close ==> hyperpolarisation ==> Down reg of glutamate ==> Horizontal and bipolar cells receive less activation
Sign inverting synapse?
When photoreceptor activated - less glutamate released
Glutamate prevents channel opening and depolarisation
On cells express metabotropic (inhibitory) glutamate receptors
Off cells express inotropic (excitatory) glutamate receptors
- What is centre surround organisation of the receptive field?
Illumination of the centre and the surround leads to responses of opposite polarities
- What are the 2 major classes of ganglion cells?
Parvocellular and magnocellular
- What are their types of responses?
Parvocellular – sustained
Magnocellular – transient
Are OFF bipolar cells hyperpolarised or depolarised by light?
hyperpolarised
Are ON bipolar cells hyperpolarised or depolarised by light?
Depolarised (reversing hyperpolarisation of photoreceptor cell)
What does an OFF center RGC receive input from? (which type of bipolar cell?
An OFF bipolar cell
What happens if light is shone on the center of an ON center cell?
Photoreceptor hyperpolarised but bipolar cell is maximally excited
What happens if light is only shone on surround of ON center cell?
Surround releases less NT and horizontal cells are not excited
horizontal cells inhibitory signals are low
Center cone doesn’t depolarise as much and bipolar cell is not as excited
