Retinal circuitry Flashcards
what types of bipolar cells does a photoreceptor connect to
on and off centre
what type of receptors do off centre bipolar cells have and what does it mean
“normal” glutamate receptors
- respond to darkness on the centre
glutamate = excitatory
what type of receptors do on centre bipolar cells have and what does it mean
metabotropic glutamate receptors (mGluR6)
- respond to light on the centre
glutamate = inhibitory
(close when glutamate is present)
what types of cells do bipolar cells connect to
on centre bipolar —> on centre ganglion cell
off centre bipolar —> off centre ganglion cell
what types of receptors do on/off centre ganglion cells have and what does it mean
both have normal glutamate receptors
glutamate = excitatory
what is the relationship between amount of light and glutamate release
dark = lots of glutamate released
light = very little glutamate released
why do off centres have a higher firing rate in the dark
- glutamate = excitatory
- lots of glutamate released in the dark
- higher firing rate
why do on centres have a higher firing rate in the light
- glutamate is inhibitory (MGluR6)
- less glutamate released in the dark
- therefore less inhibition
- higher firing rate
what will happen when the centre is illuminated (general)
cone will hyperpolarise
- results in LESS glutamate being released from the cone onto the bipolar cells
what will happen when the centre is darkened (general)
cone will depolarise
- results in MORE glutamate being released from the cone onto bipolar cells
what do off centre bipolar cells do in the case of light on the centre
hyperpolarise due to LESS glutamate
- shuts down off centre bipolar and ganglion cells
(prefers light OFF)
what do on centre bipolar cells do in the case of light on the centre
depolarise due to LESS glutamate (less inhibition)
- activates on centre bipolar and ganglion cells
(prefers light ON)
what do off centre bipolar cells do in the case of dark on the centre
depolarise due to MORE glutamate
- activates the off centre bipolar and ganglion cells
(prefers light OFF)
what do on centre bipolar cells do in the case of dark on the centre
hyperpolarise due to MORE glutamate (more inhibition)
- shuts down the on centre bipolar and ganglion cells
(prefers light ON)
what do amacrine cells contain
GABA (inhibitory)
what do photoreceptors release and have receptors for
release - glutamate
have receptors for - GABA
what type of receptors do horizontal cells (inhibitory neurons) have
normal glutamate receptors
- release GABA onto neighbouring photoreceptors
what occurs when just the centre region is lit up
- hyperpolarises the cone in the centre
- reduces its glutamate release
- depolarises on centre bipolar cell
- increases firing rate of on centre ganglion cell
what occurs when the surround cones are also lit up
- hyperpolarises the cones in the surround
- reduces their glutamate release
- hyperpolarises the horizontal cells
- LESS GABA released onto centre cone
what occurs when less GABA is released on to the centre cone when the surround is lit up
- depolarises the centre cone
- increasing its glutamate release (more inhibition)
- hyperpolarises the on centre bipolar cell
- reduces firing rate of on centre ganglion cell
what is the difference in firing rate when different parts of the centre and surround are lit up
centre lit, surround dark = highest firing rate
centre lit, surround lit = lowest firing rate
