The Retina Flashcards
to suck 20 dicks at once
The Retina
– Composed of Neurons (except Pigment Epithelium), multi-layered, covering rear, inner wall of eyeball
Receptors
Rods and Cones
Bipolars
Postsynaptic to Receptors, show Spontaneous firing, Graded Potentials
Ganglions
- Postsynaptic to Bipolars, Show Action Potentials
Blind Sport or “Optic Disk”
- where Optic Nerve leaves eye & blood vessels enter/leave;
- No Receptors there
interneurons
perpendicular to pathway, influence interactions between the above neurons
- horizontals
- amacrines
horizontals
Graded Potentials, mostly Inhibitory NT, modify interface of Receptors and Bipolars
Amacrines
– Graded Potentials, mostly Inhibitory NT, modify interface of Bipolars and Ganglions;
-Many kinds
Pigment Epithelium
- rearmost layer of (Non-Neural) cells; feeds & recycles from receptors;
- helps reflect/maximize light
Strange but True
Light turns Receptor cells OFF (down), Darkness turns them ON (up) !
Recall that Receptors show
——————– firing
Spontaneous
Graded Potentials release…
… Inhibitory NT
Dark Current
- In the absence of stimulation, Receptor’s Na+ gates open, Na+ flows in & out
As photopigments are isomerized…
…Na+ & Ca+ gates close, increasing Receptor’s polarity, decreasing NT release
in the dark
- Receptors release enough inhibitory NT to prevent Bipolars from triggering Ganglions
- So Ganglions, by not firing, in effect, report to brain: “No light”
in bright light
- Receptors are shut down, do not inhibit Bipolars, so Bipolars spontaneously release enough excitatory NT
- to pass Ganglion’s threshold for firing, so Ganglion sends message: “Bright Light!”
in dim light
- Receptors’ spontaneous release of NT is decreased (a graded reaction, more light, less NT)
- so Bipolars only somewhat inhibited & release enough excitatory NT to sometimes trigger Ganglions
Optic Nerve
formed by axons of the ganglion cells
goes to brain
Optic Disk
or Blind Spot
where Optic Nerve leaves eye and blood vessels enter/leave
No Receptors there
