The Retina

Question 1

The Retina

Answer 1

– Composed of Neurons (except Pigment Epithelium), multi-layered, covering rear, inner wall of eyeball

Question 2

Receptors

Answer 2

Rods and Cones

Question 3

Bipolars

Answer 3

Postsynaptic to Receptors, show Spontaneous firing, Graded Potentials

Question 4

Ganglions

Answer 4

• Postsynaptic to Bipolars, Show Action Potentials

Question 5

Blind Sport or “Optic Disk”

Answer 5

• where Optic Nerve leaves eye & blood vessels enter/leave;

- No Receptors there

Question 6

interneurons

Answer 6

perpendicular to pathway, influence interactions between the above neurons

• horizontals
• amacrines

Question 7

horizontals

Answer 7

Graded Potentials, mostly Inhibitory NT, modify interface of Receptors and Bipolars

Question 8

Amacrines

Answer 8

– Graded Potentials, mostly Inhibitory NT, modify interface of Bipolars and Ganglions;

-Many kinds

Question 9

Pigment Epithelium

Answer 9

• rearmost layer of (Non-Neural) cells; feeds & recycles from receptors;
• helps reflect/maximize light

Question 10

Strange but True

Answer 10

Light turns Receptor cells OFF (down), Darkness turns them ON (up) !

Question 11

Recall that Receptors show

——————– firing

Answer 11

Spontaneous

Question 12

Graded Potentials release…

Answer 12

… Inhibitory NT

Question 13

Dark Current

Answer 13

• In the absence of stimulation, Receptor’s Na+ gates open, Na+ flows in & out

Question 14

As photopigments are isomerized…

Answer 14

…Na+ & Ca+ gates close, increasing Receptor’s polarity, decreasing NT release

Question 15

in the dark

Answer 15

• Receptors release enough inhibitory NT to prevent Bipolars from triggering Ganglions
• So Ganglions, by not firing, in effect, report to brain: “No light”

Question 16

in bright light

Answer 16

• 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!”

Question 17

in dim light

Answer 17

• 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

Question 18

Optic Nerve

Answer 18

formed by axons of the ganglion cells

goes to brain

Question 19

Optic Disk

Answer 19

or Blind Spot

where Optic Nerve leaves eye and blood vessels enter/leave

No Receptors there