11. Vision and phototransduction

Photoreceptors are unusual because they are _.

depolarized and release glutamate in darkness

light _ photorecpetors by _.

hyperpolarizes, closing cGMP-gated channels

Light passes through the _. (order)

cornea, pupil, and lens before reaching the retina.

The _ has a high photoreceptor density and high _.

fovea, spatial resolution

What does the optic nerve exit do?

exit creates a blind spot that the brain fills in

Where are photoreceptors?

toward the back of the retina

Bipolar cells are _.

Intermediate

What forms the optic nerve?

ganglion cell’s are the output neurons whose axons form the optic nerve

Convergence is greater in _, and it _.

Peripheral retina, reduces spatial resolution but supports sensitivity

Dark state vs light state

cGMP-gated currents keep the photoreceptor relatively depolarized, producing ongoing glutamate release onto bipolar cells vs light changes retinal within rhodopsin, activates transducin, activates phosphodiesterase, lowers cGMP, and closes cGMP-gated channels

Consequences of light state:

Less glutamate is released, which disinhibits some bipolar pathways and changes others in the opposite direction, which alters ganglion-cell action-potential output

Rods support _.

dark vision

How is color interpreted?

relative pattern of cone activation