Lecture 46 4/30/24

Question 1

How fast does light travel?

Answer 1

186,000 miles per second

Question 2

Which cells are involved in vision?

Answer 2

-photoreceptor
-bipolar
-ganglion

Question 3

What is contained in the outer portion of the photoreceptor cell?

Answer 3

membranous discs

Question 4

Which protein is embedded in the membranous disc membranes?

Answer 4

rhodopsin

Question 5

When are the Na+ channels in the outer portion of the photoreceptor cell open?

Answer 5

when it is dark

Question 6

What does the influx of Na+ into the photoreceptor cell cause?

Answer 6

release of glutamate, an inhibitive neurotransmitter that prevents vision from functioning properly

Question 7

What is cGMP?

Answer 7

molecule that keeps the Na+ channels open in the photoreceptors

Question 8

What is retinal?

Answer 8

an aldehyde embedded within rhodopsin

Question 9

What is 11-cis retinal?

Answer 9

the native form of retinal that makes rhodopsin very stable

Question 10

What happens when a photon of light strikes rhodopsin?

Answer 10

11-cis retinal becomes all-trains retinal, and rhodopsin becomes active

Question 11

What happens once rhodopsin is activated?

Answer 11

-causes the beta and gamma subunits to come off of the transducin molecule
-causes GDP to come off of transducin
-causes GTP to attach to the remaining alpha subunit of transducin

Question 12

How does inactivated transducin differ from activated transducin?

Answer 12

inactivated:
-alpha, beta, and gamma subunits
-GDP
activated:
-alpha subunit only
-GTP

Question 13

When does the PDE molecule become activated?

Answer 13

when alpha-GTP binds to the gamma subunits of PDE

Question 14

What is the PDE molecule comprised of?

Answer 14

-one alpha subunit
-one beta subunit
-two gamma subunits

Question 15

What is phototransduction?

Answer 15

process through which rhodopsin becomes activated, which in turn activates transducin and PDE

Question 16

What is the role of activated PDE?

Answer 16

-hydrolyzes cGMP into 5’-GMP
-lack of cGMP leads to closure of Na+ channels

Question 17

Where do the axons of the ganglion cells run?

Answer 17

to the brain

Question 18

What must occur in order for an image to be seen?

Answer 18

every pixel of the image must be recreated on the retina

Question 19

What is retinotopic organization?

Answer 19

if an image is created on the retina, it can be transduced all the way to the brain

Question 20

What happens when an object is 20 feet or more away from the eye?

Answer 20

-light rays are essentially parallel
-cornea is able to recreate image on retina without additional assistance

Question 21

What happens when an object is less than 20 feet away from the eye?

Answer 21

-light rays diverge, and the cornea is not strong enough to bring them back perfectly to produce an image
-the lens helps to adjust the light rays in order to produce the image

Question 22

What happens with the lens when we look at a distant object?

Answer 22

-ciliary bodies are at rest and flattened
-ciliary zonules are taut
-lens is pulled into a flattened sphere and serves as a weak refractory surface

Question 23

What happens with the lens when we look at a close object?

Answer 23

-ciliary bodies contract
-ciliary zonules have slack
-lens is able to form its typical sphere shape and serves as a strong refractory surface

Question 24

What is accomodation?

Answer 24

process of going from distance to near vision and vice versa