Lecture 6 - Transduction

Question 1

path that light takes through the eye

Answer 1

cornea –> lens –> vitreous humor –> focused on the back of the retina

Question 2

the macula

contains?

highest what?

Answer 2

contains the fovea

high acuity area

highest concentration of cones

highest resolution vision

Question 3

ganglion cells take…

Answer 3

… all the signals generated by the eye and send them to other portions of the brain for further processing

Question 4

problem of the inverted retina

Answer 4

if light is going through the cellular matter there’s some scatter, absorption before it reaches the critical elements: rods and cones

Question 5

solution to problem of inverted retina

octupussies

Answer 5

octopuses: have their rods and cones facing the “right way” so all the other stuff comes after

Question 6

solution to problem of inverted retina

fovea

Answer 6

in the fovea, all the elements “shunted off to the side” so all the ganglion cells and bits aren’t getting in the way of the light

Question 7

solution to problem of inverted retina

Müller Glial Cells (Radial Glial Cells)

Answer 7

support cells that have a special feature: they act as a kind of optical fibers (channels) that are collecting the photons of light and speeding them right through to the rods and cones where transduction takes place

if you shine photons of light and they hit the cell it has a refractive index that allows the light to go right through all the “stuff” to the rods and cones

BEST solution

Question 8

transduction

Answer 8

changing light energy into neural signals

Question 9

Rods and cones have different properties, but function similarly during….

Answer 9

…transduction of visible light.

Question 10

intrinsically photosensitive retinal ganglion cell (ipRGC),

Answer 10

third type of visual receptor,

before the light gets through to rods and cones, this cell can respond to light coming in

important! associated with basic bodily functions: circadian rhythms and pupillary reflex!

Question 11

Transduction begins when

Answer 11

photons of light enter the outer segment of the photoreceptor.

Question 12

During transduction the photons go into

Answer 12

one of the discs containing thousands of visual pigment molecules.

Question 13

The visual pigment molecule is

Answer 13

a long protein strand called opsin.

Question 14

the one location on the protein strand reactive to light

Answer 14

the retinal

each visual pigment molecule has only one

Question 15

path of transduction

Answer 15

light hits protein chain within a disc located in the outer segment of a rod

Question 16

opsin

Answer 16

long protein chain

have thousands of them within a single disc (hundreds of discs within a particular outer segment of one rod)

Question 17

isomerization

Answer 17

process where a single photon of light is absorbed by a retinal molecule, the molecule changes shape (and later separates)

This one triggering event leads to an enzyme cascade (SPARK)

Question 18

enzyme cascade

Answer 18

thousands of chemical reactions leading to a change in receptor activity - signaling that light has been detected

Question 19

How many visual pigment molecules need to go through isomerization to be detectable by a person?

Selig Hecht and colleagues (1942)

Answer 19

attempted to answer this question with a very clever psychophysics experiment.

• Asked: How much light is needed for detection?

asked subjects: do you see the light or do you not?

• Using a precisely calibrated light source, he determined that a person could detect a flash of light containing just 100 photons (using the method of constant stimuli).

Question 20

The specific part of the visual pigment that reacts to light, triggering the enzyme cascade

Answer 20

Retinal