Photoreceptors

Question 1

Why is the visual system more efficient at detecting some wavelengths vs others?

Answer 1

Different opsin in photopigments responsible for the different absorption spectra.

Question 2

Why does this sensitivity range shift under night time conditions compared to daylight conditions?

Answer 2

Rods, which operate best under scotopic conditions, have a different photopigment with a different spectral sensitivity range compared to that of a cone system.

Question 3

Structure of rod discs in the outer segment.

Answer 3

Rod discs have a double membrane that separates them from each other and from the outer membrane of the entire cell.

Filaments hold the membranes of the discs to the outer membrane of the cell.

Question 4

Structure of cone discs in the outer segment

Answer 4

Cone outer segment cell membrane forms a comb-like appearance. They do not fully enclose the discs.

Cone discs are connected to the outer membrane throughout the outer segment and open to extracellular space.

Question 5

Where is opsin made within rods and cones

Answer 5

Opsin is made in the Inner segment and transported to the discs via the cilium. Incorporates into discs by combining with a chromophore.

Question 6

Why is the inner segment of photoreceptor cells important for cell maintenance?

Answer 6

Contains the golgi, mitochondria, and ER.

ATP generation
Extrusion of Na+ via the Na+/K+ pump
Making opsin and incorporating it into the discs at the cilium.

Question 7

Synaptic terminals of the photoreceptor cells

Answer 7

Rods- Spherules

Cones- Pedicles

Question 8

Rods are densest

Answer 8

Outside the fovea and just nasal to the optic disc.

Highest density of rods is at 20 degrees eccentricity.

Question 9

Cones are densest

Answer 9

Densest at the fovea, but found throughout the retina.

Question 10

Three types of conest

Answer 10

S- lowest in fovea. Highest at 1 degree eccentricity. About 8% throughout the rest of the retina.
L- Highest density in fovea.
M- Highest density in fovea.
(The ratio of L to M cones varies among individuals)

Question 11

Phototransduction nis the act of

Answer 11

Converting light energy into a neural response

Question 12

___ of discs per photoreceptor

___ of photopigment molecules per disc

Answer 12

hundreds

thousands

Question 13

Visual pigment is ___ and ____

Answer 13

Opsin and chromophore

Question 14

Opsin

Answer 14

Photosensitive, membrane-bound, G protein-coupled receptor. Differences in opsin portion of the molecule determines its spectral absorption (means that some wavelengths are able to trigger the opsin better than others)

Question 15

Chromophore

Answer 15

A portion of a molecule that selectively absorbs certain wavelengths of light. Gives the molecule color.

Question 16

Wavelength peak for rods and 3 cone types

Answer 16

Rods: 498 nm peak

S cone (cyanolabe, blue) 420-440 nm 
M cone (chlorolabe, green) 530-540 nm 
L cone (erythrolabe, red) 560-565 nm  

Determined by microspectrophotometry

Question 17

Majority of our photopic sensitivity curve peak (555 nm) comes from which 2 cone types?

Answer 17

L and M