BPK 105 Midterm: Module 5 - Objectives - Part 4
27 Apr 2018
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Module 5 - Objectives - Part 4
● Compare and contrast the roles of the rods and cones.
Rods are responsible for vision in low illumination (night vision).
Cones are responsible for color vision.
Rods:
- manufacture of retinal in rod cells takes time and requires vitamin A
- used for low light vision, no colour
- Rod cells contain a photosensitive pigment called rhodopsin (purple pigment).
- Rhodopsin consists of a protein opsin loosely bound to a yellow pigment called retinal
(figure 9.12f,
figure 9.13, step 1).
- When exposed to light, retinal changes shape, which then changes the activity of the
entire rhodopsin molecule.
- This change in rhodopsin stimulates a response in the rod cell, resulting in vision (figure
9.13, steps 2 and 3)
.
- Retinal then completely detaches from opsin.
- Energy (ATP) is required to reattach retinal to opsin and return rhodopsin to the form it
had before it was stimulated by light (figure 9.13, steps 4–6).
Cones:
- require light for color vision
- photosensitive pigments in cone cells are slightly different from those in rod cells.
- pigments in cone cells are sensitive to colors.
- Each color results from stimulation by a certain wavelength of light.
- Three major types of color-sensitive opsin exist; sensitive to blue, red, or green.
- many colors we can see result from the stimulation of combinations of these three types
of cones.
- outer segments of rod and cone cells are modified by numerous foldings of the cell
membrane to form discs (figure 9.12c
–e
).
- rod and cone cells synapse with bipolar cells of the sensory retina (see figure 9.12).
- These and the horizontal cells of the retina modify the output of the rod and cone cells.
- Ex. this modification helps us perceive the borders between objects of contrasting
brightness.
Document Summary
Compare and contrast the roles of the rods and cones. Rods are responsible for vision in low illumination (night vision). Rods : used for low light vision, no colour. Manufacture of retinal in rod cells takes time and requires vitamin a. Energy (atp) is required to reattach retinal to opsin and return rhodopsin to the form it had before it was stimulated by light (figure 9. 13, steps 4 6). Cones : require light for color vision photosensitive pigments in cone cells are slightly different from those in rod cells. pigments in cone cells are sensitive to colors. Each color results from stimulation by a certain wavelength of light. Many colors we can see result from the stimulation of combinations of these three types. These and the horizontal cells of the retina modify the output of the rod and cone cells. Ex. this modification helps us perceive the borders between objects of contrasting brightness.
