WEEK 8 - Topic 17 - Rods, Cones & Visual Pigments Flashcards
What is photoreception?
The process by which the eye detects light energy.
What is phototransduction?
The process by which light energy is converted into a graded receptor potential.
(REVISION) What are the two layers of the retina?
Neural layer Pigmented layer (abuts the choroid)
Another term for visual pigments
Photopigments
(REVISION) What are photoreceptors exactly?
Modified neurons
What are the outer segments of the photoreceptors? And where are they located?
- Receptive regions of rods and cones that absorb light
- Immersed in the pigmented layer of the retina
What joins the outer segment of a rod or cone to the inner segment?
Cilium
What connects the inner segment to the cell body in rods?
Outer fibre
In a cone, what connects the inner segment to the cell body?
Nothing. Inner segment connects directly to the cell body.
What is the visual pigment in rods called?
Rhodopsin
What connects the cell body to the synaptic terminal?
Inner fibre
Why are the plasma membranes of the outer segments folded into discs?
To increase the surface area available for trapping light
Are the discs continuous in rods and cones?
Rods: discs are discontinuous
Cones: discs are continuous with the plasma membrane
What phagocytises the old discs of the photoreceptors?
Pigment cells
New discs are renewed every…?
24 hours
When do we best see dimly lit objects?
- When we do not look at them directly
- When they move
Compare and list the differences between cones and rods
See Photoreceptor note 1
What is an opsin and what is its function?
Opsin is an integral protein contained in each photopigment of a photoreceptor, that surrounds and binds a chromophore molecule (retinal).
It filters light reaching the retinal and depending on the type of opsin to which it is bound, retinal absorbs different wavelengths of the visible spectrum.
The type of opsin also differs in each type of photopigment.
(REVISION) What are isomers?
Isomers are compounds with the same molecular formula but different structural formulas.
(i.e. same number of atoms, different structure/form)
Are opsin and retinal different in each type of photopigment?
Opsin differs in each type of photopigment.
Retinal is the same in all four photopigments.
What is retinal and what is its function?
Retinal is a polyene chromophore derived from vitamin A and is the light-absorbing molecule contained in each photopigment of a photoreceptor.
How many photopigments are there in the repeated layers of each photoreceptor?
Over a billion photopigment molecules
Where do the photopigments lie?
Photopigments, within photoreceptor cells, lie in specialised membranes arranged in highly ordered discs parallel to the retina
