Functioning of the Rods Flashcards
Rods:
Pigment rhodopsin bleaches to form 2 chemical components;
Opsin and retinal.
These revert back to rhodopsin under low light intensity.
Rods:
There are 2 forms of retinal that are isomers of each other.
It is the retinal component which absorbs light.
Isomers have the same chemical formula but different structure.
Cis-retinal to trans-retinal under light.
Sequence of events when light hits the photochemical pigment in a rod:
- Light hits the ____
“rhodopsin molecule”.
Sequence of events when light hits the photochemical pigment in a rod:
- Within the rhodopsin molecule, cis-retinal is ____
“converted to trans-retinal”.
Sequence of events when light hits the photochemical pigment in a rod:
- Rhodopsin breaks down into its components, ____
“opsin and retinal”.
In darkness trans reverts to cis and rhodopsin is reformed.
DARK ADAPTATION
Mitochondria – ATP – rhodopsin resynthesis
Sequence of events when light hits the photochemical pigment in a rod:
- What is pumped out of the rod?
Na+ is pumped out of the rod and cannot diffuse back in rapidly – creates generator potential.
Sequence of events when light hits the photochemical pigment in a rod:
- When threshold is reached the inside of the rod becomes _____
“more negative ie, hyperpolarisation occurs”. (opposite to most receptors and neurones)
“Causes a change in the membrane potential.”
Sequence of events when light hits the photochemical pigment in a rod:
- Where does hyperpolarisation occur?
Hyperpolarisation occurs in the bipolar neurones.
Sequence of events when light hits the photochemical pigment in a rod:
- Where does depolarisation occur?
Depolarisation occurs in the ganglion cells sending an AP in the optic nerve.
What is the process of dark adaptation?
In the absence of light;
* trans-retinene is converted back to cis-retinene
* so the rhodopsin can be reformed.
* This is controlled by the enzyme retinene isomerase.
For this to occur all rods require ~30 minutes in the dark.
Dark adaptation:
In bright conditions, the cones work but the rods are ____
“bleached”
(rhodopsin is broken down).
Dark adaptation:
In dark conditions, the cones do not work but the rods ____
“can function if the rhodopsin molecules are intact”.
Dark adaptation:
When moving from bright to dark conditions, the rhodopsin must be ____
“reformed in the rods before they can work”.
Until this happens, temporary blindness results.
Dark adaptation:
The length of this period of blindness is the time taken for the ____
“rhodopsin to reform”
i.e., dark adaptation is occurring.
