grey matter Flashcards
What is the bipolar membrane responsible for?
Connects photoreceptors to the optic nerve.
Where are rods found?
Retina
Where are cones found?
The fovea
What is the light sensitive pigment that is found in rods?
Rhodopsin
What is rhodopsin made from?
Retinal and opsin
What prevents information reaching the brain when the rods are unstimulated?
- open sodium channels causes depolarisation
- neurotransmitters released
- these inhibit the bipolar neurone
What is bleaching?
When light energy causes rhodopsin to break into retinal and opsin
What phase is the membrane in when rod cells are stimulated?
Why does this allow information to reach the brain?
Hyperpolarisation
-it prevents the release of more neurotransmitters, uninhibiting the bipolar neurone
What happens to the impulses when there is a bigger stimulus?
Action potentials fire more frequently, not more often
Outline the course of events which cause the action potential to move down the neurone
- some of the Na+ ions diffuse sideways
- this causes sodium channels in the next region of the neurone to open, and Na+ ions to diffuse into it
- this causes a wave of depolarisation to spread down the neurone
Why are impulses discrete?
- during the refractory period, ion channels can’t be opened
- this prevents action potentials from overlapping.
Why do impulses move down myelinated neurones faster?
- myelin is an electrical insulator
- depolarisation can only occur at the nodes of ranvier
- the cytoplasm conducts enough charge to depolarise the next node, the impulse jumps
What is it called when the impulse jumps down the nodes of ranvier?
Salutatory conduction
what do the sodium potassium pump and potassium ion channels regulate?
-resting potential
what does ‘resting potential’ refer to?
the polarisation of the membrane, there are more positive ions outside the cell than inside
how do the sodium potassium pump + potassium channels work?
- Na/K pumps sodium ions out of the cell via active transport, they cant diffuse back into the cell
- this creates an electrochemical gradient because there are more Na ions outside the cell
- K ions are moved back in, but the membrane is permeable to K, so they diffuse back out
- this makes the outside of the cell positively charged
why does the membrane become depolarised when a stimulus arrives?
Na+ channels open, Na+ ions diffuse into the neurone making the inside less negative
why does repolarisation occur?
Na+ channels close and K+ channels open, K+ diffuses out of the neurone
why does hyperpolarisation occur?
K+ channels are slow to close, too many leave
what is meant by ‘refractory period’?
ion channels are recovering and cannot be forced to open
what affect does habituation have on the amount of calcium ions in the pre-synaptic membrane?
decreases the number of Ca2+ ions which enter the pre-synaptic membrane, causing less neurotransmitter to be released from vesicles into the pre-synaptic cleft
what does the visual cortex do?
recieves and processes visual information
what happens when a stimulus is provided during the critical period?
synapses that receive visual stimulation and pass nerve impulses to the visual cortex are retained
what is a dopamine agonist?
something that mimics dopamine, binding to dopamine receptors in the brain and triggering an action potential
