Action potential steps

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Sodium channels and the AP- STEP 1
Neuron is at rest with the inside is negative (-70 mV) and sodium channels are closed with more sodium on the outside.
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Sodium channels and the AP- STEP 2
A small change in membrane potential occurs due to a triggering stimulus (-55 mV) and sodium channels open, sodium floods in, down its concentration and potential gradients.
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Sodium channels and the AP- STEP 3
The newly positive membrane potential (+30 mV) results in the sodium channels closing, leaving more sodium outside of the cell than inside. The channels do not just close they become inactivated.
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Potassium channels and the AP STEP 1
Neuron is at rest with the inside is negative (-70 mV) and the potassium channels are shut with more potassium inside. The channels have voltage sensitive paddles with a positive charge, attracted to the inside of the cell holding the channel shut.
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Potassium channels and the AP STEP 2 + 3
Changes to sodium channels make the inside of the cell positive
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Potassium channels and the AP STEP 4
Positive inside caused by influx of sodium repels paddles and causes potassium channels to open so potassium ions leave down their concentration gradient and (newly created) potential gradient, making the insider negative again.
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Action potential whole process STEP 1
begins at resting membrane potential (-70mV). Local change in potential-if reaches certain threshold (-50mV), depolarisation occurs
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Action potential whole process STEP 2
depolarisation is driven by the opening of voltage-gated sodium channels; once opened sodium floods into neuron (moving down their concentration gradient). carry +ive charge- thus +ive membrane potential (+35mV). VGSCs close.
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Action potential whole process STEP 3
simultaneously, voltage-gated potassium channels open. K is higher concentration inside neuron,and is a positively charged ion. because movement of sodium ions, K is in a +ive area, thus K leaves neuron
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Action potential whole process STEP 3 part 2 (repolarisation)
as K ions leave neuron, they carry +ive charge making the neuron more -ive again
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Action potential whole process STEP 4; hyperpolarisation
membrane potential overshoots its initial resting potential, thus temporarily becomes more negative. during this time, ion distribution across membrane is retuned to normal-more Na on outside and K inside neuron
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absolute refractory period
sodium channels are inactivated because they just opened/closed, so no AP can be produced
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what does this do?
limits the frequency of APs we can produce to around 1000-Hz
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relative refractory period
channel can be opened but it is further from threshold so takes a bigger trigger
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Action potential propagation a)
in response to signal, soma end of the axon becomes depolarised
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Action potential propagation b)
depolarisation spreads down axon, meanwhile, first part of the membrane repolarises. As Na+ channels are inactivated and additional K+channels opened, membrane can't depolarise again
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Action potential propagation c)
AP continues to travel down axon
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Signalling at a chemical synapse STAGE 1
APs arrive at axon terminal
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Signalling at a chemical synapse STAGE 2
voltage-gated Ca2+ channels open
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Signalling at a chemical synapse STAGE 3
Ca2+ enters the cell
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Signalling at a chemical synapse STAGE 4
Ca2+ signals to vesicles
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Signalling at a chemical synapse STAGE 5
vesicles move to membrane
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Signalling at a chemical synapse STAGE 6
docked vesicles release neurotransmitter by exocytosis
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Signalling at a chemical synapse STAGE 7
NT diffuses across synaptic cleft and binds to receptor
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iontropic receptor
receptor containing a binding site for a NT and an ion channel that opens when a molecule of the NT attaches to the biding site
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what to iontropic receptors contain?
sodium channels, once opened sodium ions enter the cell and depolarise the membrane
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metabotropic receptors
a receptor containing a binding site for a NT; activates an enzyme that begins a series of events that opens an ion channel elsewhere in the cell's membrane when a molecule of the NT attaches to the binding site
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G protein
protein coupled to a MR; conveys messages to other moles when a ligand binds with and activates the receptor
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second messenger
chemical produced when a G protein activates an enzyme; carries a signal causing the ion channels to open/cause other events in the cell
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Other cards in this set

Card 2

Front

Sodium channels and the AP- STEP 2

Back

A small change in membrane potential occurs due to a triggering stimulus (-55 mV) and sodium channels open, sodium floods in, down its concentration and potential gradients.

Card 3

Front

Sodium channels and the AP- STEP 3

Back

Preview of the front of card 3

Card 4

Front

Potassium channels and the AP STEP 1

Back

Preview of the front of card 4

Card 5

Front

Potassium channels and the AP STEP 2 + 3

Back

Preview of the front of card 5
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