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18 Cards in this Set
- Front
- Back
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What is the membrane potential due due? Inside there is a lot of what? Outside there is a lot of what? |
Inside of neurons is electrically negative compared to the outside There is a lot more potassium inside the cell than outside the cell |
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What is the RMP mostly sensitive to changes in? |
Potassium concentration outside of the cell |
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What are 3 types of ion channels in membrane? |
Voltage gated, mechanically gated that will respond to physical stimuli and chemically/ligand gated |
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What are passive (local, graded) potentials? |
Local changes in membrane potential caused by opening or closing of ion channels in response to external stimulus, they are graded because their local amplitude reflects the amount of input and distance from the stimulus |
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Why does the potential decay with distance from the stimulus site in local/graded potentials? |
Because of the leakage of K+ out of the cell- the stimulus is caused by inward positive charge so outward charge causes less depolarization |
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What properties allow for the temporal and spacial summation of graded potentials? |
They are able to spread, they outlast their stimulus, their size reflects the locality and size of the stimulus thus they can add together over time |
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When do action potentials happen? |
When passive potentials reach an area where there are voltage gated sodium channels |
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What is the feature of sodium gated channels which means APs cannot summate? |
After sodium gated channels open they inactivate and do not let any more sodium ions flow through them until the membrane has been repolarized- this means APs cannot add on top of each other and it is called the absolute refractory period |
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What is the threshold? |
The point at which inward Na+ cannot be offset by outward K+ meaning any further inward current of Na+ will have a huge effect on the membrane potential |
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What is the difference between APs and graded potentials? |
APs are all or nothing events |
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What causes repolarisation after an AP? |
The Na+ channels become inactivated so there is no more inward positive charge but K+ channels are open meaning there is outward flow of positive charge |
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How is an AP propagated along a neuron? |
It is like a wave so as it moves down the neuron the positive charge stimulates more voltage gated sodium channels to open thereby continuing the depolarization along the nerve- in an unmyelinated neuron there is continuous conduction and it spread unidirectionally because there is an absolute refractory period behind it |
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What is the role of myelin? |
- Myelin wraps around neurons to reduce leak and capacitance so there is a higher speed spread of ions that is able to reach further along the axon before regeneration is needed. - Less ions are moving so there is less pump action and therefore less energy consumption |
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What determines membrane conduction velocity? |
How fast charge can build up at a point further down the axon than where the AP is- this depends on the proportion of charge that flows along the axon compared to the amount leaking out or getting trapped in the membrane |
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What are 3 ways the conduction velocity of an AP can be sped up? |
- Decreasing the resistance to flow by making the axons diameter wider - reducing membrane capacitance - reducing leak by increasing membrane resistance |
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How does myelin reduce leakage of charge across the membrane and reduce membrane capacitance? |
- It creates a greater charge separation which means there is less capacitance - fewer channels under the myelin meaning there is less leakage of charge |
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What is the role of the nodes of Ranvier? |
Unmyelinated areas of the axon that are spaced so that the AP that reaches them is still above threshold and will therefore open voltage gated Na+ channels regenerating the AP and allowing it to spread further down the axon |
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What happens in Myasthenia Gravis? |
Number of functional Ach receptors is decreased meaning that as Ach release diminishes with repetitive activation neuromuscular transmission eventually fails. |
