Back to AI Flashcard MakerBiology /Biology IB HL - 6.5 Neurons and Synapses Part 2
What is repolarisation?
Repolarisation refers to the restoration of a membrane potential following depolarisation (i.e. restoring a negative internal charge)
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Key Terms
Term
Definition
What is repolarisation?
Repolarisation refers to the restoration of a membrane potential following depolarisation (i.e. restoring a negative internal charge)
What channels after the influx of sodium ions?
Following an influx of sodium, potassium channels open within the membrane of the axon
By what mechanism do potassium ions in/out the neuron?
As K+ ions are more concentrated inside the neuron, opening potassium channels causes a passive efflux of potassium
What does the efflux of potassium cause?
The efflux of potassium causes the membrane potential to return to a more negative internal differential (repolarisation)
What is the refractory period?
The refractory period refers to the period of time following a nerve impulse before the neuron is able to fire again
Where are sodium ions in a normal resting state?
In a normal resting state, sodium ions are predominantly outside the neuron and potassium ions mainly inside (resting potential)
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| Term | Definition |
|---|---|
What is repolarisation? | Repolarisation refers to the restoration of a membrane potential following depolarisation (i.e. restoring a negative internal charge) |
What channels after the influx of sodium ions? | Following an influx of sodium, potassium channels open within the membrane of the axon |
By what mechanism do potassium ions in/out the neuron? | As K+ ions are more concentrated inside the neuron, opening potassium channels causes a passive efflux of potassium |
What does the efflux of potassium cause? | The efflux of potassium causes the membrane potential to return to a more negative internal differential (repolarisation) |
What is the refractory period? | The refractory period refers to the period of time following a nerve impulse before the neuron is able to fire again |
Where are sodium ions in a normal resting state? | In a normal resting state, sodium ions are predominantly outside the neuron and potassium ions mainly inside (resting potential) |
What is reversed following depolarisation? | Following depolarisation (sodium influx) and repolarisation (potassium efflux), this ionic distribution is largely reversed |
What restores the resting potential during the refractory period? | Before a neuron can fire again, the resting potential must be restored via the antiport action of the sodium-potassium pump |
What are nerve impulses? | Nerve impulses are action potentials that move along the length of an axon as a wave of depolarisation |
When does depolarisation occur? | Depolarisation occurs when ion channels open and cause a change in membrane potential |
What can the channels along the axon be categorised as? | The ion channels that occupy the length of the axon are voltage-gated (open in response to changes in membrane potential) |
What does the ion channels being voltage-gated mean for depolarisation? | Hence, depolarisation at one point of the axon triggers the opening of ion channels in the next segment of the axon |
Therefore how does depolarisation spread? | This causes depolarisation to spread along the length of the axon as a unidirectional ‘wave’ |
According to what principle are action potentials generated? | Action potentials are generated within the axon according to the all-or-none principle |
What is needed for an action potential to be propagated? | An action potential of the same magnitude will always occur provided a minimum electrical stimulus is generated |
What is the threshold potential? | This minimum stimulus – known as the threshold potential (–55 mV) – is the level required to open voltage-gated ion channels |
What happens if the threshold potential is not reached? | If the threshold potential is not reached, an action potential cannot be generated and hence the neuron will not fire |
When are threshold potentials triggered? | Threshold potentials are triggered when the combined stimulation from the dendrites exceeds a minimum level of depolarisation |
What happens if the threshold potential is reached? | If the overall depolarisation from the dendrites is sufficient to activate voltage-gated ion channels in one section of the axon, the resulting displacement of ions should be sufficient to trigger the activation of voltage-gated ion channels in the next axon section |
What are oscilloscopes? | Oscilloscopes are scientific instruments that are used to measure the membrane potential across a neuronal membrane |
How is data from an oscilloscope presented? | Data is displayed as a graph, with time (in milliseconds) on the X axis and membrane potential (in millivolts) on the Y axis |
For how long will a typical action potential last? | A typical action potential will last for roughly 3 – 5 milliseconds and contain 4 key stages |
What 4 stages are shown on the graph? | resting potential; depolarisation; repolarisation; refractory period |
What is the resting potential of an oscilloscope trace? | Before the action potential occurs, the neuron should be in a state of rest (approx. –70 mV) |
What is depolarisation on an oscilloscope trace? | A rising spike corresponds to the depolarisation of the membrane via sodium influx (up to roughly +30 mV) |