Depolarization

Depolarization: a sudden change in membrane potential – usually from a (relatively) negative to positive internal charge
In response to a signal initiated at a dendrite, sodium channels open within the membrane of the axon
As Na+ ions are more concentrated outside of the neuron, the opening of sodium channels causes a passive influx of sodium
The influx of sodium causes the membrane potential to become more positive (depolarization)

Repolarization

Repolarization: the restoration of a membrane potential following depolarization (i.e. restoring a negative internal charge)
Following an influx of sodium, potassium channels open within the membrane of the axon
As K+ ions are more concentrated inside the neuron, opening potassium channels causes a passive efflux of potassium
The efflux of potassium causes the membrane potential to return to a more negative internal differential (repolarization)

Refractory period: the period of time following a nerve impulse before the neuron is able to fire again
In a normal resting state, sodium ions are predominantly outside the neuron and potassium ions mainly inside (resting potential)
Following depolarization (sodium influx) and repolarization (potassium efflux), this ionic distribution is largely reversed
Before a neuron can fire again, the resting potential must be restored via the antiport action of the sodium-potassium pump

Nerve impulses: action potentials that move along the length of an axon as a wave of depolarization
Depolarization occurs when ion channels open and cause a change in membrane potential
The ion channels that occupy the length of the axon are voltage-gated (open in response to changes in membrane potential)
Hence, depolarization at one point of the axon triggers the opening of ion channels in the next segment of the axon
This causes depolarization to spread along the length of the axon as a unidirectional ‘wave’
Action potentials are generated within the axon according to the all-or-none principle
An action potential of the same magnitude will always occur provided a minimum electrical stimulus is generated
- This minimum stimulus – known as the threshold potential (–55 mV) – is the level required to open voltage-gated ion channels
If the threshold potential is not reached, an action potential cannot be generated and hence the neuron will not fire
Threshold potentials are triggered when the combined stimulation from the dendrites exceeds a minimum level of depolarization
If the overall depolarization 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

Depolarization: a sudden change in membrane potential – usually from a (relatively) negative to positive internal charge
In response to a signal initiated at a dendrite, sodium channels open within the membrane of the axon
As Na+ ions are more concentrated outside of the neuron, the opening of sodium channels causes a passive influx of sodium
The influx of sodium causes the membrane potential to become more positive (depolarization)

Repolarization: the restoration of a membrane potential following depolarization (i.e. restoring a negative internal charge)
Following an influx of sodium, potassium channels open within the membrane of the axon
As K+ ions are more concentrated inside the neuron, opening potassium channels causes a passive efflux of potassium
The efflux of potassium causes the membrane potential to return to a more negative internal differential (repolarization)

Refractory period: the period of time following a nerve impulse before the neuron is able to fire again
In a normal resting state, sodium ions are predominantly outside the neuron and potassium ions mainly inside (resting potential)
Following depolarization (sodium influx) and repolarization (potassium efflux), this ionic distribution is largely reversed
Before a neuron can fire again, the resting potential must be restored via the antiport action of the sodium-potassium pump

Nerve impulses: action potentials that move along the length of an axon as a wave of depolarization
Depolarization occurs when ion channels open and cause a change in membrane potential
The ion channels that occupy the length of the axon are voltage-gated (open in response to changes in membrane potential)
Hence, depolarization at one point of the axon triggers the opening of ion channels in the next segment of the axon
This causes depolarization to spread along the length of the axon as a unidirectional ‘wave’
Action potentials are generated within the axon according to the all-or-none principle
An action potential of the same magnitude will always occur provided a minimum electrical stimulus is generated
- This minimum stimulus – known as the threshold potential (–55 mV) – is the level required to open voltage-gated ion channels
If the threshold potential is not reached, an action potential cannot be generated and hence the neuron will not fire
Threshold potentials are triggered when the combined stimulation from the dendrites exceeds a minimum level of depolarization
If the overall depolarization 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