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1st Year: Neuroscience Keele > Lecture 8: Action Potential > Flashcards

Lecture 8: Action Potential Flashcards

1
Q

How can Membrane potential can be visualised in real-time?

A

with an oscilloscope or specialised software

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2
Q

what are the 5 phases of action potential ?

A
  1. Resting:The membrane is at the RMP (–65 mV).
  2. Rising phase: a rapid depolarisation of Vm.
  3. Overshoot: inside of the neuron is now positive relative to the outside.
  4. Falling phase: rapid repolarisation 1 of Vm.
  5. Undershoot: inside of the neuron is now more negative than at rest (hyperpolarised).
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3
Q

whats it called when membrane potential increases, positive to rest?

A

depolarisation

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4
Q

whats it called when membrane potential decreases?

A

repolarisation

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5
Q

what will the Injection of positive current into a neuron do?

A

depolarise the membrane potential

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6
Q

The _______ the stimulus, the _____ action potential a neurone will generate

A
  1. stronger

2. more

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7
Q

The magnitude of each action potential is the ____.

A

same

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8
Q

what does tonic firing in stellate neurones look like?

A

spikes are very close together

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9
Q

what does Spike adaptation is medium pyrimidal neurons look like?

A

spikes are further apart

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10
Q

Some neurons can be toggled into more than one firing mode depending on their _____ _____.

A

membrane potential

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11
Q

Na+/K+ pumps maintain what?

A

concentration gradients across the membrane

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12
Q

Astrocytes buffer extracellular ______ concentrations.

A

potassium

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13
Q

what’s needed for a functioning nervous system?

A

Negative charge inside of a neurone is a requirement for a functioning nervous system.

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14
Q

what are the two states of a neuron?

A

action and resting

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15
Q

what are the conditions at rest?

A

there is a large concentration and electrostatic push on sodium to enter a neuron

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16
Q

what happens at an action potential?

A
  • Na+ rushing into the neurone makes the inside more positive than normal.
  • The membrane becomes permeable to Na+, diffusion and electrostatic pressure push Na+ into the neurone.
  • for an instant membrane eis more permeable to Na+.
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17
Q

The _____ _______ must cross the ______ in order for a neuron to have a action potentials.

A

membrane potential

threshold

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18
Q

at the threshold what is the membrane more permeable towards?

A

sodium

19
Q

Are voltage-gated channels sensitive to changes in membrane potential?

A

yes

20
Q

what happens at threshold, linked to activation of bolted gated Na+ channels ?

A

interior of the cell is positive enough to repel the positively-charged voltage sensor of the Na+ channel. Allowing Na+ through the pore.

21
Q

what holds the Na+ channels closed?

A

Negative interior attracts positive charge of voltage sensor and holds channel closed. More positive interior repels voltage sensor thereby opening the channel.

22
Q

what happens when sodium channels pop open for a short time?

A
  1. Depolarisation to Threshold opens Na+ channels.
  2. Na+ channels inactivate a short time later (<1 msec).
  3. A globular (glob) portion of the channel blocks the open pore.
  4. Channels remain inactivated until repolarisation to rest.
23
Q

what does depolarisation of a neurone lead too?

A

Depolarising a neuron leads to Na+ channel activation which leads to further depolarisation and the opening of more Na+ channels!

24
Q

An action potential is initiated at the _____ _____.

A

axon hillock

25
Q

where are some Na+ channels located?

A

from the hillock down the entire length of the axon

26
Q

what do Dendrites do?

A

Dendrites receive signals from other neurons.

27
Q

what happens in the rising phase?

A
  • The positive interior repels the voltage sensor thereby opening the channel
  • Voltage-gated Na+ channels open at Threshold.
  • Opening of voltage-gated Na+ channels; Vm depolarises.
  • Inactivation of Na+ channels.
28
Q

what happens in the falling phase?

A
  • K+ flows out of the neurone down both its concentration and voltage gradients.
29
Q

Voltage-gated K+ channels are known as what, and why?

A

Voltage-gated K+ channels are known as delayed rectifiers since they open about 1 ms after Na+ channels.

30
Q

Voltage-gated K+ channels _______ at _______, too, but they take ______ to open

A

activate
threshold
longer

31
Q

Are K+ channels involved in action potential the same as those that mediate RMP?

A

no they are not the same

32
Q

During the undershoot, the permeability of the membrane to K+ is what?
and this causes what?

A

higher than it is at rest causing the Vm to reach EK.

33
Q

what does the refractory periods do the regeneration of an action potential?

A

makes it difficult or impossible.

34
Q

what is the Absolute Refractory Period?

A

when Na+ channels are still inactivated therefore making it IMPOSSIBLE to generate another action potential.

35
Q

what is the Relative Refractory Period?

A

Na+ channels have de- inactivated and it takes more positive current to bring the neuron to ring threshold

36
Q

what happens to channels at rest?

A

At rest, both voltage-gated Na+ and voltage-gated K+ channels are closed.

37
Q

what is the permeability of the membrane like at rest?

A

The permeability of the membrane for Na+ is low, but high for K+ since background K+ channels are open helping to maintain the RMP.

38
Q

what happens at the rising phase of the action potential?

A
  • If the neuron is depolarised to Threshold then both voltage-gated Na+ and voltage- gated K+ channels are activated.
  • Increased positive charge in the neuron repels the voltage sensors on both voltage-gated Na+ and K+ channels.
  • Voltage-gated Na+ channels pop open and Na+ immediately flows into the neurone bringing Vm close to ENa (~ +40 mV) in <1 ms.
  • K+ channels slowly start to open.
39
Q

what happens at the overshoot phase ?

A
  • Voltage-gated Na+ channels inactivate before Vm reaches ENa due to the pore becoming blocked from the inside.
  • In less than 1 ms the Vm nearly reaches ENa, but voltage-gated Na+ channels inactivate. K+ channels have yet to fully open.
  • Na+ channels are still open, but they are inactivated due to the block by the globular portion of the channel. Voltage- gated K+ channels are still slowly opening.
40
Q

wha happens at the falling phase of the action potential?

A
  • Voltage-Gated K+ channels open and K+ leaves the neuron and repolarises Vm to a more negative value.
  • During repolarisation, Na+ channels are open, but inactivated, and K+ is pushed out of the neuron down its concentration and voltage gradients.
  • The high concentration of K+ inside of the neuron together with the fact that the Vm is close to ENa forces K+ out through the now fully-open voltage-gated K+ channels.
41
Q

what happens at the The absolute refractory period?

A
  • Na+ channels close, but K+ channels stay open which hyperpolarises the membrane to EK (–80 mV).
  • The increased membrane permeability to K+ allows it to continue flowing down its concentration gradient out of the neuron bringing Vm to EK.
  • Na+ channels, are inactivated thereby preventing the initiation of another action potential.
42
Q

what happens at the relative refractory period?

A
  • Na+ channels finally de-inactivate and K+ channels have yet to fully close. The membrane is still hyperpolarised.
  • It takes much less positive current to bring the neuron to ring Threshold when Vm is at rest at –65 mV as opposed to when it is hyperpolarised to –80 mV
  • It is now possible to generate another action potential, but it takes significantly more positive current to bring the neuron to Threshold.
43
Q

what does Lidocane do?

A

This chemical inhibits action potentials by binding to and preventing Na channels from opening.

1st Year: Neuroscience Keele (28 decks)

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