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Fundamentals of Neuroscience > The Basis of Cell Excitability > Flashcards

The Basis of Cell Excitability Flashcards

1
Q

What is the timescale for an action potential?

A

1-2msec

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2
Q

What causes depolarisation?

A

Na+ influx

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3
Q

What is depolarisation?

A

The cell becoming less negative

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4
Q

What does depolarisation do to PNa

A

It causes the opening of Na+ channels and PNa increases

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5
Q

What causes repolarisation?

A

K+ efflux

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6
Q

What is repolarisation?

A

The return of Em to resting potential

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7
Q

What does repolarisation do to Na+ gated channels?

A

Closes them

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8
Q

What is conductance of ions?

A

It is equivalent to permeability
Measured instead of permeability, membrane acts as an electrical resistor (R)
Conductance, g=1/R
Each ion has its own conductance

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9
Q

Conductance is proportional to what?

A

To the number of open ion channels

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10
Q

Change in gion will change what?

A

Em

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11
Q

What causes cells to further depolarise?

A

opening of voltage gated Na+ ion channels

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12
Q

What causes the initial depolarisation?

A 
Synaptic activity
Generator potential (sensory neurone)
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13
Q

What does Em approach in the depolarisation phase?

A

ENa

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14
Q

What happens to Na+ channels in repolarisation?

A

They inactivate

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15
Q

When do K+ channels open?

A

As the neurone is repolarising, they open at positive values of Em

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16
Q

What is hyperpolarisation?

A

Em has returned to its initial value but K+ channels are still open
Em approaches Ek

17
Q

How is hyperpolarisation dealt with?

A

The K+ channels finally close

The leak channels restore Em to resting value

18
Q

What is the all-or-nothing principle?

A

An action potential either happens or it doesn’t. They have no difference in size or power

19
Q

What causes the all-or-nothing principle?

A

Existance of a threshold value

20
Q

What is the threshold?

A

The point at which an action potential will fire

21
Q

What is happening in the neurone at the threshold value?

A

Na+ influx is greater than K+ efflux

22
Q

What is the absolute refractory period?

A

No further action potential by any stimulus regardless of size

23
Q

What is the relative refractory period?

A

A stronger stimulus will open sufficient Na+ channels and overcome increased gK that makes the threshold greater

24
Q

Explain absolute refractory period in terms of voltage-gated channels?

A

Na+ are mostly inactivated

K+ are mostly open

25
Q

Explain relative refractory period in terms of voltage-gated channels?

A

Na+ are recovering from inactivation

K+ some are still open

26
Q

Why do action potentials not travel backwards in axons (unidirectional)?

A

The membrane behind the action potential is in the refractory period

27
Q

What is electrotonic spread?

A

The propagation of an action potential in an unmyelinated axon

28
Q

How much faster is the speed of an impulse in a myelinated neurone?

A

1000x

29
Q

What happens to the impulse in a myelinated neurone

A

Jumps between nodes of Ranvier

30
Q

What does the myelin sheath do?

A

Increases the speed of action potential conduction

31
Q

What is saltatory conduction?

A

The jumping of the impulse between gaps in the myelin sheath

32
Q

Explain how an action potential is generated?

A
  • Initial stimulus causes generator potential and starts initial depolarisation
  • Opening of voltage gated na ion channels increases gNa (sodium conductance)
  • Na influx into cells leads to further depolarisation and even greater gNa
  • Na influx is greater than K efflux
  • Em surpasses threshold value (-55mV) and approaches ENa
  • Depolarisation peaks at +40mV where Na channels inactivate and Na influx stops despite stimulus
  • Decreased gNa coincides with the opening of Voltage gated K channels.
  • This opening is delayed to prevent Em from remailing equal
  • K efflux leads to repolarisation and increased gK returns to rest.
  • Em approaches Ek at hyperpolarisation
  • Voltage gated K channels close
  • Em returns to resting value (-65mV) via leak channels.
33
Q

Why is there a delay between the peak of depolarisation and the opening of Voltage gated K channels?

A

To prevent the Em from having equal charge in/out of the cell at the peak of depolarisation.

34
Q

What is caused when voltage gated ion channels are open?

A

Depolarisation

35
Q

What is caused when voltage gated ion channels are closed?

A

Repolarisation

36
Q

What affects the speed of conduction in an axon?

A

Diameter of the axon

smaller = more constricted and therefore the conduction speed is slower.

Fundamentals of Neuroscience (16 decks)

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