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Physiology and Neuroscience > The Action Potential and its propagation > Flashcards

The Action Potential and its propagation Flashcards

1
Q

How often are leak channels open?

A

All the time

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2
Q

How often are gated channels open?

A

Open in response to particular events e.g. a voltage change

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3
Q

What are some functional elements of voltage-gated ion channels?

A

Selectivity filter
Voltage sensor
Activation gate
Inactivation gate

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4
Q

What is the selectivity filter for?

A

Na+ and K+

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5
Q

What is the voltage sensor for ?

A

Na and K channels

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6
Q

What is the activation gate for?

A

Na and K channels

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7
Q

What is the inactivation gate for?

A

Na channel only

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8
Q

What are the different states for a voltage-gated channels for Na+?

A
  1. Closed
  2. Open
  3. Inactivated
  4. Closed
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9
Q

What are the different states for a voltage-gated channels for K+?

A
  1. Closed
  2. Open (1ms delay)
  3. Closed
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10
Q

When do the Na+ channels close?

A

When the K+ channels open

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11
Q

What is patch clamp recording?

A

Electrode up against the cell measuring a patch of membrane without entering the cell

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12
Q

How does the electrode measure the membrane without entering the cell?

A

By applying suction down the membrane to pull some of the membrane against the electrode

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13
Q

What do you use the electrode to do?

A

Create a small depolarisation

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14
Q

During a patch clamp recording what is the state of the cell at rest?

A

Na channels closed

K channels closed

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15
Q

During a patch clamp recording what is the state of the cell at on depolarisation immediately?

A

Na channels open (activation)
pNA increases
Em is driven down towards ENa
K channels still closed

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16
Q

During a patch clamp recording what is the state of the cell at depolarisation with a delay?

A 
Na inactivation, gates close
Na channels are closed
K channels open 
pK increases
Em is driven back to Ek
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17
Q

During a patch clamp recording what is the state of the cell has gone through the method?

A

Na activation gates closing
Na inactivation gates re-opening
K channels closing

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18
Q

What does the Na+ K+ pump act in the background to do?

A

Move Na and K ions back to their original places

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19
Q

Is the Na+/K+ essential?

A

No

A nerve can support about 10,000 action potentials even when the pump is poisoned

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20
Q

What can be seen by recording 2 points along an axon?

A

Than an action potential (AP) moves away from the point of electrical stimulation (stimulus electrode)

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21
Q

What is an electrotonic currrent/ local current?

A

Current flowing passively along an axon decays with distance beyond the block

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22
Q

What do cable properties of the membrane dictate?

A

Decay of this current

23
Q

What is electrotonic spread?

A

Detriment and voltage faults

Tells time

24
Q

What is the stimulus applied to the axon hillock to create an action potential?

A

Graded potential

25
Q

What are graded potentials?

A

A flow of positive charge

26
Q

Once an action potential occurs in the axon hillock what happens?

A

A flow of local currents allowing each new part of the membrane to progress along the membrane until the full membrane has been propagated

27
Q

Why doesn’t the local current flow backwards and create an action potential in the backward direction?

A

Flows backwards but doesn’t trigger an action potential because the voltage gated channels in the previous segments are in a refractory period meaning they can’t be activated again

28
Q

Why can’t channels be re-activated once in the refractory period?

A

Channels closed by ball and chain mechanism

When ball is in the channel the channel is inactive and can’t be triggered again

29
Q

What is the AP of the membrane at the peak?

A

Negative inside to the outside

30
Q

What occurs as a result after the peak of a AP?

A

A longitudinal electrical gradient inside the axon

31
Q

What does the longitudinal electrical gradient cause?

A

An electronic current to flow away from the point of the AP

32
Q

What happens as a result of the electronic current flowing away into the next segment of the membrane?

A

The membrane ahead of the AP becomes depolarised

33
Q

What then happens to this new depolarised part of the membrane?

A

Reaches threshold and a new AP exists

34
Q

What is repetition of this process known as?

A

Action Potential (AP) Propagation

35
Q

How fast and often do AP potentials occur during AP propagation?

A

Occur rapidly, so that the AP also conducts rapidly (rates in the range 1-10 m s-1 are typical)

36
Q

What does the electronic current release?

A

The potential energy that exists all along the nerve in the form of the electrical gradient and the concentration gradients for Na+ (and later K+)

37
Q

Which direction does electronic current flow if a point is electrically depolarised using an electrode?

A

Both directions resulting in an AP propagation along both directions of the axon

38
Q

What factors affect AP conduction velocity?

A

The effect of axon diameter

The effect of myelination

39
Q

What are possible effects of the axon diameter?

A

Conduction velocity is a function of axon diameter axons present less internal resistance to current flow (before it eventually leaks out)
This is the basis for the high conduction velocities in giant axons

40
Q

What are the possible effects of myelination?

A

Conduction velocity also depends on the extent of electrical insulation around the axon. This increases the rate of spread of electrotonic current
This is the basis for the higher conduction velocities in myelinated nerves
Myelin is formed by Schwann cells, which wrap tightly around the axons (the internodes) and leave only small uninsulated patches (nodes of Ranvier)

41
Q

What does the salutatory mechanism rely on?

A

Voltage-gated channels at the nodes

42
Q

Where are the density channels highest?

A

Density channels at nodes is extremely high (3000 micrometers2) compared with an unmyelinated nerve (300micrometers2)

43
Q

What does high density also increase?

A

Conduction velocity since the membrane comes to threshold a greater rate

44
Q

Why is there no voltage-gated channels along the internode?

A

They are not involved in AP production

45
Q

What does the density of voltage-gated channels in a patch of membrane determine?

A

Electrical excitability

46
Q

What is the membrane of an unmyelinated axon?

A

Electrically excitable

47
Q

What are patches with even greater densities of channels?

A

Particularly sensitive to electrotonic currents

48
Q

What is the membrane of an internode?

A

Electrically inexcitable and cannot transmit an AP19

49
Q

Where are extremely sensitive patches with high densities also found?

A

Where an AP is initiated naturally in a neurone
E.g. Axon hillock or spike initation zone (SIZ)
Sensory ending of a mechano-sensory neurone

50
Q

What are the dendritic membrane and soma of nerve cells?

A

Electrically inexcitable

Site where decision is made whether or not to initiate an AP

51
Q

What type of events are APs?

A

Discrete

52
Q

What does an AP represent?

A

An AP represents one pulse in a frequency code, which is very effective mechanism for transmitting information, and is resistant to perturbation (noise)

53
Q

How is information contained in an AP?

A

Both frequency and the pattern of activity

Physiology and Neuroscience (40 decks)

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