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BDS2 BAMS > Action potential mechanisms > Flashcards

Action potential mechanisms Flashcards

1
Q

A potential difference exists across the membrane of all cells. What is this called?

A

The resting membrane potential

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2
Q

In the resting membrane potential what is the ICF like in respect to ECF?

A
  • ICF is negative with respect to the ECF
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3
Q

There are equal numbers of +ve and -ve charges in the ECF and ICF. How come the ICF is negative with respect to the ECF?

A
  • Because ion/charge distribution is ‘polarised’
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4
Q

Are negative charges on the inside or outside of the plasma membrane of a cell?

A
  • On the inside
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5
Q

Are positive charges on the inside or outside of the plasma membrane of a cell?

A

Outside

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6
Q

Is energy required to keep a cell at the resting membrane potential?

A

Yes

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7
Q

Are there more Na+ ions in the ECF or the ICF?

A

The ECF

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8
Q

Are there more K+ ions in the ECF or the ICF?

A

ICF

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9
Q

Does sodium want to diffuse into or out of the cell?

A

Wants to diffuse into the cell

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10
Q

Does potassium want to diffuse into or out of the ce ll?

A

Out of the cell

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11
Q

When the cell is at resting potential is the membrane permeable to Na+ ions?

A
  • No, it is impermeable
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12
Q

When the cell is at resting potential is the membrane permeable to K+ ions?

A

It is permeable

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13
Q

What does diffusion of K+ out of the cell leave an excess of inside the cell?

A
  • Leaves an excess of -ve charge inside the cell

- This potential gradient arising from diffusion is the ‘membrane potential’

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14
Q

How does a resting membrane potential arise?

A

From the separation of charges on either side of the membrane

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15
Q

What happens to the small amount of sodium That manages to leak into the cell?

A

It is expelled by the Na+/K+ pump

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16
Q

Although the RMP is due mainly to diffusion of K+ from cell interior the Na+/K+ pump also contributes. How does it do this? (2 points)

A
  • Contributes by exchanging unequal numbers of Na+ and K+

- The pump moves 3 Na+ outwards and 2 K+ inwards

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17
Q

How many Na+ ions does the Na+/K+ pump move outwards?

A

3 ions

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18
Q

How many K+ ions does the Na+/K+ pump move inwards?

A

2 ions

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19
Q

The Na+/K+ pump is ‘electrogenic’, what does this mean?

A

It produces a change in the electrical potential of a cell

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20
Q

Is ATP required for the Na+/K+ pump to work?

A

Yes

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21
Q

What is the rising phase of an action potential due to?

A

Due to a SODIUM INFLUX

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22
Q

What is the falling phase of an action potential due to?

A
  • Due to POTASSIUM EFLUX
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23
Q

What are ion channels made from?

A

Membrane proteins (more specifically transmembrane)

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24
Q

What is an ion channel?

A

An aqueous channel through the membrane

25
Q

What are to 2 types of ‘gated opening’ ion channels?

A
  • Ligand

- Voltage

26
Q

Can a channel have more than one gated opening?

A

Yes, Sodium ion channels have a 2 gate system

27
Q

What does it mean by ion channels being selective?

A

Only a specific ion can pass through that channel

28
Q

What are the 2 gates in the voltage gated sodium channel?

A
  • M-gate

- H-gate

29
Q

When the voltage-gated sodium channel is initially closed. which gate is open and which gate is closed?

A
  • m-gate closed

- h-gate open

30
Q

When the voltage-gated sodium channel is opem. which gate is open and which gate is closed?

A
  • M-gate open

- h-gate open

31
Q

When the voltage-gated sodium channel is closed and in the refractory period. which gate is open and which gate is closed?

A

m-gate open

h-gate closed

32
Q

Is an action potential an all or none response?

A

Yes

33
Q

What happens at the ‘threshold’ of the action potential?

A
  • Voltage-gated Na+ channels open
  • Na+ diffuse in -> further depolarisation
  • Positive feedback involved here
34
Q

What happens at the peak of an action potential?

A
  • Na+ channels close; voltage-gates K+ channels open
  • K+ diffuse out -> repolarisation
  • Then return to the resting membrane potential
35
Q

When is the M-gate in the Na+ ion channel involved?

A
  • In the first phase through the action potential
36
Q

When is the H-gate in the Na+ ion channel involved?

A

In the second phase through the refractory period

37
Q

Where are the M and H-gates on the Na+ ion channel located?

A

Located on the intracellular portion of the channel

this is important if you are going to block the sodium channel - have to do this from the inside of the cell

38
Q

After an AP is initiated, the neuron cannot generate another AP until the first one has ended. What is this period of excitability called?

A
  • The refractory period
39
Q

What is the refractory period due to?

A
  • Due to the inactivation of voltage-gated sodium channels
  • The inactivation (‘h’) gates are shut, and so Na+ cannot diffuse into the neuron
  • Action potentials cannot add together; they are all-or-none events
40
Q

What are the consequences of a refractory period? (4 points)

A
  • Limits the maximum firing frequency of action potentials in axons
  • Ensures unidirectional propagation of action potentials
  • Prevents summation of action potentials
  • Prevents summation of contractions in cardiac muscle - the cardiac AP lasts as long as the ventricular contraction
41
Q

What does an AP in one section of an axon set up?

A

Longitudonal direction flow

  • This depolarises adjacent ‘resting’ parts of the axons
42
Q

What happens in AP propagation?

A
  • An AP in one section of an axon sets up longitudinal current flow
  • This depolarises adjacent ‘resting’ parts of the axon
  • The AP is regenerated further along the axon
  • More current flows, and the next region of the axon is activated
  • AP’s travel along the axon as waves of depolarisation
43
Q

How does an AP travel along the length of an axon?

A
  • Current flows in ICF and ECF from +ve to -ve regions

- This current flow alters the membrane potential in adjacent regions, and the action potential ‘creeps’ along the axon

44
Q

What does the speed of AP propagation increase with?

A
  • Increases with axon diameter

- Large axons conduct impulses more rapidly than small ones

45
Q

What speeds up the process of AP conduction along an axon?

A

The presence of the myelin sheath

46
Q

Why do axons that are myelinated use more energy?

A

As the axon will have thousands of Schwann cells - large increas ein the number of cells that need energy

47
Q

What does myelin consist of?

A

Many layers of cell membranes wrapped round the axon

48
Q

Which type of cells lays down myelin?

A

Glial cells

49
Q

Myelin forms an insulating layer, what does this do?

A

Reduces leakage of current from axon

50
Q

The myelin sheath is interrupted at intervals. What are these intervals called?

A

Nodes of Ranvier

51
Q

What happens at a node of Ranvier?

A

The axon membrane is exposed to the ECF, and ion flow can occur

52
Q

What is saltatory conduction?

A
  • In myelinated nerve, the passive currents spread further along the axon
  • There are fewer regeneration steps per unit length of axon
  • Thus, the AP propagates more rapidly that in unmyelinated axons (speeds up the propagation)
53
Q

Peripheral nerves contain many axons. These axons are different in several respects. What are these differences? (2 points)

A

Size:

  • Axon diameter & conduction velocity

Function:

  • Sensory, motor
54
Q

Are A-beta fibres myelinated or unmyelinated?

A

Myelinated

55
Q

Are A-delta fibres myelinated or unmyelinated?

A

Myelinated

56
Q

Are C fibres myelinated or unmyelinated?

A
  • Unmyelinated
57
Q

What is the function of A-beta fibres?

A

Mechanoreceptors

58
Q

What are the functions of A-delta fibres? (4 points)

A
  • Mechanoreceptors
  • Thermoreceptors (cold)
  • Nociceptors
  • Chemoreceptors (taste)
59
Q

What are the functions of C fibres? (3 points)

A
  • Mechanoreceptors
  • Thermoreceptors (hot and cold)
  • Nociceptors

BDS2 BAMS (57 decks)

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