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BDS2: LA Symposium > Action Potential > Flashcards

Action Potential Flashcards

1
Q

What is the range of resting membrane potentials across all cells?

A

20-90mV

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2
Q

What charge does the intra cellular fluid have with respect to the extra cellular fluid?

A

Negative charge

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3
Q

List the concentration values of sodium, potassium and chloride ions in EXF and ICF

A
  1. Sodium:
    •ECF = 145mM
    •ICF = 15mM
  2. Potassium:
    •ECF = 4mM
    •ICF = 150mM
  3. Chloride:
    •ECF = 110mM
    •ICF = 10mM
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4
Q

What ion is easily able to diffuse out of the ‘resting’ cell membrane?

A

Potassium

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5
Q

What creates resting membrane potential?

A

Potassium ions constantly diffuse out of the cell and leave excess -ve charge in the cell membrane.
The potential gradient arising from diffusion is the ‘resting membrane potential’

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6
Q

Summarise resting membrane potential

A
  1. RMP arises from the separation of charges on either side of the membrane
  2. The RMP is due mainly to diffusion of potassium ions from the cell interior through potassium ion channels
  3. The small amount of sodium ions that leak into the cell are expelled by the sodium/potassium pump
  4. The pump also contributes to RMP as it moves 3 K+ ions in and 2 Na+ ions out
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7
Q

What is the Action potential threshold value?

Why is this?

A

•55mV

  • at this point the voltage gated sodium channels open due to influx of sodium
  • this is the start of the rising phase
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8
Q

What causes the falling phase in action potential?

A

Efflux of potassium ions through voltage gated K- channels

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9
Q

Describe the three possible stages of a voltage-gated sodium channel

A
  1. Channel closed
    - m-gate closed
    - h-gate open
    (RMP)
  2. Channel open
    - m-gate open
    - h-gate open
    (Threshold level)
  3. Channel closed (refractory)
    - m-gate open
    - h-gate closed
    (Hyperpolerisation)
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10
Q

Summarise action potential

A
  1. At ‘threshold’:
    - voltage-gated Na+ channels open
    - Na+ diffuse in = further depolarisation
    - positive feedback involved here
  2. Peak
    - Na+ channels close; voltage-gated K+ channels open
    - potassium ions diffuse out = repolarisation
  3. Return to resting membrane potential
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11
Q

What name is given to the period of inexcitability that occurs after an AP is initiated?

A

Refractory period

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12
Q

What causes the refractory period to occur?

A

In activation of voltage gated sodium channels

- the inactivation (‘h’) gates are shut, so Na+ can’t diffuse into the neuron

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13
Q

What consequences are caused by the refractory period?

A
  1. Limits firing frequency of action potentials in axons
  2. Ensures unidirectional propagation of action potentials
  3. Prevents summation of action potentials
  4. Prevents summation of contractions in cardiac muscle - the cardiac AP lasts as longs as the ventricular contraction
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14
Q

Explain how action potential travels along axons

A
  1. An AP in one section of the axon sets up longitudinal current flow
  2. This depolarises adjacent ‘resting’ parts of the axon
  3. The AP is regenerated further along the axon
  4. More current flows and the next region of the axon is activated
  5. Action potentials travel along the axon as waves of depolarisation
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15
Q

In what direction does current flow along the axon?

A

Positive to negative regions

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16
Q

What factors increase the speed of AP propagation?

A
  1. Increased axon diameter
    - however a very large diameter increase is needed to significantly increase conduction speed in unmyelinated axons
  2. Myelin
17
Q

Briefly describe myelin and how it relates to nerve axons

I.e appearance, function

A
  1. Myelin consists of many layers of cell membranes wrapped around the axon
  2. Myelin inlaid down by glial cells
  3. Myelin forms an insulating layer, reducing leakage of current from axon
  4. Myelin sheath is interrupted at intervals (nodes of ranvier)
18
Q

What is the main function of the nodes of Ranvier?

A

Here, the axon membrane is exposed to the ECF and ion flow can occur to generate AP

19
Q

Why does AP propagate more rapidly in myelinated axons?

A
  1. In myelinated nerves, the passive currents spread further along the axon
  2. There are fewer regeneration steps per unit length of axon
  3. Therefore AP propagates more rapidly
20
Q

What type of functions do peripheral nerve axons have?

A

Sensory

Motor

21
Q

What axon types are myelinated?

A
  1. A beta and A delta fibres

2. C fibres are unmyelinated

22
Q

What function do A beta axons have?

A

Mechanoreceptors

23
Q

What functions do A delta axons have?

A
  1. Mechanoreceptors
  2. Thermoreceptors
  3. Nociceptors
  4. Chemoreceptors
24
Q

What functions do C axons have?

A
  1. Mechanoreceptors
  2. Thermoreceptors
  3. Nociceptors

BDS2: LA Symposium (7 decks)

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