Ionic Basis Of Action Potential Flashcards

1
Q

Concentration of K+ outside cell:

A

5 mM

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2
Q

Concentration of Na+ outside cell:

A

140 mM

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3
Q

Concentration of K+ inside cell:

A

140mM

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4
Q

Concentration of Na+ inside cell:

A

10 mM

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5
Q

What would happen to a cell that is only permeable to potassium?

A

Potassium equilibrium potential would be negative as positive K+ would leave cell

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6
Q

What would happen if a cell is only permeable to sodium?

A

Sodium equilibrium potential would be positive as positive NA+ enter cell

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7
Q

What are all animal cells at rest more permeable to?

A

More permeable to K+ than Na+

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8
Q

How does resting membrane potential come about?

A

Very small number of K+ diffuse out down conc. gradient

Charge separation occurs as K+ ions not accompanied by anions

Interior electrical potential of cell becomes negative compared to extracellular solution

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9
Q

How can you record resting membrane potentials?

A

Axon in saline solution

Add KCl filled microelectrodes (one in solution, one in axon)

Use a current stimulator and oscilloscope

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10
Q

Ohm’s law:

A

V = IR

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11
Q

Why is resting potential closer to K+ equilibrium potential?

A

As cell more permeable to K+

More K+ leave than Na+ entering

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12
Q

What is depolarisation?

A

Movement of membrane potential to more positive value

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13
Q

What is repolarisation?

A

Movement of membrane potential to more negative value

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14
Q

What’s hyperpolarisation?

A

More negative than normal

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15
Q

What happens when there is an injection of current in inexcitable cell?

A

Resting membrane potential depolarises slightly

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16
Q

How are excitable membranes different to inexcitable membranes?

A

Excitable membranes have voltage-sensitive Na+ channels

17
Q

What happens when current is injected in excitable membrane?

A

Threshold potential is reached which causes conformational change to Na+ voltage-sensitive channels (they open)

Rapid depolarisation and action potential generated

18
Q

WHat happens after rapid depolarisation in excitable membrane?

A

Na+ channels quickly close again - causes repolarisation

Hyperpolarisation results

Return to resting potential

19
Q

What must happen for action potential to be generated?

A

Initial depolarisation must reach critical threshold

Depolarisation peaks around +30 mV (all-or-none response)

Repolarisation back to resting level

20
Q

How does membrane repolarisation?

A

Voltage sensitive K+ channels activated by membrane potential at threshold - open slower than Na+ channels

21
Q

Why is there hyperpolarisation?

A

As existing K+ voltage-sensitive channels still open

22
Q

Ratio of permeability at rest:

A

Na+ permeability : K+ permeability

             1            :           50
23
Q

What is the upstroke (depolarisation) caused by?

A

Rapid increase in Na+ permeability (x600)

24
Q

What is repolarisation associated with?

A

Delayed 10 fold increase in K+ permeability

25
What is voltage-gated sodium channel like at resting potential?
Closed but capable of opening -70 mV
26
What is voltage-gated sodium channel like from threshold to peak potential?
Open (activated) Rapid opening triggered by threshold potential -50mV to +30 mV
27
What is voltage-gated sodium channel like from peak to resting potential?
Closed and not capable of opening (inactivated) +30 mV to -70 mV
28
When do voltage-gated sodium channels become capable of opening again after repolarisation?
At resting potential -70 mV
29
When are voltage-gated potassium channels closed?
At resting potential Delayed opening triggered at threshold + remains closed to peak potential -70 mV to +30 mV
30
When are voltage-gated potassium channels open?
From peak potential through to after hyperpolarisation +30 mV to -80 mV
31
Why is this an example of positive feedback?
Na+ channels open -> increased Na+ permeability -> increased flow of Na+ into cell -> membrane depolarisation