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Physiology and Neuroscience Semester 2 > Resting and action potentials > Flashcards

Resting and action potentials Flashcards

1
Q

Why do ions migrate at different rates?

A

According to the size of their hydrated molecules

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2
Q

How are migration rate of ions measured?

A

Under standard conditions

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3
Q

How are migration rates expressed?

A

In terms of the mobility of an ion

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4
Q

What is another way of saying mobility potentials?

A

Diffusion potentials

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5
Q

What does the magnitude of diffusion potentials depend on?

A

Ion salts

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6
Q

What is the difference in diffusion potentials with KCl and NaCl?

A

KCl- barrier removal will cause a slight change in potentials, lasting until all ions are dispersed evenly
NaCl- barrier remval will cause a much larger potential

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7
Q

Why does NaCl cause a larger potential than KCl?

A

As there is a bigger difference in mobility’s of Na and Cl ions

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8
Q

What is a semi-permeable membrane?

A

A membrane that is selectively permeable to some ions, but impermeable to others

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9
Q

What is the mobility of an impermeant ion?

A

Zero

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10
Q

In an electrical membrane potential what direction and charge is on the K ions?

A

Down their concentration gradient

Carry positive charge

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11
Q

In an electrical membrane potential what direction and charge is on the Cl ions?

A

They do not move as they are impermeant

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12
Q

What does the electrical membrane potential of K and Cl result in?

A

Positive charge build up in the right compartment

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13
Q

What then steps in?

A

Electrical gradient which opposes the movement of K ions

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14
Q

What is the result when there is no further net movement of K ions?

A

Electrical gradient equals the concentration

The system is in equilibrium

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15
Q

What does Em stand for?

A

Electrical membrane potential

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16
Q

Does the Em remain after the system is back in equilibrium?

A

Remains indefinitely since the unequal distribution of ions remain indefinitely

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17
Q

What are the major impermeant anions in cells?

A

Proteins carrying net negative charge, including neurons

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18
Q

What is the resting membrane potential inside the cell?

A

-73mV

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19
Q

What are the most permeant through the membrane of a neurone at rest?

A

K+

20
Q

What is the permeability of K+ due to?

A

The existence of ion channels in the membrane that are open in the resting state and are most selective for K+ ions

21
Q

What are these selective channels called?

A

Leak channels

22
Q

What do leak channels allow?

A

A very small number of Na+ ions to pass through

23
Q

How quickly does K+ diffuse?

A

Very quickly

24
Q

How do the concentration and electrical gradient for K+ ions act?

A

In opposite directions

25
Q

When is an equilibrium struck between the concentration and electrical gradients?

A

When these two forces exactly match each other

26
Q

How do the electrical and concentration gradients reach equilibrium?

A

Electrical gradient must increase slightly from the resting Em

27
Q

What is the value of the equilibrium potential for K+?

A

-74 mV

28
Q

Why is the inside of the cell negative?

A

Na+ and K+ pump
3 Na+ pumped out of the cell
2 K+ pumped into the cell
Accumulates to give more positive ions outside the cell, and more negative ions inside the cell

29
Q

Why would sodium like to move down it’s concentration gradient but can’t?

A

As there is a higher number of Na+ inside the cell and it would like to go into the cell but can’t because of the membrane

30
Q

What is the concentration and electrical gradient for Na+ ions?

A

Initially act in the same direction

31
Q

How should sodium enter the cell?

A

Very quickly

32
Q

Why doesn’t sodium move very quickly into the cell?

A

Permeability for Na+ is very low

33
Q

When is a Na+ equilibrium reached?

A

When the cell interior becomes sufficiently positively charged to exactly counteract the inward concentration gradient

34
Q

What is the equilibrium potential for Na+?

A

ENa= + 54mV

35
Q

Why must the resting membrane potential be a K+ potential?

A

As the resting intracellular membrane potential is -73mV and with K+ its -74mV whereas with Na+ it’s 54mV meaning it had to be a K+ potential

36
Q

Where does the Na+/K+ exchange pump act?

A

Across the membrane

37
Q

What happens to Na+ and K+ ions in this exchange pump?

A

Ions are moved aross their concentration gradients

38
Q

How does the exchange pump consume energy?

A

As the exchange of ions is coupled to the splitting of ATP

39
Q

Why is the sodium potassium pump electrogenic?

A

As it produces a change in the electrical potential of a cell.

40
Q

What is intracellular recording?

A

Measures the voltage across or passing through membranes by inserting an electrode inside the cell

41
Q

What is extracellular recording?

A

Measures electrical activity between two points outside the cell

42
Q

What is the resting potential mainly dictated by?

A

K+

43
Q

What is the threshold in an action potential?

A

The level of depolarisation required to cause an increase in Na+ permeability (pNa)
Beyond this point the action potential is an ‘all-or-none’event

44
Q

What is the rising phase of an action potential?

A

The rapid depolarisation occurs as the large driving forces causing Na+ entry (negative potential inside and concentration gradient) come into play

45
Q

What is the overshoot in an action potential?

A

The inside of the neurone becomes negative to the outside, as the system is driven towards ENa

46
Q

What is the falling phase in an action potential?

A

The switch from high pNa to high pK allows the driving forces causing K+ exit (+ve potential inside and concentration gradient) to come into play

47
Q

What is the undershoot in an action potential?

A

The system is driven towards EK, before returning

to its resting state

Physiology and Neuroscience Semester 2 (20 decks)

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