Origins of the resting membrane potential Flashcards Preview

Physiology and Neuroscience > Origins of the resting membrane potential > Flashcards

Flashcards in Origins of the resting membrane potential Deck (47):
1

Why do ions migrate at different rates?

According to the size of their hydrated molecules

2

How are migration rate of ions measured?

Under standard conditions

3

How are migration rates expressed?

In terms of the mobility of an ion

4

What is another way of saying mobility potentials?

Diffusion potentials

5

What does the magnitude of diffusion potentials depend on?

Ion salts

6

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

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

7

Why does NaCl cause a larger potential than KCl?

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

8

What is a semi-permeable membrane?

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

9

What is the mobility of an impermeant ion?

Zero

10

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

Down their concentration gradient
Carry positive charge

11

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

They do not move as they are impermeant

12

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

Positive charge build up in the right compartment

13

What then steps in?

Electrical gradient which opposes the movement of K ions

14

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

Electrical gradient equals the concentration
The system is in equilibrium

15

What does Em stand for?

Electrical membrane potentail

16

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

Remains indefinitely since the unequal distribution of ions remain indefinitely

17

What are the major impermeant anions in cells?

Proteins carrying net negative charge, including neurons

18

What is the resting membrane potential inside the cell?

-73mV

19

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

K+

20

What is the permeability of K+ due to?

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

21

What are these selective channels called?

Leak channels

22

What do leak channels allow?

A very small number of Na+ ions to pass through

23

How quickly does K+ diffuse?

Very quickly

24

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

In opposite directions

25

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

When these two forces exactly match each other

26

How do the electrical and concentration gradients reach equilibrium?

Electrical gradient must increase slightly from the resting Em

27

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

-74 mV

28

Why is the inside of the cell negative?

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

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

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

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

Initially act in the same direction

31

How should sodium enter the cell?

Very quickly

32

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

Permeability for Na+ is very low

33

When is a Na+ equilibrium reached?

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

34

What is the equilibrium potential for Na+?

ENa= + 54mV

35

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

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

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

Across the membrane

37

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

Ions are moved aross their concentration gradients

38

How does the exchange pump consume energy?

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

39

Why is the sodium potassium pump electrogenic?

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

40

What is intracellular recording?

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

41

What is extracellular recording?

Measures electrical activity between two points outside the cell

42

What is the resting potential mainly dictated by?

K+

43

What is the threshold in an action potential?

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

What is the rising phase of an action potential?

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

45

What is the overshoot in an action potential?

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

46

What is the falling phase in an action potential?

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

What is the undershoot in an action potential?

The system is driven towards EK, before returning
to its resting state