Origins of the resting membrane potential

Question 1

Why do ions migrate at different rates?

Answer 1

According to the size of their hydrated molecules

Question 2

How are migration rate of ions measured?

Answer 2

Under standard conditions

Question 3

How are migration rates expressed?

Answer 3

In terms of the mobility of an ion

Question 4

What is another way of saying mobility potentials?

Answer 4

Diffusion potentials

Question 5

What does the magnitude of diffusion potentials depend on?

Answer 5

Ion salts

Question 6

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

Answer 6

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

Question 7

Why does NaCl cause a larger potential than KCl?

Answer 7

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

Question 8

What is a semi-permeable membrane?

Answer 8

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

Question 9

What is the mobility of an impermeant ion?

Answer 9

Zero

Question 10

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

Answer 10

Down their concentration gradient

Carry positive charge

Question 11

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

Answer 11

They do not move as they are impermeant

Question 12

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

Answer 12

Positive charge build up in the right compartment

Question 13

What then steps in?

Answer 13

Electrical gradient which opposes the movement of K ions

Question 14

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

Answer 14

Electrical gradient equals the concentration

The system is in equilibrium

Question 15

What does Em stand for?

Answer 15

Electrical membrane potentail

Question 16

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

Answer 16

Remains indefinitely since the unequal distribution of ions remain indefinitely

Question 17

What are the major impermeant anions in cells?

Answer 17

Proteins carrying net negative charge, including neurons

Question 18

What is the resting membrane potential inside the cell?

Answer 18

-73mV

Question 19

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

Answer 19

K+

Question 20

What is the permeability of K+ due to?

Answer 20

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

Question 21

What are these selective channels called?

Answer 21

Leak channels

Question 22

What do leak channels allow?

Answer 22

A very small number of Na+ ions to pass through

Question 23

How quickly does K+ diffuse?

Answer 23

Very quickly

Question 24

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

Answer 24

In opposite directions

Question 25

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

Answer 25

When these two forces exactly match each other

Question 26

How do the electrical and concentration gradients reach equilibrium?

Answer 26

Electrical gradient must increase slightly from the resting Em

Question 27

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

Answer 27

-74 mV

Question 28

Why is the inside of the cell negative?

Answer 28

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

Question 29

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

Answer 29

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

Question 30

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

Answer 30

Initially act in the same direction

Question 31

How should sodium enter the cell?

Answer 31

Very quickly

Question 32

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

Answer 32

Permeability for Na+ is very low

Question 33

When is a Na+ equilibrium reached?

Answer 33

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

Question 34

What is the equilibrium potential for Na+?

Answer 34

ENa= + 54mV

Question 35

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

Answer 35

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

Question 36

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

Answer 36

Across the membrane

Question 37

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

Answer 37

Ions are moved aross their concentration gradients

Question 38

How does the exchange pump consume energy?

Answer 38

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

Question 39

Why is the sodium potassium pump electrogenic?

Answer 39

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

Question 40

What is intracellular recording?

Answer 40

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

Question 41

What is extracellular recording?

Answer 41

Measures electrical activity between two points outside the cell

Question 42

What is the resting potential mainly dictated by?

Answer 42

K+

Question 43

What is the threshold in an action potential?

Answer 43

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

Question 44

What is the rising phase of an action potential?

Answer 44

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

Question 45

What is the overshoot in an action potential?

Answer 45

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

Question 46

What is the falling phase in an action potential?

Answer 46

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

Question 47

What is the undershoot in an action potential?

Answer 47

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