Membrane and Action Potentials

Question 1

What are the properties of diffusion?

Answer 1

Over short distances
Spontaneous
No energy input required

Question 2

What is flux?

Answer 2

The number of molecules that cross a unit area per unit of time

Question 3

What is voltage?

Answer 3

Potential difference

Generated by ions to produce a charge gradient

Question 4

What is current?

Answer 4

Movement of ions due to a potential difference

Question 5

What is resistance?

Answer 5

Barrier that prevent the movement of ions

Question 6

How do we measure membrane potential?

Answer 6

A reference electrode is place outside the cell (Zero volt level)
Another electors places inside the cell
Measures voltage difference that is negative compared with outside

Question 7

Why do we need ion channels?

Answer 7

Lipid cell membrane is a barrier to ion movement

Channels can be selective for different types of ion

Question 8

What is electrochemical equilibrium?

Answer 8

Achieved the electrical force prevents further diffusion across the membrane

Question 9

How can equilibrium potential be calculated?

Answer 9

The Nernst equation

Question 10

What are typical concentrations of K+?

Answer 10

150mM inside

5mM outside

Question 11

What are typical concentrations of Na+?

Answer 11

10mM inside

150mM outside

Question 12

What is the equilibrium potential for K+?

Answer 12

Ek= -90mV

Question 13

What is the equilibrium potential for Na+?

Answer 13

ENa= +72mV

Question 14

Why do membrane potentials not set at EK or ENa?

Answer 14

Membranes have mixed K+ and Na+ permeability

Question 15

How can we describe resting membrane potential?

Answer 15

The Goldman-Hodgkin-Katz (GHK) equation

Takes into account K+/Na+/Cl- concentrations

Question 16

Define depolarisation

Answer 16

Membrane potential increases from negative towards 0mV

Question 17

Define repolarisation

Answer 17

Membrane potential decrease towards resting potential (becomes more negative)

Question 18

Define overshoot

Answer 18

Membrane potential becomes more positive

Question 19

Define hyperpolarisation

Answer 19

Membrane potential decreased beyond resting potential

Question 20

What are graded potentials?

Answer 20

Change in membrane potential in response to stimulation
Occurs at synapses an in sensory receptors
Contribute to initiating or preventing action potentials

Question 21

What happens as an impulse propagates?

Answer 21

Charge leaks

Question 22

In what cells do action potentials occur in?

Answer 22

All excitable cells
Mainly neutrons and muscle cells
Also some endocrine tissues

Question 23

What does permeability of the membrane depend on?

Answer 23

Conformational state of ion channels

Question 24

What does the conformational state of ion channels depend on?

Answer 24

Opened by membrane depolarisation
Inactivated by sustained depolarisation
Closed by membrane hyper-polarisation/ repolarisation

Question 25

What are the 5 phases of action potential?

Answer 25

``` Resting membrane potential Depolarising stimulus Upstroke Repolarisation After-hyperpolarisation ```

Question 26

What's the deal with Phase I?

Answer 26

Permeability for K>Na

Question 27

What's the deal with Phase II?

Answer 27

The stimulus depolarise the membrane potential | Moves it in the positive direction towards threshold

Question 28

What's the deal with Phase III?

Answer 28

Starts at threshold potential Na+ channels open quickly and Na+ enter cell K+ channels open slowly and K+ leaves the cell

Question 29

What's the deal with Phase IV?

Answer 29

VGSC close and Na+ entry stops More VGKC open and remain open K+ leaves cell Absolute refractory period

Question 30

What's the deal with Phase V?

Answer 30

VGKC are still open K+ continuaste leave the cells down electrochemical gradient Membrane potential moves close to K+ equilibrium Some VGKC's close Membrane potential returns to resting potential Relative refractory period

Question 31

What's the deal with passive propagation?

Answer 31

Only resting K+ channels open | Internal and membrane resistance alters propagation distance and velocity

Question 32

How is an AP propelled down the axon?

Answer 32

Active area at peak of AP | Local current flow depolarises adjacent region toward threshold

Question 33

Where are VGCs mainly found?

Answer 33

At nodes

Question 34

What influences conduction velocity?

Answer 34

Axon diameter Myelination Reduced with reduced diameter and myelination Cold Anoxia Compression Drugs

Question 35

Wh

Answer 35

Concentration of the ion on both sides of the membrane Charge on the ion Voltage across the membrane