Membrane Potentials

Question 1

What is the sodium concentration inside and outside cells?

Answer 1

Inside 15mM

Outside 150mM

Question 2

What is the potassium concentration inside and outside cells?

Answer 2

Inside 140mM

Outside 5mM

Question 3

What is a potassium leak?

Answer 3

Potassium moves out of the cell down its concentration gradient, through the k+ channels in the cell membrane
Leaving behind the negatively charged onions

Question 4

What is a membrane potential?

Answer 4

Voltage across the plasma membrane

Question 5

What is a resting potential?

Answer 5

The membrane potential of a cell not sending signals (-70mV)

Question 6

What is the Nernst equation used for?

Answer 6

Used to calculate the equilibrium potential of a specific ion in a cell

Question 7

What is an equilibrium potential?

Answer 7

The membrane potential at which the electrical and chemical gradients of a specific ion are balanced

Question 8

What is the Goldman equation used for?

Answer 8

To calculate the resting potential of a cell, taking into account multiple ion permeabilites

Question 9

What is the equilibrium potential of sodium?

Answer 9

+60mV

Question 10

What is the equilibrium potential of potassium?

Answer 10

-90mV

Question 11

What is the equilibrium potential of membrane?

Answer 11

-70mV

Question 12

Why is the membrane closer to Ek than ENa?

Answer 12

Membrane is more permeable to k+

Question 13

What happens in depolarisation?

Answer 13

Membrane potential is more positive than the resting potential

Question 14

What happens in repolarisation?

Answer 14

Membrane potential returns to resting potential after depolarisation

Question 15

What happens in hyperpolarisation?

Answer 15

Membrane potential is more negative than the resting potential

Question 16

Why do changes in membrane potential occur?

Answer 16

Cells contain gated ion channels that open or close in response to stimuli

Question 17

Give the 5 basic steps of a neuronal action potential

Answer 17

1- stimulation 
2- depolarisation (Na+ ions in)
3- Repolarisation (K+ ions out)
4- hyperpolarisation
5- resting state

Question 18

What happens if the stimulus doesn’t cause sufficient depolarisation?

Answer 18

The membrane doesn’t reach ENa as channels inactivate

Question 19

How does local anaesthetic work?

Answer 19

By blocking the sodium channels - you don’t get depolarisation and so no action potential will take place

Question 20

What happens at the synapse of a neuronal nerve?

Answer 20

Action potential causes neurotransmitter release. Calcium floods in allowing the fusion of vesicles to cell membrane and neurotransmitters bind to the receptor which causes an effect on the cell

Question 21

What is the resting potential of a cardiac action potential?

Answer 21

-90mV

Question 22

What are the differences between cardiac and neuronal action potentials?

Answer 22

Shape, duration and resting membrane potentials

Question 23

Give the basic stages in a cardiac action potential

Answer 23

0-depolarisation
1- repolarisation begins
2- plateau
3- repolarisation

Question 24

What happens when a cardiac action potential depolarises?

Answer 24

Sodium channels open

Question 25

What happens when a cardiac action potential starts repolarisation?

Answer 25

Sodium channels inactivate and potassium channels open

Question 26

What happens when a cardiac action potential plateaus?

Answer 26

Potassium channels are still open but some calcium channels are activated too

Question 27

What is the calcium used for in cardiac action potentials?

Answer 27

Needed to initiate contraction of myocytes

Question 28

What happens when a cardiac action potential repolaroises?

Answer 28

Calcium channels close and potassium channels open

Question 29

What do action potentials do in the heart?

Answer 29

Control rhythm and synchronicity of contractions of the heart