Membrane and Action Potentials

Question 1

What is the potassium concentration like in the cells?

Answer 1

[K+] levels are high INSIDE compared to the outside.

Question 2

What is the sodium concentration like in the cells?

Answer 2

[Na+] levels are high OUTSIDE compared to inside.

Question 3

What is ATP broken down into?

Answer 3

It is broken down into ADP and inorganic molecules.

Question 4

What is extrinsic breakdown?

Answer 4

It is an active transport mechanism so requires energy. -

Question 5

In a concentration gradient, what will the [K+] try to do?

Answer 5

It will try to move out and therefore, decrease the concentration gradient.

Question 6

Explain the potassium leak.

Answer 6

Potassium moves out the cell (DOWN CONC GRADIENT)
Leaves via potassium channels and so leaves behind the negatively charged molecules.
An imbalance of charges is created due to there being such a very selective membrane.

Question 7

Explain the electrical gradient.

Answer 7

A potential difference is created because there is a separation of positive and negative charged ions.
MORE NEGATIVE IS INSIDE THE CELL

Question 8

Explain what is a membrane potential.

Answer 8

Voltage (difference in electrical charge) across the plasma membrane.

Question 9

Explain what is a resting potential.

Answer 9

The membrane potential of a cell not sending signals.

Question 10

What produces a concentration gradient?

Answer 10

Sodium - Potassium Pump

Question 11

What produces an electrical gradient?

Answer 11

Potassium Leak

Question 12

What influences a membrane potential to be generated?

Answer 12

An electrical gradient across the membrane results in a membrane potential.

Question 13

Explain what an equilibrium potential is.

Answer 13

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

Question 14

Which equation is used to calculate the equilibrium potential of a specific ion in a cell?

Answer 14

The Nernst equation used to calculate the potential of a specific ion.

Question 15

Which equation is used to calculate the resting membrane potential of a cell taking into account multiple ion permeabilities?

Answer 15

The Goldman equation is used.

Question 16

What are the different activities of an ion channel?

Answer 16

Depolarisation // Repolarisation // Hyperpolarisation.

Question 17

What are the differences in potentials in depolarisation?

Answer 17

Membrane potential is MORE POSITIVE than resting potential.

Question 18

What are the differences in potentials in repolarisation?

Answer 18

Membrane potential RETURNS to resting potential after depolarisation.

Question 19

What are the differences in potentials in hyper polarisation?

Answer 19

Membrane potential is MORE NEGATIVE than the resting potential.

Question 20

Why do changes in the membrane potential occur?

Answer 20

Cells contain gated ion channels which open / close in response to stimuli.

Question 21

What causes an action potential?

Answer 21

When a depolarisation shifts the membrane potential sufficiently.

Question 22

Why does the membrane potential not reach E(na)?

Answer 22

This is because the channels inactivate here the membrane potential does not reach E(na).

Question 23

How do you raise the voltage above the threshold?

Answer 23

The stimulus needs to cause sufficient depolarisation in order to raise the voltage.

Question 24

Why does depolarisation occur?

Answer 24

It occurs because there is an influx of sodium ions into the cell.

Question 25

Why does depolarisation occur?

Answer 25

It occurs because there is an influx of potassium ions leaving the cell.

Question 26

How do nerves send electrical signals?

Answer 26

The action potential is spread along the axon from the soma to the axon to the axon terminal.
The depolarisation spreads from the soma to axon to axon terminal.
The stages which follow the depolarisation stages are: Repolarizing and Resting.

Question 27

What causes a neurotransmitter release?

Answer 27

An action potential at the synapse causes the neurotransmitter to be released.

Question 28

What is the difference in cardiac and neuronal action potentials?

Answer 28

With cardiac action potentials, there is no threshold level.
Depolarisation is very fast and this is due to LESS SODIUM activity in the heart.

Question 29

What is the time difference in action potentials between action potentials

Answer 29

Cardiac is 300 milliseconds whereas neuronal is 5 milliseconds.
So neuronal is quicker than cardiac.

Question 30

What is stage zero of the cardiac action potential?

Answer 30

Depolarisation occurs.

Sodium channels open.

Question 31

What is stage one of the cardiac action potential?

Answer 31

Depolarisation occurs.
Sodium channels become inactive.
Potassium channels open.

Question 32

What is stage two of the cardiac action potential?

Answer 32

Plateau.
Potassium channels are open but some calcium channels are activated too.
Results in plateau stage.

Question 33

What is stage three of the cardiac action potential?

Answer 33

Repolarisation occurs.
Calcium channels close.
Potassium channels open.

Question 34

What is stage four of the cardiac action potential?

Answer 34

Most sodium and potassium channels are closed.

Question 35

What is the purpose of a cardiac action potential?

Answer 35

They underlie the electrical conduction system in the heart.
Controls the rhythm and synchronicity of contractions of the heart.

Question 36

What mediates membrane depolarisation?

Answer 36

Potassium LEAVES the cell.