How Nerves Work 2

Question 1

What are the three types of potential and what are they used for?

Answer 1

A resting potential is used to keep the cell ready to respond.
A Graded potential is used to decide whether an action potential should be fired or not.
An action potential is used to transmit signals over a long distance.

Question 2

Describe how the resting potential of a cell happens

Answer 2

The sodium potassium pump pumps sodium out of the cell and potassium into the cell which creates a concentration gradient. Leaky potassium channels let potassium flow out along its concentration gradient. This leaves a negative charge within the cell.

Question 3

Explain what the equilibrium potential is in terms of potassium

Answer 3

As potassium flows out of the cell along its concentration it doesn’t come back into the cell via these channels due to an electrical gradient being created and making the inside of the cell negative. Eventually it reaches an equilibrium where the electrical gradient is equal and opposite to the concentration gradient (equilibrium potential). The initial concentration gradient determined the equilibrium potential.

Question 4

What is the Nernst equation and what does it do?

Answer 4

The Nernst equation is

E = RT/zF ln [ion]o/[ion]i
Where
R=gas constant
T=absolute temperature
z= valence of the ion
F= faraday constant 

It is used to predict the equilibrium potential for a single ion species.

Question 5

Explain the importance of the blood brain barrier in terms of ion concentration

Answer 5

If more potassium was ingested this would reduce the concentration gradient and therefore a smaller electrical gradient. So the cell is depolarised and the resting potential is reduced. So the blood brain barrier protects the brain from changes in ion concentration in the plasma due to astrocytes and tight junctions between endothelial cells.

Question 6

What does the Goldman equation do?

Answer 6

It predicts the equilibrium potential predicted by several ions.

Question 7

Why is normal resting membrane potential nearer -70mV?

Answer 7

This is due to other leaky channels such as chloride and sodium. The electrogenic (produce change in electrical potential) nature of the sodium potassium pump affects this as well as negative intercellular charged molecules.

Question 8

Describe the concentration and electrical gradients of potassium, sodium, chloride and calcium in the resting potential and say what would happen to the cell if these channels were opened.

Answer 8

Potassium has a larger concentration inside the cell so it’s concentration gradient runs out of the cell and its electrical gradient is opposite (cell would hyperpolarise)
Sodium has a larger concentration outside of the cell so it’s concentration gradient runs into the cell and it’s electrical gradient is the same (cell would depolarise)
Chloride has a larger concentration outside of the cell so it’s concentration gradient runs into the cell and it’s electrical gradient is opposite (cell would depolarise)
Calcium has a larger concentration outside of the cell so it’s concentration gradient runs into the cell and it’s electrical gradient is the same (cell would depolarise)

Question 9

Name the terms involved in the resting potential and the cause associated with them.

Answer 9

Depolarising (-70mV - 0mV)
Overshoot (0mV - +60mV)
Repolarising (+60mV - -70mV)
Hyperpolarising (-70mV - -90mV)