Question 1

1分

If we measure Em?right now, it will be:

A. 0 mV.

B. positive.

C. negative.

Now let's think about what happens when we have an imbalance of ion concentrations. We'll focus on one particular ion - potassium. Let’s introduce a concentration imbalance and increase the number of potassium ions inside the cell relative to the number outside the cell, just like in an actual neuron, as shown in the figure below. We will keep the intracellular and extracellular fluids electroneutral by making sure that there's an appropriate number of matching negative ions on both sides of the membrane.?

We still have an impermeable membrane - the only thing that we've changed was to alter the relative potassium concentrations.

Question 2

1 分

The concentration of potassium ions is 5 mM outside and 100 mM inside, but the membrane is impermeable to these ions. We will keep the intracellular and extracellular fluids electroneutral by making sure that there's an appropriate number of matching negative ions (depicted as ‘A-’ above) on both sides of the membrane.

If we measure Em?in this new situation, it will be:

A. 0 mV.

B. positive.

C. negative.

What happens if we add a channel to the membrane? Specifically, let’s add a potassium channel (purple), as shown in the figure below.

Channels are passages through which ions can travel. Think about what happens to the potassium ions now that we've added a potassium channel.?

Question 3

1 分

If we have 100 millimolar potassium inside of the cell and 5 millimolar potassium outside, which direction do you think potassium ions will flow after we add the potassium channel?

A. It will move out of the cell.

B. It will not move.

C. It will move into the cell.

Question 4

1分

By now, you may have already predicted that this migration of positively charged ions would create an electric field. Let's see how well you understand this idea.

As K+?ions move across the membrane out of the cell, what will the membrane potential become?

A. 0 mV

B. A positive voltage

C. A negative voltage