Nerve conduction - Action Potential

Question 1

The ion channels (pores) allow which ions to enter/leave

Answer 1

Na+ and K+

Question 2

The membrane contains billions of channels that can admit billions of what ions?

Answer 2

Na+

Question 3

When threshold of excitation is reached on the membrane

Answer 3

• opening of channels is triggered by depolarization of membrane potential (i.e. immediately adjacent membrane charge changing to negative. Thus they are called voltage dependent ion channels).
• Diffusion and electrostatic forces propel Na+ into neuron.
• Influx of Na+ causes rapid change of membrane potential (charge) from –70 mV to 40 mV

Question 4

K+ ion channels are less sensitive than what? Require more what, and open after what?

Answer 4

Less sensitive than Na+ and require more depolarization (change in membrane charge) to open, and open after Na+ channels

Question 5

What happens to Na+ at peak of action potential (i.e., membrane charge reaches 40 mV)?

Answer 5

They become refractory - they are blocked, and no more Na+ can enter until membrane resting potential is restored.

Question 6

When K+ channels are open, what happens to cause them to close?

Answer 6

Because of influx of Na+, inside of membrane is positively charged and immediate outside of membrane is negatively charged. K+ is driven out of the neuron by diffusion and attracted out by electrostatic forces. This causes the membrane potential to begin returning to normal. As this happens K+ channels are closed

Question 7

Why do Na+ channels reset?

Answer 7

So another depolarization can cause them to open again

Question 8

What happens when there is an accumulation of K+ outside of the membrane?

Answer 8

causes the membrane to “overshoot” and become hyperpolarized, i.e. charge goes below –70 mV. K+ diffuses away and membrane returns to –70 mV

Question 9

Na+ - K++ transporters eventually do what to Na+ and K+?

Answer 9

They eventually remove Na+ from neuron and retrieve K+

Question 10

Are Na+ and K+ transporters that essential in restoring Na+ and K+ levels after action potential?

Answer 10

No. The small amount of these ions that cross the membrane is small relative to the overall concentration in the neuron and is “hardly noticeable”.

Question 11

Transporters are most important on a long-term basis to…?

Answer 11

prevent the slight amount of Na+ that leaks into the neuron (because of the slight permeability of the membrane to Na+) from causing too high a concentration in the neuron that would prevent it from functioning