Action potential generation

Question 1

What is an action potential?

Answer 1

electrical signals that are produced by the differences in ion concentrations and electrical potential across the cell membrane

Question 2

What is the reversal potential of the sodium channels?

Answer 2

Ena

Question 3

What is the activation gate (m)?

Answer 3

Na+ gate that opens during depolarization

Question 4

What is the inactivation gate (h)?

Answer 4

• Na+ gate open at rest
• closes as the membrane potential increases (reducing the membrane’s permeability to sodium ions)
• significantly slower than the activation gates

Question 5

How do the voltage gated K+ channels work?

Answer 5

• open after Na+ influx has raised the membrane potential

- K+ rushes out of the cell, quickly pushing the membrane potential back down to baseline

Question 6

What is the absolute refractory period?

Answer 6

• membrane potential is slightly below resting potential
• Na+ activation and inactivation gates are both closed
• K+ channels are open
• positive feedback ability of the Na+ channels is absent and an AP cannot be triggered

Question 7

What is the relative refractory period?

Answer 7

• Na+ channels are back to their resting state (inactivation gate is open)
• many K+ channels are still open (if membrane starts to depolarize, K+ will rush out)
• takes a strong depolarizing current to get the cell to generate an AP

Question 8

What can offset a small increase in Na+ current caused by activating a small number of Na+ channels?

Answer 8

the relative permeability of K+ ions -> increase in outward K+ currents

Question 9

What is the threshold voltage?

Answer 9

Where the Na+ and K+ currents are equal

Question 10

What is accommodation?

Answer 10

• if the cell has been slightly depolarized for a long time, Na+ inactivation gates will start to close
• this causes the effective spiking threshold to go up (because Na+ currents are suppressed)
• larger than normal depolarizations are needed before the Na+ current exceeds the K+ one

Question 11

How is information encoded or transmitted by neurons?

Answer 11

• the precise timing of the action potentials

- the rates at which action potentials are emitted

Question 12

Why can neurons generate lots of action potentials before the Na+ and K+ concentrations is substantially affected (even with the Na+/K+ pump inactive)?

Answer 12

Because a single AP changes the intracellular Na+ and K+ concentrations by less than 0.1 mM