Module 1: Section 4

Question 1

Action potential

Answer 1

• Caused by a triggering event or stimulus
• Results in a localized depolarization
• It conducts throughout the entire membrane and does not diminish in strength
• Can be used for long distance signalling

Question 2

What is the threshold in an action potential?

Answer 2

minimum potential needed to trigger rapid depolarization

Question 3

Steps of an action potential

Answer 3

1. Threshold reached
2. Depolarization (inside positive)
3. Repolarization (inside negative)
4. Hyperpolarization (too negative) - only sometimes
5. Return to resting

Question 4

Voltage-gated ion channels

Answer 4

• Large transmembrane proteins
• Contain a voltage sensor and a pore

Question 5

Voltage-gated ion channels - Closed

Answer 5

• The activation gate within the pore keeps the pore closed
• No Na+ can enter the cell

Question 6

Voltage-gated ion channels - Open

Answer 6

• Once threshold potential is reached, the activation gate opens
• Sodium rapidly enters the cell

Question 7

Voltage-gated ion channels - Inactive

Answer 7

• The intracellular inactivation gate moves to block the inside of the pore to stop Na+ from entering the cell
• Activation gate can still be open but channel is inactivated so no current flows

Question 8

Structure of voltage-gated Na+ channel

Answer 8

• One large transmembrane protein
• Single activation gate and single inactivation gate

Question 9

Structure of voltage-gated K+ channels

Answer 9

• Have four subunits
• Each contribute to activation and inactivation

Question 10

Refractory period

Answer 10

Brief period of time following an action potential in which another action potential cannot be generated

Question 11

Action potential - at rest

Answer 11

• Voltage-gated Na+ and K+ channels are closed but can open
• Incoming graded potentials can depolarize the membrane to threshold if strong enough

Question 12

Action potential - Threshold and rising phase

Answer 12

• Threshold reached, Na⁺ channels open, Na⁺ permeability spikes (greater than K⁺)
• membrane potential approaches the Na+ equilibrium potential
• K⁺ channels then open

Question 13

Action potential - Failing phase

Answer 13

• Na+ channels inactivate
• K+ channels are still open,
• K+ permeability is higher and membrane potential will move towards the K+ equilibrium potential
• RMP restored