1.4d Generation of a Nerve Impulse

Question 1

What is resting membrane potential?

Answer 1

a state where there is no net flow of ions across the membrane

Question 2

What does the transmission of a nerve impulse require?

Answer 2

changes in the membrane potential of the neuron’s plasma membrane

Question 3

What is an action potential?

Answer 3

a wave of electrical excitation along a neuron’s plasma membrane

Question 4

What do neutrotransmitters do?

Answer 4

initiate a response by binding to their receptors at a synapse

Question 5

What are neurotransmitter receptors?

Answer 5

ligand-gated ion channels

Question 6

What is depolarisation?

Answer 6

a change in the membrane potential to a less negative value inside

Question 7

How does further depolarisation occur?

Answer 7

• depolarisation of the plasma membrane as a result of the entry of positive ions
• triggers the opening of voltage-gated sodium channels,
• and further depolarisation occurs

Question 8

How is the resting membrane potential restored?

Answer 8

inactivation of the sodium channels and the opening of potassium channels

Question 9

Explain the steps of the travel of the action potential

Answer 9

1) Binding of a neurotransmitter triggers the opening of ligand-gated ion channels at the synapse

2) Ion movement occurs and there is depolarisation of the plasma membrane.

3) If sufficient ion movement occurs, and the membrane is depolarised beyond a threshold value, the opening of voltage-gated sodium channels is triggered and sodium ions enter the cell down their electrochemical gradient

4) this leads to a rapid and large change in the membrane potential

5) a short time after opening the sodium channels become inactivated

6) voltage-gated potassium channels then open to allow potassium ions to move out of the cell to restore the resting membrane potential

Question 10

What effect does depolarisation have on neighbouring regions of membrane?

Answer 10

• Causes them to depolarise and go through the same cycle,
• as adjacent voltage gated sodium channels are opened

Question 11

What happens when the action potential reaches th end of the neuron?

Answer 11

• It causes vesicles containing neurotransmitter to fuse with the membrane
• This releases the neurotransmitter, which stimulates a response in a connecting cell

Question 12

What does restoration of the resting membrane potential allow?

Answer 12

• the inactive voltage-gated sodium channels to return to a conformation that allows them to open again in response to depolarisation of the membrane
• ion concentration gradients are re-established by the sodium potassium pump, which actively transports excess ions in and out of the cell

Question 13

What happens after repolarisation?

Answer 13

• the sodium and potassium ion concentration gradients are reduced
• the sodium potassium pump restores the sodium and potassium ions back to resting potential levels