KA4: communication and signalling: nerve impulse transmission: generation of 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

define the term “action potential”

Answer 3

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

Question 4

how do neurotransmitters initiate a response?

Answer 4

by binding to their receptors (ligand-gated ion channels) at a synapse

Question 5

What are neurotransmitters 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

what does depolarisation of the plasma membrane as a result of the entry of positive ions trigger?

Answer 7

the opening of voltage-gated sodium channels, and further depolarisation occurs

Question 8

what restores the resting membrane potential?

Answer 8

inactivation of sodium channels and opening of potassium channels

Question 9

describe how wave depolarisation passes along the length of a neuron

Answer 9

• Binding of a neurotransmitter triggers the opening of ligand-gated ion channels at a synapse.
• Ion movement occurs and there is depolarisation of the plasma membrane.
• If sufficient ion movement occurs, and the membrane is depolarised beyond a threshold value, the opening of voltage-gated sodium channels is triggered
• sodium ions enter the cell down their electrochemical gradient.
• This leads to a rapid and large change in the membrane potential.
• A short time after opening, the sodium channels become inactivated.
• 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 does the depolarisation of a patch of membrane cause?

Answer 10

neighbouring regions of membrane to depolarise and go through the same cycle as adjacent voltage-gated sodium channels are opened

Question 11

describe what happens when an action potential reaches the end of a neuron?

what is released?

Answer 11

-it causes vesicles containing neurotransmitter to fuse with the membrane

• a 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

Question 13

How are ion concentration gradients re-established?

Answer 13

by the sodium-potassium pump-> actively transports excess ions in and out of the cell

Question 14

what happens following repolarisation?

Answer 14

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