Nerve Impulse Transmission

Question 1

Resting membrane potential

Answer 1

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

Question 2

Transmission of a nerve impulse along a neuron

Answer 2

Transmission of a nerve impulse along a neuron requires changes in the membrane potential of the neuron’s plasma membrane.

Question 3

Action potential

Answer 3

An action potential is a wave of electrical excitation along a neuron’s plasma membrane

Question 4

Neurotransmitters initiate a response by binding to their receptors at a synapse

Answer 4

Neurotransmitter receptors are ligand-gated ion channels.

Question 5

Depolarisation

Answer 5

Depolarisation is a change in the membrane potential to a less negative value inside.

Question 6

Triggering an action potential

Answer 6

Binding of a neurotransmitters 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 and 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 7

Triggering an action potential

Answer 7

Binding of a neurotransmitters 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 and 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

Depolarisation of a patch of membrane causes neighbouring regions of membrane to depolarise and go through the same cycle, as adjacent voltage-gated sodium channels are opened.

When the action potential reaches the end of the neuron, it causes vesicles containing neurotransmitters to fuse with the membrane - this releases neurotransmitters, which stimulate a response in a connecting cell.

Question 8

Resetting the resting potential

Answer 8

Restoration the resting membrane potential allows the inactive voltage-gated sodium channel;s to return to a conformation that allows them to open again in response to depolarisation of the membrane

Question 9

Resetting the resting potential

Answer 9

Restoration the resting membrane potential allows the inactive voltage-gated sodium channels to close to, return to a conformation that allows them to open again in response to depolarisation of the membrane. Voltage-gated K+ channels open, moving K+ out of the cell to return the membrane potential back to resting.

Ion concentration gradients are re-established by the sodium-potassium pump which actively transports excess ions in and out of the cell.

Following repolarisation the sodium and potassium ion concentration gradients are reduced. The sodium-potassium pump restores the sodium and potassium ions back to resting potential levels.