Photo AI
Explain how a resting potential is maintained across the axon membrane in a neurone - AQA - A-Level Biology - Question 2 - 2021 - Paper 2
Question 2
Explain how a resting potential is maintained across the axon membrane in a neurone. Explain why the speed of transmission of impulses is faster along a myelinated... show full transcript
Worked Solution & Example Answer:Explain how a resting potential is maintained across the axon membrane in a neurone - AQA - A-Level Biology - Question 2 - 2021 - Paper 2
Step 1
Explain how a resting potential is maintained across the axon membrane in a neurone.
Answer
To maintain a resting potential, there is a higher concentration of potassium ions (K") inside the neurone and a higher concentration of sodium ions (Na") outside.
-
Ion Diffusion: Potassium ions diffuse out of the neurone, while sodium ions are less permeable and do not easily enter. This creates a negative charge inside the neurone.
-
Membrane Permeability: The axon membrane is more permeable to potassium ions than sodium ions, leading to the net movement of K" ions out, which contributes to the negative resting potential.
-
Active Transport: The sodium-potassium pump actively transports sodium ions out and potassium ions in, maintaining the ion gradients essential for resting potential.
Step 2
Explain why the speed of transmission of impulses is faster along a myelinated axon than along a non-myelinated axon.
Answer
Myelination provides electrical insulation, allowing for:
-
Saltatory Conduction: In myelinated axons, action potentials jump from one node of Ranvier to the next, significantly increasing the speed of impulse transmission compared to the continuous conduction in non-myelinated axons.
-
Electrical Insulation: The myelin sheath minimizes ion leakage and reduces capacitance, enabling quicker depolarization and repolarization processes at the nodes.
-
Distance Efficiency: Non-myelinated axons experience slower transmission because the entire length of the axon must undergo depolarization.
Step 3
Explain why.
Answer
The addition of a respiratory inhibitor affects the neurone's energy supply:
-
No ATP Production: The inhibitor leads to a lack of ATP, which is crucial for the sodium-potassium pump to function.
-
No Active Transport: Without ATP, the pump cannot extrude Na" from inside the cell and cannot take K" in, resulting in an equalization of ion concentrations.
-
Electrical Gradient Disruption: As Na" accumulates inside and K" is not brought back in, the neurone's resting potential decreases, resulting in the observed change from -70 mV to 0 mV.