Unit 6 3.6.2.1 Nerve Impulses

Question 1

Explain how a resting potential is maintained across the axon membrane in a neurone. [3]

Answer 1

1. Higher concentration of potassium ions inside and higher concentration of sodium ions outside the neurone
2. Membrane more permeable to potassium ions
3. Sodium ions (actively) transported out and potassium ions in;

Question 2

Explain why the speed of transmission of impulses is faster along a myelinated axon than along a non-myelinated axon. [3]

Answer 2

1. Myelination provides (electrical) insulation;
2. Saltatory conduction OR depolarisation only at nodes of Ranvier;
3. In non-myelinated depolarisation occurs along whole length of axon;

Question 3

Why would the resting potential of the neurone change from –70 mV to 0 mV in the presence of a respiratory inhibitor? [3]

Answer 3

1. No/less ATP produced;
2. No/less active transport OR sodium/potassium pump inhibited;
3. Electrochemical gradient not maintained OR it results in the same concentration of sodium and potassium ions on either side of membrane

Question 4

The graph shows ion permeability during an action potential.
Explain the shape of the curve for sodium ions between 0.5 ms and 0.7ms. [3]

Answer 4

1. Ion channel proteins open, sodium in;
2. Makes membrane potential positive OR depolarisation OR reaches threshold;
3. More sodium channels open OR positive feedback;

Question 5

The graph shows ion permeability during an action potential. During an action potential, the membrane potential rises to +40 mV and then falls. Use information from the graph to explain the fall in membrane potential. [3]

Answer 5

1. Potassium channels open;
2. Potassium out;
3. Sodium channels close;

Question 6

After exercise, some ATP is used to re-establish the resting potential in axons. Explain how the resting potential is re-established. [2]

Answer 6

1. Pump / active transport / transport against concentration gradient;
2. Of sodium from axon / sodium out / of potassium in;

Question 7

The diagram shows the plasma membrane of a neurone and the three different proteins that are involved in maintaining the resting potential.

Protein C requires ATP to function. Describe the role of protein C. [2]

Answer 7

1. Transports Na+ and K+ ;
2. By active transport / pump / against concentration gradient;

Question 8

The diagram shows the plasma membrane of a neurone and the three different proteins that are involved in maintaining the resting potential.

The plasma membrane of the neurone is more permeable to potassium ions than to sodium ions. Give the evidence from the diagram that supports this observation. [1]

Answer 8

fewer protein B molecules, which transport sodium ions OR more
protein A molecules, which transport potassium ions;

Question 9

The diagram shows the change in the charge across the surface membrane of a non-myelinated axon when an action potential is produced.

Describe how the change shown in the diagram occurs when an action potential is produced. [2]

Answer 9

1. sodium channels open;
2. sodium ions enter axon;

Question 10

When a neurone transmits a series of impulses, its rate of oxygen consumption increases. Explain why. [3]

Answer 10

1. More respiration;
2. More ATP supplied;
3. For active transport of ions OR sodium -potassium pump functioning