Nervous Coordination

Question 1

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

Answer 1

1. Higher concentration of potassium ions inside and higher concentration of sodium ions outside (the neurone) OR potassium ions diffuse out
2. (Membrane) more permeable to potassium ions (leaving than sodium ions entering) OR
   (Membrane) less permeable to sodium ions (entering than potassium ions leaving);
   Accept for ‘less permeable to sodium ions’ is ‘impermeable to sodium ions’ or ‘sodium
   gates/channels are closed’ (alternative explanation).
3. Sodium ions (actively) transported out and potassium ions in;
   Accept 3 Na+ out and 2 K+ in but reject if numbers used are incorrect.

Question 2

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

Answer 2

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