3.6.3: 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;
   reference to ions or Na+ and K+ is required. If mentioned once allow for
   all mark points.
   If an answer provides two or three of these mark points without any
   reference to ions – award one maximum mark.
   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;
   Reject thermal 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);