Nerve impulses and synapsesEdexcel A-Level Biology B: Flashcards

Exam questions on Nerve impulses and synapses

1. A researcher records the potential difference across the membrane of a resting mammalian axon using a microelectrode. The inside of the axon is 70 mV negative relative to the outside. The membrane contains sodium-potassium pumps and potassium ion leak channels, but very few sodium ion leak channels.
   Predict what would happen to the resting potential over several hours if the axon was supplied with a poison that stopped ATP production. Explain your answer.2 marks
2. A neurone is stimulated and the membrane potential is recorded. The potential rises slowly from −70 mV to about −55 mV, then rises rapidly to +40 mV. It then falls rapidly, overshoots to about −80 mV, and finally returns to −70 mV. The whole event lasts about 3 ms.
   Explain the fall in potential from +40 mV to below −70 mV.2 marks
3. A myelinated mammalian motor axon conducts impulses at 80 m s⁻¹, whereas a non-myelinated axon of similar diameter conducts impulses at 1 m s⁻¹. In the myelinated axon, Schwann cells wrap the axon in layers of myelin, leaving small gaps, the nodes of Ranvier, about 1.5 mm apart. A motor axon carrying impulses from the spinal cord to a foot muscle is 1.2 m long.
   Explain why the myelinated axon conducts impulses faster than the non-myelinated axon.3 marks