Question 18M.2.SL.TZ2.c
| Date | May 2018 | Marks available | [Maximum mark: 7] | Reference code | 18M.2.SL.TZ2.c |
| Level | SL | Paper | 2 | Time zone | TZ2 |
| Command term | Explain | Question number | c | Adapted from | N/A |
Every cell is surrounded by a cell surface membrane which regulates the movement of materials into and out of the cell.
Explain the events that occur during a nerve impulse and how the impulse is propagated along an axon.
[7]
a. nerve impulses are action potentials propagated along axons of neurons
b. resting potential is −70 mV
OR
relatively negative inside in comparison to the outside
c. Na+/K+ pumps maintain/re-establish «the resting potential»
d. more sodium ions outside than inside «when at the resting potential»
OR
more potassium ions inside than outside «when at the resting potential»
e. action potential stimulates «wave of» depolarization along the membrane/axon
f. «when neuron is stimulated» if threshold potential is reached Na+ channels open
g. sodium ions diffuse/move in
h. «Na+ move in» causing depolarization / inside of the neuron becomes more positively charged than the outside of the neuron
i. potassium ion channels open
OR
potassium ions diffuse/move out
j. «K+ move out» causing repolarization
k. local currents
OR
description of Na+ ion diffusion between depolarized region and next region of axon to depolarize
l. myelination increases propagation speed/allows saltatory conduction
Accept any of the points clearly explained in an annotated diagram.
