Lesson 8.1.2

8.1.2 Action potentials and saltatory conduction Quiz: Pearson Edexcel Biology A (Salters-Nuffield), Unit 8

20 questions

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Lesson 8.1.2, Action potentials and saltatory conduction: 20 multiple choice questions for the Pearson Edexcel Biology A (Salters-Nuffield) (9BI0), Unit 8: Grey Matter, written with Revision Ninja.

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The 20 questions

  1. What is the resting potential of a typical neurone?

    • About -70 mV, with the inside of the membrane negative relative to the outside at rest
    • About 0 mV, since the membrane has equal numbers of positive and negative charges at rest
    • About -200 mV, which is the strongest negative charge that the membrane can hold at rest
    • About +40 mV, with the inside of the membrane positive relative to the outside at rest

  2. During the depolarisation phase of an action potential, which ion movement causes the change in potential?

    • Rapid efflux of potassium ions out of the axon through open voltage-gated potassium channels
    • Rapid influx of sodium ions through voltage-gated sodium channels into the axon
    • Influx of chloride ions into the axon through channels that remain open throughout the impulse
    • Efflux of calcium ions from the myelin sheath into the extracellular fluid around the node

  3. Which ion movement is responsible for repolarisation of the axon membrane?

    • Calcium ions entering the axon terminal to trigger the release of neurotransmitter vesicles into the cleft
    • Potassium ions leaving the axon through voltage-gated channels that open later in the action potential
    • Sodium ions entering the axon through the channels that opened during the rising phase of the impulse
    • Chloride ions leaving the myelin sheath through the nodes of Ranvier at the start of the impulse

  4. What is the all-or-nothing principle as it applies to action potentials?

    • Once the threshold is reached, a full action potential of the same size is produced, or none is produced
    • A stronger stimulus produces a larger action potential, so the size of the impulse increases with stimulus strength
    • Action potentials can be partly produced at any stimulus strength, so the size depends on how strong the stimulus is
    • Action potentials only occur when the stimulus is removed from the receptor, which allows the membrane to reset

  5. What is the refractory period of a neurone?

    • The time that an impulse takes to cross a synapse from one neurone to the next in the chain
    • The period during which the myelin sheath is formed around a newly grown axon by Schwann cells
    • The time taken for the neurotransmitter to be released into the cleft after an impulse reaches the terminal
    • The time during which a neurone cannot be stimulated to fire again, while it resets its membrane potential

  6. Why does the refractory period make action potentials travel in one direction only?

    • It stops the axon from producing potassium ions, which would otherwise carry the impulse back to the receptor
    • It causes sodium ions to flow backwards along the axon, which pushes the impulse towards the cell body
    • It causes the membrane behind the impulse to be unable to re-fire, so the impulse moves forward
    • It increases the speed of the impulse in both directions, so the signal reaches both ends of the axon at once

  7. In saltatory conduction, where does depolarisation occur along a myelinated axon?

    • Only in the cell body, which is the only part of the neurone with the ability to generate action potentials
    • Only at the nodes of Ranvier, where the axon membrane is exposed and voltage-gated channels are concentrated
    • Continuously along the whole length of the axon, since the myelin does not change the membrane potential at all
    • Only in the synaptic knob, where the impulse triggers the release of neurotransmitter into the synaptic cleft

  8. What is the main advantage of saltatory conduction?

    • It allows impulses to travel backwards along the axon, so the signal can be sent to both ends at once
    • It uses less energy than any other form of conduction, because ions never need to be moved across the membrane
    • It makes the action potential larger, so the impulse is stronger when it reaches the synapse
    • It makes impulses travel faster and uses less energy than continuous conduction

  9. A myelinated axon conducts an impulse at 100 m per second and an unmyelinated axon of the same diameter conducts at 1 m per second. How many times faster is the myelinated axon?

    • 100 times, since 100 m per second divided by 1 m per second gives a ratio of 100 to 1
    • 0.01 times, since the unmyelinated axon is the faster of the two in this comparison
    • 10 times, since the speed of the myelinated axon is ten times that of the unmyelinated axon in this example
    • 1000 times, since the speed difference is measured in millimetres rather than metres per second

  10. Which ion pump helps restore the resting potential after an action potential?

    • Water pump, which moves water molecules into the axon to restore its volume after the impulse has passed
    • Sodium-potassium pump, which actively moves sodium ions out and potassium ions in, using ATP
    • Glucose pump, which moves glucose molecules into the axon for use in respiration during the impulse
    • Calcium pump, which moves calcium ions into the myelin sheath to keep the axon insulated

  11. During an action potential, the membrane potential briefly reaches about +40 mV. Why does the potential not continue to rise indefinitely?

    • The myelin sheath prevents any further change in potential, since it acts as a physical barrier to ion movement
    • Sodium ions start to be actively pumped into the cell by the sodium-potassium pump, which stops the rise
    • Sodium channels close and potassium channels open, reversing the flow of ions and repolarising the membrane
    • Calcium ions block all sodium movement, which stops the membrane from becoming more positive at the peak

  12. A student applies a stimulus that is below threshold to a neurone. Which observation is most likely?

    • A smaller action potential is generated, since a weak stimulus always produces a reduced impulse
    • No action potential is generated, since too few sodium channels open to reach the threshold
    • A full action potential is generated, since any stimulus of any strength will produce a complete impulse
    • The neurone fires continuously, since a subthreshold stimulus keeps the membrane permanently depolarised

  13. Which statement about myelin and conduction speed is correct?

    • Myelin increases conduction speed by insulating the axon and restricting depolarisation to the nodes
    • Myelin produces the action potential directly, since the sheath generates the electrical signal along the axon
    • Myelin is only present in the brain and has no effect on the speed of impulses in peripheral nerves
    • Myelin slows conduction because it blocks the flow of ions, so impulses must pass through the sheath slowly

  14. Which of the following would most likely reduce the speed of an action potential along a neurone?

    • Increasing the number of voltage-gated sodium channels at the nodes, which allows them to open more readily
    • Demyelination of the axon, which removes saltatory conduction and forces the impulse to travel continuously
    • Increasing the number of nodes of Ranvier, which gives the impulse more places to be regenerated along the axon
    • Increasing the diameter of the axon, which lowers the internal resistance to the flow of ions along it

  15. A student plots the speed of nerve impulses against axon diameter for unmyelinated axons. What general trend is expected?

    • Speed rises as diameter increases, because a wider axon has less internal resistance, so currents spread faster
    • Speed is highest for the thinnest axons, because the narrow cross-section allows the impulse to be generated fastest
    • Speed does not depend on diameter, since the speed of an impulse is set only by the number of synapses
    • Speed falls as diameter increases, since a wider axon has more membrane through which ions can leak away

  16. Which feature of voltage-gated sodium channels is important in the action potential?

    • They are opened only by noradrenaline, which is released at the synapse by the presynaptic neurone
    • They are permanently open at rest, which keeps the membrane depolarised at all times
    • They transport glucose into the axon, which provides the energy needed for each action potential
    • They open in response to a change in membrane potential, allowing rapid sodium influx into the axon

  17. What is the main function of the myelin sheath in terms of ion movement?

    • To store sodium ions for use in the synapse, which releases them when the impulse reaches the terminal
    • To pump potassium ions out of the axon, which keeps the resting potential at a constant level
    • To allow ions to pass through the sheath freely at all points, so that the membrane potential changes evenly
    • To prevent ion movement across most of the membrane, so ion exchange occurs only at the nodes

  18. An action potential spreads from one node to the next along a myelinated axon. Which statement best describes the local current that drives this?

    • Local currents flow between depolarised and resting regions, depolarising the next node to threshold
    • Sodium ions diffuse across the myelin sheath from node to node, carrying the charge along the outside of the axon
    • Potassium ions are pumped from one node to the next by ATP, which carries the impulse forward along the axon
    • Myelin itself carries electrical charge along its length, so the sheath acts as a conductor for the impulse

  19. Which statement correctly evaluates the claim that action potentials travel at constant speed in all neurones?

    • Incorrect, because action potentials never travel along axons, so no speed can be measured in any neurone
    • Incorrect, because speed depends on myelination and axon diameter, so neurones vary in conduction speed
    • Correct, because all action potentials are identical in size and shape, so their speed is always the same
    • Correct, because every neurone has the same axon diameter and myelination, so the speed is the same everywhere

  20. A myelinated axon has nodes of Ranvier spaced 1 mm apart. How many nodes are there along 500 mm of axon?

    • 5 nodes, since the nodes occur only at each end and at the midpoint of the axon
    • 500 nodes, one for each millimetre of the axon
    • 0.5 nodes, found by dividing the 500 mm length by the 1000 millimetres in a metre
    • 50 nodes, since one node is found in every ten millimetres of the myelinated axon

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