8.1.3 Synapses and neurotransmitters Quiz: Pearson Edexcel Biology A (Salters-Nuffield), Unit 8

The 20 questions

1. What is the name of the gap between the presynaptic and postsynaptic neurone?

   • Synaptic cleft, the narrow gap across which neurotransmitter diffuses from one neurone to the next
   • Node of Ranvier, a short gap in the myelin sheath where the axon membrane is exposed to the extracellular fluid
   • Axon hillock, the region of the cell body where the axon begins and action potentials are first generated
   • Myelin gap, a space between two adjacent Schwann cells where the insulation is absent along the axon

2. Which neurotransmitter is released at many synapses and at neuromuscular junctions?

   • Insulin, a polypeptide hormone that lowers blood glucose and is secreted by the beta cells of the pancreas
   • Acetylcholine, a widely used neurotransmitter found at many synapses and at neuromuscular junctions
   • Adrenaline, which is a hormone released by the adrenal medulla and acts only in the brain at synapses
   • Glucagon, a hormone released by the alpha cells of the pancreas that raises blood glucose levels

3. What causes neurotransmitter to be released from the presynaptic neurone?

   • Breakdown of the myelin sheath, which exposes the vesicles inside the presynaptic neurone to the cleft
   • Diffusion of sodium ions out of the cleft, which pushes the neurotransmitter back into the presynaptic knob
   • Arrival of insulin at the synapse, which opens channels in the membrane of the presynaptic neurone
   • Arrival of an action potential that causes calcium ions to enter the synaptic knob and trigger vesicle fusion

4. What happens to acetylcholine after it has bound to receptors on the postsynaptic membrane?

   • It is stored permanently in the postsynaptic cell, where it builds up to trigger future impulses
   • It is converted into glucose in the postsynaptic cell, which then supplies energy to the next neurone
   • It is broken down by acetylcholinesterase in the cleft, so that it stops acting and its components can be recycled
   • It is pumped into the myelin sheath, where it remains until the next impulse arrives at the synapse

5. Why must acetylcholine be removed from the synaptic cleft after transmission?

   • To allow myelin to form on the postsynaptic neurone, which needs acetylcholine to start the process
   • To stop calcium entering the synaptic knob, which would otherwise trigger the release of more neurotransmitter
   • To prevent continuous stimulation of the postsynaptic neurone, so that the synapse can reset for the next impulse
   • To increase the length of the refractory period in the presynaptic neurone, which protects it from damage

6. Which statement describes the direction of transmission across a chemical synapse?

   • In both directions equally, since neurotransmitter can be released from either side of the cleft
   • From postsynaptic to presynaptic neurone only, since receptors release neurotransmitter back into the terminal
   • From presynaptic neurone to postsynaptic neurone only, because release and receptor binding occur in that order
   • Across the myelin sheath only, which guides the neurotransmitter from one neurone to the next in a single direction

7. A synapse takes 0.5 ms to transmit a signal. A reflex arc has 3 synapses. What is the total synaptic delay?

   • 3.0 ms, since the delay at each of the three synapses adds to six times the single value of 0.5 ms
   • 0.5 ms, since the delay is the same at the whole arc as it is at a single synapse in the pathway
   • 1.5 ms, since three synapses each contribute a delay of 0.5 ms to the total
   • 0.167 ms, found by dividing the single synapse delay of 0.5 ms by the number of synapses in the arc

8. A drug blocks acetylcholinesterase in the synaptic cleft. What is the most likely effect on the postsynaptic neurone?

   • Calcium ions cannot enter the postsynaptic neurone, which stops the membrane from depolarising at all
   • Acetylcholine is removed more quickly, which reduces the size of the response in the postsynaptic neurone
   • Acetylcholine remains active for longer, so the postsynaptic neurone is over-stimulated after each impulse
   • The presynaptic neurone stops releasing any neurotransmitter, which removes all stimulation of the postsynaptic cell

9. Which ion channel on the postsynaptic membrane opens when acetylcholine binds, leading to depolarisation?

   • Chemically-gated sodium channels, which open when acetylcholine binds to its receptor on the membrane
   • Potassium pumps, which move potassium ions into the cell and so depolarise the membrane when activated
   • Chloride channels that open only during repolarisation, which make the membrane more negative after the impulse
   • Voltage-gated calcium channels only, which open in response to the change in potential across the membrane

10. Why do synapses introduce a delay into a nerve pathway?

    • Potassium ions move more slowly than sodium ions in the axon, which delays the signal at the synapse
    • Action potentials slow down inside myelin sheaths, which are present at every synapse in the body
    • Impulses must travel through the cytoplasm of the cell body only, which is slower than travel along the axon
    • Neurotransmitter must diffuse across the cleft and bind receptors, which takes time

11. A student compares electrical and chemical synapses. Which statement is the most accurate evaluation?

    • Electrical and chemical synapses are identical in every way, since both use the same ions to transmit the signal
    • Chemical synapses allow the signal to be modified and one-way, but are slower than the direct transfer of current at electrical synapses
    • Chemical synapses are faster than electrical synapses in all cases, because neurotransmitter diffuses more quickly than current flows
    • Electrical synapses only occur in plants, which is why they are not found in the nervous systems of animals

12. Which statement describes what happens to the postsynaptic membrane when an excitatory neurotransmitter binds?

    • It depolarises, making an action potential more likely if threshold is reached
    • It loses all its receptors permanently, which stops any further transmission across the synapse
    • It becomes hyperpolarised, making an action potential less likely, because the inside becomes more negative
    • It releases acetylcholine back into the cleft, which sends the signal back to the presynaptic neurone

13. Which of the following is a function of the synaptic vesicles in the presynaptic neurone?

    • To store and release neurotransmitter when calcium enters the synaptic knob
    • To store sodium ions for the next action potential, which are released when the vesicles fuse with the membrane
    • To produce myelin for the axon, which is secreted by vesicles along the length of the neurone
    • To transport oxygen to the mitochondria, which are needed to produce ATP for the synapse

14. A neurotransmitter is released at a rate of 200 vesicles per second, each containing 5000 molecules. How many molecules are released per second?

    • 1 000 000 molecules per second, found by multiplying 200 vesicles by 5000 molecules per vesicle
    • 205 000 molecules per second, found by adding 200 vesicles to 5000 molecules
    • 2500 molecules per second, found by dividing 5000 molecules by 200 vesicles
    • 40 000 molecules per second, found by multiplying 200 by 200

15. Which statement best describes the role of calcium ions in synaptic transmission?

    • They stop neurotransmitter being released, which protects the postsynaptic neurone from overstimulation
    • They break down acetylcholine in the cleft, which removes the neurotransmitter after it has bound the receptors
    • They make the postsynaptic membrane hyperpolarised, which prevents the next impulse from being generated
    • They trigger the fusion of vesicles with the presynaptic membrane, releasing neurotransmitter into the cleft

16. Which statement about a synapse that uses an inhibitory neurotransmitter is correct?

    • It has no effect on the postsynaptic membrane, since inhibitory transmitters are not able to bind receptors
    • It permanently destroys the postsynaptic neurone, which is why inhibitory transmitters are rarely found in the body
    • It makes the postsynaptic membrane more likely to fire, because it causes further depolarisation of the membrane
    • It hyperpolarises the postsynaptic membrane, making an action potential less likely to be generated

17. Which feature of a synapse helps to ensure that impulses travel in one direction only?

    • Both neurones have identical receptors and vesicles, so the signal can pass in either direction across the cleft
    • The synaptic cleft is filled with myelin, which seals the gap and stops the impulse from travelling backwards
    • Impulses cross synapses via gap junctions only in all cases, which allows signals to travel in both directions
    • Neurotransmitter is released only from the presynaptic neurone and binds only to receptors on the postsynaptic neurone

18. A drug mimics the action of acetylcholine at the postsynaptic receptor but is not broken down. What is the likely effect?

    • No effect, because the receptor only binds natural acetylcholine and cannot respond to any other molecule
    • Increased release of calcium from the myelin sheath, which strengthens the signal at the postsynaptic membrane
    • Complete destruction of the presynaptic neurone, which is damaged by the drug binding to its receptors
    • Continuous stimulation of the postsynaptic neurone, since the drug keeps the receptor activated for longer than normal

19. Which evaluation is most appropriate for the claim that a synapse always increases the speed of nerve transmission?

    • Correct, because synapses are made of myelin, which is known to speed up all transmission in the nervous system
    • Correct, because a synapse always speeds up an impulse, as the chemical signal is faster than electrical conduction along the axon
    • Incorrect, because synapses cannot transmit impulses at all, so the claim is not relevant to any nerve pathway
    • Incorrect, because synapses introduce a delay, although they allow the signal to be controlled and directed

20. Which pair correctly matches a process with its location?

    • Diffusion of neurotransmitter: myelin sheath, which lets the neurotransmitter move along the axon quickly
    • Release of neurotransmitter: postsynaptic membrane, where the vesicles fuse with the membrane of the receiving cell
    • Binding to receptors: postsynaptic membrane, where neurotransmitter attaches to the receptor molecules
    • Breakdown of acetylcholine: presynaptic vesicles, which contain the enzyme that digests the neurotransmitter

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