Question 1
A neuron has a cell body with several short branched fibres and one long fibre. What is the role of the long single fibre?
A.
Receiving impulses from nearby neurons
B.
Releasing ATP to maintain the cell body
C.
Containing the nucleus and most cytoplasm
D.
Conducting impulses away from the cell body
Question 2
Why is a nerve impulse described as electrical?
A.
It involves electrons flowing along the cytoplasm of the axon
B.
It involves ATP molecules carrying charge between adjacent neurons
C.
It involves neurotransmitter molecules diffusing along the whole axon
D.
It involves movement of positively charged ions across the membrane
Question 3
What movement of ions by the sodium-potassium pump helps generate the negative resting potential of a neuron?
A.
Three out and two in
B.
Two out and three in
C.
Three in and two out
D.
Two in and three out
Question 4
Why does a typical chemical synapse transmit a signal in one direction only?
A.
Vesicles are presynaptic and receptors are postsynaptic
B.
The synaptic cleft contains voltage-gated sodium channels
C.
Neurotransmitter diffuses only in one direction through water
D.
The postsynaptic cell pumps neurotransmitter into vesicles
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Question 5
An axon membrane reaches threshold potential. What ion movement causes the rapid depolarization phase of the action potential?
A.
diffuses out of the axon through the sodium-potassium pump
B.
diffuses into the axon through voltage-gated channels
C.
diffuses into the axon through voltage-gated channels
D.
diffuses out of the axon through leak channels
Question 6
How does saltatory conduction increase the speed of impulse transmission in myelinated axons?
A.
Neurotransmitters diffuse between adjacent nodes of Ranvier
B.
The sodium-potassium pump is absent from the nodes of Ranvier
C.
Action potentials are regenerated at nodes of Ranvier rather than along all membrane
D.
Action potentials are generated continuously under the myelin sheath
Question 7
The diagram shows a neuron with structures labelled A, B and C.
State the name of the long single nerve fibre labelled A.
[1]
State the function of dendrites in a neuron.
[1]
Outline why the cell body is essential for the neuron.
[1]
Question 8
A study of non-myelinated axons gives a correlation coefficient of between axon diameter and conduction speed. What conclusion is best supported?
A.
Conduction speed explains of variation in axon diameter
B.
Larger axon diameter is associated with faster conduction speed
C.
Axon diameter is unrelated to conduction speed
D.
Larger axon diameter causes slower conduction speed
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Question 9
What happens when acetylcholine binds to its receptor on a postsynaptic membrane at many synapses?
A.
A channel closes and positive ions leave, producing an EPSP
B.
A channel opens and positive ions enter, producing an EPSP
C.
Vesicles fuse with the postsynaptic membrane, releasing acetylcholine
D.
Acetylcholinesterase enters the postsynaptic cell and triggers depolarization
Question 10
What explains propagation of an action potential from one region of an axon to the next?
A.
The refractory region behind the impulse becomes depolarized again
B.
Neurotransmitter diffuses inside the axon to open distant receptors
C.
The original sodium ions travel unchanged to the axon terminal
D.
Local currents depolarize adjacent membrane until threshold is reached
Question 11
An oscilloscope trace from a sensory neuron shows five action potential spikes in . What is the firing frequency?
A.
B.
C.
D.
Question 12
What is the effect of cocaine on synaptic transmission involving dopamine?
A.
It opens chloride channels, producing an inhibitory postsynaptic potential
B.
It breaks down dopamine, shortening stimulation of postsynaptic receptors
C.
It blocks acetylcholine receptors, preventing dopamine release
D.
It blocks dopamine reuptake, prolonging stimulation of postsynaptic receptors
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Question 13
A neuron at rest has a membrane potential of about .
Define membrane potential.
[1]
Explain how the sodium-potassium pump contributes to the resting potential.
[3]
Question 14
A nerve impulse travels along an axon as an action potential.
State why a nerve impulse is described as electrical.
[1]
Outline how an action potential is propagated along a nerve fibre.
[2]
Question 15
The diagram shows a motor neuron with four labelled regions.
State the letter that identifies the axon.
[1]
Outline one way in which the structure of dendrites is related to their function.
[1]
Suggest why an impulse in this neuron normally passes from the dendrites towards the terminal branches.
[1]
Question 16
A postsynaptic neuron receives two EPSPs and one IPSP at nearly the same time. The combined membrane potential remains below threshold. What is the expected outcome?
A.
No action potential is generated in the postsynaptic axon
B.
Neurotransmitter release stops at all presynaptic neurons
C.
A smaller action potential is generated in the postsynaptic axon
D.
The IPSP becomes an EPSP because inputs arrive together
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Question 17
The scatter graph shows the relationship between axon diameter and conduction speed in a group of non-myelinated axons. A fitted line is shown with . A separate comparison of two fibres of the same diameter shows a higher conduction speed in the myelinated fibre.
Describe the correlation between axon diameter and conduction speed in the graph.
[1]
Calculate the coefficient of determination, , for the fitted line.
[1]
Compare impulse transmission in myelinated and non-myelinated fibres of the same diameter.
[2]
Question 18
The diagram shows a chemical synapse at the end of a motor neuron.
State the role of calcium ions in neurotransmitter release.
[2]
Outline how neurotransmitter molecules leave the presynaptic neuron.
[2]
Question 19
Acetylcholine is released at many synapses, including neuromuscular junctions.
Define synapse.
[1]
Explain how acetylcholine generates an excitatory postsynaptic potential.
[3]
Question 20
An oscilloscope trace records the membrane potential of an axon during one action potential.
State the approximate resting potential shown by the trace.
[1]
Explain the cellular event causing the steep rising phase of the trace.
[2]
Explain the cellular event causing the falling phase of the trace.
[1]
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Question 21
An action potential has depolarized one small region of an axon membrane.
Outline how local currents cause the next region of membrane to reach threshold.
[2]
State why the action potential normally travels in one direction along the axon.
[1]
Question 22
The diagram shows part of a myelinated axon with gaps in the myelin sheath.
State the name of the gaps between adjacent myelin sheath segments.
[1]
Explain how myelination increases the speed of impulse transmission.
[3]
Question 23
Capsaicin from chilli peppers can stimulate free nerve endings in the skin.
Explain how stimulation of free nerve endings can lead to pain perception.
[3]
State why consciousness is described as an emergent property of the brain.
[1]
Question 24
The diagram represents ion movements across the plasma membrane of a resting neuron. The table gives relative ion concentrations inside and outside the axon.
Property | / mmol dm | / mmol dm | Large anions / mmol dm |
|---|---|---|---|
Inside axon | 15 | 140 | 155 |
Outside axon | 145 | 5 | 0 |
Relative leak rate / a.u. | 1 | 8 | 0 |
One pump cycle / ions moved | 3 out | 2 in | 0 |
State the numbers of sodium ions and potassium ions moved by one cycle of the sodium-potassium pump.
[1]
Calculate the net movement of positive charge caused directly by one pump cycle.
[1]
Explain, using the information in the diagram, why the resting potential is negative inside the neuron.
[2]
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Question 25
A recording electrode was placed at three positions along a non-myelinated axon. The graph shows the membrane potential recorded at each position after the axon was stimulated at one end.
Describe the evidence from the graph that the impulse was propagated along the axon.
[1]
Outline why the nerve impulse is described as electrical.
[1]
Explain why the action potentials recorded at the three positions have approximately the same maximum membrane potential.
[2]
Question 26
The diagram shows a chemical synapse between a presynaptic neuron and a postsynaptic cell.
State the name of the narrow gap between the two cells.
[1]
Outline why transmission at this synapse occurs in one direction only.
[2]
State one type of postsynaptic cell that could receive a signal at a synapse.
[1]
Question 27
An oscilloscope trace was recorded from a sensory neuron during a constant stimulus. The trace shows repeated action potentials over a measured time interval.
Calculate the firing frequency in impulses per second for the interval shown.
[1]
Identify the cellular event represented by region P, the steep rising phase of one spike.
[1]
Explain the cellular event represented by region Q, the falling phase of one spike.
[2]
State what is indicated by the return of the trace to a near-horizontal line between spikes.
[1]
Question 28
Neonicotinoids and cocaine are exogenous chemicals that affect synaptic transmission.
Outline how neonicotinoids affect synaptic transmission in insects.
[2]
Compare this with the effect of cocaine at dopamine synapses.
[2]
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Question 29
A postsynaptic neuron receives signals from several presynaptic neurons at the same time. Some inputs are excitatory and some are inhibitory.
Distinguish between an excitatory postsynaptic potential and an inhibitory postsynaptic potential.
[2]
Explain how summation determines whether the postsynaptic neuron fires an action potential.
[2]
Question 30
The scatter graph shows the relationship between axon diameter and conduction speed in non-myelinated axons from several animal species. A line of best fit is shown. A second graph compares conduction speed in myelinated and non-myelinated mammalian axons of similar diameter.
Describe the relationship between axon diameter and conduction speed shown in the scatter graph.
[1]
The coefficient of determination for the line of best fit is . Calculate the correlation coefficient, , assuming the relationship is positive.
[1]
Apply the value of to the data in the scatter graph.
[1]
Compare the effects of large diameter and myelination on conduction speed using the data displays.
[2]
Question 31
A presynaptic neuron was stimulated while the concentration of calcium ions outside the synaptic knob was varied. The graph shows the amount of neurotransmitter released into the synaptic cleft.
Describe the effect of increasing extracellular concentration on neurotransmitter release.
[1]
Explain the role of in neurotransmitter release from the presynaptic membrane.
[2]
Suggest why neurotransmitter release does not continue to increase at the highest concentrations shown.
[2]
Question 32
The graph shows an oscilloscope trace of membrane potential during one action potential in an axon. The opening states of voltage-gated sodium and potassium channels are indicated below the trace.
State the membrane potential at which threshold is reached in this trace.
[1]
Explain the rapid depolarization phase shown in the trace.
[2]
Explain why the membrane potential falls after the peak of the action potential.
[1]
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Question 33
The diagram shows three adjacent regions of an unmyelinated axon during propagation of an action potential. Region B is depolarized, while regions A and C are initially at resting potential.
State the ion mainly responsible for local currents inside the axon after region B has depolarized.
[1]
Explain how local currents cause region C to generate an action potential.
[2]
Suggest why the action potential normally does not propagate back into region A.
[1]
Question 34
The diagram and graph compare impulse conduction in a myelinated axon and a non-myelinated axon of the same diameter.
State the name of the gaps in the myelin sheath shown in the diagram.
[1]
Describe the difference in conduction speed shown in the graph.
[1]
Explain how myelination increases conduction speed.
[2]
Question 35
The diagram shows a motor neuron and an enlarged section of its axon membrane at rest.
I.
Distinguish between the roles of dendrites and an axon in a neuron.
[2]
II.
State what is meant by membrane polarization in a resting neuron.
[1]
Explain how the sodium-potassium pump and ion permeability contribute to the resting potential.
[4]
Question 36
A stimulus is applied to the middle of an isolated non-myelinated axon. Changes in ion distribution are observed in neighbouring regions of the axon membrane.
I.
Explain why a nerve impulse is described as electrical rather than as a flow of electrons.
[2]
II.
State the meaning of all-or-nothing in relation to an action potential.
[1]
Explain how depolarization of one region of axon leads to propagation of an action potential along the fibre.
[3]
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Question 37
The diagram shows a chemical synapse between a presynaptic neuron and a postsynaptic neuron.
I.
Identify two features of the diagram that show the synapse transmits in one direction only.
[2]
II.
State the role of calcium ions in the presynaptic terminal.
[1]
Explain the sequence of events leading to neurotransmitter release from the presynaptic membrane.
[4]
Question 38
At a neuromuscular junction, acetylcholine released from a motor neuron can initiate contraction of a muscle fibre.
I.
Outline how acetylcholine reaches receptors on the muscle fibre membrane after it is released.
[1]
II.
Explain how binding of acetylcholine can generate an excitatory postsynaptic potential.
[2]
Discuss why acetylcholine must be rapidly removed from the synaptic cleft after transmission.
[4]
Question 39
The table summarizes results from two investigations into the effects of exogenous chemicals on synaptic transmission. One investigation used insect cholinergic synapses exposed to a neonicotinoid pesticide. The other used mammalian dopamine synapses exposed to cocaine.
Investigation | Synapse | Exogenous chemical | Site of action | Observed effect |
|---|---|---|---|---|
1 | Insect cholinergic synapse | Neonicotinoid pesticide | Nicotinic acetylcholine receptors on the postsynaptic membrane | ACh-mediated transmission is disrupted; insects become paralyzed |
2 | Mammalian dopamine synapse | Cocaine | Dopamine reuptake transporters on the presynaptic membrane | Dopamine remains in the synaptic cleft longer; postsynaptic stimulation lasts longer |
Compare the sites of action of the two exogenous chemicals shown in the table.
[2]
Explain why cocaine increases the duration of postsynaptic stimulation at dopamine synapses.
[2]
Suggest why the neonicotinoid-treated insects show paralysis despite acetylcholine being released.
[1]
Question 40
A postsynaptic neuron receives inputs from four presynaptic neurons. The graph shows changes in membrane potential at the axon hillock when excitatory and inhibitory neurotransmitters are released at different times.
State what is meant by summation in a postsynaptic neuron.
[1]
Explain why an inhibitory postsynaptic potential decreases the probability that the postsynaptic neuron will fire.
[2]
Using the graph, explain why an action potential is produced at one time but not at another time shown.
[2]
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Question 41
Researchers measured axon diameter and conduction speed in several non-myelinated nerve fibres from marine invertebrates. A second set of measurements compared myelinated and non-myelinated fibres of similar diameter.
I.
Describe the correlation shown between axon diameter and conduction speed in non-myelinated fibres.
[2]
II.
If the coefficient of determination for Panel A is , interpret this value.
[1]
Compare the effect of large axon diameter with the effect of myelination on conduction speed.
[2]
Evaluate whether the data alone prove that increasing axon diameter causes increased conduction speed.
[3]
Question 42
An experimental drug reduces ATP production in neurons. After several minutes, the resting membrane potential becomes less negative and synaptic transmission becomes less reliable.
Time after drug / min | ATP production / % of control | Resting membrane potential / mV | Synaptic response success / % |
|---|---|---|---|
0 | 100 | -70 | 96 |
2 | 90 | -69 | 95 |
4 | 75 | -67 | 89 |
6 | 55 | -64 | 77 |
8 | 35 | -60 | 60 |
I.
Suggest why reducing ATP production affects the resting potential.
[2]
II.
State one ion distribution normally maintained by the sodium-potassium pump.
[1]
Explain why changes in resting potential and ion gradients can reduce reliable transmission of impulses and synaptic signals.
[3]
Evaluate the statement: ATP is used directly to move the nerve impulse along the axon.
[2]
Question 43
An intracellular electrode is used to record membrane potential from an axon during stimulation. The oscilloscope trace shows one complete action potential followed by a return to resting potential.
Trace | Point | Time / ms | Membrane potential / mV |
|---|---|---|---|
1 | A | 0.0 | -70 |
1 | B | 0.5 | -65 |
1 | C | 1.0 | -55 |
1 | D | 1.1 | -20 |
1 | E | 1.2 | +30 |
1 | F | 1.4 | +10 |
1 | G | 1.8 | -80 |
1 | H | 2.3 | -70 |
2 | P1 | 0 | -70 |
2 | P2 | 25 | +30 |
2 | P3 | 50 | -70 |
2 | P4 | 75 | +30 |
2 | P5 | 100 | -70 |
2 | P6 | 125 | +30 |
2 | P7 | 150 | -70 |
2 | P8 | 175 | +30 |
2 | P9 | 200 | -70 |
2 | P10 | 225 | +30 |
2 | P11 | 250 | -70 |
2 | P12 | 275 | +30 |
2 | P13 | 300 | -70 |
I.
Explain the cellular events responsible for the rising phase of the trace after threshold is reached.
[2]
II.
Explain the cellular events responsible for the falling phase and undershoot of the trace.
[2]
Explain why a threshold potential is necessary for an action potential.
[2]
A second trace contains 6 action potential spikes in . Calculate the firing frequency in impulses per second.
[2]
Question 44
A short region of axon has just depolarized. Adjacent regions of membrane are still at resting potential.
I.
Define a local current in an axon.
[1]
II.
Explain how local currents can cause the threshold potential to be reached in the next region of membrane.
[2]
Explain why the action potential normally moves in one direction along the axon rather than spreading equally in both directions.
[2]
Compare the movement of ions during propagation with the movement of the action potential itself.
[2]
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Question 45
The figure compares two axons of the same diameter. One axon is myelinated and the other is non-myelinated.
I.
State what is meant by a node of Ranvier.
[1]
II.
Explain why ion channels and pumps are clustered at nodes of Ranvier.
[2]
Discuss how saltatory conduction increases conduction speed compared with continuous conduction in a non-myelinated axon.
[4]
Question 46
Two exogenous chemicals affect synaptic transmission. Neonicotinoids are used as insecticides. Cocaine is a psychoactive drug that affects dopamine synapses.
I.
Explain how neonicotinoids affect synaptic transmission in insects.
[2]
II.
Explain how cocaine affects dopamine synapses.
[2]
Compare and contrast the effects of neonicotinoids and cocaine on synaptic signalling.
[4]
Question 47
Capsaicin from chilli peppers can activate pain-detecting free nerve endings in the skin. General anaesthesia can prevent the conscious perception of pain even when sensory neurons are stimulated.
I.
Explain how capsaicin can initiate nerve impulses in a pain-detecting free nerve ending.
[2]
II.
State where pain is perceived after impulses have been generated in skin receptors.
[1]
Discuss why the perception of pain and consciousness are considered properties of interacting neural systems rather than properties of single neurons.
[4]
Question 48
A postsynaptic neuron in the brain receives input from several presynaptic neurons. Some release excitatory neurotransmitters and others release inhibitory neurotransmitters.
I.
Distinguish between an EPSP and an IPSP.
[2]
II.
Explain one mechanism by which an inhibitory neurotransmitter can produce an IPSP.
[2]
Evaluate how summation allows many graded synaptic inputs to produce an all-or-nothing output in the postsynaptic neuron.
[4]
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