IB Biology Quiz: Understand Neural Signalling
20 questions · exam conditions
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Understand Neural SignallingQuestion 1 of 20

A drug that functions as a selective serotonin reuptake inhibitor (SSRI) is administered. How does this drug affect signalling at a serotonergic synapse?

It prevents serotonin from being released from the presynaptic neuron.
It blocks the postsynaptic receptors, preventing serotonin from binding.
It increases the concentration and duration of serotonin in the synaptic cleft.
It accelerates the enzymatic breakdown of serotonin in the synaptic cleft.
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IB Biology Quiz

IB Biology Quiz: Understand Neural Signalling

Practice Understand Neural Signalling in IB Biology with focused quiz questions that help you check what you know, review explanations, and build confidence with test-style prompts.

What this quiz covers

This quiz focuses on Understand Neural Signalling, giving you a quick way to practice the rules, question types, and explanations that matter most for IB Biology.

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Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

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Question 1

A drug that functions as a selective serotonin reuptake inhibitor (SSRI) is administered. How does this drug affect signalling at a serotonergic synapse?

  1. It prevents serotonin from being released from the presynaptic neuron.
  2. It blocks the postsynaptic receptors, preventing serotonin from binding.
  3. It increases the concentration and duration of serotonin in the synaptic cleft. (correct answer)
  4. It accelerates the enzymatic breakdown of serotonin in the synaptic cleft.
Explanation: Reuptake inhibitors work by blocking the transporter proteins on the presynaptic membrane that normally remove the neurotransmitter from the synaptic cleft. By inhibiting this process, the drug causes serotonin to remain in the cleft for a longer period, increasing its concentration and enhancing its effect on the postsynaptic neuron.

Question 2

Nerve impulses travel in one direction along an axon, from the axon hillock to the terminal. What is the primary reason for this unidirectional propagation?

  1. The concentration gradient of neurotransmitters is only present at the axon terminal.
  2. The sodium-potassium pumps are located only at the axon hillock.
  3. The myelin sheath acts as a one-way insulator for the electrical current.
  4. The refractory period following an action potential prevents backward propagation. (correct answer)
Explanation: When a segment of the axon membrane fires an action potential, it enters a refractory period during which its voltage-gated Na⁺ channels are inactivated. This prevents the action potential from re-stimulating the segment it just passed. Therefore, the wave of depolarization can only move forward, away from the region that is currently refractory.

Question 3

A neurotoxin is discovered that specifically blocks voltage-gated calcium channels at the presynaptic terminals of motor neurons. What is the most immediate consequence of this toxin at the neuromuscular junction?

  1. The action potential will fail to propagate along the motor neuron's axon.
  2. The postsynaptic muscle cell will be unable to repolarize after contraction.
  3. Neurotransmitter vesicles will not fuse with the presynaptic membrane. (correct answer)
  4. Acetylcholinesterase will be inhibited, leading to continuous muscle contraction.
Explanation: The influx of Ca²⁺ through voltage-gated calcium channels at the presynaptic terminal is the direct trigger for the fusion of synaptic vesicles with the membrane and the subsequent release of neurotransmitters. Blocking these channels would prevent this fusion. The action potential propagation itself (A) depends on Na⁺ and K⁺ channels. Postsynaptic repolarization (B) and acetylcholinesterase activity (D) are events that occur after neurotransmitter release and binding.

Question 4

A postsynaptic neuron receives input from an inhibitory synapse. The neurotransmitter released binds to receptors that open ligand-gated Cl⁻ channels. If the neuron's resting potential is -65 mV and the equilibrium potential for Cl⁻ is -70 mV, what will be the effect?

  1. A small depolarization known as an Excitatory Postsynaptic Potential (EPSP).
  2. A large depolarization that triggers an action potential.
  3. A small hyperpolarization known as an Inhibitory Postsynaptic Potential (IPSP). (correct answer)
  4. No significant change, as the potential is already close to the Cl⁻ equilibrium.
Explanation: Opening Cl⁻ channels will cause Cl⁻ ions to flow down their electrochemical gradient. Since the membrane potential (-65 mV) is less negative than the Cl⁻ equilibrium potential (-70 mV), Cl⁻ ions will flow into the cell, making the inside more negative. This small hyperpolarization is an IPSP, which makes it harder for the neuron to reach its firing threshold.

Question 5

The absolute refractory period after an action potential is a brief time when a second action potential cannot be initiated, regardless of stimulus strength. What is the molecular basis for this period?

  1. The slow closing of voltage-gated K⁺ channels, causing hyperpolarization.
  2. The inactivation of voltage-gated Na⁺ channels. (correct answer)
  3. The depletion of Na⁺ and K⁺ ion gradients across the membrane.
  4. The time required for neurotransmitter reuptake at the synapse.
Explanation: The absolute refractory period is caused by the inactivation gates of the voltage-gated Na⁺ channels closing. Until these gates reset to their resting state, they cannot be opened by depolarization, making a new action potential impossible. The slow closing of K⁺ channels (A) contributes to the relative refractory period.

Question 6

[HL only] Neonicotinoid pesticides act as agonists at nicotinic acetylcholine receptors in insects. This means they bind to and activate the receptors, but are not broken down by acetylcholinesterase. What is the ultimate effect on the insect's nervous system?

  1. Blockage of all synaptic transmission, leading to flaccid paralysis.
  2. Prevention of acetylcholine release, causing a lack of nerve signals.
  3. Continuous, uncontrolled stimulation of postsynaptic neurons, leading to spastic paralysis. (correct answer)
  4. Rapid depletion of acetylcholine from the presynaptic terminals.
Explanation: By constantly activating the acetylcholine receptors, neonicotinoids cause continuous firing of the postsynaptic neurons. This overstimulation leads to uncontrolled muscle contractions (spastic paralysis), exhaustion, and eventual death of the insect. The effect is persistent because the pesticide is not removed from the receptor or the synapse.

Question 7

A neuron has a resting potential of -70 mV and a threshold potential of -50 mV. It receives two simultaneous excitatory signals (EPSPs) of +15 mV each and one inhibitory signal (IPSP) of -10 mV. What will be the resulting membrane potential at the axon hillock and will an action potential be generated?

  1. The potential will be -50 mV, and an action potential will be generated. (correct answer)
  2. The potential will be -40 mV, and an action potential will be generated.
  3. The potential will be -60 mV, and no action potential will be generated.
  4. The potential will remain at -70 mV, as the signals cancel each other out.
Explanation: The net change in potential is calculated by summing the inputs: (+15 mV) + (+15 mV) + (-10 mV) = +20 mV. The new membrane potential will be the resting potential plus this change: -70 mV + 20 mV = -50 mV. Since this potential reaches the threshold of -50 mV, an action potential will be generated.

Question 8

Local anaesthetics, like lidocaine, block pain by binding to voltage-gated sodium channels. Which part of the neural signalling process is directly inhibited?

  1. The maintenance of the resting membrane potential.
  2. The release of neurotransmitters from the presynaptic terminal.
  3. The binding of neurotransmitters to postsynaptic receptors.
  4. The generation of the depolarization phase of the action potential. (correct answer)
Explanation: The rapid depolarization phase of an action potential is caused by a massive influx of Na⁺ ions through voltage-gated sodium channels. By blocking these channels, local anaesthetics prevent the neuron from reaching the threshold and firing an action potential. Without an action potential, the pain signal cannot be transmitted to the CNS.

Question 9

How does a sensory neuron encode and transmit information about the intensity of a stimulus, such as the difference between a light touch and a firm press?

  1. By increasing the amplitude (peak voltage) of each action potential.
  2. By increasing the frequency of action potentials fired per unit of time. (correct answer)
  3. By increasing the speed of conduction of the action potential along the axon.
  4. By releasing different types of neurotransmitters from the axon terminal.
Explanation: Action potentials operate on an 'all-or-none' principle, meaning their amplitude is constant. The speed of conduction is also constant for a given axon. The nervous system encodes stimulus intensity by modulating the frequency of action potentials. A more intense stimulus generates a higher frequency of firing.

Question 10

A neuron is treated with a drug that inhibits the sodium-potassium pump. What is the expected long-term effect on the neuron's resting potential and ability to fire action potentials?

  1. The resting potential will become more negative (hyperpolarize), increasing the threshold for firing.
  2. The resting potential will gradually become less negative, eventually preventing the generation of action potentials. (correct answer)
  3. The resting potential will be unaffected, but the peak of the action potential will be lower.
  4. The neuron will fire action potentials continuously without any stimulus.
Explanation: The sodium-potassium pump actively transports 3 Na⁺ out and 2 K⁺ in, maintaining the concentration gradients essential for the negative resting potential. Inhibiting the pump allows these gradients to slowly dissipate through leak channels, causing the resting potential to become less negative (depolarize). Eventually, the gradients will be too weak to support the generation of an action potential.

Question 11

During the repolarization phase of an action potential, what is the status of the principal voltage-gated ion channels?

  1. Voltage-gated Na⁺ channels are open, and voltage-gated K⁺ channels are closed.
  2. Voltage-gated Na⁺ channels are inactivated, and voltage-gated K⁺ channels are open. (correct answer)
  3. Both voltage-gated Na⁺ channels and voltage-gated K⁺ channels are open.
  4. Both voltage-gated Na⁺ channels and voltage-gated K⁺ channels are closed.
Explanation: Repolarization is caused by the efflux of K⁺ ions. This occurs because the voltage-gated K⁺ channels are open. At the same time, the voltage-gated Na⁺ channels are in an inactivated state, which prevents Na⁺ influx and also contributes to the absolute refractory period.

Question 12

Which of the following represents a key difference between a graded potential (like an EPSP) and an action potential?

  1. Graded potentials are always depolarizing, while action potentials can be hyperpolarizing.
  2. Graded potentials involve voltage-gated channels, while action potentials involve ligand-gated channels.
  3. Graded potentials are transmitted long distances, while action potentials decay over short distances.
  4. The amplitude of a graded potential varies with stimulus strength, while an action potential is all-or-none. (correct answer)
Explanation: A fundamental distinction is that graded potentials (EPSPs and IPSPs) vary in size depending on the amount of neurotransmitter released. In contrast, an action potential has a fixed amplitude; as long as the threshold is reached, it will fire with the same peak voltage. The other options mischaracterize the properties: graded potentials decay locally (C) and are generated by ligand-gated channels (D), while action potentials are all-or-none depolarizations (A).

Question 13

A motor neuron has its cell body located in the spinal cord and its axon terminating on a muscle in the arm. The cell body is part of the  , while the axon is part of the  .

  1. central nervous system (CNS); peripheral nervous system (PNS) (correct answer)
  2. peripheral nervous system (PNS); central nervous system (CNS)
  3. central nervous system (CNS); central nervous system (CNS)
  4. peripheral nervous system (PNS); peripheral nervous system (PNS)
Explanation: The central nervous system (CNS) consists of the brain and spinal cord. The peripheral nervous system (PNS) consists of all nerves that extend outside the CNS. The cell body (soma) of a motor neuron is located within the grey matter of the spinal cord (CNS), while its axon extends outwards to connect with muscles, making the axon part of the PNS.

Question 14

After an action potential, the membrane briefly hyperpolarizes, becoming more negative than the resting potential. Which event is the primary cause of this hyperpolarization?

  1. The voltage-gated K⁺ channels remaining open after the membrane has repolarized. (correct answer)
  2. The rapid influx of Na⁺ ions through newly opened channels.
  3. The increased activity of the sodium-potassium pump.
  4. The influx of Cl⁻ ions through ligand-gated channels.
Explanation: Voltage-gated potassium channels are slower to close than voltage-gated sodium channels. After the membrane potential returns to the resting level during repolarization, some K⁺ channels are still open, allowing K⁺ to continue leaving the cell. This extra efflux of positive charge makes the membrane temporarily more negative than the normal resting potential.

Question 15

A simple reflex arc, such as withdrawing a hand from a hot object, involves a sensory neuron, a relay neuron (interneuron), and a motor neuron. What is the role of the relay neuron in this circuit?

  1. To transmit the sensory signal directly to the brain for conscious processing.
  2. To form a synapse with the sensory neuron and the motor neuron within the CNS. (correct answer)
  3. To carry the motor command from the brain to the effector muscle.
  4. To detect the initial stimulus at the skin's surface and generate an action potential.
Explanation: In a polysynaptic reflex arc, the relay neuron (or interneuron) is located entirely within the central nervous system (CNS). It serves as a connection point, receiving a signal from the sensory neuron and transmitting it to the motor neuron, allowing for processing within the spinal cord.

Question 16

What is the direct role of the myelin sheath in nerve impulse transmission?

  1. It contains the ion channels necessary for generating the action potential at all points along the axon.
  2. It provides metabolic support to the axon by producing ATP for the sodium-potassium pump.
  3. It acts as an electrical insulator, forcing the action potential to regenerate only at the nodes of Ranvier. (correct answer)
  4. It functions as a storage site for neurotransmitters that are released along the axon.
Explanation: The myelin sheath is a lipid-rich layer that provides electrical insulation. It prevents the leakage of ions across the axon membrane in the internodal regions. This forces the ionic current to flow down the axon to the next node of Ranvier, where the high concentration of voltage-gated channels allows the action potential to be regenerated. This process is called saltatory conduction.

Question 17

What is the defining characteristic of the threshold potential?

  1. The membrane potential at which the opening of voltage-gated Na⁺ channels becomes a regenerative, positive feedback loop. (correct answer)
  2. The potential at which the net movement of K⁺ ions across the membrane is zero.
  3. The maximum hyperpolarization a neuron can achieve after an action potential.
  4. The potential maintained solely by the sodium-potassium pump in the absence of any ion flow.
Explanation: The threshold potential is the critical level of depolarization that must be reached to trigger an action potential. At this potential, the influx of Na⁺ through opening voltage-gated Na⁺ channels overcomes the outward leak of K⁺. This causes further depolarization, which opens more Na⁺ channels, creating a positive feedback cycle that leads to the rapid spike of the action potential.

Question 18

Which statement accurately describes the state of ion gradients and membrane permeability in a neuron at resting potential?

  1. The concentration of Na⁺ is higher inside the cell, and the membrane is most permeable to Na⁺.
  2. The concentration of K⁺ is higher inside the cell, and the membrane is most permeable to K⁺. (correct answer)
  3. The concentrations of Na⁺ and K⁺ are equal inside and outside the cell, and permeability is low.
  4. The concentration of K⁺ is higher outside the cell, and the membrane is most permeable to Na⁺.
Explanation: At rest, the Na⁺/K⁺ pump establishes high K⁺ concentration inside the cell and high Na⁺ concentration outside. The resting membrane's permeability is primarily determined by potassium 'leak' channels, which are open. Therefore, the membrane is much more permeable to K⁺ than to Na⁺, and the outward leak of positive K⁺ ions is the main reason for the negative resting potential.

Question 19

What is the primary advantage of saltatory conduction in myelinated axons compared to continuous conduction in unmyelinated axons?

  1. It allows the amplitude of the action potential to increase as it travels along the axon.
  2. It eliminates the need for ATP, making nerve impulse transmission more energy efficient.
  3. It allows for a much faster propagation of the action potential with less energy expenditure. (correct answer)
  4. It enables the transmission of both excitatory and inhibitory signals along the same axon.
Explanation: Saltatory conduction, where the action potential 'jumps' between nodes of Ranvier, is significantly faster than continuous propagation. It is also more energy-efficient because the Na⁺/K⁺ pumps only need to restore ion gradients at the nodes, not along the entire length of the axon membrane.

Question 20

[HL only] What would be the consequence for an action potential if a drug were to block the inactivation gate of voltage-gated Na⁺ channels, leaving them able to open and close but not inactivate?

  1. The neuron would be unable to depolarize and fire an action potential.
  2. The action potential would have a lower peak amplitude.
  3. The repolarization phase of the action potential would be significantly prolonged. (correct answer)
  4. The neuron would fire action potentials with a much higher frequency.
Explanation: The inactivation of Na⁺ channels is crucial for shutting off the influx of Na⁺ and allowing the K⁺ efflux to repolarize the membrane. If the channels could not inactivate, they would remain open as long as the membrane was depolarized, counteracting the repolarizing effect of K⁺ efflux. This would lead to a much-prolonged action potential and a delayed return to the resting state.