AP Psychology Quiz: The Neuron And Neural Firing

What this quiz covers

This quiz focuses on The Neuron And Neural Firing, giving you a quick way to practice the rules, question types, and explanations that matter most for AP Psychology.

How to use this quiz

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.

Question 1

1. The membrane potential becomes less negative (more positive), moving toward threshold due to ion movement. (correct answer)
2. The membrane potential becomes more negative, moving away from threshold, increasing firing probability.
3. The action potential becomes smaller when depolarization is weak and larger when depolarization is strong.
4. The synapse transmits the impulse electrically only, so depolarization requires no chemical neurotransmitters.

Explanation: Depolarization occurs when the neuron's membrane potential becomes less negative (more positive), typically due to the influx of positive ions like sodium through opened ion channels. This electrical change moves the membrane potential from resting level (around -70 mV) toward threshold (around -55 mV). When sufficient depolarization reaches threshold, voltage-gated sodium channels open rapidly, initiating an all-or-none action potential that travels down the axon with constant amplitude. The action potential triggers neurotransmitter release at axon terminals, enabling electrochemical communication across synapses to the next neuron. Following the action potential, the refractory period temporarily prevents the neuron from firing again immediately, ensuring proper timing and directionality of neural signals.

Question 2

1. It is electrochemical overall, but the action potential along the axon is an electrical change in membrane voltage. (correct answer)
2. It is purely electrical from one neuron to the next, with no neurotransmitters, receptors, or synaptic cleft involved.
3. It is graded, so the action potential becomes larger when more neurotransmitters are present in the synapse.
4. It is chemical along the axon, because neurotransmitters diffuse down the axon to the terminal buttons.

Explanation: Neural transmission along an axon is fundamentally electrical, involving rapid changes in membrane voltage as the action potential propagates. However, overall neural communication is electrochemical because it combines electrical transmission within neurons (action potentials) with chemical transmission between neurons (neurotransmitters at synapses). The action potential follows the all-or-none principle, maintaining constant amplitude regardless of stimulus strength as it travels down the axon. When the electrical signal reaches axon terminals, it triggers neurotransmitter release into synaptic clefts. These chemical messengers then bind to receptors on the next neuron, potentially triggering another electrical action potential. The refractory period following each action potential temporarily prevents immediate refiring, ensuring proper signal timing and direction.

Question 3

1. Neurotransmitters must be released into the synaptic cleft and bind to receptors on the postsynaptic neuron. (correct answer)
2. The action potential must cross the synaptic cleft as electrical current, since synapses do not use chemicals.
3. The neuron must generate a larger action potential if the message is important, ensuring the next neuron fires.
4. Dendrites must send the action potential backward to the soma, where neurotransmitters are created and released.

Explanation: When an action potential reaches the end of an axon, neurotransmitters must be released from vesicles into the synaptic cleft and then bind to receptor sites on the postsynaptic neuron for communication to continue. This conversion from electrical to chemical signaling is essential in electrochemical neural communication. The action potential that traveled down the axon followed the all-or-none principle, maintaining constant amplitude regardless of the original stimulus strength. Once neurotransmitters bind to postsynaptic receptors, they can influence whether the receiving neuron reaches threshold to fire its own action potential. This chemical step across the synapse is necessary because electrical signals cannot jump directly across the synaptic cleft. After any resulting action potential in the postsynaptic neuron, the refractory period will temporarily prevent immediate refiring, maintaining proper timing in neural networks.

Question 4

1. Neurotransmitter release into the synaptic cleft from the presynaptic neuron's terminal buttons. (correct answer)
2. Action potential generation as a graded response, where spike size depends on stimulus intensity.
3. Electrical-only synaptic transmission, where current crosses the cleft without neurotransmitters or receptors.
4. Reception of messages by the axon, which normally contains receptor sites that bind neurotransmitters.

Explanation: When a toxin prevents vesicles from fusing with the presynaptic membrane, it blocks the crucial step of neurotransmitter release into the synaptic cleft. The action potential can still travel down the axon following the all-or-none principle and reach the terminals, but the electrical signal cannot be converted to chemical communication because neurotransmitter-containing vesicles cannot release their contents. This disrupts the normal electrochemical transmission process where electrical action potentials trigger chemical signaling across synapses. Without neurotransmitter release, the postsynaptic neuron cannot receive the chemical message, even though the presynaptic neuron fired normally and experienced its typical refractory period. This blockade effectively breaks the chain of neural communication at the critical electrical-to-chemical conversion step that occurs at axon terminals.

Question 5

1. Action potential travels down axon; terminal buttons release neurotransmitters; neurotransmitters bind receptors on next neuron. (correct answer)
2. Dendrites release neurotransmitters; synaptic cleft generates action potential; axon receives the message at receptor sites.
3. Cell body sends graded action potentials; stronger stimuli create larger spikes; spikes cross synapse electrically only.
4. Myelin releases neurotransmitters; nodes of Ranvier act as receptors; dendrites carry the outgoing signal to terminals.

Explanation: Neural communication begins when an action potential travels down the axon as an electrical change in membrane voltage, maintaining constant amplitude due to the all-or-none principle. When this electrical signal reaches the axon terminals, it triggers vesicles to fuse with the membrane and release neurotransmitters into the synaptic cleft. These chemical messengers then diffuse across the gap and bind to specific receptor sites on the postsynaptic neuron, converting the signal back to electrical changes in the receiving neuron. If sufficient excitatory input reaches threshold, the postsynaptic neuron fires its own all-or-none action potential. The refractory period after each firing ensures that signals travel in one direction and maintains proper timing in neural networks.

Question 6

1. Neurotransmitters remain in the synaptic cleft longer, increasing the duration of their effects on receptors. (correct answer)
2. Neurotransmitters are prevented from being released, so the synapse becomes electrical-only to compensate.
3. Action potentials become larger and smaller depending on how many neurotransmitters are left in the cleft.
4. Myelin breaks down immediately, slowing conduction because neurotransmitters can no longer jump between nodes.

Explanation: When reuptake transporters are inhibited, neurotransmitters remain in the synaptic cleft for a longer duration because they cannot be efficiently removed by the presynaptic neuron. This prolonged presence increases the time that neurotransmitters can bind to postsynaptic receptors, potentially amplifying and extending their effects. The action potential that originally triggered neurotransmitter release followed the all-or-none principle, maintaining constant amplitude as it traveled down the axon. Normal neural communication involves electrochemical signaling - electrical action potentials within neurons and chemical neurotransmitter signaling across synapses. During the refractory period following the action potential, the presynaptic neuron cannot immediately fire again, but the extended presence of neurotransmitters in the cleft can continue to influence the postsynaptic neuron.

Question 7

1. All-or-none principle, meaning the neuron fires a full action potential or not at all once threshold is crossed. (correct answer)
2. Graded response principle, meaning stronger stimuli produce larger action potentials traveling down the axon.
3. Electrical-only transmission, meaning synapses pass current directly without neurotransmitters or receptors.
4. Dendritic release principle, meaning dendrites release neurotransmitters to determine action potential amplitude.

Explanation: The all-or-none principle states that once a neuron reaches threshold, it fires a complete action potential of fixed amplitude, or if threshold is not reached, no action potential occurs at all. The size and speed of the action potential do not vary based on stimulus intensity - a barely threshold stimulus produces the same action potential as a much stronger stimulus. This electrical signal travels down the axon maintaining constant amplitude until it reaches the terminal buttons. There, the action potential triggers neurotransmitter release into the synaptic cleft, where chemical messengers cross to the postsynaptic neuron. Following each action potential, the refractory period temporarily prevents another firing, ensuring proper signal timing and preventing backward propagation of the electrical signal.

Question 8

1. It decreases the likelihood of an action potential by hyperpolarizing the postsynaptic neuron away from threshold. (correct answer)
2. It increases firing by depolarizing the neuron and producing a larger action potential when the stimulus is stronger.
3. It makes synaptic transmission electrical-only, so the action potential crosses the cleft without chemicals.
4. It causes dendrites to release neurotransmitters into the cleft, initiating the action potential in the soma.

Explanation: When an inhibitory neurotransmitter binds to postsynaptic receptors, it typically causes hyperpolarization by opening ion channels that allow negative ions to enter or positive ions to exit the cell. This makes the membrane potential more negative than resting level (more negative than -70 mV), moving it farther from threshold (-55 mV) and decreasing the likelihood that the neuron will fire an action potential. If the neuron does eventually reach threshold despite inhibitory input, it will still fire a full all-or-none action potential that travels down the axon with constant amplitude. The action potential triggers neurotransmitter release at synapses, and the refractory period following firing temporarily prevents another immediate action potential, maintaining proper neural timing.

Question 9

1. It cannot immediately fire another action potential, helping ensure one-way transmission and limiting firing rate. (correct answer)
2. It fires a smaller, graded action potential if the stimulus is weak and a larger one if the stimulus is strong.
3. It transmits the message across the synapse purely electrically, bypassing neurotransmitter release entirely.
4. Its dendrites temporarily become axons, carrying the outgoing action potential to the next neuron's terminals.

Explanation: During the refractory period, a neuron cannot fire another action potential immediately after the previous one, which serves several important functions in neural communication. This temporary inability to fire helps ensure that action potentials travel in one direction down the axon (from cell body to terminals) and limits the maximum firing rate of neurons. The refractory period occurs because sodium channels become temporarily inactivated and potassium channels remain open longer, making it difficult or impossible to reach threshold again. This mechanism is crucial for proper neural timing and prevents the chaotic firing that would occur if neurons could fire continuously. The action potential itself follows the all-or-none principle, maintaining constant amplitude as it travels to trigger neurotransmitter release at synapses.

Question 10

1. They are proteins on the postsynaptic membrane that bind specific neurotransmitters, influencing postsynaptic firing likelihood. (correct answer)
2. They are gaps between myelin segments that release neurotransmitters and determine action potential amplitude.
3. They are structures in the synaptic cleft that convert chemical signals directly into electrical current without binding.
4. They are located on axons to receive incoming signals, while dendrites carry outgoing action potentials to terminals.

Explanation: Receptor sites are specialized protein molecules located on the postsynaptic neuron's membrane (typically on dendrites and cell body) that bind specific neurotransmitters in a lock-and-key fashion. When neurotransmitters released from presynaptic terminals cross the synaptic cleft and bind to these receptors, they cause ion channels to open or close, altering the postsynaptic neuron's membrane potential. This binding can either increase (excitatory) or decrease (inhibitory) the likelihood that the postsynaptic neuron will reach threshold and fire an all-or-none action potential. This represents the crucial chemical-to-electrical conversion in electrochemical neural communication. If threshold is reached, the action potential travels down the axon to trigger further neurotransmitter release. During the refractory period following any action potential, the postsynaptic neuron cannot immediately fire again, ensuring proper timing of neural signals.

Question 11

1. Sending action potentials away from the cell body to communicate with other neurons or muscles. (correct answer)
2. Receiving incoming chemical messages from other neurons via receptor sites on dendrites.
3. Maintaining the synaptic cleft, which is required to transmit impulses electrically without neurotransmitters.
4. Producing graded action potentials of varying size, which normally occur in the axon during strong stimulation.

Explanation: If a neuron's axon is severed, it cannot send action potentials away from the cell body to communicate with other neurons, muscles, or glands. The axon serves as the neuron's output pathway, carrying all-or-none action potentials from the integration site (axon hillock) to the terminal buttons where neurotransmitter release occurs. Without an intact axon, the neuron loses its ability to influence postsynaptic cells, even though it may still receive and integrate incoming signals at its dendrites and cell body. The electrochemical communication process is disrupted because the electrical signal cannot reach the terminals to trigger chemical neurotransmitter release across synapses. While the neuron might still experience depolarization and reach threshold, no action potential can propagate to complete the communication process, and the normal refractory period that follows action potentials would not occur at the severed terminals.

Question 12

1. Reduced saltatory conduction slows action potential propagation along axons because insulation between nodes is lost. (correct answer)
2. Demyelination makes synapses electrical-only, eliminating neurotransmitter delay and therefore speeding reactions.
3. Demyelination makes action potentials graded, so weaker stimuli create smaller spikes that travel more slowly.
4. Demyelination prevents dendrites from receiving messages, but speeds axons because less insulation reduces resistance.

Explanation: Demyelination reduces the effectiveness of saltatory conduction, where action potentials normally jump between nodes of Ranvier along myelinated axons. Without proper myelin insulation, action potentials must propagate through slower continuous conduction along the entire axon membrane, significantly reducing transmission speed. This slower neural conduction directly translates to increased reaction times in behavioral responses. The action potential itself still follows the all-or-none principle, but travels much more slowly to reach axon terminals where neurotransmitter release occurs. The electrochemical nature of neural communication remains the same - electrical signals within neurons and chemical signals across synapses - but the reduced speed affects the timing of the entire neural circuit. The refractory period still occurs after each action potential, but the overall message delivery is delayed.

Question 13

1. By firing rate and number of neurons recruited, not by producing larger action potentials in each neuron. (correct answer)
2. By producing larger action potentials when stimuli are stronger and smaller action potentials when stimuli are weaker.
3. By transmitting the impulse purely electrically across synapses, eliminating variability caused by neurotransmitters.
4. By shifting the location of neurotransmitter release from axon terminals to dendrites for stronger stimuli.

Explanation: Since action potentials follow the all-or-none principle and maintain constant amplitude regardless of stimulus strength, stimulus intensity cannot be encoded by varying the size of individual action potentials. Instead, stronger stimuli are encoded through increased firing rate (frequency coding) and by recruiting more neurons to fire simultaneously (population coding). A weak stimulus might cause a neuron to fire slowly and activate fewer neurons, while a strong stimulus causes rapid firing and activates many neurons in the network. Each individual action potential travels down the axon with the same amplitude and triggers the same amount of neurotransmitter release at terminals. The electrochemical communication across synapses remains consistent, and each neuron experiences the same refractory period after firing. This frequency and population coding allows the nervous system to represent stimulus intensity despite the binary nature of action potentials.

Question 14

1. Faster action potential conduction along the axon, because myelin normally insulates and speeds signal transmission. (correct answer)
2. Neurotransmitter synthesis in dendrites, because myelin is the site where chemical messengers are manufactured and stored.
3. Direct electrical transmission across synapses, because myelin normally forms a wire that bridges the synaptic cleft.
4. Graded action potential amplitude control, because myelin adjusts how large each action potential becomes based on stimulation strength.

Explanation: Myelin is a fatty insulation that wraps around axons in segments, dramatically increasing the speed of action potential conduction through saltatory conduction - the signal "jumps" between gaps in myelin called nodes of Ranvier. Multiple sclerosis damages this myelin sheath, causing slower and less reliable signal transmission along axons. This can lead to various neurological symptoms depending on which neurons are affected. Myelin doesn't synthesize neurotransmitters (that occurs in the cell body and terminals), doesn't bridge synaptic gaps (which remain chemical), and doesn't control action potential amplitude (which follows the all-or-none principle). The refractory period ensures proper signal spacing regardless of myelin.

Question 15

1. All-or-none firing, where neurotransmitters are removed when the presynaptic neuron fires a smaller action potential repeatedly.
2. Reuptake, where transporter proteins in the presynaptic membrane take neurotransmitters back into the sending neuron. (correct answer)
3. Myelination, where myelin absorbs neurotransmitters and converts them into an electrical signal across the synapse.
4. Axonal reception, where the postsynaptic axon terminals pull neurotransmitters in and immediately fire a graded action potential.

Explanation: After neurotransmitters bind to receptors on the postsynaptic neuron, they must be cleared from the synaptic cleft to terminate the signal and prepare for the next transmission. Reuptake is the primary mechanism where specialized transporter proteins in the presynaptic membrane actively pump neurotransmitters back into the sending neuron for recycling or breakdown. This process is crucial for proper neural function - many antidepressants work by blocking reuptake transporters. Enzymes can also break down neurotransmitters in the cleft. The all-or-none principle refers to action potential firing, not neurotransmitter removal, and myelin insulates axons rather than absorbing neurotransmitters.

Question 16

1. Myelin sheath, which insulates the axon and allows faster conduction by enabling action potentials to jump nodes. (correct answer)
2. Synaptic cleft, which speeds conduction by letting action potentials cross directly as electrical current.
3. Dendrites, which speed conduction by amplifying spike size when the stimulus intensity is higher.
4. Cell body, which speeds conduction by releasing neurotransmitters down the axon to the terminal buttons.

Explanation: The myelin sheath acts as electrical insulation around axons, enabling saltatory conduction where action potentials jump rapidly between nodes of Ranvier rather than traveling continuously along the membrane. This jumping pattern dramatically increases the speed of neural transmission, which is crucial for quick reflex responses. The action potential maintains constant amplitude due to the all-or-none principle as it propagates to the axon terminals. Fast transmission ensures that the electrochemical signal - electrical within the neuron and chemical across synapses - reaches its target quickly. At the terminals, neurotransmitter release occurs when the action potential arrives, and during the subsequent refractory period, the neuron cannot immediately fire another action potential. This rapid, efficient transmission is essential for protective reflexes that require immediate responses.

Question 17

1. Myelin sheath, which secretes neurotransmitters and increases the amplitude of action potentials in a graded manner.
2. Terminal buttons (axon terminals), which release neurotransmitters from vesicles into the synaptic cleft. (correct answer)
3. Dendrites, which release neurotransmitters and carry messages away from the cell body to the next neuron.
4. Axon hillock, which releases neurotransmitters directly into the cleft and makes transmission purely electrical.

Explanation: Terminal buttons (also called axon terminals) are the endpoints of the axon that contain vesicles filled with neurotransmitters. When an action potential reaches these terminals, it triggers voltage-gated calcium channels to open, causing vesicles to fuse with the presynaptic membrane and release their chemical contents into the synaptic cleft. This process converts the electrical signal of the action potential into chemical communication across the synapse. The neurotransmitters then diffuse across the gap and bind to specific receptor sites on the postsynaptic neuron. During the refractory period, the presynaptic neuron cannot immediately fire another action potential, helping ensure proper signal timing and unidirectional flow of information.

Question 18

1. The neurotransmitter's effect ends sooner because it is broken down, reducing continued receptor activation. (correct answer)
2. The postsynaptic neuron produces a smaller action potential because the neurotransmitter amount controls spike amplitude.
3. The synapse becomes electrical-only, so breakdown increases the speed of transmission by removing chemical delay.
4. The axon begins receiving signals through receptors, reversing the usual direction of information flow in neurons.

Explanation: When neurotransmitters are quickly broken down by enzymes in the synaptic cleft, their effect on postsynaptic receptors ends sooner, reducing the duration of receptor activation and postsynaptic response. This enzymatic breakdown is one mechanism for terminating synaptic transmission and clearing the cleft for subsequent signals. The original action potential that triggered neurotransmitter release followed the all-or-none principle as it traveled down the axon. Normal electrochemical communication involves electrical action potentials within neurons and chemical neurotransmitter signaling across synapses. Quick enzymatic breakdown ensures that each synaptic signal is brief and discrete, preventing prolonged activation that could interfere with subsequent neural messages. The refractory period in the presynaptic neuron still occurs after the action potential, maintaining proper timing for future electrical signals even as the chemical signal is rapidly terminated.

Question 19

1. Axon, a long fiber that conducts an all-or-none action potential away from the cell body toward terminals. (correct answer)
2. Dendrites, which carry action potentials away from the cell body and release neurotransmitters at their tips.
3. Synaptic cleft, a gap that transmits the message only electrically with no chemical step involved.
4. Cell body, which sends a stronger or weaker action potential depending on stimulus intensity, like a graded response.

Explanation: The axon is a long fiber that carries action potentials away from the cell body (soma) toward the terminal buttons. When the neuron reaches threshold, an all-or-none action potential is generated at the axon hillock and travels down the axon as an electrical change in membrane voltage. This electrical signal maintains constant amplitude regardless of the original stimulus strength. At the axon terminals, the electrical signal triggers the release of neurotransmitters into the synaptic cleft. These chemical messengers then cross the gap to bind with receptors on the next neuron. After firing, the neuron enters a refractory period during which it cannot immediately fire another action potential.

Question 20

1. Vesicles fuse with the presynaptic membrane and release neurotransmitters into the synaptic cleft. (correct answer)
2. Dendrites generate a graded action potential whose size depends on how much neurotransmitter is released.
3. The synaptic cleft becomes electrically conductive, allowing the action potential to jump directly to the next axon.
4. Myelin produces neurotransmitters that bind to receptors on the same neuron to amplify spike amplitude.

Explanation: When an action potential arrives at axon terminals, it triggers voltage-gated calcium channels to open, allowing calcium ions to enter the terminal. This calcium influx causes synaptic vesicles containing neurotransmitters to fuse with the presynaptic membrane and release their chemical contents into the synaptic cleft. This process converts the electrical signal of the action potential into chemical communication across the synapse. The action potential that triggered this release followed the all-or-none principle, maintaining constant amplitude as it traveled down the axon. The released neurotransmitters then bind to receptors on the postsynaptic neuron, and during the refractory period, the presynaptic neuron cannot immediately fire another action potential.