Lecture 3: Excitable cells & Signal Transmission Flashcards
Opening ligand-gated Na⁺ channels typically leads to:
A) Hyperpolarization
B) Inhibition
C) Excitation
D) No change in membrane potential
c
Opening ligand-gated K⁺ channels typically results in:
A) Excitation
B) Hyperpolarization
C) Depolarization
D) No effect on membrane potential
Answer: B
If an inhibitory signal opens ligand-gated K⁺ channels, what happens to the likelihood of an action potential?
A) Increases, because the cell becomes more positive
B) Decreases, because the cell loses positive charge
C) Stays the same, because K⁺ does not affect membrane potential
D) Increases, because the cell gains negative charge
Answer: B
What happens if two excitatory signals and one inhibitory signal are integrated at the axon hillock?
A) An action potential always occurs
B) An action potential never occurs
C) It depends on whether the total signal reaches threshold
D) Only inhibitory signals influence the action potential
Answer: C
The process of combining multiple excitatory and inhibitory signals at the axon hillock is called:
A) Temporal summation
B) Spatial summation
C) Threshold activation
D) Action potential propagation
Answer: B
What is the key characteristic of temporal summation?
A) Multiple neurons firing at the same time
B) A single neuron firing multiple times in quick succession
C) Both excitatory and inhibitory signals arriving at the same time
D) A single stimulus triggering an immediate action potential
B)
What is required for temporal summation to successfully trigger an action potential?
A) Multiple neurons synapsing onto the same target
B) A single neuron firing rapidly so that graded potentials build up
C) The presence of an inhibitory stimulus to balance excitation
D) Neurotransmitter degradation before the second stimulus arrives
b
What is the main difference between temporal and spatial summation?
A) Temporal summation relies on multiple signals from different neurons, while spatial summation involves a single neuron firing repeatedly
B) Temporal summation involves a single neuron firing rapidly, while spatial summation integrates multiple inputs from different neurons
C) Temporal summation only occurs with inhibitory inputs, while spatial summation is always excitatory
D) Temporal summation is independent of neurotransmitter release, while spatial summation depends on it
Answer: B
The action potential is considered an “all-or-none” response because:
A) The neuron fires only if the threshold potential is reached
B) The neuron fires at different intensities depending on the stimulus
C) The neuron can partially fire without reaching full depolarization
D) The neuron can regulate the strength of the signal
A
The refractory period ensures that:
A) The neuron can fire multiple action potentials at the same time
B) Action potentials only travel in one direction
C) The membrane potential remains above the threshold
D) The neuron can generate a stronger-than-normal response
b
What is the role of Na⁺/K⁺ pumps after an action potential?
A) To maintain the resting membrane potential by restoring ion gradients
B) To keep Na⁺ inside the cell to continue depolarization
C) To inhibit further action potentials
D) To generate another action potential immediately
Answer: A
What is meant by the term “equilibrium potential” for an ion?
A) The voltage at which there is no net movement of the ion across the membrane
B) The voltage at which the ion is at its highest concentration inside the cell
C) The voltage at which an action potential is always triggered
D) The voltage at which all ion channels close
A
What is the approximate equilibrium potential of sodium (Na⁺) in neurons?
A) -90 mV
B) -70 mV
C) 0 mV
D) +70 mV
Answer: D
What is the approximate equilibrium potential of potassium (K⁺) in neurons?
A) -90 mV
B) -70 mV
C) 0 mV
D) +70 mV
a
What is the role of K⁺ leak channels in neurons?
A) To depolarize the membrane and trigger an action potential
B) To allow passive diffusion of K⁺ out of the cell, maintaining resting membrane potential
C) To actively transport K⁺ into the cell using ATP
D) To rapidly bring Na⁺ into the cell during depolarization
b
The Na⁺/K⁺ pump (Na⁺-K⁺ ATPase) maintains resting membrane potential by:
A) Pumping 3 Na⁺ ions into the cell and 2 K⁺ ions out
B) Pumping 3 Na⁺ ions out of the cell and 2 K⁺ ions in
C) Allowing passive diffusion of Na⁺ and K⁺ across the membrane
D) Depolarizing the neuron to trigger an action potential
b
Which type of ion channel is primarily responsible for graded potentials?
A) Voltage-gated channels
B) Ligand-gated channels
C) Leak channels
D) Mechanically-gated channels
Answer: B
Which type of ion channel is directly responsible for depolarization during an action potential?
A) K⁺ leak channels
B) Ligand-gated K⁺ channels
C) Voltage-gated Na⁺ channels
D) Na⁺/K⁺ ATPase
Answer: C
Practice question: Describe the steps if an action potential and the proteins or channels involved in them. (you would have to draw it and explain).
- Resting Potential (-70mV) – Maintained by the Na⁺/K⁺ ATPase pump.
✅ 2. Threshold (-55mV) is reached → Voltage-gated Na⁺ channels open.
✅ 3. Depolarization → Na⁺ rushes in, making the inside more positive.
✅ 4. Peak of Action Potential (+30mV) → Na⁺ channels inactivate, and K⁺ channels open.
✅ 5. Repolarization → K⁺ rushes out, bringing the neuron back toward -70mV.
✅ 6. Hyperpolarization (~-90mV) → K⁺ channels stay open too long, making the inside extra negative.
✅ 7. Resting Potential Restored → Na⁺/K⁺ ATPase pump kicks in, pumping 3 Na⁺ out and 2 K⁺ in, restoring -70mV.
Which ion channel remains open at rest, contributing to the resting membrane potential?
A) Voltage-gated Na⁺ channel
B) Voltage-gated K⁺ channel
C) K⁺ leak channel
D) Ligand-gated Na⁺ channel
c
At resting potential, what is the relative permeability of Na⁺ and K⁺?
A) Na⁺ permeability is greater than K⁺
B) K⁺ permeability is greater than Na⁺
C) Na⁺ and K⁺ have equal permeability
D) Both Na⁺ and K⁺ are impermeable at rest
Answer: B
What causes the opening of voltage-gated Na⁺ channels?
A) Binding of a neurotransmitter
B) A decrease in extracellular Na⁺ concentration
C) Reaching the threshold potential (~ -55mV)
D) The closing of K⁺ channels
Answer: C
What is the main result of voltage-gated Na⁺ channel activation?
A) The neuron becomes more negative inside
B) The neuron depolarizes as Na⁺ rushes into the cell
C) The neuron hyperpolarizes due to K⁺ influx
D) The Na⁺/K⁺ pump immediately restores resting potential
Answer: B
What happens to Na⁺ channels once the membrane potential reaches its peak (~ +30 mV)?
A) They close immediately
B) They become inactivated, preventing further Na⁺ entry
C) They remain open indefinitely
D) They switch to transporting Na⁺ out of the cell
B
Why does an action potential not occur every time Na⁺ channels open?
A) The threshold potential must be reached for Na⁺ channels to activate
B) Na⁺ channels are always inactivated at rest
C) K⁺ channels open simultaneously, preventing depolarization
D) The neuron must first be in a refractory period
A
What happens immediately after Na⁺ channels inactivate?
A) K⁺ channels open, allowing K⁺ to exit the cell
B) The Na⁺/K⁺ pump restores the resting membrane potential
C) The neuron remains depolarized indefinitely
D) Na⁺ continues to flow into the cell until equilibrium is reached
A
What causes repolarization of the neuron after an action potential?
A) Na⁺ channels opening
B) K⁺ leak channels closing
C) Opening of voltage-gated K⁺ channels, allowing K⁺ to exit
D) Na⁺ continuing to enter the cell
Answer: C
Why do voltage-gated K⁺ channels open during repolarization?
A) To maintain a constant membrane potential
B) Because Na⁺ channels are still open
C) To allow K⁺ to exit, restoring the negative charge inside the neuron
D) To stop the Na⁺/K⁺ ATPase from working
Answer: C
Why does the membrane potential overshoot (hyperpolarization) below resting potential?
A) Because voltage-gated Na⁺ channels reopen
B) Because voltage-gated K⁺ channels remain open too long, allowing excess K⁺ efflux
C) Because the Na⁺/K⁺ ATPase stops working
D) Because the neuron has permanently lost Na⁺
Answer: B
What is the refractory period, and why does it occur?
A) A time when the neuron is more excitable than normal
B) A period when another action potential cannot be triggered due to Na⁺ channel inactivation and hyperpolarization
C) A phase where K⁺ channels switch to transporting Na⁺
D) A phase where the membrane potential remains at zero
Answer: B
What is the Hodgkin Cycle?
A) A negative feedback loop that prevents excessive Na⁺ entry
B) A positive feedback loop where Na⁺ entry causes more Na⁺ channels to open
C) The process of K⁺ exiting the neuron to restore resting potential
D) The refractory period where no action potentials can occur
Answer: B
What initiates the Hodgkin Cycle?
A) The closing of K⁺ leak channels
B) The membrane reaching threshold potential (~ -55mV)
C) The hyperpolarization phase of an action potential
D) The Na⁺/K⁺ pump becoming inactive
Answer: B
How does the Hodgkin Cycle contribute to depolarization?
A) It slows down Na⁺ entry to maintain resting potential
B) It stops Na⁺ from entering the neuron after an action potential
C) It amplifies depolarization by allowing Na⁺ influx to trigger more Na⁺ channel openings
D) It prevents an action potential from occurring
Answer: C
What makes voltage-gated Na⁺ channels unique compared to other ion channels?
A) They have two gates: an activation gate and an inactivation gate
B) They require ATP to function
C) They allow Na⁺ to enter and exit simultaneously
D) They remain permanently open once activated
Answer: A
At resting membrane potential (~ -70mV), what is the state of the voltage-gated Na⁺ channel gates?
A) Activation gate is closed, inactivation gate is open
B) Activation gate is open, inactivation gate is closed
C) Both gates are open
D) Both gates are closed
Answer: A
What happens to the Na⁺ channel at the peak of the action potential (~ +30mV)?
A) The inactivation gate closes, preventing further Na⁺ influx
B) The activation gate closes, while the inactivation gate remains open
C) The channel allows Na⁺ to exit instead of entering
D) The channel remains fully open indefinitely
Answer: A
Why can Na⁺ not enter the cell during the absolute refractory period?
A) Because the inactivation gate is closed, even though the activation gate is open
B) Because Na⁺ has reached its equilibrium potential
C) Because the Na⁺/K⁺ pump removes all Na⁺ from the cell
D) Because the neuron is too depolarized to allow ion movement
A
When does the inactivation gate reopen, allowing the Na⁺ channel to reset?
A) During repolarization, as the membrane potential returns to resting (~ -70mV)
B) At the peak of the action potential (~ +30mV)
C) During hyperpolarization (~ -80mV)
D) It never reopens; the neuron creates new Na⁺ channels instead
A
During the absolute refractory period, why is it impossible to generate another action potential?
A) Because the inactivation gate of voltage-gated Na⁺ channels is closed
B) Because K⁺ is still entering the cell
C) Because ligand-gated Na⁺ channels are still open
D) Because the neuron is at resting potential
Answer: A
What happens to K⁺ during the absolute refractory period?
A) K⁺ channels are open, allowing K⁺ to exit the cell
B) K⁺ is actively pumped into the neuron
C) K⁺ channels remain closed
D) K⁺ enters the neuron, causing further depolarization
Answer: A
Why is it harder to trigger an action potential during the relative refractory period?
A) Because some Na⁺ channels are still inactivated, requiring a stronger-than-normal stimulus
B) Because the neuron has already reached equilibrium
C) Because K⁺ is still entering the cell, making it more positive
D) Because Na⁺ channels remain fully open
Answer: A
Which phase of the action potential corresponds to the absolute refractory period?
A) Depolarization and the peak (+30mV)
B) Hyperpolarization (-80mV)
C) Resting potential (-70mV)
D) Synaptic transmission
a
Which phase of the action potential corresponds to the relative refractory period?
A) The repolarization and hyperpolarization phase
B) The resting potential
C) The depolarization phase
D) The threshold potential phase
Answer: A
If a neuron is in the relative refractory period, what is required to trigger another action potential?
A) A stronger-than-normal stimulus to overcome hyperpolarization
B) A weaker stimulus than normal
C) No stimulus, as action potentials fire continuously
D) Inhibition of Na⁺ channels
Answer: A
What is the mechanism of action of tetrodotoxin (TTX)?
A) It blocks voltage-gated Na⁺ channels, preventing action potentials
B) It increases Na⁺ entry, causing excessive neuronal firing
C) It blocks K⁺ channels, preventing repolarization
D) It increases neurotransmitter release at synapses
Answer: A
Why is TTX lethal to most animals?
A) It prevents action potentials, causing paralysis and respiratory failure
B) It speeds up action potentials, leading to seizures
C) It stops K⁺ from leaving the neuron, preventing repolarization
D) It prevents neurotransmitter uptake, leading to overstimulation
Answer: A
How are puffer fish resistant to TTX?
A) They have a mutation in their voltage-gated Na⁺ channel gene
B) They produce an enzyme that neutralizes TTX
C) They never come into contact with TTX
D) They have stronger action potentials that override the block
Answer: A
What is the evolutionary significance of California newts and garter snakes?
A) Newts produce TTX as a defense, and garter snakes have evolved resistance through Na⁺ channel mutations
B) Garter snakes avoid newts to prevent poisoning
C) Garter snakes produce their own TTX
D) Newts have evolved resistance to TTX to avoid self-poisoning
Answer: A
Why do not all garter snake populations have TTX resistance?
A) Only populations that co-evolved with toxic newts have developed Na⁺ channel mutations
B) Some populations prefer different prey
C) TTX resistance is not genetically inheritable
D) All garter snakes have TTX resistance
Answer: A
Why is an action potential an “all-or-nothing” response?
A) It either reaches threshold and fires completely or does not fire at all
B) The neuron can partially fire depending on the stimulus strength
C) The neuron continuously adjusts the strength of the signal
D) The action potential can stop midway through propagation
a
How does Na⁺ movement affect adjacent areas of the membrane?
A) It attracts nearby negative charges, causing depolarization in adjacent segments
B) It prevents further depolarization
C) It causes hyperpolarization in nearby segments
D) It immediately restores resting potential
A
How does the strength of a stimulus affect action potential frequency?
A) Stronger stimuli generate a higher frequency of action potentials
B) Stronger stimuli make action potentials larger
C) Stronger stimuli change the resting membrane potential
D) Weak stimuli stop neurons from firing entirely
a
What happens when a subthreshold stimulus is applied?
A) No action potential occurs
B) A weak action potential is generated
C) An action potential occurs at lower frequency
D) The neuron hyperpolarizes
a
What happens when a threshold stimulus is applied to a neuron?
A) An action potential occurs at a normal frequency
B) No action potential occurs
C) The neuron depolarizes but does not fire an action potential
D) The neuron hyperpolarizes
A
Why does a sustained suprathreshold stimulus lead to higher frequency of action potentials?
A) It triggers additional action potentials during the relative refractory period
B) It increases the strength of each individual action potential
C) It allows more K⁺ to enter the neuron
D) It lowers the threshold potential
a
Why does a sustained threshold stimulus not generate extra action potentials beyond the normal rate?
A) Because the refractory periods limit how frequently APs can occur
B) Because K⁺ prevents additional depolarization
C) Because Na⁺ channels stay open indefinitely
D) Because resting potential never resets
Answer: A
What happens when a suprathreshold stimulus is applied?
A) It increases action potential frequency by triggering APs during the relative refractory period
B) It makes each action potential larger in size
C) It reduces the refractory period to zero
D) It permanently inactivates Na⁺ channels
Answer: A
How does a stronger stimulus increase action potential frequency?
A) By triggering additional APs during the relative refractory period
B) By making individual APs stronger
C) By bypassing the absolute refractory period
D) By increasing K⁺ permeability
Answer: A
If a weak threshold stimulus is applied for an extended period, what will happen?
A) APs will occur, but only at the normal firing rate
B) AP frequency will increase indefinitely
C) No APs will occur
D) The neuron will stay depolarized without firing
a
Which of the following will increase conduction velocity of an action potential?
A) Decreasing internal resistance (increasing axon diameter)
B) Increasing the number of voltage-gated Na⁺ channels
C) Increasing the internal resistance of the axoplasm
D) Decreasing membrane resistance
a
Why does decreasing the internal resistance of the axoplasm speed up action potential conduction?
A) It allows charge to spread more easily through the axon
B) It makes the neuron fire more frequently
C) It increases the number of voltage-gated channels
D) It decreases the amount of Na⁺ entering the cell
a
How does increasing membrane resistance improve conduction velocity?
A) It reduces ion leakage, ensuring the signal stays strong over long distances
B) It allows more Na⁺ to enter the cell
C) It increases K⁺ efflux, speeding up repolarization
D) It slows down the refractory period
A
What effect does increasing temperature have on conduction velocity?
A) It increases conduction speed by improving ion channel function
B) It decreases action potential firing rate
C) It prevents voltage-gated Na⁺ channels from opening
D) It has no effect on conduction velocity
a
Why do myelinated axons conduct action potentials faster than unmyelinated axons?
A) Myelin increases membrane resistance, reducing ion leakage and allowing saltatory conduction
B) Myelin adds extra Na⁺ channels to the axon
C) Myelin increases the neuron’s resting potential
D) Myelin increases the number of synapses
a
What is the main reason larger-diameter axons conduct signals faster?
A) They have lower internal resistance, allowing current to flow more easily
B) They contain more Na⁺ and K⁺
C) They have a higher threshold potential
D) They have more neurotransmitter receptors
Answer: A
Why do giant squid axons have a large diameter?
A) To allow fast signal transmission for rapid escape responses
B) To increase the number of synapses
C) To make neurotransmitter release more efficient
D) To conserve space in the nervous system
a
How do mammals compensate for not having giant axons?
A) They use myelin to insulate axons and increase conduction speed
B) They increase the number of Na⁺ channels
C) They rely on neurotransmitters instead of electrical conduction
D) They use thicker dendrites instead of larger axons
Answer: A
How does increasing axon diameter affect conduction velocity?
A) It decreases internal resistance, allowing charge to flow more easily
B) It increases the number of Na⁺ channels
C) It slows down conduction
D) It increases membrane resistance
a
Why do giant squid axons have a large diameter?
A) To allow fast signal transmission for rapid escape responses
B) To increase the number of synapses
C) To make neurotransmitter release more efficient
D) To conserve space in the nervous system
Answer: A
How does internal resistance affect action potential propagation?
A) Lower internal resistance allows faster signal transmission
B) Higher internal resistance makes action potentials stronger
C) Internal resistance does not affect action potentials
D) Higher internal resistance speeds up conduction
a
A researcher is comparing two neurons:
Neuron A has a large-diameter axon with low internal resistance.
Neuron B has a small-diameter axon with high internal resistance.
Which neuron will conduct action potentials faster and why?
A) Neuron A, because lower internal resistance allows faster current flow
B) Neuron B, because higher resistance makes signals stronger
C) Neuron A, because larger axons have more synapses
D) Neuron B, because smaller axons generate larger action potentials
Answer: A
How does myelin increase conduction velocity?
A) It increases membrane resistance, preventing ion leakage and allowing saltatory conduction
B) It increases the number of Na⁺ channels
C) It makes the axon more permeable to ions
D) It shortens the absolute refractory period
a
What type of glial cells produce myelin in the PNS (peripheral nervous system)?
A) Schwann cells
B) Oligodendrocytes
C) Astrocytes
D) Microglia
Answer: A
What type of glial cells produce myelin in the CNS (central nervous system)?
A) Oligodendrocytes
B) Schwann cells
C) Astrocytes
D) Microglia
a
What are the gaps in the myelin sheath where action potentials occur?
A) Nodes of Ranvier
B) Axon hillock
C) Synaptic clefts
D) Internodes
A
Why do action potentials only occur at Nodes of Ranvier in myelinated axons?
A) Because these regions have a high concentration of voltage-gated Na⁺ and K⁺ channels
B) Because myelin prevents Na⁺ from entering anywhere else
C) Because internodes generate their own action potentials
D) Because neurotransmitters are only released at the nodes
A
What is the purpose of increasing membrane resistance with myelin?
A) To reduce ion leakage and allow the electrical signal to travel farther and faster
B) To increase ATP consumption in neurons
C) To allow K⁺ to flow more easily
D) To decrease conduction velocity
a
What is saltatory conduction?
A) The jumping of action potentials from node to node along a myelinated axon
B) The continuous propagation of action potentials along an unmyelinated axon
C) The backward flow of action potentials during the refractory period
D) The blocking of ion flow by myelin
Answer: A
Why do action potentials only regenerate at the Nodes of Ranvier?
A) Because these nodes contain high concentrations of voltage-gated Na⁺ and K⁺ channels
B) Because myelin increases ion permeability
C) Because action potentials cannot travel through myelin
D) Because neurotransmitters are only released at these points
A
How does temperature affect voltage-gated ion channels?
A) Higher temperatures make them open and close more quickly, increasing conduction speed
B) Higher temperatures cause them to inactivate permanently
C) Lower temperatures increase conduction velocity
D) Temperature does not affect ion channel function
A
What combination of adaptations allows mammals and birds to have fast conduction velocities despite having relatively small axons?
A) Endothermy + Myelination
B) Large synapses + Increased ATP production
C) Higher neurotransmitter release + Longer axons
D) More Na⁺ channels + Higher resting potential
Answer: A
Which of the following is a key characteristic of graded potentials?
A) They degrade with distance
B) They follow an “all-or-none” principle
C) They occur only in axons
D) They always result in an action potential
A
Where do graded potentials typically occur?
A) Dendrites and cell body
B) Axon only
C) Synaptic cleft
D) Nodes of Ranvier
a
How do action potentials differ from graded potentials?
A) Action potentials do not degrade with distance
B) Action potentials occur only in dendrites
C) Graded potentials always trigger an action potential
D) Graded potentials travel long distances
Answer: A
What type of ion channels are involved in action potentials?
A) Voltage-gated ion channels only
B) Ligand-gated ion channels only
C) Mechanically-gated ion channels
D) Leak channels
a
Which of the following statements about graded potentials is true?
A) They can be either excitatory or inhibitory
B) They are “all or none”
C) They are always excitatory
D) They do not degrade with distance
a
Which type of synapse is more common in the human nervous system?
A) Chemical synapses
B) Electrical synapses
C) Both occur equally
D) Neither are present in humans
a
How is information transmitted in an electrical synapse?
A) Direct ion flow through gap junctions
B) Neurotransmitter release into the synaptic cleft
C) Activation of second messenger pathways
D) Diffusion of sodium ions across the synaptic cleft
a
What is the primary difference between electrical and chemical synapses?
A) Electrical synapses transmit signals directly via gap junctions, while chemical synapses use neurotransmitters
B) Chemical synapses transmit signals faster than electrical synapses
C) Electrical synapses require neurotransmitter release
D) Chemical synapses can only be excitatory, while electrical synapses can be inhibitory
a
What happens at a chemical synapse when an action potential reaches the presynaptic terminal?
A) Neurotransmitters are released into the synapse and bind to receptors on the postsynaptic cell
B) The action potential continues into the postsynaptic neuron directly
C) The postsynaptic cell fires an action potential immediately
D) Sodium ions flow through gap junctions
a
Which type of synapse is most useful for rapid, synchronized activity, such as in cardiac muscle or some brain circuits?
A) Electrical synapses
B) Chemical synapses
C) Both function the same way
D) Neither are involved in synchronization
a
Which structure allows for the direct passage of ions in an electrical synapse?
A) Synaptic cleft
B) Gap junctions
C) Vesicles
D) Axon hillock
Answer: B
Which of the following is true about electrical synapses?
A) They are the most common type of synapse in the nervous system
B) They rely on neurotransmitters for communication
C) They allow for nearly instantaneous transmission of signals
D) They are unidirectional
c
Where are electrical synapses most commonly found?
A) In reflex pathways, like the crayfish escape response
B) In motor neurons controlling skeletal muscles
C) In all human neurons
D) In sensory receptors of the skin
a
In electrical synapses, the proteins that form gap junction channels in vertebrates are called:
A) Connexons
B) Innexins
C) Neurotrophins
D) Dopamine transporters
a
What is the primary function of a neurotransmitter in a chemical synapse?
A) To transmit signals between neurons by binding to postsynaptic receptors
B) To directly pass electrical currents to the next neuron
C) To form gap junctions
D) To break down action potentials
a
Which of the following is NOT a characteristic of chemical synapses?
A) Signals can travel in either direction
B) They involve neurotransmitter release
C) They have a synaptic delay
D) They use receptors on the postsynaptic membrane
a
What must happen for a neurotransmitter to be classified as such?
A) It must be made in the postsynaptic cell
B) It must be synthesized in the presynaptic terminal, released upon stimulation, and bind to receptors on the postsynaptic cell
C) It must be recycled by astrocytes
D) It must always cause an excitatory response
b
What type of potential is created when a neurotransmitter binds to its receptor on the postsynaptic cell?
A) Resting potential
B) Post-synaptic potential (PSP)
C) Threshold potential
D) Refractory potential
b
What is the correct sequence of events during an action potential?
a) Depolarization → Repolarization → Hyperpolarization → Resting potential
b) Hyperpolarization → Depolarization → Repolarization → Resting potential
c) Depolarization → Hyperpolarization → Repolarization → Resting potential
d) Resting potential → Depolarization → Repolarization → Hyperpolarization
d)
What is the function of voltage-gated calcium (Ca²⁺) channels in chemical synaptic transmission?
a) Block sodium from entering the axon terminal
b) Trigger vesicle fusion with the membrane to release neurotransmitters
c) Prevent potassium from leaving the neuron
d) Directly depolarize the postsynaptic neuron
b
What happens when calcium (Ca²⁺) enters the presynaptic neuron?
a) It causes vesicles to release neurotransmitters into the synaptic cleft
b) It blocks sodium channels to stop the action potential
c) It depolarizes the postsynaptic membrane directly
d) It inhibits neurotransmitter release
a
After neurotransmitters are released into the synaptic cleft, how do they affect the postsynaptic neuron?
a) They immediately degrade without any effect
b) They bind to receptors, leading to the opening of ion channels
c) They enter the postsynaptic neuron through voltage-gated Ca²⁺ channels
d) They block further action potentials
b
What would happen if voltage-gated calcium (Ca²⁺) channels in the presynaptic terminal were blocked?
a) Action potentials would fail to reach the axon terminal
b) Vesicles would not release neurotransmitters into the synaptic cleft
c) The postsynaptic neuron would become hyperpolarized
d) Sodium (Na⁺) channels in the presynaptic neuron would not open
b
Which of the following correctly describes an ionotropic receptor?
a) It activates second messengers before causing an effect
b) It is a ligand-gated ion channel that opens upon neurotransmitter binding
c) It blocks action potentials from propagating
d) It functions only in the presynaptic neuron
b
Which of the following is the primary role of synaptotagmin in neurotransmitter release?
a) It forms the SNARE complex to dock vesicles at the membrane.
b) It binds to Ca²⁺ and triggers vesicle fusion with the presynaptic membrane.
c) It blocks neurotransmitter release until an action potential arrives.
d) It transports neurotransmitters back into the presynaptic neuron.
b
What happens immediately after calcium (Ca²⁺) enters the presynaptic neuron?
a) Neurotransmitters diffuse back into the presynaptic cell.
b) Voltage-gated Na⁺ channels open, prolonging the action potential.
c) Synaptotagmin binds to Ca²⁺ and triggers vesicle fusion.
d) Postsynaptic ligand-gated ion channels open automatically.
c
What is the function of the SNARE proteins (Synaptobrevin, Syntaxin, Snap-25) in neurotransmitter release?
a) They sense calcium levels in the presynaptic neuron.
b) They create the fusion machinery to dock and merge vesicles with the membrane.
c) They prevent vesicles from fusing until an action potential arrives.
d) They transport neurotransmitters across the synaptic cleft.
b
Which of the following proteins is NOT part of the SNARE complex involved in vesicle docking?
a) Synaptobrevin
b) Syntaxin
c) Snap-25
d) Synaptotagmin
d
Which of the following statements about synaptic transmission is TRUE?
a) Once neurotransmitters are released, they cannot be removed from the synaptic cleft.
b) The SNARE complex disassembles after vesicle fusion to allow recycling of vesicle components.
c) Calcium (Ca²⁺) is not required for vesicle fusion, only for action potential propagation.
d) Vesicle fusion occurs randomly, independent of neural activity.
b
What directly triggers the opening of voltage-gated Ca²⁺ channels at the presynaptic terminal?
a) Binding of neurotransmitters to the presynaptic neuron
b) Arrival of an action potential and membrane depolarization
c) Release of vesicles from the SNARE complex
d) Influx of potassium ions
b
What is the role of synaptotagmin in synaptic transmission?
a) It acts as a Ca²⁺ sensor that triggers vesicle fusion with the presynaptic membrane
b) It depolarizes the postsynaptic neuron
c) It prevents neurotransmitter release until an action potential arrives
d) It actively transports neurotransmitters across the synaptic cleft
a
Which of the following correctly describes the sequence of events in neurotransmitter release?
a) Neurotransmitters diffuse into the postsynaptic cell → Ca²⁺ binds to synaptotagmin → action potential propagates
b) Action potential arrives at the terminal → voltage-gated Ca²⁺ channels open → Ca²⁺ binds synaptotagmin → vesicle fusion occurs
c) Vesicles fuse with the membrane → Ca²⁺ enters the presynaptic neuron → action potential is triggered
d) Ca²⁺ binds to neurotransmitters → vesicles dock to the membrane → action potential reaches the postsynaptic neuron
b
What happens immediately after calcium (Ca²⁺) binds to synaptotagmin?
a) Voltage-gated Na⁺ channels open in the presynaptic membrane
b) Vesicles dock at the presynaptic membrane, preparing for fusion
c) The SNARE complex undergoes conformational change, allowing vesicle fusion
d) The neurotransmitters enter the postsynaptic neuron via active transport
c
What neurotransmitter is released at a cholinergic synapse?
a) Dopamine
b) Acetylcholine (ACh)
c) Serotonin
d) Glutamate
b
Where are cholinergic synapses most commonly found?
a) Only in the central nervous system (CNS)
b) Only in skeletal muscles
c) CNS, all neuron-to-neuron synapses in the PNS, and neuromuscular junctions
d) Only in the autonomic nervous system
c
What type of receptor does acetylcholine (ACh) bind to at the postsynaptic membrane?
a) Voltage-gated Na⁺ channel
b) Ligand-gated ion channel
c) G-protein-coupled receptor (GPCR) only
d) Voltage-gated Ca²⁺ channel
b
What is the function of acetylcholinesterase (AChE) at a cholinergic synapse?
a) It enhances the binding of ACh to receptors.
b) It breaks down ACh into acetate and choline.
c) It transports ACh back into the presynaptic neuron.
d) It triggers the release of more ACh into the synaptic cleft.
b
Where is acetylcholine (ACh) synthesized in the neuron?
a) In the synaptic cleft
b) In the mitochondria of the presynaptic neuron
c) In the postsynaptic membrane
d) In the dendrites of the presynaptic neuron
b
What enzyme catalyzes the conversion of choline and acetyl CoA into acetylcholine (ACh)?
a) Acetylcholinesterase (AChE)
b) Choline acetyltransferase
c) Synaptotagmin
d) Tyrosine hydroxylase
b
What happens to acetylcholine (ACh) after it is released into the synaptic cleft?
a) It is immediately broken down by acetylcholinesterase (AChE).
b) It binds to its receptor on the postsynaptic cell.
c) It is recycled directly back into the presynaptic neuron without modification.
d) It triggers an action potential in the presynaptic neuron.
b
What is the function of acetylcholinesterase (AChE) in the synaptic cleft?
a) It helps ACh bind more effectively to its receptor.
b) It breaks down ACh into acetate and choline, terminating the signal.
c) It repackages ACh into synaptic vesicles for reuse.
d) It prevents the breakdown of ACh to sustain neurotransmission.
b
Which of the following lists the correct order of events for acetylcholine (ACh) synthesis, release, and recycling?
a) Choline is taken up by the presynaptic neuron → ACh is synthesized → ACh binds to postsynaptic receptors → ACh is packaged into vesicles → ACh is broken down by AChE → ACh is released into the synapse
b) Acetyl CoA is made in mitochondria → ACh is synthesized by choline acetyltransferase → ACh is packaged into vesicles → ACh is released into the synaptic cleft → ACh binds to receptors → ACh is broken down by AChE → Choline is taken up for recycling
c) ACh binds to postsynaptic receptors → Acetyl CoA is made → ACh is synthesized → ACh is released into the synapse → ACh is packaged into vesicles → ACh is broken down by AChE → Choline is recycled
d) ACh is broken down by AChE → Acetyl CoA is synthesized → ACh is packaged into vesicles → ACh is released into the synaptic cleft → ACh binds to receptors → Choline is taken up for recycling → ACh is synthesized
b
What happens if a neuron fires action potentials at a very low frequency?
a) More neurotransmitter is released.
b) Less calcium (Ca²⁺) enters the presynaptic neuron.
c) More vesicles fuse with the membrane.
d) The postsynaptic neuron becomes overstimulated.
b
Why does high-frequency AP firing lead to increased neurotransmitter release?
a) More calcium (Ca²⁺) enters, and calcium ATPases cannot remove it fast enough.
b) More sodium (Na⁺) enters, causing rapid depolarization.
c) The presynaptic neuron produces extra neurotransmitters.
d) Acetylcholinesterase (AChE) is inhibited.
a
How does acetylcholinesterase (AChE) affect synaptic transmission?
a) It speeds up action potentials in the presynaptic neuron.
b) It breaks down ACh, reducing signal duration.
c) It increases the amount of neurotransmitter released.
d) It helps ACh bind more effectively to receptors.
b
What would happen if acetylcholinesterase (AChE) was inhibited?
a) ACh would stay in the synapse longer, increasing signal strength.
b) ACh would be broken down faster, weakening the signal.
c) More vesicles would be released by the presynaptic neuron.
d) The presynaptic neuron would stop firing action potentials.
a
What is the primary effect of Sarin gas on the nervous system?
a) It prevents acetylcholine (ACh) from binding to receptors, leading to muscle relaxation.
b) It inhibits acetylcholinesterase (AChE), causing ACh to accumulate and overstimulate the nervous system.
c) It blocks voltage-gated sodium (Na⁺) channels, preventing action potentials.
d) It increases the breakdown of ACh, leading to a weaker neural signal and muscle paralysis.
b
Which type of receptor directly opens an ion channel when a neurotransmitter binds?
a) Ionotropic
b) Metabotropic
c) Ligand gated
d) graded receptor
e) G-protein coupled receptor
a
What makes metabotropic receptors slower than ionotropic receptors?
a) They require multiple neurotransmitters to bind.
b) They use second messengers (G-protein cascade) to produce an effect.
c) They rely on diffusion instead of ion channels.
d) They require calcium influx before they can work.
b
Which of the following is a characteristic of ionotropic receptors?
a) They influence gene expression.
b) They require a G-protein to activate an ion channel.
c) They produce rapid changes in membrane potential.
d) They are found only in the central nervous system.
c
Which of the following occurs during an excitatory postsynaptic potential (EPSP)?
a) Na⁺ channels open, allowing Na⁺ to enter the cell.
b) K⁺ channels open, causing the cell to lose positive charge.
c) Cl⁻ channels open, making the membrane potential more negative.
d) The membrane potential moves further from threshold.
a
Why does an inhibitory postsynaptic potential (IPSP) make it harder for a neuron to fire an action potential?
a) It depolarizes the membrane closer to threshold.
b) It increases the number of voltage-gated sodium (Na⁺) channels.
c) It causes hyperpolarization, making the membrane potential more negative.
d) It prevents neurotransmitters from binding to the receptor.
c
What ion movement is most likely to occur during an IPSP?
a) Na⁺ enters the neuron.
b) K⁺ exits or Cl⁻ enters the neuron.
c) Ca²⁺ enters the neuron.
d) K⁺ enters the neuron.
d
If a drug blocked all inhibitory synapses in the brain, what would most likely happen?
a) The brain would become overexcited, leading to seizures.
b) Neurons would stop firing action potentials altogether.
c) The brain would shut down, leading to unconsciousness.
d) The resting membrane potential would become more negative, making neurons unresponsive.
a
Why do axosomatic synapses have a greater influence than axodendritic synapses?
a) They are closer to the axon hillock, so their signals decay less.
b) They always release more neurotransmitter.
c) They only release inhibitory signals, which have a stronger effect.
d) They use a different type of neurotransmitter than axodendritic synapses.
a
What happens to synaptic signals as they travel further from the axon hillock?
a) They increase in amplitude.
b) They remain the same strength.
c) They decay, making them less likely to cause an action potential.
d) They trigger automatic firing of the neuron.
c
If a neuron receives an excitatory signal from an axodendritic synapse and an inhibitory signal from an axosomatic synapse at the same time, what is the most likely outcome?
a) The neuron will fire an action potential.
b) The neuron will not fire an action potential.
c) The excitatory signal will always override the inhibitory one.
d) Both signals will cancel out completely.
b
Which of the following statements is TRUE about axodendritic synapses?
a) They are more influential than axosomatic synapses.
b) They require stronger or multiple signals to have an effect.
c) They do not contribute to action potential firing.
d) They cause automatic inhibition of the neuron.
b
