Lecture 2: Excitable cells Flashcards
What happens to potassium (K⁺) ions when K⁺ channels in the cell membrane open?
A) K⁺ moves into the cell due to its concentration gradient.
B) K⁺ moves out of the cell due to its concentration gradient.
C) K⁺ remains evenly distributed on both sides of the membrane.
D) K⁺ moves out of the cell due to the electrical gradient.
Correct Answer: B
What causes the electrical gradient to develop as potassium (K⁺) exits the cell?
A) The outside of the cell becomes more negatively charged.
B) The inside of the cell becomes more positively charged.
C) The outside of the cell becomes more positively charged, while the inside becomes more negative.
D) There is no change in charge across the membrane.
Correct Answer: C
At equilibrium potential for K⁺, which of the following is true?
A) The concentration gradient and electrical gradient work in the same direction.
B) The concentration gradient pushing K⁺ out is balanced by the electrical gradient pulling K⁺ back in.
C) There is no movement of K⁺ across the membrane.
D) Both the inside and outside of the cell are positively charged.
Correct Answer: B
What is the main factor driving K⁺ ions out of the cell when channels first open?
A) Electrical gradient
B) Concentration gradient
C) ATP energy
D) Osmotic pressure
Correct Answer: B
Why doesn’t K⁺ continue to flow out of the cell indefinitely?
A) The concentration gradient is too weak.
B) The electrical gradient opposes the concentration gradient as positive charges build outside the cell.
C) The K⁺ channels close automatically after a few seconds.
D) There is no concentration gradient for K⁺.
Correct Answer: B
What is the result of potassium ion movement on the membrane potential when K+ moves OUT of the cell ?
A) The membrane potential becomes more positive.
B) The membrane potential becomes more negative.
C) The membrane potential remains unchanged.
D) The membrane potential fluctuates randomly.
Correct Answer: A
When does net movement of K⁺ stop?
A) When the concentration gradient is stronger than the electrical gradient.
B) When the electrical gradient is stronger than the concentration gradient.
C) When the concentration gradient equals the electrical gradient.
D) When all K⁺ ions have left the cell.
Correct Answer: C
Which type of molecule can freely pass through the lipid bilayer of a cell membrane without assistance?
A) Sodium ions (Na⁺)
B) Glucose
C) Oxygen (O₂)
D) Potassium ions (K⁺)
c)
Why can ions like Na⁺ and K⁺ not move passively across the cell membrane?
A) They are too large to pass through the membrane.
B) The hydrophilic part of the membrane blocks their movement.
C) The hydrophobic core of the lipid bilayer repels charged particles.
D) The cell actively prevents ions from leaving or entering.
Correct Answer: C
What is the main function of ion channels in the cell membrane?
A) To allow ions to diffuse along their concentration gradients.
B) To break down ions for energy.
C) To prevent ions from crossing the membrane.
D) To dissolve lipid-soluble molecules.
Correct Answer: A
What happens if the membrane is impermeable to ions?
A) Ions can still diffuse through passive diffusion.
B) No voltage difference forms across the membrane.
C) The cell actively pumps ions out.
D) The membrane potential becomes very large.
Correct Answer: B
Which transport mechanism requires energy to move molecules against their concentration gradient?
A) Passive diffusion
B) Facilitated diffusion
C) Active transport
D) Osmosis
Correct Answer: C
What determines whether an ion like K⁺ will flow through its channel?
A) Its molecular size
B) The direction of its concentration gradient
C) The availability of ATP
D) Its solubility in lipids
Correct Answer: B
Which of the following is an example of facilitated diffusion?
A) Na⁺ moving through an ion channel down its concentration gradient
B) Glucose being broken down by enzymes
C) CO₂ diffusing across the membrane freely
D) ATP pumping K⁺ ions into the cell
Correct Answer: A
Which of the following is NOT true about passive diffusion?
A) It does not require energy.
B) It moves substances down their concentration gradient.
C) It involves the use of carrier proteins.
D) It is the main transport method for gases like O₂ and CO₂.
Correct Answer: C
What determines the direction of ion movement across a membrane?
A) The size of the ion
B) The availability of ATP
C) The concentration gradient and electrical gradient
D) The number of ion channels
Correct Answer: C
When do ions experience a high rate of diffusion?
A) When the concentration gradient and electrical gradient oppose each other
B) When the electrical gradient equals the concentration gradient
C) When the concentration gradient and electrical gradient work in the same direction
D) When there are no ion channels
Correct Answer: C
What happens when the electrical gradient opposes the concentration gradient?
A) Diffusion speeds up significantly
B) Diffusion slows down or stops completely
C) Ions move randomly in both directions
D) The membrane potential becomes neutral
Correct Answer: B
What is the relationship between the concentration gradient and electrical gradient at equilibrium?
A) They reinforce each other
B) They are irrelevant to ion movement
C) They are balanced, resulting in no net ion movement
D) They allow ions to move freely through the membrane
Correct Answer: C
What is required for ions to cross the membrane?
A) ATP
B) A concentration gradient
C) A semi-permeable membrane and ion channels
D) Equal concentrations of ions on both sides
Correct Answer: C
Explain why sodium ions (Na⁺) diffuse quickly when the concentration and electrical gradients reinforce each other.
Sodium ions diffuse quickly because both the concentration gradient (higher concentration on one side) and the electrical gradient (attraction to the negative charge) drive them in the same direction, increasing the rate of diffusion.
What happens when the electrical gradient opposes the concentration gradient?
The opposing forces slow the movement of ions. If the electrical gradient is strong enough, it can completely stop or reverse the direction of ion diffusion.
What role do ion channels play in the movement of ions like Na⁺ and K⁺?
Ion channels provide a pathway for ions to move across the membrane, allowing them to follow their concentration and electrical gradients.
What is a membrane potential?
A) The concentration gradient of ions across the membrane
B) The voltage difference between the inside and outside of a cell
C) The movement of water across the membrane
D) The number of ion channels present in the membrane
Correct Answer: B
Why are cells usually negative inside relative to the outside?
A) There is more potassium outside the cell than inside.
B) The inside of the cell contains negatively charged macromolecules and proteins.
C) Sodium ions constantly enter the cell.
D) The cell membrane does not allow potassium to move across.
Correct Answer: B
What is the role of potassium (K⁺) leak channels in generating membrane potential?
A) They keep the inside of the cell positively charged.
B) They allow potassium ions to move out of the cell, making the inside more negative.
C) They prevent ions from crossing the membrane.
D) They move potassium ions into the cell to maintain a positive charge.
Correct Answer: B
Which statement about neurons is true?
A) Neurons maintain a constant membrane potential.
B) Changes in membrane potential allow neurons to communicate over long distances.
C) Neurons are not influenced by membrane potentials.
D) Neurons are negatively charged on the outside relative to the inside.
Correct Answer: B
What causes the difference in ion concentration inside and outside the cell?
A) Active transport of ions across the membrane
B) The impermeability of the membrane to ions
C) Equal distribution of ions on both sides of the membrane
D) The presence of water molecules
Correct Answer: A
Define membrane potential and explain its importance in cell signaling.
Membrane potential is the voltage difference between the inside and outside of a cell, caused by unequal distribution of ions. It is crucial for cell signaling, especially in neurons, where changes in membrane potential allow for communication and coordination of activities across the body.
How does the movement of potassium ions through leak channels contribute to the resting membrane potential?
Potassium ions move out of the cell through leak channels due to their concentration gradient. As they leave, they create a net negative charge inside the cell, contributing to the resting membrane potential.
Explain how neurons use changes in membrane potential to communicate over long distances.
Neurons rapidly alter their membrane potential by opening and closing ion channels, generating electrical signals (action potentials) that propagate along their length to transmit information.
What is the typical resting membrane potential of a neuron?
A) +30 mV
B) 0 mV
C) -70 mV
D) -90 mV
Correct Answer: C
What is the difference between membrane potential and equilibrium potential?
A) Membrane potential refers to the voltage difference across the entire cell membrane, while equilibrium potential is the voltage at which the net movement of a specific ion across the membrane stops.
B) Membrane potential is specific to potassium ions, while equilibrium potential applies to all ions.
C) Membrane potential is the electrical gradient inside the cell, while equilibrium potential is the concentration gradient outside the cell.
D) Membrane potential is constant, while equilibrium potential changes with the number of ion channels.
Correct Answer: A
What is the key distinction between the Nernst equation and the Goldman equation?
A) The Nernst equation calculates the resting membrane potential, while the Goldman equation calculates the equilibrium potential for a single ion.
B) The Nernst equation determines the equilibrium potential for a specific ion, while the Goldman equation calculates the membrane potential considering multiple ions and their permeabilities.
C) The Nernst equation is used for ions like sodium, while the Goldman equation is used only for potassium.
D) The Nernst equation calculates the membrane potential under dynamic conditions, while the Goldman equation applies only to resting conditions.
Correct Answer: B
Which ion is found in higher concentration inside the neuron at resting membrane potential?
A) Sodium (Na⁺)
B) Potassium (K⁺)
C) Chloride (Cl⁻)
D) Calcium (Ca²⁺)
Answer: B) Potassium (K⁺)
Which ion is found in higher concentration outside the neuron at resting membrane potential?
A) Potassium (K⁺)
B) Sodium (Na⁺)
C) Phosphate (PO₄³⁻)
D) Magnesium (Mg²⁺)
Answer: B) Sodium (Na⁺)
What is the main ion responsible for maintaining the resting membrane potential?
A) Sodium (Na⁺)
B) Potassium (K⁺)
C) Chloride (Cl⁻)
D) Calcium (Ca²⁺)
Answer: B) Potassium (K⁺)
How do sodium (Na⁺) and potassium (K⁺) ions move across the neuron membrane at rest?
A) Both actively move into the neuron.
B) Both actively move out of the neuron.
C) Na⁺ diffuses into the cell, and K⁺ diffuses out via leak channels.
D) Na⁺ diffuses out of the cell, and K⁺ diffuses in via leak channels.
Answer: C) Na⁺ diffuses into the cell, and K⁺ diffuses out via leak channels.
Why do most sodium (Na⁺) channels remain closed in resting neurons?
A) To maintain a higher concentration of sodium inside the cell.
B) To prevent depolarization and maintain resting membrane potential.
C) Because sodium is not essential for neuron function.
D) Because sodium must constantly leave the cell to generate action potentials.
Answer: B) To prevent depolarization and maintain resting membrane potential.
Which of the following can freely diffuse across the cell membrane without a channel or transporter?
A) Na⁺ (Sodium)
B) CO₂ (Carbon dioxide)
C) Glucose
D) Cl⁻ (Chloride)
Answer: ✅ B) CO₂ (Small uncharged molecules like CO₂, O₂, and H₂O can pass freely.)
Why do ions require channels to move across the membrane?
A) Ions are too large to pass through the membrane.
B) The membrane is hydrophobic, and ions are charged, making it difficult for them to pass.
C) Ions dissolve easily in lipids, so they need a channel.
D) Ions can move passively without a channel.
Answer: ✅ B) The membrane is hydrophobic, and ions are charged, making it difficult for them to pass.
Which of the following molecules needs a transporter to cross the membrane?
A) Oxygen (O₂)
B) Hydrocarbons
C) Glucose
D) Water
Answer: ✅ C) Glucose (Glucose is a large, polar molecule and requires a transporter.)
What type of diffusion involves a protein channel but does NOT require energy?
A) Passive diffusion
B) Facilitated diffusion
C) Active transport
D) Endocytosis
Answer: ✅ B) Facilitated diffusion (Facilitated diffusion uses a channel or permease but follows the concentration gradient, so it does not require energy.)
What happens to the membrane potential if the membrane is impermeable to ions?
A) It becomes more negative.
B) It becomes more positive.
C) It remains at 0 mV (no voltage difference).
D) It fluctuates randomly.
answer: ✅ C) It remains at 0 mV (no voltage difference).
(Since no ions can move, there is no charge separation, and the membrane potential stays at zero.)
What is required for a voltage difference (membrane potential) to exist across a membrane?
A) Equal distribution of anions and cations on both sides.
B) Selective permeability to certain ions.
C) No ion movement.
D) A membrane that is completely impermeable to all ions.
Answer: ✅ B) Selective permeability to certain ions.
(For a membrane potential to exist, some ions must be able to move, leading to charge separation.)
If the number of anions and cations is the same on both sides of a membrane, what will the membrane potential be?
A) -70 mV
B) +30 mV
C) 0 mV
D) -90 mV
Answer: ✅ C) 0 mV
(Without charge separation, the voltage difference is zero.)
Why does K⁺ stop moving out of the cell at equilibrium?
A) The concentration gradient disappears.
B) The electrical gradient opposes further K⁺ movement.
C) K⁺ is no longer needed outside the cell.
D) The sodium-potassium pump stops working.
Answer: ✅ B) The electrical gradient opposes further K⁺ movement.
(As K⁺ exits, the outside becomes more negative, creating an electrical gradient that pulls K⁺ back inside, balancing the outward concentration gradient.)
Which of the following statements best describes the balance between the electrical and chemical gradients for K⁺?
A) The electrical gradient pushes K⁺ out of the cell.
B) The chemical gradient pulls K⁺ into the cell.
C) The chemical gradient moves K⁺ out, while the electrical gradient pulls it back in.
D) There is no relationship between the electrical and chemical gradients.
Answer: ✅ C) The chemical gradient moves K⁺ out, while the electrical gradient pulls it back in.
(K⁺ wants to leave the cell due to its high intracellular concentration, but as it does, the cell becomes more negative, creating an electrical force that pulls K⁺ back in.)
Where is potassium (K⁺) concentration the highest in a resting neuron?
A) Inside the cell
B) Outside the cell
C) Equally distributed inside and outside
D) It depends on the membrane potential
Answer: ✅ A) Inside the cell
(K⁺ is much higher inside the neuron than outside.)
Where is sodium (Na⁺) concentration the highest in a resting neuron?
A) Inside the cell
B) Outside the cell
C) Equally distributed inside and outside
D) It depends on the action potential
Answer: ✅ B) Outside the cell
(Na⁺ is much higher outside the neuron than inside.)
Which ion primarily determines the resting membrane potential of a neuron?
A) Sodium (Na⁺)
B) Potassium (K⁺)
C) Chloride (Cl⁻)
D) Calcium (Ca²⁺)
Answer: ✅ B) Potassium (K⁺)
(The resting membrane potential is mostly determined by K⁺ leak channels, allowing K⁺ to diffuse out.)
What does the Na⁺/K⁺ pump do?
A) Pumps 3 Na⁺ out and 2 K⁺ in
B) Pumps 2 Na⁺ in and 3 K⁺ out
C) Passively moves Na⁺ and K⁺
D) Pumps Na⁺ and K⁺ in equal amounts
Answer: ✅ A) Pumps 3 Na⁺ out and 2 K⁺ in
(The Na⁺/K⁺ ATPase maintains ion gradients by removing 3 Na⁺ and bringing in 2 K⁺, making the inside of the cell more negative.)
Why is the Na⁺/K⁺ pump considered an “electrogenic” pump?
A) It moves equal numbers of Na⁺ and K⁺, maintaining a neutral charge.
B) It moves more positive charges out than in, contributing to a negative charge inside the cell.
C) It only affects the concentration gradient, not the electrical charge.
D) It does not use ATP.
Answer: ✅ B) It moves more positive charges out than in, contributing to a negative charge inside the cell.
(The pump removes 3 Na⁺ and brings in only 2 K⁺, creating a net negative charge inside the neuron.)
What would happen if the Na⁺/K⁺ pump stopped working?
A) The resting membrane potential would become more positive.
B) The neuron would become hyperpolarized.
C) The ion gradients would remain unchanged.
D) The neuron would no longer be able to generate action potentials.
Answer: ✅ D) The neuron would no longer be able to generate action potentials.
(Without the pump, Na⁺ and K⁺ gradients would dissipate, preventing neurons from firing action potentials.)
What are the three types of ion channels?
A) Passive, voltage-gated, and ligand-gated channels
B) Gated channels, ligand-gated channels, and leak channels
C) Voltage-gated channels, mechanically-gated channels, and sodium-potassium pumps
D) Aquaporins, sodium channels, and potassium pumps
Answer: ✅ B) Gated channels, ligand-gated channels, and leak channels
(These are the main types of ion channels affecting membrane potential.)
What happens if voltage-gated Na⁺ channels open?
A) The inside of the cell becomes more negative.
B) The inside of the cell becomes more positive.
C) Na⁺ leaves the cell.
D) The resting membrane potential is restored.
Answer: ✅ B) The inside of the cell becomes more positive.
(Opening Na⁺ channels allows Na⁺ to enter, leading to depolarization.)
What happens if voltage-gated K⁺ channels open?
A) The inside of the cell becomes more positive.
B) The inside of the cell becomes more negative.
C) K⁺ enters the cell.
D) Na⁺ follows K⁺ out of the cell.
Answer: ✅ B) The inside of the cell becomes more negative.
(When K⁺ exits, the cell becomes more negative, leading to repolarization or hyperpolarization.)
How do leak channels differ from gated channels?
A) Leak channels are always open, while gated channels open in response to signals.
B) Leak channels require ATP, while gated channels do not.
C) Leak channels are found only in neurons, while gated channels are found in all cells.
D) Leak channels transport ions against their concentration gradient.
Answer: ✅ A) Leak channels are always open, while gated channels open in response to signals.
(Leak channels allow passive ion movement, while gated channels open due to stimuli like voltage or ligands.)
What triggers a voltage-gated ion channel to open?
A) The binding of a specific molecule
B) A change in membrane potential
C) The presence of ATP
D) The diffusion of water molecules
Answer: ✅ B) A change in membrane potential
(Voltage-gated channels open when there is a shift in the electrical charge across the membrane.)
What type of transport do voltage-gated Na⁺ and K⁺ channels use?
A) Simple diffusion
B) Active transport
C) Facilitated diffusion
D) Endocytosis
Answer: ✅ C) Facilitated diffusion
(These channels allow ions to move passively down their concentration gradient, but they require a trigger to open.)
What are the two main types of transport used to move ions across the membrane?
A) Simple diffusion and osmosis
B) Facilitated diffusion and active transport
C) Endocytosis and exocytosis
D) Passive diffusion and vesicular transport
Answer: ✅ B) Facilitated diffusion and active transport
(Facilitated diffusion moves ions passively using channels, while active transport requires ATP.)
Why does K⁺ leak out of the cell more than Na⁺ enters?
A) The membrane is more permeable to K⁺ than Na⁺.
B) There is no Na⁺ outside the cell.
C) The Na⁺/K⁺ pump stops working at rest.
D) K⁺ is actively pushed out by the pump.
Answer: ✅ A) The membrane is more permeable to K⁺ than Na⁺.
(K⁺ leak channels are always open, allowing more K⁺ to leave than Na⁺ can enter.)
What is the correct sequence of events in a motor neuron?
A) Signal conduction → Signal reception → Signal transmission → Signal integration
B) Signal reception → Signal integration → Signal conduction → Signal transmission
C) Signal integration → Signal transmission → Signal reception → Signal conduction
D) Signal reception → Signal conduction → Signal transmission → Signal integration
Answer: ✅ B) Signal reception → Signal integration → Signal conduction → Signal transmission
(Neurons receive signals at dendrites, integrate them at the soma, conduct action potentials along the axon, and transmit signals at the synapse.)
Where does a motor neuron receive incoming signals?
A) Axon hillock
B) Dendrites
C) Myelin sheath
D) Axon terminal
Answer: ✅ B) Dendrites
(Dendrites contain receptors that receive chemical neurotransmitter signals from other neurons.)
What happens when neurotransmitters bind to receptors on dendrites?
A) It directly triggers an action potential.
B) It opens or closes ion channels, leading to a graded potential.
C) It stops the neuron from firing.
D) It blocks ion movement.
Answer: ✅ B) It opens or closes ion channels, leading to a graded potential.
(Neurotransmitter binding causes ion channels to open or close, changing the membrane potential.)
What is a graded potential?
A) A large, all-or-nothing change in membrane potential
B) A small change in membrane potential that varies based on stimulus strength
C) A permanent depolarization of the neuron
D) The voltage level required to trigger an action potential
Answer: ✅ B) A small change in membrane potential that varies based on stimulus strength
(Graded potentials occur at dendrites and soma; they can be stronger or weaker depending on input.)
What determines whether a neuron will generate an action potential?
A) The presence of a neurotransmitter
B) Whether the graded potential reaches the axon hillock threshold
C) The number of dendrites receiving signals
D) The amount of myelin on the axon
Answer: ✅ B) Whether the graded potential reaches the axon hillock threshold
(If graded potentials add up to reach threshold at the axon hillock, an action potential is triggered.)
What determines the strength of a graded potential?
A) The number of open ion channels and amount of ion movement
B) The number of axons in the neuron
C) Whether the neuron is myelinated
D) The length of the axon
Answer: ✅ A) The number of open ion channels and amount of ion movement
(The more ion channels open, the greater the graded potential.)
What happens if graded potentials build up quickly before the cell can remove the neurotransmitter?
A) The neuron resets immediately.
B) The neuron stops responding to new stimuli.
C) The neurotransmitter builds up, leading to a stronger response.
D) The action potential is permanently blocked.
Answer: ✅ C) The neurotransmitter builds up, leading to a stronger response.
(Frequent signaling can lead to more neurotransmitter accumulation, enhancing the response.)
What type of ion channel is responsible for initiating graded potentials?
A) Voltage-gated channels
B) Ligand-gated channels
C) Leak channels
D) Mechanically-gated channels
Answer: ✅ B) Ligand-gated channels
(Ligand-gated channels open when a neurotransmitter binds, allowing ions to enter and triggering a graded potential.)
What happens to the strength of a graded potential as it moves away from the channel?
A) It increases.
B) It stays the same.
C) It decreases.
D) It reverses direction.
Answer: ✅ C) It decreases.
(Graded potentials decay with distance because ions diffuse, reducing the signal strength.)
Why does the graded potential weaken as it spreads?
A) Because the membrane is fully insulated
B) Due to ion leakage and resistance in the cytoplasm
C) Because the neuron runs out of neurotransmitter
D) Because Na⁺ channels close immediately
Answer: ✅ B) Due to ion leakage and resistance in the cytoplasm
(As the charge spreads, some ions leak out, and the cytoplasm resists current flow, weakening the signal.)
What must happen for a graded potential to trigger an action potential?
A) The graded potential must reach the axon hillock and exceed the threshold.
B) The graded potential must remain at the dendrites.
C) The graded potential must immediately trigger neurotransmitter release.
D) The graded potential must remain constant in strength.
Answer: ✅ A) The graded potential must reach the axon hillock and exceed the threshold.
(If the graded potential is strong enough at the axon hillock, it triggers an action potential.)
How do graded potentials spread through the neuron?
A) Through active transport of ions
B) By electron movement along the axon
C) By electrotonic current spread
D) By vesicle-mediated ion transport
Answer: ✅ C) By electrotonic current spread
(Graded potentials travel passively through the neuron by electrotonic current spread, where positive and negative charges interact.)
Why do new Na⁺ ions move toward negative charges inside the cell?
A) Because Na⁺ is repelled by other positive ions
B) Because Na⁺ moves against its gradient
C) Because Na⁺ is attracted to negative charges inside the neuron
D) Because Na⁺ does not contribute to depolarization
Answer: ✅ C) Because Na⁺ is attracted to negative charges inside the neuron
(Na⁺ enters the cell and is attracted to the more negative areas, helping to spread depolarization.)
Why are graded potentials considered short-distance signals?
A) They decay as they spread due to ion leakage and resistance.
B) They regenerate along the axon.
C) They move faster than action potentials.
D) They use ATP to maintain their strength.
Answer: ✅ A) They decay as they spread due to ion leakage and resistance.
(Graded potentials weaken over distance due to ion leakage and cytoplasmic resistance.)
Where does the integration of graded potentials occur in a neuron?
A) Dendrites
B) Axon terminals
C) Axon hillock
D) Myelin sheath
Answer: ✅ C) Axon hillock
(The axon hillock is the trigger zone, where the neuron decides whether to fire an action potential.)
What must happen for an action potential to be initiated?
A) The neuron must reach its threshold potential.
B) The neuron must hyperpolarize.
C) The neuron must remain at resting membrane potential.
D) The neuron must stop all ion movement.
Answer: ✅ A) The neuron must reach its threshold potential.
(If the graded potential is strong enough to reach threshold at the axon hillock, an action potential occurs.)
What is the threshold potential required to trigger an action potential?
A) -90 mV
B) -70 mV
C) -55 mV
D) +30 mV
Answer: ✅ C) -55 mV
(The threshold potential is around -55 mV, meaning the neuron must depolarize by about +15 mV to fire an action potential.)
What is a subthreshold potential?
A) A graded potential that is strong enough to trigger an action potential
B) A graded potential that is not large enough to reach threshold
C) An action potential that does not reach completion
D) A graded potential that immediately triggers neurotransmitter release
B
What is a suprathreshold potential?
A) A graded potential that just reaches the threshold
B) A graded potential that is stronger than necessary to trigger an action potential
C) An action potential that does not fire
D) A resting membrane potential
Answer: ✅ B) A graded potential that is stronger than necessary to trigger an action potential
(A suprathreshold potential exceeds the -55 mV threshold, ensuring an action potential fires.)
Which of the following best describes the difference between spatial and temporal summation?
A) Spatial summation occurs when multiple graded potentials arrive from different locations, while temporal summation occurs when multiple graded potentials arrive in quick succession from the same location.
B) Spatial summation occurs only in sensory neurons, while temporal summation occurs only in motor neurons.
C) Spatial summation results in hyperpolarization, while temporal summation results in depolarization.
D) Spatial summation involves only inhibitory inputs, while temporal summation involves only excitatory inputs.
Answer: ✅ A) Spatial summation occurs when multiple graded potentials arrive from different locations, while temporal summation occurs when multiple graded potentials arrive in quick succession from the same location.
(Spatial summation combines signals from multiple synapses at the same time, while temporal summation combines repeated signals from a single synapse over time.)
What is spatial summation?
A) When multiple action potentials add up over time
B) When graded potentials from different locations combine at the axon hillock
C) When a single neuron fires multiple times in quick succession
D) When neurotransmitters are released from a single synapse
Answer: ✅ B) When graded potentials from different locations combine at the axon hillock
(Spatial summation occurs when multiple synapses contribute graded potentials at the same time.)
A neuron receives two excitatory inputs and one inhibitory input at the same time. What determines whether an action potential will be generated?
A) The total amount of neurotransmitter released by the excitatory neurons
B) Whether the combined excitatory and inhibitory inputs depolarize the membrane to -55 mV at the axon hillock
C) The strength of the inhibitory signal alone
D) The number of synapses activated, regardless of their effect on membrane potential
Answer: ✅ B) Whether the combined excitatory and inhibitory inputs depolarize the membrane to -55 mV at the axon hillock
