Lecture 2: Excitable cells

Question 1

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.

Answer 1

Correct Answer: B

Question 2

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.

Answer 2

Correct Answer: C

Question 3

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.

Answer 3

Correct Answer: B

Question 4

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

Answer 4

Correct Answer: B

Question 5

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⁺.

Answer 5

Correct Answer: B

Question 6

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.

Answer 6

Correct Answer: A

Question 7

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.

Answer 7

Correct Answer: C

Question 8

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⁺)

Answer 8

c)

Question 9

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.

Answer 9

Correct Answer: C

Question 10

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.

Answer 10

Correct Answer: A

Question 11

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.

Answer 11

Correct Answer: B

Question 11

Which transport mechanism requires energy to move molecules against their concentration gradient?
A) Passive diffusion
B) Facilitated diffusion
C) Active transport
D) Osmosis

Answer 11

Correct Answer: C

Question 11

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

Answer 11

Correct Answer: B

Question 12

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

Answer 12

Correct Answer: A

Question 12

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.

Answer 12

Correct Answer: C

Question 12

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

Answer 12

Correct Answer: C

Question 13

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

Answer 13

Correct Answer: C

Question 14

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

Answer 14

Correct Answer: B

Question 15

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

Answer 15

Correct Answer: C

Question 16

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

Answer 16

Correct Answer: C

Question 17

Explain why sodium ions (Na⁺) diffuse quickly when the concentration and electrical gradients reinforce each other.

Answer 17

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.

Question 18

What happens when the electrical gradient opposes the concentration gradient?

Answer 18

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.

Question 19

What role do ion channels play in the movement of ions like Na⁺ and K⁺?

Answer 19

Ion channels provide a pathway for ions to move across the membrane, allowing them to follow their concentration and electrical gradients.

Question 20

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

Answer 20

Correct Answer: B

Question 21

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.

Answer 21

Correct Answer: B

Question 22

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.

Answer 22

Correct Answer: B

Question 23

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.

Answer 23

Correct Answer: B

Question 24

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

Answer 24

Correct Answer: A

Question 25

Define membrane potential and explain its importance in cell signaling.

Answer 25

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.

Question 26

How does the movement of potassium ions through leak channels contribute to the resting membrane potential?

Answer 26

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.

Question 27

Explain how neurons use changes in membrane potential to communicate over long distances.

Answer 27

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.

Question 28

What is the typical resting membrane potential of a neuron? A) +30 mV B) 0 mV C) -70 mV D) -90 mV

Answer 28

Correct Answer: C

Question 29

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.

Answer 29

Correct Answer: A

Question 30

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.

Answer 30

Correct Answer: B

Question 31

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 31

Answer: B) Potassium (K⁺)

Question 32

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 32

Answer: B) Sodium (Na⁺)

Question 33

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 33

Answer: B) Potassium (K⁺)

Question 34

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 34

Answer: C) Na⁺ diffuses into the cell, and K⁺ diffuses out via leak channels.

Question 35

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 35

Answer: B) To prevent depolarization and maintain resting membrane potential.

Question 36

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 36

Answer: ✅ B) CO₂ (Small uncharged molecules like CO₂, O₂, and H₂O can pass freely.)

Question 37

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 37

Answer: ✅ B) The membrane is hydrophobic, and ions are charged, making it difficult for them to pass.

Question 38

Which of the following molecules needs a transporter to cross the membrane? A) Oxygen (O₂) B) Hydrocarbons C) Glucose D) Water

Answer 38

Answer: ✅ C) Glucose (Glucose is a large, polar molecule and requires a transporter.)

Question 39

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 39

Answer: ✅ B) Facilitated diffusion (Facilitated diffusion uses a channel or permease but follows the concentration gradient, so it does not require energy.)

Question 40

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 40

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.)

Question 41

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 41

Answer: ✅ B) Selective permeability to certain ions. (For a membrane potential to exist, some ions must be able to move, leading to charge separation.)

Question 42

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 42

Answer: ✅ C) 0 mV (Without charge separation, the voltage difference is zero.)

Question 43

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 43

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.)

Question 44

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 44

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.)

Question 45

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 45

Answer: ✅ A) Inside the cell (K⁺ is much higher inside the neuron than outside.)

Question 46

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 46

Answer: ✅ B) Outside the cell (Na⁺ is much higher outside the neuron than inside.)

Question 47

Which ion primarily determines the resting membrane potential of a neuron? A) Sodium (Na⁺) B) Potassium (K⁺) C) Chloride (Cl⁻) D) Calcium (Ca²⁺)

Answer 47

Answer: ✅ B) Potassium (K⁺) (The resting membrane potential is mostly determined by K⁺ leak channels, allowing K⁺ to diffuse out.)

Question 48

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 48

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.)

Question 49

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 49

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.)

Question 50

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 50

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.)

Question 51

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 51

Answer: ✅ B) Gated channels, ligand-gated channels, and leak channels (These are the main types of ion channels affecting membrane potential.)

Question 52

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 52

Answer: ✅ B) The inside of the cell becomes more positive. (Opening Na⁺ channels allows Na⁺ to enter, leading to depolarization.)

Question 53

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 53

Answer: ✅ B) The inside of the cell becomes more negative. (When K⁺ exits, the cell becomes more negative, leading to repolarization or hyperpolarization.)

Question 54

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 54

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.)

Question 55

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 55

Answer: ✅ B) A change in membrane potential (Voltage-gated channels open when there is a shift in the electrical charge across the membrane.)

Question 56

What type of transport do voltage-gated Na⁺ and K⁺ channels use? A) Simple diffusion B) Active transport C) Facilitated diffusion D) Endocytosis

Answer 56

Answer: ✅ C) Facilitated diffusion (These channels allow ions to move passively down their concentration gradient, but they require a trigger to open.)

Question 57

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 57

Answer: ✅ B) Facilitated diffusion and active transport (Facilitated diffusion moves ions passively using channels, while active transport requires ATP.)

Question 58

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 58

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.)

Question 59

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 59

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.)

Question 60

Where does a motor neuron receive incoming signals? A) Axon hillock B) Dendrites C) Myelin sheath D) Axon terminal

Answer 60

Answer: ✅ B) Dendrites (Dendrites contain receptors that receive chemical neurotransmitter signals from other neurons.)

Question 61

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 61

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.)

Question 62

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 62

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.)

Question 63

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 63

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.)

Question 64

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 64

Answer: ✅ A) The number of open ion channels and amount of ion movement (The more ion channels open, the greater the graded potential.)

Question 65

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 65

Answer: ✅ C) The neurotransmitter builds up, leading to a stronger response. (Frequent signaling can lead to more neurotransmitter accumulation, enhancing the response.)

Question 66

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 66

Answer: ✅ B) Ligand-gated channels (Ligand-gated channels open when a neurotransmitter binds, allowing ions to enter and triggering a graded potential.)

Question 67

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 67

Answer: ✅ C) It decreases. (Graded potentials decay with distance because ions diffuse, reducing the signal strength.)

Question 68

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 68

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.)

Question 69

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 69

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.)

Question 70

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 70

Answer: ✅ C) By electrotonic current spread (Graded potentials travel passively through the neuron by electrotonic current spread, where positive and negative charges interact.)

Question 71

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 71

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.)

Question 72

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 72

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.)

Question 73

Where does the integration of graded potentials occur in a neuron? A) Dendrites B) Axon terminals C) Axon hillock D) Myelin sheath

Answer 73

Answer: ✅ C) Axon hillock (The axon hillock is the trigger zone, where the neuron decides whether to fire an action potential.)

Question 74

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 74

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.)

Question 75

What is the threshold potential required to trigger an action potential? A) -90 mV B) -70 mV C) -55 mV D) +30 mV

Answer 75

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.)

Question 76

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

Answer 76

B

Question 77

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 77

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.)

Question 78

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 78

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.)

Question 79

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 79

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.)

Question 80

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 80

Answer: ✅ B) Whether the combined excitatory and inhibitory inputs depolarize the membrane to -55 mV at the axon hillock