Question 1

Which of the following best describes the difference between an action potential and a graded potential in neurons?

Accepted Answer

Action potentials are all-or-none signals that travel long distances, while graded potentials vary in magnitude and travel short distances.

Question 2

During the depolarization phase of an action potential, which ion movement is primarily responsible for the change in membrane potential?

Accepted Answer

Sodium ions ($$\mathrm{Na^+}) $$move into the cell.

Question 3

What is the typical value of the resting membrane potential in neurons, and what does this indicate about the charge inside the cell relative to the outside?

Accepted Answer

$$-70\ \mathrm{mV}$$; the inside of the cell is more negative than the outside.

Question 4

Which event marks the peak of the action potential, and what happens to the sodium channels at this point?

Accepted Answer

Sodium channels close, stopping further sodium entry.

Question 5

What is the main function of the Na$$^+/K$^+$$ pump during hyperpolarization?

Accepted Answer

It restores the membrane potential to $$-70\ \mathrm{mV} by $$exchanging $$3\ \mathrm{Na^+}$$ out for $$2\ \mathrm{K^+} in.$$

Question 6

Which of the following best explains the 'all-or-none' phenomenon of action potentials?

Accepted Answer

Once the threshold is reached, an action potential is always generated and propagated, regardless of stimulus strength.

Question 7

A neuron is stimulated, but the membrane potential only depolarizes by $$10\ \mathrm{mV}$$ from the resting value. What is the likely outcome?

Accepted Answer

A graded potential will occur, but no action potential will be generated.

Question 8

During the absolute refractory period, what is true about the neuron's ability to respond to another stimulus?

Accepted Answer

The neuron is incapable of responding to any stimulus, no matter how strong.

Question 9

Which process is responsible for restoring the membrane potential to a negative value during repolarization?

Accepted Answer

Opening of potassium channels and efflux of potassium ions.

Question 10

In myelinated axons, how does the propagation of an action potential differ from that in unmyelinated axons?

Accepted Answer

Action potentials jump from node to node (saltatory conduction) in myelinated axons, increasing speed.

Question 11

Which statement about graded potentials is correct?

Accepted Answer

Graded potentials decrease in magnitude as they travel away from the stimulus site.

Question 12

A sensory neuron is excited by light, resulting in a local change in membrane potential. What is this local change called?

Accepted Answer

Receptor potential

Question 13

If a neuron is in the relative refractory period, what is required for it to generate another action potential?

Accepted Answer

A stimulus that is stronger than usual to reopen sodium channels.

Question 14

Which equation best represents the net effect of the Na$$^+/K$^+$$ pump in maintaining the resting membrane potential?

Accepted Answer

$$3\ \mathrm{Na^+}$$ out, $$2\ \mathrm{K^+} in$

Question 15

Which of the following best describes the threshold for action potential generation in a neuron?

Accepted Answer

The membrane potential must be depolarized by $$15$$–$$20\ \mathrm{mV}$$ from resting value.

Question 16

A patient is experiencing repeated weak stimuli to a neuron, but no nerve impulses are generated. What is the most likely explanation?

Accepted Answer

The stimuli are subthreshold and only produce graded potentials.

Question 17

Which phase of the action potential is characterized by the membrane potential becoming more negative than the resting potential?

Accepted Answer

Hyperpolarization

Question 18

If the sodium ion concentration in the extracellular fluid decreases significantly, what effect would this have on the generation of action potentials?

Accepted Answer

Action potentials would be less likely to occur due to reduced sodium influx during depolarization.

Question 19

Which of the following best illustrates the analogy of the 'all-or-none' phenomenon using the match and twig example?

Accepted Answer

If enough sodium ions enter the cell to reach threshold, the action potential will be generated and propagated regardless of continued stimulus.

Question 20

Which statement about the propagation of action potentials in unmyelinated axons is correct?

Accepted Answer

The repolarization wave chases the depolarization wave down the length of the axon.

Membrane Potentials and Nerve Impulse Transmission: Action and Graded Potentials

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