High School Biology : Understanding Action Potentials

Study concepts, example questions & explanations for High School Biology

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Example Questions

Example Question #730 : High School Biology

How does the sodium-potassium pump establish a resting potential in neurons?

Possible Answers:

It pumps three sodium ions out of the cell and two potassium ions into the cell

It pumps two potassium ions out of the cell and three sodium ions into the cell

It pumps two sodium ions out of the cell and three potassium ions into the cell

It pumps three potassium ions out of the cell and two sodium ions into the cell

Correct answer:

It pumps three sodium ions out of the cell and two potassium ions into the cell

Explanation:

The sodium potassium-pump is used in order to establish the negative resting potential in neurons. Since both sodium and potassium ions are positively charged, there needs to be more ions leaving the cell compared to ions entering. The pump accomplishes this by pumping three sodium ions out of the cell, while pumping two potassium ions into the cell. This loss of positive charge inside the cell results in the negative resting potential of neurons.

Thank about the net transfer of ions. Three positive sodium ions out of the cell for every two positive potassium ions into the cell is the same as one positive ion leaving the cell. When positive ions leave, the inside of the cell becomes more negative, helping the cell reach its resting potential of around –70mV.

Example Question #1 : Understanding Action Potentials

What is the name of the process that results in a positive voltage inside the neuron?

Possible Answers:

Bipolarization

Repolarization

Hyperpolarization

Depolarization

Correct answer:

Depolarization

Explanation:

In the beginning of an action potential voltage-gated sodium channels begin to open, allowing sodium ions to rush into the cell. This influx of positive ions results in a change in the polarity of the cell, making the voltage become positive inside the cell. This process is called depolarization.

Hyperpolarization comes after depolarization, and is caused by potassium ions leaving the cell interior. The removal of these positive ions causes the cell to become more negative than the resting potential.

Repolarization is the final process to return the cell to its resting potential. The sodium-potassium pump brings potassium ions back into the cell and removes the sodium ions, returning the cell to its normal resting state.

Example Question #2 : Understanding Action Potentials

What are action potentials?

Possible Answers:

Electrical signals transmitted by muscle cells

Chemical signals transmitted by neurons

Chemical signals transmitted by muscle cells

None of these

Electrical signals transmitted by neurons

Correct answer:

Electrical signals transmitted by neurons

Explanation:

Action potentials are electrical signals transmitted by neurons. When a neuron is stimulated, a signal is transmitted down the axon. This signal is the action potential.

An action potential in a neuron can help to stimulate a muscle to contract, but the muscle itself will not conduct an action potential.

Example Question #3 : Understanding Action Potentials

Which structure of the neuron is myelinated to promote propogation of the action potential?

Possible Answers:

Soma

Nucleus

Axon

Spines

Dendrite

Correct answer:

Axon

Explanation:

The axon is wrapped in fatty bundles called myelin sheaths that promote fast transmission of an electrical signal. The other structures listed here are not myelinated. 

Example Question #4 : Understanding Action Potentials

Consider a neuron with a resting membrane potential of .

Which of the following membrane potential values is likely to be the membrane potential of this neuron during its refractory period?

Possible Answers:

Correct answer:

Explanation:

The refractory period occurs when the cell repolarizes/hyperpolzarizes beyond the resting potential; that is, the membrane potential drops to a value more negative than when it is at rest. This prevents the firing of another action potential immediately after one has been fired. The other values represent the resting potential (), the threshold (), and values that are more positive, and are therefore incorrect.

Example Question #5 : Understanding Action Potentials

What causes the hyperpolarization during an action potential?

Possible Answers:

An excess of anion enters the cell, making the inside of the cell relatively more negative to the surroundings

The sodium channels continue to stay open as the potassium channels are open

The potassium channels are slower than the calcium channels to close 

An influx of calcium into the cell will cause the cell's potential to become more negative

The potassium channels are slower than the sodium channels to close

Correct answer:

The potassium channels are slower than the sodium channels to close

Explanation:

As an action potential begins, there's a rapid influx of sodium in to cell, causing the cell's membrane potential to rapidly increase, depolarizing the cell. Once the cell has reached its action potential peak, the sodium channels begin to close. This closing activates the potassium channels. These channels allow potassium to leave the cell. Since potassium is a positive ion, as it leaves, the cell's membrane potential becomes more negative, repolarizing. The slight dip in the action potential curve, labeled as hyperpolarization, is result of the potassium channels lagging to close, and potassium loss is "overshot". As a result, too much potassium lost from the cell will cause the cell's potential to become more negative relative to its normal potential.

Example Question #6 : Understanding Action Potentials

 An action potential is generally driven by the movement of which two ions?

Possible Answers:

Sodium and potassium

Chloride and potassium

Chloride and magnesium

Calcium and potassium

Correct answer:

Sodium and potassium

Explanation:

Action potentials are largely due to the movements of potassium  and sodium  across a membrane. While other ions and neurotransmitters can affect action potential firing, the movements of these two ions have the greatest effect on a neuron firing.

Example Question #7 : Understanding Action Potentials

Once an action potential arrives at the synaptic bud, what kind of ion channels open?

Possible Answers:

Voltage-gated calcium

Voltage-gated potassium

Chemical-gated sodium

Chemical-gated calcium

Voltage-gated sodium

Correct answer:

Voltage-gated calcium

Explanation:

As an action potential is essentially an electrical current, it makes sense for it to open voltage-gated channels. Specifically, voltage-gated calcium channels are opened to allow calcium ions to flow into the cell and bind to synaptic vesicles. 

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