Human Anatomy and Physiology : Help with Action Potential Physiology

Study concepts, example questions & explanations for Human Anatomy and Physiology

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Example Questions

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Example Question #1 : Help With Action Potential Physiology

What part of the action potential results in the depolarization of the cell?

Possible Answers:

Closing of voltage-gated sodium channels

Opening of voltage-gated sodium channels

Opening of voltage-gated potassium channels

Closing of voltage-gated potassium channels

Correct answer:

Opening of voltage-gated sodium channels

Explanation:

When at rest, the neuron initially has a negative membrane potential. At the beginning of an action potential, voltage-gated sodium channels open, allowing sodium ions to enter the cell. This causes the cell to become positively charged compared to the outside of the cell. This process is called depolarization.

After depolarization occurs, the sodium channels close, initiating the absolute refractory period. Voltage-gated potassium channels then open and potassium ions exit the cell. This results in hyperpolarization and the relative refractory period. The potassium channels then close and the sodium-potassium pump returns the cell to its resting potential by removing sodium and collecting potassium.

Example Question #2 : Help With Action Potential Physiology

Which of the following does NOT take place during an action potential?

Possible Answers:

Potentialization

Hyperpolarization

Repolarization

Depolarization

Correct answer:

Potentialization

Explanation:

An action potential across a cell membrane has five phases:

1. The resting membrane potential is a negative membrane potential established by the sodium-potassium pump and maintained by potassium leak channels.

2. Depolarization involves opening of voltage-gated sodium channels and results in a rapid influx of positively-charged sodium ions into the cell, creating a positive membrane potential.

3. Overshoot occurs during the maximal value (peak) of the action potential.

4. Hyperpolarization occurs when sodium channels close and potassium channels open, allowing potassium to leak out the cell, and establishing a negative membrane potential below the resting potential.

5. Repolarization occurs when voltage-gated potassium channels eventually close and the membrane potential returns to the resting value via action of the sodium-potassium pump.

Potentiation refers to the phenomenon when nerves become more effective at transmitting signals due to extensive use of the same pathway.

Example Question #3 : Help With Action Potential Physiology

Which of the following statements is true concerning the absolute refractory period?

Possible Answers:

A larger than normal stimulus is needed in order to create an action potential during this time

No stimulus can result in an action potential during this time

Even the smallest stimulus will create an action potential during this time

Sodium channels are still open from a pervious stimulus

The action potential will proceed, but will take place in the opposite direction, re-stimulating previously stimulated neurons

Correct answer:

No stimulus can result in an action potential during this time

Explanation:

Once an action potential has been created, the membrane has a period of time during which it cannot be stimulated to create another action potential. The absolute refractory period occurs when the voltage-gated sodium channels initially close. The first gating mechanism of these channels cannot be overcome by an electrical stimulus, and the sodium channels will remain closed even if a large electrical stimulus is present. During this period, even a very large stimulus cannot result in neural depolarization.

Following this, the secondary gating mechanism for the channel becomes active. This mechanism is sensitive to electrical stimuli, but keeps the channels closed when the neuron is at rest. The relative refractory period results when sodium channels are capable of opening, but the cell is hyperpolarized, making it very difficult to initiate a stimulus that reaches the action potential threshold.

Example Question #4 : Help With Action Potential Physiology

What are the two gates of the voltage-gated  channels along the axonal plasma membrane?

Possible Answers:

Activation and reactivation

Positive and negative

 and 

Activation and inactivation

Correct answer:

Activation and inactivation

Explanation:

The voltage-gated  channels along the axonal plasma membrane open and close in response to changes in voltage, and may exist in three distinct states: deactivated, activated, and inactivated. While the axon is at rest, these channels are said to be deactivated; they are impermeable to sodium ions since their activation gates are closed. Once the neuron gets depolarized to the threshold of the voltage-gated sodium channels, the activation gates open, allowing the influx of sodium down its concentration gradient into the cell. During this time the channels are in their activated state. At the peak of the action potential the activation gates are still open, but the inactivation gates close, stopping the flow of sodium through the channels. The channels are in the inactivated state due to the cell becoming depolarized. Once the membrane potential drops back down towards resting, the inactivation gates open, and the activation gates close, thereby deactivating the channels again, until another action potential depolarizes the membrane.

Example Question #5 : Help With Action Potential Physiology

Which of the following are in the correct order regarding action potentials?

Possible Answers:

1. The neuron has a resting potential.
2. Sodium ions enter the cell and alter the membrane potential.
3. The membrane potential depolarizes all the way up to the threshold level.
4. An action potential is fired, which means that the depolarization spreads down the neuron's axon.

1. The neuron has a resting potential.
2. The membrane potential depolarizes all the way up to the threshold level.
3. Sodium ions enter the cell and alter the membrane potential.
4. An action potential is fired, which means that the depolarization spreads down the neuron's axon.

1. The neuron has a resting potential.
2. Sodium ions exit the cell and hyperpolarize the membrane potential.
3. The membrane potential then reaches the threshold level.
4. An action potential is fired, which means that the hyperpolarization spreads down the neuron's axon.

1. The neuron has a resting potential.
2. Sodium ions enter the cell and alter the membrane potential.
3. The membrane potential hyperpolarizes beyond the threshold level.
4. An action potential is fired, which means that the depolarization spreads down the neuron's axon.

Correct answer:

1. The neuron has a resting potential.
2. Sodium ions enter the cell and alter the membrane potential.
3. The membrane potential depolarizes all the way up to the threshold level.
4. An action potential is fired, which means that the depolarization spreads down the neuron's axon.

Explanation:

The neuron has a resting potential. In its resting state, the neuron has a resting potential with a slightly negative interior compared to the exterior. Sodium ions  enter the cell and alter the membrane potential. Through voltage-gated channels,  enters and makes the interior less negative therefore decreasing the membrane potential difference, which is known as depolarization. The membrane potential depolarizes all the way up to the threshold level. After enough  enters, the threshold membrane potential is reached. This opens more  channels. An action potential is fired, which means that the depolarization spreads down the neuron's axon. This travels down the entire axon, eventually reaching the dendrite and signaling to other neurons.

Example Question #6 : Help With Action Potential Physiology

Which type of signal is transmitted along a neuron?

Possible Answers:

Mechanical

Osmosis

Electrical

Chemical

Hormonal

Correct answer:

Electrical

Explanation:

To support the general function of the nervous system, neurons must communicate within the cell (intracellular signaling) and between other cells (intercellular signaling). In order to achieve long distance and rapid communication, neurons have special abilities for sending electrical signals (action potentials) along axons. This mechanism is called conduction, and it is how the neuron's cell body communicates with its own terminals via the axon. Communication between neurons is achieved at synapses by the process of neurotransmission. 

Example Question #7 : Help With Action Potential Physiology

When an action potential occurs, the permeability of __________ across the cell membrane becomes much greater. 

Possible Answers:

Potassium 

Sodium 

Calcium 

Magnesium 

Chloride 

Correct answer:

Sodium 

Explanation:

At resting potential, the cell membrane is about 25 times more permeable to potassium ions than it is to sodium ions. During an action potential, the membrane becomes much more permeable to sodium ions than potassium ions, causing the membrane potential to become more positive, as sodium flows down its concentration gradient into the cell. Note that this concentration gradient is largely set up by the action of the sodium-potassium ATPase, which pumps three sodium ions out of the cell in exchange for two potassium ions into the cell. 

Example Question #8 : Help With Action Potential Physiology

The junction between the transmitting and receiving neuron is called a(n) __________.

Possible Answers:

node of Ranvier 

neurotransmitter

myelin sheath 

action potential 

synapse 

Correct answer:

synapse 

Explanation:

A synapse is a specialized junction between cells. It is involved in the integration and converging of signals between neurons. At a synaptic junction, the membranes of the pre- and post- synaptic neurons are separated by a gap called a synaptic cleft, which is the site of neurotransmitter release. 

Example Question #9 : Help With Action Potential Physiology

Which of the following is responsible for opening sodium channels in the plasma membrane of the receiving neuron, leading to an action potential or more excitable neuron? 

Possible Answers:

Calcium 

Glutamate 

Chloride 

GABA (gamma-aminobutyric acid)

Norepinephrine 

Correct answer:

Glutamate 

Explanation:

Glutamate opens sodium channels in the plasma membrane of the receiving neuron, moving the action potential towards (depolarize) the sodium Nernst potential (81mV). GABA is an inhibitory neurotransmitter which opens chloride channels in the plasma membrane of the receiving neuron, making the neuron more difficult to excite (hyperpolarized). 

Example Question #10 : Help With Action Potential Physiology

The resting membrane potential (RMP) is primarily determined by which ion?

Possible Answers:

Potassium

Sodium

Magnesium

Chloride

Calcium

Correct answer:

Potassium

Explanation:

The resting membrane potential is based on the difference in electrical charges of the ions that flow through the membrane. The membrane potential has a greater permeability to potassium when at rest which causes a shift in its potential. Thus, potassium has the strongest affect on the RMP and causes it to be closer to potassium's reversal potential. Side note: This potential is strongly held by the sodium potassium pump.

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