AP Biology : Neural Physiology

Study concepts, example questions & explanations for AP Biology

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Example Questions

Example Question #24 : Understanding Action Potentials

Which of the given options occurs last during an action potential?

Possible Answers:

Potassium gates open

Sodium gates close

Potassium gates close

The cell reaches threshold

The cell depolarizes

Correct answer:

Potassium gates close

Explanation:

Once the cell reaches threshold, an action potential is fired. Sodium, a positive ion, enters the cell, and causes the charge on the membrane to rise, or depolarize. After a certain point, sodium gates close. Potassium, another positive ion, then leaves the cell, and the charge on the membrane decreases. As the potassium ions exit, the membrane potential plunges even lower than the resting potential, causing it to become hyperpolarized. At this point, the sodium/potassium pump works to repolarize the cell to return to the resting membrane potential.

1. The cell reaches threshold

2. Sodium gates open, and sodium floods into the cell

3. The cell depolarizes

4. Sodium gates close

5. Potassium gates open and potassium leaves the cell

6. The cell hyperpolarizes

7. Potassium gates close

8. Na/K pump repolarizes the cell during refractory period

Example Question #21 : Understanding Action Potentials

Before a muscle can contract, an action potential must be initialized from a neuron that is innervating the muscle. An action potential begins when the cell’s voltage-gated sodium channel opens. Once opened, sodium rushes into and depolarizes the cell. Once the neuron is depolarized, it is able to release neurotransmitters onto the post-synaptic cleft located on the muscle. Downstream, the neurotransmitters collectively will generate another action potential within the muscle and allow it to release calcium needed for muscle contraction.

Hyponatremia occurs when the sodium concentration in the blood is low. Which of the following best describes how this will affect muscle contractions?

Possible Answers:

Hyponatremia will not affect the difficulty in being able to contract muscles

Hyponatremia will make it harder to contract muscles

Hyponatremia will make it easier to contract muscles

None of these

Hyponatremia will make the muscle easier to contract at first then more difficult over time

Correct answer:

Hyponatremia will make it harder to contract muscles

Explanation:

All muscle types (cardiac, skeletal, and smooth), require sodium to enter the cell to initiate an action potential. The action potential then travels down the axon, elicits neurotransmitters, activates calcium channels, and causes the muscle to contract. In order to initiate the action potential, sodium must enter the cell in large quantity. This depolarizes the cell above the action potential threshold. If the cell does not reach the action potential threshold, then there will be no action potential and no muscle contraction.

Example Question #26 : Understanding Action Potentials

Influx of  (sodium) ions into the neuron will cause which of the following?

Possible Answers:

Hyperpolarization

Depolarization

Neurotransmitter release

Repolarization

Polarization

Correct answer:

Depolarization

Explanation:

When sodium ions enter the neuron, the membrane begins to lose its negative charge and therefore become depolarized. Hyperpolarization, repolarization, and polarization all occur with the efflux of  potassium ions out of the neuron. Note that an action potential stimulates the influx of sodium ions. The sodium potassium pump uses ATP to drive the establishment of the resting membrane potential by pumping three sodium ions out of the cell in exchange for two potassium ions into the cell. Both of these ions are being pumped against their concentration gradients. Neurotransmitter release is stimulated by the influx of calcium ions.

Example Question #21 : Understanding Action Potentials

With respect to action potentials, what is responsible for depolarization? 

Possible Answers:

Potassium ions enter the cell

Sodium ions enter the cell

Potassium ions exit the cell

Sodium ions exit the cell

Calcium ions enter the cell

Correct answer:

Sodium ions enter the cell

Explanation:

First it is important to realize that there is a higher concentration of potassium ions inside of the cell and a higher concentration of sodium ions outside of the cell. When depolarization occurs, sodium ion channels open. With this information, we can get rid of any answer choices that do not mention sodium ions. Now we must see if sodium ions enter or exit the cell. Since there is a higher concentration of sodium ions outside of the cell, sodium ions will enter the cell by going down the concentration gradient. 

Example Question #1 : Understanding Neurotransmitters

What kind of molecule can be used to inhibit the effects of a neurotransmitter?

Possible Answers:

Antagonistic molecules

Agonistic molecules

Synergistic molecules

None of these

Protagonistic molecules

Correct answer:

Antagonistic molecules

Explanation:

Neurotransmitters in the human body are under tight control. Many drugs, such as anti-depressants or drugs for ADHD, limit neurotransmitter responses. Antagonistic molecules will inhibit neurotransmitters and are used in many drugs. These molecules structurally interact with receptor proteins, either blocking the active site or binding allosterically to alter the binding site shape. Antagonists can be competitive or uncompetitive.

In contrast, agonists are molecules that structurally resemble the ligand for a certain receptor and can bind to the active site to trigger a response. Nicotine, for example, is an agonist to certain acetylcholine receptors and can trigger these receptors.

Example Question #2 : Understanding Neurotransmitters

Which of the following is true regarding a synapse?

I. The neurotransmitter attaches to receptors on the presynaptic neuron

II. Propagation of the nerve signal is slowest at the synapse

III. Calcium ion channels located on the membrane of postsynaptic neuron facilitate the release of neurotransmitters

Possible Answers:

I and III

II and III

II only

I only

Correct answer:

II only

Explanation:

Neurotransmitters, such as acetylcholine, are chemical signals that transmit action potentials from one neuron to another. This process occurs at the synapse, where a neurotransmitter is released from the presynaptic neuron. This neurotransmitter travels across the synaptic cleft and binds to a receptor on the postsynaptic neuron. Statement I is thus false.

The rate of propagation of a nerve signal is limited by the synapse because neurotransmitters must diffuse across the gap; statement II is true.

Calcium ions are very important in the release of neurotransmitters. Voltage-gated calcium channels are located on the axon of the presynaptic neuron. When an action potential reaches the synapse, calcium ions are allowed to enter into the presynaptic neuron. This influx of calcium ions interacts with vesicles containing neurotransmitters and causes them to release their contents into the synaptic cleft. Statement III is false because calcium ion channels are located on the membrane of presynaptic neuron, not postsynaptic neuron.

Example Question #3 : Understanding Neurotransmitters

A postsynaptic neuron has undergone a mutation that renders its SNARE proteins nonfunctional. What is the result of this mutation?

Possible Answers:

Neurons are unable to maintain resting membrane potential

Neurons are unable to synthesize neurotransmitter

Action potentials are unable to propagate down the postsynaptic axon

Neurons are unable to deliver neurotransmitter into the synaptic cleft

None of the other answers

Correct answer:

Neurons are unable to deliver neurotransmitter into the synaptic cleft

Explanation:

The SNARE proteins are responsible for allowing vesicles filled with neurotransmitter to fuse with the cell membrane at the synaptic cleft, resulting in exocytosis. Without these proteins, the neurotransmitter cannot propagate the signal to any other cells.

Neurotransmitter synthesis occurs via translation or synthesis in the smooth endoplasmic reticulum, depending on the identity of teh molecule. Resting potential is determined by the sodium-potassium pump, and action potential propagation relies heavily on voltage-gated sodium channels and myelin.

Example Question #1 : Understanding Neurotransmitters

Which of the following types of molecules could potentially be a neurotransmitter?

I. Peptides

II. Gases

III. Monoamines

Possible Answers:

I and III

I and II

I, II, and III

III only

Correct answer:

I, II, and III

Explanation:

All of the choices could potentially be neurotransmitters.

Peptide neurotransmitters are proteins. An example of a peptide neurotransmitter is somatostatin. Nitric oxide is the most well-known gaseous neurotransmitter. Monoamines are molecules that contain an amine group connected to an aromatic ring. These molecules are derived from aromatic amino acids. Dopamine, norepinephrine, and epinephrine are very well-known monoamine neurotransmitters.  

Example Question #1 : Understanding Neurotransmitters

Which answer gives the two possible effects of a neurotransmitter on a postsynaptic neuron?

Possible Answers:

Apoptotic or no effect

Excitatory or no effect

Inhibitory or excitatory

Inhibitory or no effect

Correct answer:

Inhibitory or excitatory

Explanation:

Receptors on postsynaptic neurons are connected to ion channels. When the neurotransmitter binds to the receptor, the channel opens, making that neuron more or less likely to have an action potential depending upon which type of ion the channel allows to enter or exit the neuron. The result is either an excitatory postsynaptic potential (EPSP) or an inhibitory postsynaptic potential (IPSP).

Example Question #6 : Understanding Neurotransmitters

Which of the following is true regarding the parasympathetic nervous system?

Possible Answers:

It is a part of the central nervous system

It works to elevate heart rate and blood pressure

It works to decrease heart rate and blood pressure

It works to funnel blood to the muscles in preparation for a fight-or-flight response

It is a part of the somatic nervous system

Correct answer:

It works to decrease heart rate and blood pressure

Explanation:

The parasympathetic division of the autonomic nervous system promotes the "rest and digest mode." The somatic nervous system controls voluntary skeletal muscles, but the parasympathetic nervous system controls involuntary smooth & cardiac muscles. The neurons of the parasympathetic nervous system release acetylcholine, which is a neurotransmitter that leads to a decrease in heart rate and blood pressure. Results of increased parasympathetic activity include: decreasing blood flow to skeletal muscles, increasing blood flow to the gut, constricting pupils, and glycogenesis. 

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