Q: Which equation best represents the Nernst equation for calculating the equilibrium potential ($E_{ion}$) for a particular ion?

$E_{ion} = \frac{RT}{zF} \ln \left( \frac{[\text{ion}]_{\text{outside}}}{[\text{ion}]_{\text{inside}}} \right)$

Question 1

Which of the following best describes the primary function of myelin in the nervous system?

Accepted Answer

Myelin increases the speed of action potential propagation by insulating axons and enabling saltatory conduction.

Question 2

A neuron at rest has a membrane potential of approximately $-70\ \mathrm{mV}$. Which of the following best explains why the inside of the neuron is negative relative to the outside?

Accepted Answer

The sodium-potassium pump moves $3$ Na$^+$ ions out and $2$ K$^+$ ions in, and the membrane is more permeable to K$^+$ than Na$^+$.

Question 3

During the rising phase of an action potential, which of the following occurs?

Accepted Answer

Voltage-gated Na$^+$ channels open, allowing Na$^+$ to flow into the cell, causing depolarization.

Question 4

Which equation best represents the Nernst equation for calculating the equilibrium potential ($E_{ion}$) for a particular ion?

Accepted Answer

$E_{ion} = \frac{RT}{zF} \ln \left( \frac{[	ext{ion}]_{	ext{outside}}}{[	ext{ion}]_{	ext{inside}}} ight)$

Question 5

A patient is diagnosed with multiple sclerosis, a disease that damages myelin sheaths. Which of the following symptoms is most likely to result from this condition?

Accepted Answer

Slower conduction of action potentials along axons, leading to muscle weakness and impaired coordination.

Question 6

Which of the following best describes the difference between an excitatory postsynaptic potential (EPSP) and an inhibitory postsynaptic potential (IPSP)?

Accepted Answer

An EPSP depolarizes the postsynaptic membrane, making an action potential more likely; an IPSP hyperpolarizes it, making an action potential less likely.

Question 7

If a neuron receives simultaneous EPSPs and IPSPs at different locations on its dendrites, what is the likely outcome at the axon hillock?

Accepted Answer

The neuron will integrate the signals, and the net effect will determine whether the threshold for an action potential is reached.

Question 8

Which of the following best explains why action potentials are unidirectional along an axon?

Accepted Answer

The refractory period prevents the action potential from traveling backward.

Question 9

A researcher applies a drug that blocks voltage-gated K$^+$ channels in a neuron. What effect will this have on the action potential?

Accepted Answer

Repolarization will be delayed, causing the action potential to last longer.

Question 10

Which of the following is a direct result of the opening of ligand-gated ion channels at a chemical synapse?

Accepted Answer

A graded potential is generated in the postsynaptic membrane.

Question 11

Which of the following scenarios best illustrates the concept of saltatory conduction?

Accepted Answer

An action potential jumps from one node of Ranvier to the next along a myelinated axon.

Question 12

A neuron is exposed to a toxin that increases the permeability of the membrane to Na$^+$. What is the most likely immediate effect on the membrane potential?

Accepted Answer

The membrane potential will become more positive (depolarize).

Question 13

Which of the following best describes the role of the axon hillock in neuronal signaling?

Accepted Answer

It integrates incoming signals and initiates action potentials if the threshold is reached.

Question 14

A patient is given a drug that blocks the reuptake of neurotransmitters at the synaptic cleft. What is the most likely effect on synaptic transmission?

Accepted Answer

Neurotransmitters will remain in the synaptic cleft longer, prolonging the postsynaptic response.

Question 15

Which of the following is NOT a function of the nervous system?

Accepted Answer

Producing hormones for long-term regulation of metabolism.

Question 16

If the extracellular concentration of K$^+$ increases significantly, what effect will this have on the resting membrane potential of a neuron?

Accepted Answer

The resting membrane potential will become less negative (depolarize).

Question 17

Which of the following best explains why graded potentials decrease in strength as they spread from the site of origin?

Accepted Answer

They are subject to passive current leak and resistance in the membrane.

Question 18

A neuron receives two subthreshold EPSPs in rapid succession at the same synapse. What is this phenomenon called, and what is its effect?

Accepted Answer

Temporal summation; the EPSPs may combine to reach threshold and trigger an action potential.

Question 19

Which of the following best describes the effect of opening ligand-gated Cl$^-$ channels on the postsynaptic membrane?

Accepted Answer

It causes hyperpolarization, making an action potential less likely.

Neurons, Action Potentials, and Synapses: Electrical Signaling in Animals

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