Question 1

Which of the following statements best describes the gating mechanism of ligand-gated ion channels (LGICs)?

Accepted Answer

LGICs open when a specific ligand binds to the orthosteric site, causing a conformational change.

Question 2

A researcher applies a competitive antagonist to a neuron expressing nAChRs. What is the most likely effect on the postsynaptic current when acetylcholine is released?

Accepted Answer

The postsynaptic current will decrease because the antagonist blocks the ligand binding site.

Question 3

Which equation correctly describes the current through a ligand-gated ion channel for a given ion species n?

Accepted Answer

$$I_n = G_n (V_m - V_n)$$

Question 4

Which of the following is a distinguishing structural feature of cys-loop receptors?

Accepted Answer

They contain a cysteine-cysteine bond forming a loop in the N-terminal domain.

Question 5

A mutation disrupts the M2 transmembrane segment of a cys-loop receptor. What is the most likely consequence?

Accepted Answer

The ion conduction through the channel will be impaired.

Question 6

Which of the following drugs acts as a positive allosteric modulator (PAM) of GABA$$_A$$ receptors?

Accepted Answer

Diazepam

Question 7

Why are currents through ligand-gated ion channels typically transient, even when the ligand is present?

Accepted Answer

The channels rapidly desensitize, closing even while the ligand is still bound.

Question 8

Which of the following best explains why GABA$$_A$$ receptor activation is typically inhibitory in mature neurons?

Accepted Answer

GABA$$_A$$ receptors are permeable to Cl$$^-$$, leading to hyperpolarization.

Question 9

Which of the following would support the hypothesis that an observed effect in neurons is mediated by nAChRs?

Accepted Answer

Any of the above (A, B, or C).

Question 10

Which of the following is NOT a member of the cys-loop receptor family?

Accepted Answer

AMPARs

Question 11

A voltage clamp experiment is performed on a neuron expressing GABA$$_A$$ receptors. The current-voltage (I-V) relationship is linear and crosses the x-axis at -65 mV. What does this reversal potential indicate?

Accepted Answer

The channel is permeable to anions, likely Cl$$^-.$$

Question 12

Which of the following best describes the pharmacological action of acetylcholinesterase (AChE) inhibitors at the neuromuscular junction?

Accepted Answer

They increase the duration of nAChR activation by preventing ACh breakdown.

Question 13

Which of the following is a correct statement about the structure of cys-loop receptors?

Accepted Answer

Five subunits assemble to form a functional channel.

Question 14

Which of the following would most likely result from applying a benzodiazepine to cultured neurons expressing GABA$$_A$$ channels in the absence of GABA?

Accepted Answer

No channel opening will occur because benzodiazepines require GABA to be present.

Question 15

Which of the following best explains why the response to ligand-gated ion channel activation is smaller at increasing distances from the synaptic release site?

Accepted Answer

The ligand concentration decreases due to diffusion away from the release site.

Question 16

Which of the following is a feature that distinguishes ligand-gated ion channels from voltage-gated ion channels?

Accepted Answer

LGICs are opened by the binding of specific ligands.

Question 17

Which of the following is a correct pairing of endogenous ligand and receptor?

Accepted Answer

Serotonin and 5-HT$$_3R$$

Question 18

Which of the following best describes the effect of a non-competitive antagonist on a ligand-gated ion channel?

Accepted Answer

It binds to a different site and blocks channel opening regardless of ligand binding.

Question 19

Which of the following cys-loop receptors is excitatory?

Accepted Answer

nAChR

Ligand-Gated Ion Channels 1

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