question:

a researcher is studying a novel synapse in the central nervous system. under whole-cell voltage-clamp, they record an excitatory postsynaptic current (epsc) with a reversal potential of exactly 0 mv. assuming typical physiological intracellular and extracellular ionic concentrations for a mammalian neuron, which of the following mechanisms best explains this reversal potential?

a. the postsynaptic channels are exclusively permeable to $\text{k}^+$ and $\text{na}^+$, allowing an equal net flux of both ions at 0 mv.
b. the postsynaptic channels are equally permeable to $\text{na}^+$, $\text{k}^+$, and $\text{cl}^-$, driving the membrane potential to the weighted average of their nernst potentials.
c. the postsynaptic current is entirely mediated by voltage-gated calcium channels opening at the soma.
d. the postsynaptic receptors are ligand-gated cation channels (e.g., ampa or nmda) that do not allow $\text{cl}^-$ passage, but are permeable to both $\text{k}^+$ and $\text{na}^+$.

Question

question:

a researcher is studying a novel synapse in the central nervous system. under whole-cell voltage-clamp, they record an excitatory postsynaptic current (epsc) with a reversal potential of exactly 0 mv. assuming typical physiological intracellular and extracellular ionic concentrations for a mammalian neuron, which of the following mechanisms best explains this reversal potential?

a. the postsynaptic channels are exclusively permeable to $\text{k}^+$ and $\text{na}^+$, allowing an equal net flux of both ions at 0 mv.
b. the postsynaptic channels are equally permeable to $\text{na}^+$, $\text{k}^+$, and $\text{cl}^-$, driving the membrane potential to the weighted average of their nernst potentials.
c. the postsynaptic current is entirely mediated by voltage-gated calcium channels opening at the soma.
d. the postsynaptic receptors are ligand-gated cation channels (e.g., ampa or nmda) that do not allow $\text{cl}^-$ passage, but are permeable to both $\text{k}^+$ and $\text{na}^+$.

Accepted Answer

{ "quality": "clear", "question_count": 1, "skills_matched": [ "direct_cot", "multiple_choice_formatter", "explain_then_answer", "quick" ], "needs_drawing": false, "concepts_used": [], "new_concepts": [ "Reversal Potential", "Ligand-Gated Channels", "Synaptic Transmission" ], "current_concepts": [ "Reversal Potential", "Ligand-Gated Channels", "Synaptic Transmission" ] } ## Analyze the reversal potential of EPSCs $$ \begin{aligned} &E_{\text{rev}} = 0\text{ mV} \ &E_{\text{K}} \approx -80\text{ to }-90\text{ mV} \ &E_{\text{Na}} \approx +50\text{ to }+65\text{ mV} \ &E_{\text{rev}} \approx \frac{g_{\text{Na}}E_{\text{Na}} + g_{\text{K}}E_{\text{K}}}{g_{\text{Na}} + g_{\text{K}}} \approx 0\text{ mV} \end{aligned} $$ ## Evaluate channel properties and permeability $$ \begin{aligned} &\text{AMPA/NMDA receptors: ligand-gated non-selective cation channels} \ &P_{\text{Na}} \approx P_{\text{K}}, \quad P_{\text{Cl}} = 0 \ &\text{At } V_{\text{m}} = 0\text{ mV}: I_{\text{net}} = I_{\text{Na}} + I_{\text{K}} = 0 \ &\text{Note: Channels are not "exclusively" permeable to only these two at all potentials, but are ligand-gated cation channels.} \end{aligned} $$ ## Compare options $$ \begin{aligned} &\text{Option A: Incorrectly states "exclusively permeable to } \text{K}^+ \text{ and } \text{Na}^+ \text{ allowing equal net flux at } 0\text{ mV}" \ &\text{Option B: Incorrectly includes Cl}^- \ &\text{Option C: EPSCs are mediated by ligand-gated channels at dendrites/soma, not voltage-gated Ca}^{2+} \text{ channels} \ &\text{Option D: Correctly identifies ligand-gated cation channels (AMPA/NMDA) permeable to both } \text{K}^+ \text{ and } \text{Na}^+ \text{ but not } \text{Cl}^- \end{aligned} $$

A. The postsynaptic channels are exclusively permeable to K⁺ and Na⁺, allowing an equal net flux of both ions at 0 mV.

B. The postsynaptic channels are equally permeable to Na⁺, K⁺, and Cl⁻, driving the membrane potential to the weighted average of their Nernst potentials.

C. The postsynaptic current is entirely mediated by voltage-gated calcium channels opening at the soma.

D. The postsynaptic receptors are ligand-gated cation channels (e.g., AMPA or NMDA) that do not allow Cl⁻ passage, but are permeable to both K⁺ and Na⁺.

{ "subject": "Natural Science", "question_type": "Multiple Choice", "knowledge_point": [ "Natural Science", "Biology", "Neurobiology" ] }

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Explanation:

Analyze the reversal potential of EPSCs

Evaluate channel properties and permeability

Compare options

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