Which of the following events will cause an excitatory postsynaptic potential (EPSP) in a neuron?

• A. Opening of ligand-gated Cl\(^-\) channels, allowing Cl\(^-\) to enter the postsynaptic cell
• B. Opening of ligand-gated K\(^+\) channels, allowing K\(^+\) to leave the postsynaptic cell
• C. Inhibition of voltage-gated Ca\(^{2+}\) channels in the presynaptic terminal
• D. Opening of ligand-gated Na\(^+\) channels, allowing Na\(^+\) to enter the postsynaptic cell

Answer: (D)

Verified step by step guidance

1. Step 1: Understand the concept of an excitatory postsynaptic potential (EPSP). An EPSP is a temporary depolarization of the postsynaptic membrane caused by the flow of positively charged ions into the cell. This depolarization makes the neuron more likely to fire an action potential.
2. Step 2: Analyze the role of ion channels in generating EPSPs. Ligand-gated ion channels open in response to neurotransmitters, allowing specific ions to flow across the membrane. For an EPSP, positively charged ions like Na\(^+\) or Ca\(^{2+}\) typically enter the postsynaptic cell, leading to depolarization.
3. Step 3: Evaluate the options provided in the problem. Opening ligand-gated Cl\(^-\) channels would allow negatively charged ions to enter the cell, causing hyperpolarization (inhibitory effect). Opening ligand-gated K\(^+\) channels would allow positively charged ions to leave the cell, also causing hyperpolarization. Inhibition of voltage-gated Ca\(^{2+}\) channels in the presynaptic terminal would reduce neurotransmitter release, indirectly decreasing the likelihood of an EPSP.
4. Step 4: Focus on the correct answer: Opening ligand-gated Na\(^+\) channels. When these channels open, Na\(^+\) ions (positively charged) flow into the postsynaptic cell, causing depolarization and generating an EPSP.
5. Step 5: Summarize the reasoning. The correct event that causes an EPSP is the opening of ligand-gated Na\(^+\) channels, as this allows the influx of positively charged ions, leading to depolarization of the postsynaptic membrane.