Neurophysiology and Synapses · USMLE Step 1

What ionic movement is most commonly responsible for generating an excitatory postsynaptic potential (EPSP)?

  1. Cl⁻ influx
  2. K⁺ efflux
  3. Na⁺ or Ca²⁺ influx
  4. Mg²⁺ influx
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Correct answer: Na⁺ or Ca²⁺ influx

EPSPs are generally produced when neurotransmitter binding opens ion channels that allow positive ions (e.g., Na⁺ or Ca²⁺) to enter the postsynaptic neuron, depolarizing the membrane.

Difficulty: Medium Question 4 of 28

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