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Neurophysiology and Synapses · USMLE Step 1

What primarily distinguishes an inhibitory postsynaptic potential (IPSP) from an excitatory postsynaptic potential (EPSP)?

  1. IPSP increases membrane potential (depolarization), EPSP decreases it.
  2. An IPSP makes the neuron less likely to fire, an EPSP makes it more likely.
  3. IPSP uses neuropeptides, EPSP uses small-molecule neurotransmitters.
  4. An IPSP is always mediated by glutamate, an EPSP always by GABA.
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Correct answer: An IPSP makes the neuron less likely to fire, an EPSP makes it more likely.

An IPSP hyperpolarizes or stabilizes the postsynaptic membrane, decreasing likelihood of action potential firing; an EPSP depolarizes the membrane, increasing that likelihood.

Difficulty: Medium Question 14 of 28

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