Neurophysiology and Synapses · USMLE Step 1

Which of the following statements about synaptic vesicle release is true in the context of quantal neurotransmitter release?

  1. Neurotransmitters are released continuously and smoothly as a concentration gradient.
  2. Each vesicle fusion releases a discrete quantum of neurotransmitter.
  3. Vesicle release occurs independently of calcium ions.
  4. Vesicle fusion always releases the entire vesicle contents gradually over seconds.
Show answer and explanation

Correct answer: Each vesicle fusion releases a discrete quantum of neurotransmitter.

Quantal release refers to the idea that neurotransmitters are released in discrete packets (quanta), each packet corresponding to a vesicle; each quantum produces a measurable postsynaptic potential such as a miniature end-plate potential (MEPP).

Difficulty: Medium Question 6 of 28

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