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Synaptic Communication

Synaptic Communication. 5 March 2012. Anatomy of the NMJ. Anatomy of the NMJ. The story of MEPPs. Scientists recorded membrane potentials from the end-plate (EPPs), evoked by nerve stimulation They also observed spontaneous depolarizations of approximately 1mV

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Synaptic Communication

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  1. Synaptic Communication 5 March 2012

  2. Anatomy of the NMJ

  3. Anatomy of the NMJ

  4. The story of MEPPs Scientists recorded membrane potentials from the end-plate (EPPs), evoked by nerve stimulation They also observed spontaneous depolarizations of approximately 1mV These looked like miniature EPPs that they could evoke by nerve stimulation They could evoke these MEPPs, or “minis,” under conditions that limited ACh release (low Ca2+, high Mg2+)

  5. MEPPs: Miniature End Plate Potentials A: Spontaneous MEPPs recorded from frog muscle in normal Ringer's solution. Arrows indicate 1 mV, 20 ms. B: Response recorded from end-plate region of frog muscle to repeated nerve stimulation at arrows. Low-Ca Ringer's solution with neostigmine bromide (1 g/ml). Note stepwise fluctuation in EPP's on successive trials. Voltage scale, 1 mV. Images From Fatt & Katz (1956)

  6. EPPs vs. MEPP Amplitudes From Martin and Brodie, 1956

  7. Quantum Hypothesis • Hypothesis: Single quantal events (minis) are the building blocks for the synaptic potentials evoked by stimulation • Each quanta is a packet of neurotransmitter, and each quanta contains the same amount of NT • How much? • Varies; about 7000 ACh molecules at the NMJ

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