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An electrophysiologist is studying the electrical properties of an isolated squid neuron placed in normal extracellular...

An electrophysiologist is studying the electrical properties of an isolated squid neuron placed in normal extracellular fluid. She places a recording electrode inside the cell to record the potential difference across the membrane. She records a resting membrane potential of -70 mV.

She then applies an electric current across the membrane and records a slight change in the membrane potential. When she increases the current and stimulates the cell again, she notices a rapid reverse in the membrane potential to +30 mV followed by a drop in membrane potential to -75 mV before it returns to -70 mV. When she increases the current some more and stimulates the cell again, she records the same electrical pattern that is the same as what was obtained with the previous current that was applied.

The research then changes the extracellular solution (making sure to keep the osmolarity the same) so the it contains double the concentration of Ca2+.

  1. Would resting membrane potential change? Why /why not?
  2. When she stimulated the cell with the highest current, would the shape of the electrical pattern change? Why / why not?
  3. Would synaptic transmission change? Explain
Science   Anatomy-And-Physiology   
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Answer #1
  1. Resting membrane potential will not change because of hypercalcemia or hypocalcemia . this is because calcium has zero conductance at RMP.
  2. calcium actually has membrane stabilising action. it restrict the entry of sodium through voltage gated sodium channels. So if there is excess calcium is in the ECF, restriction to the entry of sodium channel is more. so action potential graph will be slightly less taller because of restricted entry of sodium ions during depolarisation. and symptoms are occurring because of this.
  3. synaptic transmission would increase because calcium influx is required for neurotransmitter release. so more calcium in the ECF, more influx and more neurotransmitter release.

*even though there is more neurotransmitter release, there is still muscle weakness because of problems with action potential as explained above.  

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