Which of the following changes would cause a shift in the membrane potential of a neuronal cell from –70 mV to –50 mV?a)A decrease in K+ permeabilityb)An increase in Na+ permeabilityc)An increase in K+ permeabilityd)A decrease in Na+ permeabilityCorrect answer is option 'A,B'. Can you explain this answer?

Question

Which of the following changes would cause a shift in the membrane potential of a neuronal cell from &ndash;70 mV to &ndash;50 mV?a)A decrease in K+ permeabilityb)An increase in Na+ permeabilityc)An increase in K+ permeabilityd)A decrease in Na+ permeabilityCorrect answer is option 'A,B'. Can you explain this answer?

Answer

Understanding Membrane Potential Changes
The membrane potential of a neuronal cell is influenced by the permeability of ions, particularly potassium (K+) and sodium (Na+). A shift from –70 mV to –50 mV indicates depolarization, where the inside of the cell becomes less negative.
Factors Causing Shift to –50 mV
- A decrease in K+ permeability:
- K+ ions typically flow out of the cell, maintaining the negative resting potential.
- A decrease in K+ permeability means fewer K+ ions exit, reducing the negative charge inside the cell, thus causing depolarization.
- An increase in Na+ permeability:
- When Na+ channels open, Na+ ions rush into the cell due to the concentration gradient.
- This influx of positive charge increases the internal voltage, contributing to the shift towards –50 mV.
Factors That Do Not Cause the Shift
- An increase in K+ permeability:
- More K+ ions leaving the cell would further hyperpolarize it, moving the potential further from –50 mV.
- A decrease in Na+ permeability:
- Lower Na+ entry would maintain or even increase the negativity of the membrane potential, preventing depolarization.
Conclusion
The correct options that cause the membrane potential to shift from –70 mV to –50 mV are a decrease in K+ permeability and an increase in Na+ permeability. Understanding these ionic movements is crucial for grasping neuronal excitability and signal transmission.

Answer

And:b,c

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