Q.19 The resting membrane potential of neuronal cell is maintained by
1. higher intracellular K+ ion conc. and lower extracellular Na+ ion conc.
2. higher extracellular K+ ion conc. and lower intracellular Na* ion conc.
3. higher intracellular K+ ion conc. and higher extracellular Na+ ion conc.
4. lower intracellular K+ ion conc. and higher extracellular Na* ion conc.
Neuronal Resting Membrane Potential: Maintained by Ion Gradients
The resting membrane potential of neurons is maintained by higher intracellular K+ and higher extracellular Na+ concentrations, making option 3 correct.
Ion Gradients Basics
Neurons maintain ~ -70 mV resting potential due to unequal ion distribution across the membrane.
Intracellular [K+] is high (~140 mM) while extracellular [K+] is low (~4 mM).
Extracellular [Na+] is high (~145 mM) while intracellular [Na+] is low (~12 mM).
Correct Answer Explanation
Option 3 states “higher intracellular K+ ion conc. and higher extracellular Na+ ion conc.”, exactly describing the gradients.
Na+/K+-ATPase pump sustains this by exporting 3 Na+ for 2 K+ import.
K+ leak channels make membrane more permeable to K+, driving potential toward K+ equilibrium (~ -90 mV).
Physiological Role
These gradients enable action potentials; depolarization opens Na+ channels.
Goldman-Hodgkin-Katz equation quantifies combined effects:
Vm =RT/F ln PK[K+]o +PNa[Na+]o / PK[K+]i +PNa[Na+]i
