Feb 14, 2023
Membrane potentials and resting membrane potential are important topics for the NEET PG exam as they form the basic foundation for understanding cellular physiology, and a thorough understanding of these concepts is crucial for the study of various physiological systems.
In addition to that, understanding membrane potentials and resting membrane potential is essential for integrating and linking the different physiological systems, including the nervous, cardiovascular, and renal systems.
Any cell inside the membrane is negatively charged compared to the exterior. If exterior ECF is taken to be zero, then the inside of the membrane has – ve charge. There are excess anions in the ICF in the form of protein & phosphates.
To be Remembered: When we talk of any potential of any cells, we are essentially talking about the inside of the membrane. RBCs, Epithelial cells: The potential is less negative, somewhere between -8 and -20 mV. Smooth muscle cells have a membrane potential of -35 to -45 mV. SA nodal cells have a membrane potential of -55 to -65 mV. Nerve has a membrane potential of -70 mV. Skeletal muscle & Purkinje fiber in heart has a membrane potential of -90mV.
Trans-membrane Electrical Gradient
So its voltage is not zero but something above zero because of these +ve charges. It has got +80 mV.
It is called Endocochlear potential or Endolymphatic potential.
Due to varying concentrations inside and outside the cell, the resting membrane potential is the outcome. The resting membrane potential is primarily determined by the difference in the quantity of positively charged potassium ions (K+) inside and outside the cell.Due to a net movement with the concentration gradient, K+ ions build up inside the cell when the membrane is at rest. By elevating the concentration of cations in the extracellular fluid relative to the cytoplasm outside the cell, the negative resting membrane potential is established and sustained. The cell membrane's greater permeability to potassium ion movement than to sodium ion transport results in the negative charge present within the cell.The potassium and sodium cations can diffuse down their concentration gradients because the cell has leaky channels that allow them to do so.
The number of potassium leakage channels in neurons is significantly higher than that of sodium leakage channels. Potassium therefore diffuses out of the cell considerably more quickly than sodium seeps in. The cell's interior is negatively charged in comparison to the cell's exterior because more cations are exiting the cell than are entering. Once the resting potential is established, the sodium potassium pump contributes to its maintenance. Remember that for every ATP expended by sodium potassium pumps, two K+ ions are brought into the cell and three Na+ ions are removed. The internal charge of the cell remains negative compared to the extracellular fluid because more cations are released from the cell than are taken in. It should be noted that chloride ions (Cl-) are attracted to negatively charged proteins in the cytoplasm and tend to accumulate outside the cell.
EMF (mV) = ±61×log(c1/c2)
C1 & C2 → Concentration of that individual ion on either side of the membrane.
It is a cation & because of its concentration gradient, it will move from outside to inside initially. It will carry the positive charges to the inside & then eventually it will reach equilibrium. When it reaches equilibrium, the charge on the membrane will be +. After putting the values in the equation, equilibrium potential for this cation will be +61 mV.
– 61 mV
Because all other things will remain the same. Since this is an anion & by its initial concentration, it will go from outside to inside & carry the negative charges to the inside. So, when it reaches equilibrium, charge on the membrane will be –ve.
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