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Origin of Resting Membrane Potential



  • Under resting conditions inside of the cell is electronegative.

  • Example: Resting membrane potential in a neuron is -90 mV


Factors Responsible For Generation of Resting Membrane Potential

Diffusion of Potassium
  • Cells contain potassium leak channels. These channels are open even during resting conditions.

Potassium concentration is high inside the cell as compared to outside

Potassium diffuses out of the cell through potassium leak channels

Exit of positively charged potassium makes inside of the cell electronegative

  • This is the main factor behind generation of resting membrane potential.

Electrogenic Nature of Na-K ATPase pump

Na-K ATPase pump moves 3 sodium ions out, and 2 potassium ions in during each cycle

Exit of net 1 positively charged ion

Makes the inside of the cell electronegative

  • Provides a small contribution to generation of action potential.

  • Although the direct contribution is small, the activity of Na-K ATPase pump is very important for establishing resting action potential. This is because the diffusion of Potassium (the main factor as discussed above) is made possible by concentration gradient of potassium, and this gradient in tern is developed by Na-K ATPase pump only.

 

Notes for Nerds

Potassium

K concentration inside the cell is about 140 mEq/L and outside is 4 mEq/L

Concentration gradient from inside to outside

K diffuses out

Makes inside of the cell electronegative

Electronegativity inside the cell attracts positively charged K back into the cell

K stops moving out when electrical gradient balances concentration gradient

At this equilibrium, voltage tends to be -94 mV inside the cell


Sodium

Na concentration is high outside and low inside

Concentration gradient from outside to inside

Na enters the cell

shifts voltage to positivity.


However, during resting conditions, Na channels are mostly closed

Amount of Na entering is small

Contribution in voltage is small i.e. + 8 mV


Na-K ATPase Pump

Causes net removal of one positive ion from cell as explained above

Makes the cell electronegative

Contribution is -4 mV


Total:

= (Contribution from K) + (Contribution from Na) + (Contribution from NaK ATPase pump)

= (-94) + (+8) + (-4)

= -90 mV

 

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vipul41
vipul41
28 июн. 2022 г.

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