Resting membrane potential (the guyton and hall physiology)

RESTING MEMBRANE POTENTIAL
Potential difference across the cell membrane at rest is called RMP
All living cells has RMP
RMP is negative inside with respect to outside
Recording is done by using two microelectrodes
One is inserted into the cell and other on the outer surface of membrane and both attached to meter
Micro electrodes are made up of silver containing silver chlorideValues of RMP in different tissues:
Nerve fiber and skeletal muscle= -90 mV
Cardiac muscle = -85 - -90 mV
Smooth muscle = -55 - -60 mV
SA nodal fibers = -55 - -60 mV
All the voltage gated channels are closed at RMP i.e. voltage gated Na, K, Ca Channels.
Leak Channels i.e. Potassium Sodium leak channels are open at RMP
Ligand Gated Channels also known as chemical gated channels open and close when a ligand binds with the receptors of channels. Ligand may be a neurotransmitter or a hormone e.g. Acetylcholine gated channels in the muscle membrane at the neuromuscular junction.
Pumps are also present like sodium potassium ATPase pump, calcium pump. Generally in cell membrane there is Na K ATPase pump.
Na K pump pumps actively Na and K
Both leak channels and Na K pump are active at rest

1. RESTING MEMBRANE POTENTIAL Source: The Guyton and Hall physiology Maryam Fida (o-1827)

2. RESTING MEMBRANE POTENTIAL Potential difference across the cell membrane at rest is called RMP All living cells has RMP RMP is negative inside with respect to outside Recording is done by using two microelectrodes One is inserted into the cell and other on the outer surface of membrane and both attached to meter Micro electrodes are made up of silver containing silver chloride

3. Values of RMP Values of RMP in different tissues: Nerve fiber and skeletal muscle= -90 mV Cardiac muscle = -85 - -90 mV Smooth muscle = -55 - -60 mV SA nodal fibers = -55 - -60 mV

4. All the voltage gated channels are closed at RMP i.e. voltage gated Na, K, Ca Channels. Leak Channels i.e. Potassium Sodium leak channels are open at RMP Ligand Gated Channels also known as chemical gated channels open and close when a ligand binds with the receptors of channels. Ligand may be a neurotransmitter or a hormone e.g. Acetylcholine gated channels in the muscle membrane at the neuromuscular junction. Pumps are also present like sodium potassium ATPase pump, calcium pump. Generally in cell membrane there is Na K ATPase pump. Na K pump pumps actively Na and K Both leak channels and Na K pump are active at rest

5. K concentration inside cell = 140 mEq /L K concentration outside cell = 4 mEq /L K is 35 times greater inside than outside so the potassium is having 35 times gradient to move outside Na concentration outside cell = 140 mEq /L Na concentration inside cell = 14 mEq /L Na is 10 times greater outside than inside so the sodium is having 10 times gradient to move inside. Na K leak channels are 100 times more permeable to potassium as compared to sodium Inside the cell there are certain non diffusible anions i.e. Proteins anions, organic phosphate and organic sulfate ions.

6. Mechanism of RMP The major factor involved in RMP is outward diffusion of K through the K Na Leak Channels. Net movement of K to outside is not much because the non diffusible cations attract the K. Na K Electrogenic pump pumps out more positive i.e. Na ions, so contributing electro negativity inside. Sodium concentration changes in ECF do not produce any significant effect on RMP. But changes if K Concentration in ECF changes then there are marked effect on RMP. Example: In hypokalemia, there is more negative RMP known as Hyperpolarization and tissue becomes difficult to excite. Periodic Familial Paralysis: K conc. In ECF falls periodically, leading to Hyperpolarization ultimately causing muscle paralysis. In hyperkalemia there is less negative RMP.

7. Chloride has no effect on RMP Inward Sodium diffusion actually generates a potential of +8 mV K Nernst potential is -94 mV So the net potential generated by the movement of Na and K is -94 + + 8 = -86mV Na K pump will generate a potential of -4 mV And the actual RMP comes to -86 + -4 = -90 mV