Membrane Potential

1. Dr. Tanuja Sawant
MD (Ayurved)
Associate Professor
Tilak Ayurved Mahavidyalaya, Pune

2.  Potential difference between external
surface and internal surface of a resting cell
membrane.
 Magnitude of RMP - −70mV

3.  Selective permeability of cell membrane
 N+-K+ - ATPase
 Nearnst Equation
 Goldmnn’s Equation
 Gibbs-Donnan Equilibrium

4.  Diameter of hydrated Na+ ions > K+ ions
 ECF - Na+ ions – less permeable
Cl- ions – permeable
ICF- K+ ions – freely permeable
Protein ions
Phosphate ions impermeable
So, ECF – electropositive
ICF – electronegative

5.  Negative ions (Protein, Phosphate) are
attracted by ECF due to – Positive ions (Na+,K+)
- chemical gradient
Positive ions are attracted by ICF due to –
Negative ions (Cl- )
- chemical gradient
Excess cations on external surface
Excess anions on internal surface
Everywhere else – no. of cations = no. of anions

6.  RMP is a phenomenon of cell membrane
surface
 RMP is mainly due to difference of
concentrations of K+ ions in ECF and ICF
 = K+ equilibrium potential

7.  Pumps out 3 Na+ ions out of the cell into ECF
from ICF
 Draws in 2 K+ ions in exchange into ICF from
ECF
 Thus helps to maintain electronegativity in ICF
 Na+-K+ ATPase can be influenced by drugs (e.g.
digitalis), hormones (e.g. thyroxine/insulin)

8.  Reversal of polarity developed due to action
developed at a particular spot on a cell
membrane
 Typical AP – nerve fibre
- skeletal muscle fibre
- cardiac muscle fibre
Atypical AP – smooth muscle fibre
Required for – muscle contraction
- conduction of nerve impulse

10.  If stimulus is too weak – no depolarization
 If stimulus is adequate – Depolarization
 If stimulus is more than adequate –
AP is not bigger than when the strength was
adequate – it will propagate with the same
strength throughout the cell
Stronger APs can be produced by other
methods
e.g. increasing Na+ concentration of ECF
Repolarization – starts at first in the point
where depolarization first developed .

11. Stimulus
Na+ ion channel opens
Entry of Na+ from ECF to ICF
Excess Na+ ions in ICF and deficit Na+ in ECF
(Depolarization)
Reversal of polarity
Repolarisation starts
Na+ channel close and K+ channel opens
Emigration of K+ from ICF to ECF and no new Na+ in ICF
Creation of negativity in ICF
Emigration of K+ continues until resultant negativity in cell
becomes sufficient to prevent further exodus of K+ ions
Restoration of RMP