MEMBRANE POTENTIAL Specific learning objectives At the end

MEMBRANE POTENTIAL

Specific learning objectives At the end of the class You must know. . § Understand the concept of resting membrane potential. § Explain the Mechanism of genesis and maintenance of RMP. § Give the normal value of RMP of different excitable tissue

PLASMA MEMBRANE §Plasma membrane of neurons is filled with channels that allow specific ions to cross.

1. Passive or leakage channels – usually open and allow specific ions to pass (i. e. , K+) 2. Gated channels ü only open when appropriate signal received. Chemically (ligand) gated channels – only open when the appropriate chemical or neurotransmitter present. Voltage gated channels only open when the membrane voltage is at an appropriate level.

TYPES OF ION CHANNELS

4 4 140

BASIC PHYSICS OF MEMBRANE POTENTIAL

Membrane Potential + Caused by Diffusion of K

Membrane Potential + Caused by Diffusion of Na

§ The concentration difference of ions across a selectively permeable membrane can , under appropriate conditions cause a creation of a membrane potential

NERNST EQUATION ALLOWS THEORETICAL MEMBRANE POTENTIAL TO BE CALCULATED FOR A PARTICULAR ION. § The potential level across the membrane that prevents the net diffusion of an ion in either direction through the membrane is called “NERNST POTENTIAL FOR THAT ION” EMF(millivolts) = ± 61 log Conc inside/Conc outside § Equilibrium potential for K+ = - 94 m. V. § Equilibrium potential for Na+ = + 61 m. V.

Goldman-Hodgkin-Katz equation Allows theoretical membrane potential to be calculated for a different ions.

0 m. V

-90 m. V

Resting membrane potential: When the cell is under resting condition, potntial differences exists across the cell membrane

Recording of Resting membrane potential • If we measure voltage between the inside of a neuron and the outside we find that the neuron is more negative inside than outside with a potential of about – 90 m. V. 9

Origin of normal RMP § Contribution of potassium diffusion through the nerve membrane. § Contribution of sodium diffusion through the nerve membrane § Contribution of anion § Contribution of sodium potassium pump

Active transport of sodium and potassium ions through the membrane outside)- 142 m. Eq/L Na+( inside)14 m. Eq/L K+ ( outside)- 4 m. Eq/L Na+( K+( inside)- 140 m. Eq/L Ratio of these two respective ions from inside to outside Na+ = 0. 1 and K+ =35. 0

Resting membrane potentials of various excitable tissues § § § § RMP of large myelinated nerve=-90 m. V, RMP of average myelinated nerve=-70 m. V, RMP of skeletal muscle fibre=-90 m. V, RMP of ventricular muscle fibre=-90 m. V, RMP of atrial muscle fibre=-85 m. V, RMP of purkinje fiber=-95 m. V, RMP of pacemaket tissue=-65 m. V, RMP of smooth muscle fibre=-50 to 60 m. V.

SUMMARY

REFERENCES 1. Comprehensive Textbook of physiology for dental student (Vol 1 first edition)- G K Pal 2. Text book of physiology for BDS (Vol 2 6 th edition)- A K Jain. 3. Essentials of physiology for dental student (6 th edition)- K Sembulingam and prema Sembulingam