MEMBRANE POTENTIALS

3. MEMBRANE POTENTIALS

4. At the end of this lecture you should know: 1. Ionic distribution across the cell membrane 2. Different types of channels present in the cell membrane. 3. Role of different ions in the development of Resting Membrane Potential OBJECTIVES

5. Definition: Tissues which are capable of responding to stimuli to highest degree than other tissues of the body in the form of electrical signals. Imp. Excitable tissues have LOW Threshold of Stimulation -Nerve -Muscle Excitable Tissues

6. Definition Potential difference existing across the cell membrane under resting condition. Resting Membrane Potential

7. Distribution of Ions across the membrane • Na+ mainly extracellular--- • 142 mEq/L • K+ mainly intracellular----- • 140 mEq/L • Cl- mainly extra cellular– • 108 mEq/L • Non-diffusible intracellular anions. • -- HPO4 – • --SO4-- • ---Intracellular proteins • (4times as in the plasma) Proteins x 10 times HPO4--

8. Types of Channels in the cell Membrane Na+ * Leak Channels (Slow) K+ -Voltage gated channels ( Fast ) — For Na+ & K+ Slow Ca++ - Na+ Channels -Ligand Gated Channels --- Neurotransmitters, Hormones Acetylcholine gated channels -Na+ - K+ Pump ( ATP ase ) -Mechanical Gated Channels – Hair Cells ( inner Ear)

9. Leak Channels Why K+ Leak Channels are More Permeable than Na+ Leak Channels 0.5 x 0.3 nm 0.3 x 0.3 nm Na+ K+

10. Potassium Leak Channels

12. NERNST POTENTIAL

13. The potential across the cell membrane at which the net diffusion of ions across the cell membrane due to concentration gradient stops. The electrical potential necessary to balance a given ionic concentration gradient across a membrane so that the net flux of the ion is zero. Nernst Potential

14. Nernst Equation: EMF = ± 61 x log (Cin / Cout) Where 61 is constant & is = RT / z F Where R= Universal Gas constt T = Absolute Temp, z = ion Valence F = Faraday, an electrical Constt

15. Equilibrium (Nernst) Potential for Na+ Na+ outside = 142 m Eq/L } 61x log 0.1 = +61mv Na+ inside = 14 m Eq/L

16. Equilibrium(Nernst) Potential for K+ K+ outside = 4.0 m Eq/L }61x log 35= –94mv K+ inside = 140 m Eq/L

17. Na+ - K+ PUMP (ATPase) Intracellular portion of alpha subunit has: Na+ binding site (1), Phosphorylation site (4) an ATP binding site (5). Extracellular portion has : K+ binding site (2) & Ouabain site (3)

18. Contribution of Na+-K+ Pump (ATPase) -4mv

19. 1. As an Enzyme (Cleaves ATP to ADP) 2. Electrogenic. (Contributes -4mv in RMP) 3. Homeostasis of Main Electrolytes and Water & hence volume of the cell. Hormones Increasing functions of ATPase -Thyroxin, Aldosterone & Insulin. - Dopamin decreases its function Functions of Na+ - K+ Pump (ATPase)

20. Goldman Hodgkin-Katz- Equation EMF(mv)= CNa+ in PNa+ + CK+ in PK+ + CCl-out PCl- -61. Log CNa+out PNa+ + CK+out PK+ + CCl- inPCl- Where ‘C’=Concentration P= Permeability

21. Goldman Hodgkin-Katz- Equation • Is used to calculate the Diffusion potential when the membrane is permeable to different ions . 1.Polarity of electrical charge. 2.Permeability of the membrane to ions. 3.Concentration of the respective ion on inside or outside

22. Large Mylinated Nerve fibers Skeletal Muscle Fibers= -90mv Ventricular Muscle fibers Smooth Muscle fiber & } = -55 to -60 mv Self Excitatory Tissues Resting Membrane Potential in Various Excitable Tissues

23. Measurement of RMP

24. TWO Types: Non-Propagated Potentials. - Synaptic - Generator Catelectrotonic - Electrotonic { Anelctrotonic Propagated – Action Potential Types of Disturbances across the Cell Membrane

25. ACTION POTENTIAL

26. Definition: Abrupt / sudden Change (reversal) in resting membrane potential in response to a threshold stimulus. Stimulus: Defn: “AnyChange inthe environment” TYPES: a. Electrical b. Mechanical c. Chemical ACTION POTENTIAL

27. -Polarized state (Resting membrane Potential) -Depolarization - Repolarization -Positive After Potential (After-Hyper polarization) Phases of Action Potential

28. Voltage gated channels (fast) ----- Na / K Slow Ca++- Na+ Channels Ligand Gated Channels Mechanical Gated Channels (Hair Cells ) Types of Channels involved in Various Excitable Tissues

29. Voltage Gated Na+ Channels

30. Voltage Gated Na+ Channels

31. Voltage Gated K+ Channels

32. Role of Other Ions In the development of Action Potential • Calcium pump • Voltage gated Ca Channels– Cardiac muscle Smooth muscle • Increased permeability of sodium channels when there is a deficit of Extracellular calcium

33. Threshold for Initiation of Action Potential • Action potential will not occur till the initial rise in membrane potential is great enough to create a positive feedback . • Large nerve fiber--- -65 mv (threshold for stimulation)

34. ACTION POTENTIAL IN VARIOUS TISSUES

35. Action Potential in Large MyelinatedNerve fiber

36. Action Potential with Plateau (Cardiac Muscle) Red curve shows rise and fall in tension of ventricular myocyte

37. Action Potential in Self Excitatory Tissues(S-A Node) -55- -55 Diastolic DepolarizationDepolarization)

38. Action Potential in Smooth Muscle

39. Compound Action Potential

40. Biphasic Action Potential(Both electrodes are outside the membrane)

41. Recording of Membrane and Action Potential

42. Propagation (Transmission) of Action Potential • Electrotonic Conduction.

43. Direction of propagation • All or Nothing Principal

44. Propagation of Action Potential-II(Saltatory Conduction) 2000-12000 channels/ Sq Micro Meter

45. (Saltatory Conduction) 2000-12000 channel/ Sq Micro Meter