MEMBRANE POTENTIAL

1. MEMBRANE POTENTIAL DR. ZAHOOR ALI SHAIKH Lecture ---7

2. Membrane Potential • Plasma membrane or cell membrane of all living cells have a membrane potential or they are polarized. • Membrane potential is Negative inside.

3. Membrane Potential • What is Membrane Potential ? • It is the electrical potential across the cell membrane. • It is due to the separation of opposite charges across the Membrane. • It is due to the number of Cations(+) charged particles and Anions(-) charged particles in intracellular fluid and extracellular fluid.

4. Membrane Potential (cont) • When there is difference in the number of positive and negative charges between the two sides( inside and outside)of cell membrane, than we say Membrane potential is present. • Potential is measured is volts(as we do in electricity) but as membrane potential is low, the unit we use is millivolt (mv). • 1mv = 1/1000 volt

6. Membrane Potential (cont) • What is the cause of Membrane Potential ? • It is due to the differences in the concentration and permeability of ions across the cell membrane.

7. Excitable Tissue • Nerve cell and Muscle are excitable tissue, they produce rapid, transient changes, in their membrane potential when stimulated . • These changes in potential cause Electrical signals.

8. Resting Membrane Potential • When cells are at rest (not stimulated) – there is Resting Membrane Potential.

9. Resting Membrane Potential • Q- What is the cause of Resting Membrane Potential (RMP)? • Ans: RMP is due to 1) Concentration of ions(Na+& K+) across the cell membrane. 2) Permeability of ions (Na+&K+) across the cell membrane. 3) Na+ - K+ pump. 4) Protein inside the cell(A-), they are negatively charged and plasma membrane is impermeable.

12. Equilibrium Potential of K+ Calculation by Nernst Equation

13. Na+ - K+ Pump • The Na+ - K+ PUMP transports THREE Na+ out, for TWO K+ it transports inside the cell. • As both are positive ions, unequal transport causes more positive charge outside negative charge inside.

14. Specialized Use Of Membrane Potential In Nerve & Muscle Cells • Nerve and Muscle can rapidly change their membrane permeabilities to the ions, when stimulated. • Therefore, bring changes in membrane potentials. • These rapid changes in membrane potential are responsible for producing nerve impulses in nerves and contraction in muscle cells.

15. SUMMARY • All living cells have membrane potential. • Cell is negative inside. • Nerve and Muscle are excitable tissues. • Nerves send electrical signal or nerve impulses. • Rapid changes in membrane potential in muscle cell cause muscle contraction.

16. REMEMBER • Resting membrane potential in Neuron (nerve cell) is -70 mv.

17. Terms Used For Changes In Membrane Potential

18. Terms Used For Membrane Potential • Polarization It means electrical changes are present on both sides of membrane, therefore, membrane has potential.

19. Terms Used For Membrane Potential (cont) • Depolarization During Depolarization, membrane becomes less negative inside as Na+ enters the cell therefore potential moves towards 0 mv (e.g. change from -70 to +20). • Repolarization It is due to K+ efflux [going outside]. The membrane returns to resting membrane potential i.e. -70 mv .

20. Terms Used For Membrane Potential (cont) • Hyperpolarization It is because of more K+ going outside. Therefore, membrane becomes more negative inside than resting membrane potential like -80 mv now, instead of -70 mv.

21. Changes in Membrane Permeability • Changes in Membrane Permeability can be brought by: • Electrical & Mechanical Stimulation • Changing channel permeability • Action of Chemicals

22. Channels In Plasma Membrane • There are • Leaky Channels – which are open all the time • Gated Channels – these channels work like gate i.e. they open and close to the different stimuli.

23. Channels In Plasma Membrane Types of Gated Channels: (i). Voltage Gated Channel – Open and close due to changes in charges on membrane potential. (ii). Chemically Gated Channel – Open and close due to effect of chemical messenger. (iii). Mechanically Gated Channel – Open and close due to mechanical stimulus. E.g. Stretching (iv). Thermal Gated Channel – respond to local changes in temperature. These stimuli can change the permeability of cell membrane.

24. Different Stimuli Cause Electrical Signals • Electrical Signals are produced due to changes in ions movement across the membrane. • Electrical Signals produce: 1. Graded Potential or Local Potential 2. Action Potential – It sends signal over long distance.

25. Graded Potential • Graded Potential is local change in the membrane potential. E.g. RMP changes from -70 mv to -60 mv (a 10mv change). • Graded Potential is due to Na+ entry at the small region of plasma membrane. • It is localized change in the membrane. • Graded Potential can be summated by giving stronger stimulus.

27. GRADED POTENTIAL‘Important Points’ • It is localized. • It can be summated. • Longer the stimulus – longer the duration of graded potential. • Graded Potential die down over short distance. • Example of Graded Potential: - Receptor Potential, Pace-maker Potential

28. What You Should Know From This Lecture • What is Membrane Potential? - The electrical potential across the cell membrane. • Resting Membrane Potential in Nerve Cell – [-70 mv] • What is the cause of Resting Membrane Potential? - Concentration of ions, permeability of ions, Na+-K+ pump, protein inside the cell. • Na+ - K+ pump – it transports 3 Na+ out and 2 K+ inside the cell. • Nerve cell and Muscle cell are excitable tissue. • Channels present in cell membrane – - Leaky Channels - Gated Channels • Stimuli which can open the Gated Channels – Electrical, Chemical, Mechanical, and Thermal Stimuli. • Depolarization, Repolarization, Hyperpolarization • Graded Potential and its characteristics - It is local potential, can be summated, does not propagate, dies down.

29. Thank you