Bioelectricpotentials.pptx Physiology for MBBS/MD

This is a ppt about bioelectrical potentials a topic in physiology for mbbs and MD students

1. BIOELECTRIC POTENTIALS Dr Vasant Bikkad Dept of Physiology Dr V M G M C , Solapur

2. BIOELECTRIC POTENTIALS : R efer to the electrical signals generated by living organisms. These electrical impulses arise from the movement of ions across cellular membranes. They play a crucial role in various physiological processes, including nerve signaling, muscle contraction, cardiac rhythm and cardiac muscle contraction .

3. Bioelectric potentials A re the result of the complex interplay of ion channels, ion pumps, and cellular membranes. These electrical signals can be measured and analyzed to gain insights into the functioning of biological cells .

4. Bioelectrical potential The Fundamental Unit of living organism is cell . There are Unicellular organisms like amoeba whose cell structure is simple one . There are multicellular organisms such as Animals and Human Beings There are 100 trillion cells in Human body , 75 trillion are present in organ system while 25 trillion are present as Red blood cells . Thus Red Blood cells are the most abundant of all cells in body .

5. All cells can produce have resting membrane potential. There are a few specialized cells which can produce Action potential. Many organs in the human body such as heart , brain , Muscles , and eyes manifest their function through electric activity . Brain – EEG , Muscle – EMG , Heart – ECG , Eye- EOG Bioelectrical potential

6. Luigi Galvani 1771 1800Alessandro Volta

7. String galvanometer By Luigi Galvani

8. 1780

9. Augustus Desiré Waller

10. Augustus Waller 1887

11. William Einthoven

12. ECG Machine

13. William Einthoven 1901: Einthoven invented the first practical electrocardiogram (ECG or EKG) in 1901. This device could record the electrical activity of the heart and represented a major breakthrough in cardiology. 1902: He introduced the terms "P wave," "QRS complex," and "T wave" to describe the various deflections seen in an ECG recording. These terms are still in use today to describe the different components of the ECG waveform. 1903: Einthoven published his seminal work "The Theory of Electrocardiography," which provided a comprehensive understanding of the electrical activity of the heart and laid the foundation for modern electrocardiography. 1924: He was awarded the Nobel Prize in Physiology or Medicine for his contributions to the discovery of the mechanism of the electrocardiogram. This recognition cemented his legacy as one of the pioneers in the field of cardiovascular physiology.

14. Action Potential In Neuron 1956

15. Bioelectrical potential

16. Chemical Composition Chemical compostion of Extracellular and Intracellular Fluids Lipid Bilayer is a barrier against movement of Water molecules and water soluble substances It allows free movement of Lipid soluble substances

17. Cell Membrane

18. Diffusion All molecules and ions including water molecules and dissolved substances are in constant motion Motion of these molecules is called “Heat” Continuos movement of molecules among one another and in liquids or in gases is called diffusion Net diffusion rate is proportional to concentration difference across membrane

19. Voltage gated channels Diffusion through Gating of Channels for sodium and potassium Selective permeability – Potasium channel has 1000 thousand times more than they permit sodium At top of channel are pore loops which form selectivity filter Most important sodium channel is 0.3*0.5 nm inner surfaces lined by negatively charged Amino Acids

20. Voltage Gated Channel vs Ligand Gated Voltage gated – A strong negative charge inside cell membrane keeps outside gates tightly closed for sodium , when inside of cell membrane looses its negative charge these gates open and allow soudium to pass inward Ex. Sodium potassium channel Ligand Gated – protein channel requires bonding of chemical substance that causes conformational change Ex. Acetylcholine channel

21. Diffusion Net diffusion Rate : Rate of net diffusion into the cell is proportional to the concentration on the outside minus the concentration on the inside Net diffusion on α C – C 1

22. Nernst Potential Concentration of negative ions is same on both side When a positive charge is applied to right side of membrane negative to left creating a electrical gradient across cell membrane Positive charge attracts negative ions while negative charge repels So net diffusion occurs from left to right . After some time large quantity neg ions moved to right This produces a concentration difference of the ions developed in the opposite direction of the electrical potential diffrenece Concentration diff now tends to move ions to the left while electrical difference tends to move them to right . When the concentration difference rises high enough they try to balance each other. At Normal body temp 37 deg electrical diff that will balance a given conc diff of UNIVALENT IONS is given by Nernst equation EMF = ± 61 x Log concentration inside z concentration outside

23. Sodium – Potasium ATPase Pump All cell membranes of the body have powerfull Na+- K+ Pump called as electrogenic pump It pumps more positive charges outside than to inside leaving a net deficit of positive ions on the inside and causing Negative potential inside the cell membrane . This potential difference is caused at resting membrane condition

24. Origin of Normal Resting Membrane Potential Contribution of Potasium diffusion channel : The potassium ions inside to outside ratio of 35: 1 , The Nernst potential corresponding to this ratio is -94 mV Contribution of Sodium diffusion through Nerve membrane : Ratio of sodium ions inside to outside is 0.1 which corresponds to + 61 mV of inside of membrane

25. Gibbs – Donnan Phenomenon Inside the cell are many negatively charged ions that cannot pass through the membrane channels . They include anions of Protein molecules , many organic phosphate,sulphate compounds . As these compounds cannot leave the cell , Any deficit of positive ions inside the membrane leaves excess of these impermeant anions . These negatively charged anions contribute to negative charge inside the cell when there is net deficit of positively charged potassium ions

26. Action Potential in Neuron There is Overshoot of potential in some neurons due to excess and large amount of sodium ions inside the cell

27. Action Potential in Neuron and nerve fibre Nerve signals are transmitted by action potentials which are rapid changes in membrane potential that spread rapidly along the nerve fibre membrane. Each action potential begins with sudden change from normal resting membrane potential to a positive potential and ends with equally rapid change back to negative potential . Stages : Resting stage : Membrane is said to be polarized because of -90 mV membrane potential at resting state.

28. Action Potential in Neuron and nerve fibre Depolarisation Stage : At this time membrane suddenly becomes permeable to sodium ions allowing tremendous number of positively charged sodium ions to diffuse to interior of the axon . Normal polarized membrane with -90 mV potential is rapidly changed to positive direction Repolarisation Stage : Within a tenthousands of a second membrane becomes permeable to sodium , sodium channels begin to close and potassium channels open to agreater extent , rapid diffusion of potassium ions to exterior reestablishes normal negative RMP This is called repolarization .

29. Cardiac Action Potential RESTING MEMBRANE POTENTIAL OF CARDIAC TISSUES: 1 Cardiac Muscle fibre -90 mV 2 Purkinje fibres -95 mV 3 Pacemaker Cells -60 mV

30. SA NODE Ionic Currents Involved : Sodium Current Calcium current Potasium current Pacemaker current

31. Sodium Current Sodium current is the largest current There are 200 Na+ Channels per sq micron of tissue Ina+ is not present in pacemaker cells SA or AV nodal cells The ion channel responsible for Ina+ is Voltage Gated Na+ channel which are always Fast sodium channels (0.1-0.2 ms ) Activation : Has 2 Gates The Outer Gate opens at beginning of depolarisation causing rapid influx of Na+ The Inner gate closes at end of depolarisation that stops Na+ influx

32. Sodium current INACTIVATION : When the membrane potential becomes positive These channels close automatically . This procedure occurs slowly but in 1 ms . Inactivation of Na+ current is partly responsible for rapid repolarization of Action potential in Phase 1 . IMPORTANCE: Antiarrhythmic drugs like Lidocaine exert their effect by blocking Na+ current.

33. Calcium Current Exists in all cardiac tissue L –Type Channel –Long lasting ,causes inward movement of positive charges by calcium influx and also is responsible for release of Ca++ from sarcoplasmic reticulum . This channel is responsible for upstroke or depolarization of SA, AV nodal action potentials . Is responsible for sustained plateu phase of action potential of myocardial cells IMPORTANCE : Calcium channel blockers Verapamil , Diltiazem , Nifedipine Act by inhibiting L –Type Calcium channels .

34. T- Type Calcium channel : This is Transient type Voltage Gated Ca++ channel Present only in SA And AV nodal cells. Responsible for later part of the prepotential or pacemaker potential . Calcium Current

35. Two types of potassium channels Voltage Gated Ik Ligand Gated Ik channels Voltage Gated Ik channels : Inward rectifying – Maintain RMP ( Phase 4) by allowing efflux of K+ at highly negative membrane potential. Outward Transient rectifying – Voltage gated , Activated by Depolarisation but is rapidly inactivated , Contributes to Phase 1 of repolarization by transiently permitting outflux of K+ at positive membrane potential. Outward Delayed Rectifying : Phase 3 , slowly activates in muscle , Purkinje fibres ,responsible for repolarizing the membrane and early part of prepotential . Potasium Current

36. G Protein –Activated K+ Channel: Activated by Acetylcholine and adenosine Prominent in SA and AV Nodal cells – Hyperpolarises the Membrane in Phase 4 that slows the pacemaker potential . Potasium Current

37. Pacemaker current Found in SA , AV Nodal cells Hyperpolarisation activated cyclic nucleotide gated channels : conduct both Na+ and K+ . Called Funny Channels or h channels . Produce inward depolarizing current at end of phase 3 and contribute for phase 4 of depolarization .

38. Action Potential in Muscle VS Nervous Tissue

39. Action Potential in Smooth Muscle The quantitative voltage of the membrane potential of smooth muscle depends on the momentary condition of the muscle. In the normal resting state, the intracellular potential is usually about −50 to −60 millivolts, which is about 30 millivolts less negative than in skeletal muscle.