Bioelectric potentials refer to the electrical signals generated by living organisms through the movement of ions across cellular membranes, playing a crucial role in various physiological processes such as nerve signaling and muscle contraction. Key concepts include action potentials in neurons, resting membrane potential, and the contributions of different ion channels, which are essential for understanding physiological functions like cardiac activity. Significant advancements in the field, such as Einthoven's work on electrocardiograms, laid the groundwork for modern cardiovascular physiology.

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

2. BIOELECTRIC POTENTIALS :
Refer 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
Are 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 17711800Alessandro Volta

7. String galvanometer By Luigi Galvani

8. 1780

9. Augustus Desiré Waller

11. Augustus Waller 1887

12. William Einthoven

13. ECG Machine

14. William Einthoven
1.1901: 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.
2.1902: 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.
3.1903: 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.
4.1924: 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.

16. Action Potential In Neuron
1956

18. Bioelectrical potential

19. 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

20. Cell Membrane

21. 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

22. 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

23. 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

24. 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 C0 – C1

25. 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

26. 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

27. 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

28. 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

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

30. 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.

31. 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 .

32. 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

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

40. 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

41. 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.

42. 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 .

43. 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

44. • 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

45. • 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

46. 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 .

48. Action Potential in Muscle VS Nervous Tissue

57. 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.