The document discusses bioelectric potentials, which are electrical potentials generated by the movement of ions across cell membranes in living tissues. It describes how ion concentration gradients across neuronal cell membranes generate a resting membrane potential of around -70 mV. When a stimulus causes the membrane to depolarize past a threshold, an all-or-none action potential is triggered, involving changes in sodium and potassium permeability. The action potential propagates along axons without diminishing in amplitude due to its distinct phases of rapid depolarization and repolarization.

1. BIOELECTRIC POTENTIAL
By:-
DR. ANJU JHA
MBBS. MD. PGDMCH

2.  The existence of electrical potentials at
rest and during excitation in experimental
animals- proved by Dubois Reymond in
later half of 19th century.
 Recording of electric potentials from the
biological fluid:
 string galvanometer,
 microelectrodes and
 cathode ray oscilloscope (CRO).

6.  Communication within neuron
 electrical signal.
 Electric current: Movement of electrons.
 Bioelectric potential : movement of ions.

7. Significance
The electric potentials generated
in human tissues are widely used
for diagnostic purposes.
Clinicians utilizes them for the diagnosis
of nerve, muscle, cardiac, brain, visual and
auditory functions.

8. ION DISTRIBUTION
 Particles / molecules
 electrically charged
 Anions
 negatively charged
 Cations
 positively charged

9.  Anions (-)
 Large intracellular proteins
 Chloride ions Cl-
 Cations (+)
 Sodium Na+
 Potassium K+
ION DISTRIBUTION

10. The cell membrane separates the
intracellular fluid from extracellular fluid.
Both the compartments having widely
different ionic compositions.

12.  All living cells have an electrical potential
difference across their surface membranes
 All the bioelectric potentials are basically
generated due to diffusion of ions across
the membrane either during resting or at
any moment of excitation.

13.  Concentration gradients of ions across the
membrane are the immediate supplier of
the energy to create and maintain the
resting potential.
 Bioelectric potentials exist between interior
and exterior of all cell membranes of the
living body.
 Generated by the charged ions that line on
either side of the cell membrane.

14.  Neurons have an electrical potential
(voltage) across the cell membrane.
 The inside of the cell is more negative
than the outside at rest
called the Resting Membrane Potential

15.  The resting potential is necessary for:
 Electrical excitability of nerve and muscle
cells.
 Sensory reception.
 CNS computation.
 To help regulate transfer of ions across the
membrane.

16. The generation of the resting potential
and all of the changes in potential
depend on:
The concentration gradients of ions
across the cell membrane.

17. RESTING MEMBRANE POTENTIAL
Membrane
outside
inside
Na+
Na+
Cl-
Cl-
K+
K+
A-
+ + + + + + + + + + +
-----------
+ + + + + + + + + + +
-----------

18.  RMP is primarily due to difference in
concentration of ions between intracellular
and extracellular fluid.
 A potential is so generated is called a
diffusion potential.
 RMP is dependent on equilibrium potential
for each ion present inside and outside the
cell.

19. RESTING MEMBRANE POTENTIAL
 How is it generated?
1. Differential distribution of ions
inside and outside the cell.
2. Selective permeability of the
membrane to some ions.
Equilibrium potential is the potential when diffusion
of an ion is in equilibrium. It means that diffusion due
to concentration gradient will be equal to diffusion
due to electrical gradient.

20. Why this ionic differences in the ionic composition
of ICF and ECF?
1)Resting cell membrane is moderately permeable to
Na+.
2)Resting cell membrane is freely permeable to K+ &
Cl-.
3)Cell membrane is practically impermeable to most of
the intracellular anions like Proteins & organic
phosphate ions.

21. Why are there difference in the permeability of
cell membrane to various Small ions?
The ions in the body are hydrated.
Atomic wt of K+ is greater than Na+ but hydrated Na+
ion is larger then hydrated K+ ion.

22. SUMMARY OF GENESIS OF RMP
 Difference between intracellular and
extracellular K+ concentration.
 Impermeability of membrane to protein
anions.
 Poor permeability of membrane to Na+.
 Sodium pumps.

23. GIBBS- DONNAN MEMBRANE EQUILIBRIUM
Solution
A
Solution
B
Each solution is electrically neutral ie
Cations A = Anions A
Cations B = Anions B
The product of diffusible ions on one side of the membrane
will be equal to product of diffusible ions on other side. SO
Cations A X Anions A = Cations B X Anions B.
Cations A Anions B
------------------ = ---------------------
Cations B Anions A

24. But if there is one or more non diffusible ions also present
in one solution what will be the result?
BA
K+
Cl-
X-
K+
Cl-
The penetrating ions K+ and Cl- diffuse until equilibrium is attained
So electrical neutrality of both ion will be
(K+) A= (Cl-)A + (X-)A
(K+)B =(Cl-)B
AND
products of diffusible ions and ratio of diffusible ions will be
(K+)A X (Cl-)A = (K+)B X (Cl-)B
(K+)A (Cl-)B
----------- = -----------------
(K+)B (Cl-)A

25.  As there is more excess Anion in solution A
thus K+ will be more than Cl- ie more diffusible Cation
than diffusible Anion to maintain neutrality.
(K+)A > (Cl-)A
Hence
(K+)A > (K+)B
And
(Cl-)A < (Cl-)B

26. i) If the diffusible cation concentration on the side
of membrane containing non- diffusible anions is
greater than diffusible cation concentration on
other side.
ii) The diffusible anion concentration will be
greater on the side without diffusible anions.
This is GIBBS DONNAN EQUILIBRIUM

27.  The magnitude of equilibrium potential for
an ion may be predicted from the Nernst
equation.
 Diffusion potential of each ion can be
calculated by this equation.

28. NERNST EQUATION
[ ]
ln
[ ]
I
II
RT X
Ex
zF X

Equilibrium Potential
of X ion (eg. K+) in Volts
Valence of
ion (-1, +1, +2) Faraday constant
Gas Constant
Temp (K) Ion Concentration I
Ion Concentration II

29. At normal body temperature at 37oC the
Nernst equation can be simplified by
substituting the constants (R, T & F) and
converting to common logarithms, then
C in
E ion = - 61.5 log -------------
C out

30.  In a mammalian muscle cell, the K+conc. is
155mEq/L in intracellular fluid and 4mEq/L
extracellular fluid.
 The equilibrium potential for Potassium may
be calculated as:
E
= -61log 38.75
= - 61 X 1.5883
= -97mV.

32. Equilibrium potential for important ions in a neuron
ENa+ = +60mV EK+ = -90mV
ECa+ = +130mV EH+ = -25mV
ECl- = - 70mV EHCO3-= -25mV

34. GOLDMAN- HODGKIN-KATZ EQUATION
The magnitude of the membrane potential at
any given time depends upon-
The distribution of Na+, K+ and Cl-
and
The permeability of the membrane to each
of these ions.

35. Equation that describes relationship of
membrane potential with ion distribution
across the cell membrane is Goldman-
Hodgkin-Katz equation.
CNa+i PNa+ + CK+i PK+ + CCl-o
PCl-
EMF = -61log
CNa+o PNa+ + CK+oPK+ + CCl-i
PCl-

36. The genesis and the ionic basis of these
potentials were clearly elucidated by using
–
 Voltage clamp techniues.
 Channel blockers
 Patch clamp techniques.

37.  Resting membrane potential.
 Local potential
 Genesis of action potential.
 Summated potentials.
 Conduction & transmission of nerve
impulse.

38.  A resting nerve or muscle cell become
active as a result of a stimulus.
 Irrespective of the nature of stimulus the
response is in terms of a change in
membrane potential.

39.  It could be graded potential or action
potential.
 Graded means that its magnitude depends
on intensity of stimulus.
 If magnitude of the depolarization
exceeds the threshold value, it leads to a
well defined electrical change known as
ACTION POTENTIAL.

40.  The sequence of changes which occur in
the membrane potential following
excitation is called Action potential.
 Action potentials are also referred to as
‘impulses’ or ‘spikes’.
 The exact duration and to some extent ,
magnitude of action potential depend on
the tissue.

41.  Action potential(in nerves) is the signal that is
conducted along the axon over along
distance without change in amplitude.
 Except the action potential, all other signals
fade out after travelling short distance.

42. All-or-none law:
 An action potential is usually full sized with
fixed amplitude of about 110mV( from -70
to +40mV).
 Sub-threshold stimuli can not trigger action
potential.
 Once triggered, an action potential runs its
entire course producing a full fledged
spike.
 This is known as the all-or-none law.

45. Phases of action potential
 Resting phase.
 Prepotential
 Depolarization
 Repolarization.
 After-depolarization
 Hyperpolarization/after-potential

46. +40
0
Millivolt
Time in
Millisec
-55
-70

47. +40
0
Millivolt
Time in
Millisec
-55
-70 Pre potential
Threshold potential
Depolarizatio
n
Repolarization
After
depolarization
Hyperpolarization

48. +40
0
Millivolt
Time in
Millisec
-55
-70
Pre potential
Threshold potential
Depolarizatio
n
Repolarization
After
depolarization
Hyperpolarization

49. Overshoot
(+20 to +30mV)

50. Pre-potential-
 Also k/as foot of action potential.
 Slow drift of local membrane potential
towards -55mV.
 Up to firing level of action potential.
 Not a part of action potential (it may be
present in other potentials too.)

51. Depolarization – the potential shoots
up to + 40mV in less than a
millisecond.
Repolarization – during this phase
potential drops to about -40mV in less
than a millisecond.

52.  After-depolarization- the rate of
repolarization slows down and gradually
returns to RMP in 2ms.
 After-hyperpolarization - intracellular
negativity overshoots the resting value -
70mV to -75mV. It takes 40msec before
returning to RMP.

53. Ionic basis of action potential
 Na+ permeability.
 K+ permeability.
 Na K ATPase pump

59. Refractory period:
 Absolute refractory period.
 Relative refractory period.

60. DIFFERENCES BETWEEN GRADED POTENTIAL AND ACTION POTENTIAL
Graded potential Action potential
Amplitude proportionate to
stimulus strength and can
get summated.
Amplitude constant for all
suprathreshold stimuli and
can not be summated.
Can be a depolarization or
hyperpolrization.
Always depolarization
Conduction is associated
with reduction in magnitude.
Conducted without
reduction in magnitude.
Can be generated
spontaneously in response
to physical or chemical
stimuli.
Generated only response to
membrane depolarization.
Does not obey all-or-none
law.
Obeys all-or-none law.

61. Summary:
 Phases of action potential
 Ionic basis of action potential.
 Refractory period.
 Differences between graded potential and
action potential.

62. REFERANCES
 Text book of medical physiology. Guyton&
hall.
 Ganong’s review of medical Physiology.
 Principles of medical physiology by S. Sircar.
 Understanding medical physiology by RL
Bijlani & S. Manjunatha.