1. RESTING POTENTIAL & ACTION
POTENTIAL
BY :
BASAVARAJ .V & ABHISHEK DHANDGOND
BAMS 1ST YEAR
TGAMC BELLARY
2. INRTODUCTION
MEMBRANE PHYSIOLOGY
the structure of plasma membrane
posses several physiological
properties
1. Cellular communication
2. Electro chemical gradient
3. Selective permeability
3. ELECTROCHEMICAL
GRADIENT
Plasma membrane encloses cellular
content & seperates them from ECF
The CM maintains Electrical and
chemical gradients between inside &
outside the cell is called ECG
The CM seperates ECFb & ICF i.e., it
seperates two components having
different ionic composition
4. What causes the difference in
the ionic composition of ICF &
ECF?
Resting CM slightly impermeable
sodium ions
Resting CM is freely permeable to
pottasium ions
It is also impermeable to intracellular
anions like Organic phosphate ions
and some protiens
On the cell membrane not only ions
are present but also some molecules
are present,like Glucose.
5. Why pottasium ions are more
permeable than sodium ions ?
Because in hydrated form, sodium
attract more number of ions from its
surroundings, so sodium become
larger in size as compared to
pottasium.
So that it is difficult to pass through
membrane
6. MEMBRANE POTENTIAL
In the presence of Electro chemical
gradient, there is a formation of
Voltage takes place, so it is called as
membrane potential.
BASIC PHYSICS OF MP
MP is caused by diffusion process by
diffusion potential
Diffusion potential is caused by ions
present either side of the membrane
7. RESTING MEMBRANE
POTENTIAL
The electrical potential difference is called
RMP
Channels in the cell membrane
1. Leakage channels:- It leaks towards
concentration gradient
2. Na+VGC :- closed during the normal RMP
3. K+ VGC : - closed during the normal RMP
4. Ca+ Na+ channels : present in the cardiac
and smooth muscles
8. PUMPS IN THE CELL
MEMBRANE
Sodium – potassium pump
Calcium pump
Role of channels & pumps in the
maintainance of RMP
Leak channels are also called as
positive channels because they
transport only positive ions
These transport sodium ions outside
the cell & pottasium ions inside the
cell
9. Cont..
Sodium and potassium VGC are
closed during RMP and they play
important role in the action potential
K+& Na+ pump , pumps the two K+
ions into the cell & Three Na+ outside
the cell ., so that cell membrane gets
+ve charge on its outer membrane
and –ve charge on inner membrane.
11. Cont..
The normal value of RMP is -70mV
Exchange of ions takes place untill the
cell membrane get potential of -70mV
RMP values varies from tissue to
tissue
Ex: excitable cells like neuron & cell of
muscles have more negative RMP
value
i.e., -70mV to -90mV
12. Cont…
Non excitable cells like RBC &
Epithelial cells have less –ve RMP
value
i.e., For RBC: -8.5mV .,
For Epithelial cells : -23mV
13. EXAMPLES OF RMP
Transfer of impulse along the axonal
membrane of the neuron
14. Cont..
Neurons are polarised cells because it
consist of charged ions on its
membrane.
Outside the axonal membrane it
consist more number of Na+ ions &
less number of K+ ions.
And inside the axonal membrane it
consist more number of potassium
ions and less number of Na+ ions and
also some negatively charged ions
15. Cont..
Na+ & K+ pump, pumps three Na+
ions outside the cell And two K+ ions
inside the cell by active transport [ by
using ATP present in the cell]
So that cell membrane get positive
charge on outer membrane And
negative charge on inner membrane.
So like this ,the RESTING
MEMBRANE POTENTIAL will be
established.
16. ACTION POTENTIAL
Action potential is defined as a series of
electrical changes that occure in the
membrane potential, when the muscle or
nerve is stimulated
It is also defined as wave of electrical
discharge that travels along the
membrane of the cell.
The A.P occurs in 2 phases
1. Depolarisation
2. Repolarisation
17. 1.DEPOLARISATION
Depolarizationis the initial phase of action
potential in which the interior of the
muscle becomes “Positive” and Exterior
of the muscle becomes “negative”.
i.e., the polarized state[RMP] is
abolished resulting in depolarization.
18. 2.REPOLARISATION
It is the phase of AP when the potential inside
the muscle reverse back to the resting
membrane potential[RMP].
i.e., within a short time after depolarization,
the interior of muscle becomes “negative”
And the outside becomes “positive” so the
polarized state of muscle is re-established.
19. PROPORTIES OF AP
Propogative
Long distance signal
Bi-phasic-depolarization&
repolarization
Obeys- All or none Law
Summation is not possible
Has refractory period
20. ACTION POTETIAL CURVE
1.STIMULUS ARTIFACT
The RMP is recorded as a straight base line
-70mV
When a stimulus is applied , there is a slight
irregular deflection of base line for a very short
period of time.
This is called stimulus artifact.
the stimulus artifact is follwed by latent period,
which ends with the next changes
21. Cont…
Latent period
This is the period when no change
occurs in the electrical potential
[immediately after applying of
stimulus]
It is a very short period with duration
of 0.5 -1 min.
23. DEPOLARISATION.
FIRING LEVEL AND
DEPOLARISTION.
Depolarisation starts after the latent period
Initially, it is very slow depolarisation about
15mV[upto -35mV]
The point at which the depolarisation
increases suddenly is called firing level
(threshold excitation)
24. Cont..
OVERSHOOT
From firing level, the curve reaches iso-electric
potential (0 potential) rapidly and then shoots up
(overshoots)beyond 0 pot. Upto +55mV. It is called
OVERSHOOT
25. REPOLARISATION
When the depolarisation is completed
(+55mV), the repolarisation occurs.
Initially repolarisation occurs rapidly
and then it becomes slow.
26. Cont..
SPIKE POTENTIAL
The rapid rise in the depolarisation and
rapid fall in the repolarisation are togeather
known as spike potential.
It lasts for 0.4 milliseconds
27. After depolarisation.
The rapid fall of repolarisation is
followed by a slow repolarisation
It is called after depolarisation
Its duration is 2-4 mil.seconds
28. After Hyperpolarisation
After reaching the resting level(-
90mV), it becomes more negative
beyond restng level. This is called
after hyperpolarisation
Lasts for more than 50mil.seconds
After this the normal RMP is restored
–ve slowly.
29. Electrical potentials
Some cells such as nerve and muscle
cells are capable of generating rapidly
changing electrochemical impulses at
their membranes
these impulses are tend to trnsmit
signals along the nerve or muscles
membranes
31. Membrane potential is caused
mainly diffusion
Caused by the
diffussion of
pottassium ion
outside through a
membrane that is
selectively
permiable to K+
ions
33. Cont..
Thus in both ,contineous diffussion of
ions across a a selectively permiable
membrane, under appropriate
condition creates a membrane
potential.
Sodium ions, pottassium ions and
chloride ions most important ions
involved in the development of
memb.potin nerve or muscle fibre.
34. ORIGIN OF AP
Nerve or Muscle fibers/cells generate
AP when they are stimulated by a
change in memb.pot
It is due to the disturbance in the ionic
equillibrium across thereceptive zone
of cell memb.
Nerve signals are transmitted AP
which are rapid changes in the MP
that spread rapidlyalong the nerve
fiber membrane.
