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Introduction to Physiology
Kamal Mohammad 0912683842
Faculty Of Medicine Dept.Of Physiology
Membrane potential and
Resting membrane potential
Faculty Of Medicine2nd Year Semster4
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Membrane Potential
Membrane Potential : The difference in ionic
distribution between inside and outside of cells
which results in electrical potential difference
across the cell membrane.
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Charged Substances in Body Fluids
Many molecules in our body fluids have electrical
charges due to the presence of negative groups (e.g.
phosphate, RCOO-) or positive groups such as RNH3+.
Also most mineral elements such as sodium, potassium,
chloride, and calcium (Na+, Cl-, K+, Ca++) present in our
body fluids as ions.
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Positive Charges Negative Charges
Na+
K+
Ca++
Mg++
RNH3+
Cl_
HCO3
-
PO42-
Proteins
Fixed Anions
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Distribution of Main Charged Substances in Body
Fluids
Na+
Na+Na+
Cl_
Cl_
Cl_ Cl
_
Cl_
Cl_
Cl_
Cl_
Cl_
Na+
Na+ Na+
Na+
Na+
Na+
Na+ Cl_
Cl_ K+ K+
K+
K+
K+
K+
K+K+
K+
K+
K+
K+
_ _
FIXED ___
_ _
FIXED ___
_ _
FIXED ___
_ _
FIXED ___
_ _
FIXED_
__
CELLECF
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Properties of Charged Chemicals
Distribution of various charges outside and
inside the cell play a significant role in cell
function. Excitable cells such as muscle and
nerve use this phenomenon to generate and
propagate electrical signals.
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Properties of Charged Chemicals
Like charges repel each other.
+ +Electrical
Force
_ _Electrical
Force
Opposite charges attract each other.
+_Electrical
Force
This creates force at
opposite direction
of each charge.
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Distribution of Charges
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Distribution of Charges The membrane potential is due to small excess of
negative ions inside of the cell and small excess of
positive ions outside of the cell.
The negative charges are attracted to the positive
charges and they form a thin layer of negative inside
and positive outside of the cell.
The rest of intracellular and extracellular fluid remain
neutral.
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Resting Membrane potential
In excitable cells the potential difference
between inside and outside of the cell during
rest is called “resting membrane potential”
RMP
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The difference in potential across the cell membrane can
be measured by special device called the cathode ray
oscilloscope (voltmeter)
Using electrodes placed on the two sides of the
membrane
The magnitude of the RMP differs in different types of
cells , for example :-
In muscle cell = -90 m V
In a nerve cell = -70 m V
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Membrane Potential Can be Measured
The potential difference across the cell membrane can
be measured using microelectrodes and a sensitive
voltmeter.
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Causes of RMP
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Membrane Potential
_ _
FIXED ___
K+
K+
Na+Na+
ATP
2 K+
3 Na+
Gated Na+
Channel
Gated K+
Channel
Non-gated K+
Channel
Sodium potassium
leak channels
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The resting cell membrane is 50-100 times more
permeable to K+ than to Na+
K+ tends to leak out side of the cell down its
concentration gradient, carrying positive charge with it,
K+ moves easily but Na+ with difficulty why ?
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1- the membrane Na+ channels are closed under resting condition, while the K+ channels are open (leak
channels)
2-The Na+ channels are guarded by Ca2+ from outside that form gates which repel Na+ and prevent its entry under resting condition
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(2) The Na+ -K+ pump
• It transmits 3 Na+ ions to the outside for each 2 K+ ions transmitted to the inside of the membrane .
• This pump causing a potential difference (creating negativity inside & positivity outside).
• The pump is an active process
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(3) Presence of non diffusible anions inside the nerve fibers
These anions include: Proteins and other organic molecules in the cell.
are negatively charged (anions),
can not cross the cell membrane therefore this makes inside of the cell negative
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These fixed anions does not pass through the cell
membrane due to:
1.Their large molecular weight
2.Repelling by proteins in the cell membrane
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_ _
FIXED ___
High resistance
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Development of the RMP (SUMMARY)
Membrane permeability is greater for K+ than to Na+ , thus more
K+ leave the inside of the cells through the leak channels
The Na+ -K+ pump causes more transport of the positive (3Na+)
than to the inside (2K+).
Most of the negative ions inside the nerve fibers are non
diffusible and remain inside
The inside becomes negative while the
out side becomes positive
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ANY
QUESTION????????Any Question
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Answer the following question:
(1)What is the resting membrane potential
(2)How the membrane potential was measured
(3)Factors responsible for genesis of the resting membrane potential
(4)Discuss the role of the sodium potassium pump in the genesis of the membrane potential
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THANK YOU