Membrane Potentials Notes | EduRev

Created by: Gagandeep Singh

: Membrane Potentials Notes | EduRev

 Page 1


1
Agenda
• Membrane potentials – what they are
• Formation of membrane potentials
• Types and uses of membrane potentials
• The significance of membrane potentials
Membrane Potentials       What They Are
Membrane Potential
Any animal cell’s 
phospholipid bi-layer 
membrane and associated 
structures
A difference in electrical 
charge across (ECF – ICF) 
this membrane, representing 
potential energy.
Can also be called a transmembrane potential.
Formation of Membrane Potentials
• Requires a selectively permeable membrane
– Due to membrane components
• Force involved is electrochemical
– “Electro” due to the charges of the ions on either side 
of the membrane
– “chemical” due to the number and types of ions on 
either side of the membrane
– Main components?
•Na
+
& K
+ 
•Cl
-
•A
-
negatively charged anions
•H
+
(proton gradient) – specialized use
Page 2


1
Agenda
• Membrane potentials – what they are
• Formation of membrane potentials
• Types and uses of membrane potentials
• The significance of membrane potentials
Membrane Potentials       What They Are
Membrane Potential
Any animal cell’s 
phospholipid bi-layer 
membrane and associated 
structures
A difference in electrical 
charge across (ECF – ICF) 
this membrane, representing 
potential energy.
Can also be called a transmembrane potential.
Formation of Membrane Potentials
• Requires a selectively permeable membrane
– Due to membrane components
• Force involved is electrochemical
– “Electro” due to the charges of the ions on either side 
of the membrane
– “chemical” due to the number and types of ions on 
either side of the membrane
– Main components?
•Na
+
& K
+ 
•Cl
-
•A
-
negatively charged anions
•H
+
(proton gradient) – specialized use
2
Formation of Membrane Potential
• Ion Concentrations (millimoles/liter)
-63mV
+122mV
-90mV
+60mV
E
ion
at 37
°
C
1 150 5 K
+
negligible 10 108 Cl
-
negligible .0001 1 Ca
2+
.04 15 150 Na
+
Permeability ICF ECF Ion
Formation of Membrane Potential
So, if we take those numbers and look graphically at what 
happens between Na
+
, K
+
and A
-
…
ECF
ICF
Concentration gradient for K
+
Electrical gradient for K
+
Concentration gradient for Na
+
Electrical gradient for Na
+
A
-
K
+
E
K
= -90mV
Na
+
E
Na
= +60mV
--- - - -- - - - - - - - - - - -
+    +    +        +     +      +    +     +     +       +      +   +     +        +    +       +     +    +           +
[K
+
]=5 mmole/L [Na
+
]=150 mmole/L
[K
+
]=150 mmole/L
[Na
+
]=15 mmole/L
Formation of Membrane Potential
• The cell membrane is about 40 times less permeable to 
Na
+
than K
+
, putting the resting potential closer to E
K
+
(which is -90mV)
• The equilibrium potentials of K
+
, Na
+
, Cl
-
and A
-
result in 
a membrane potential of -70mV
– This determined by the Goldman-Hodgkin-Katz equation
This equation boils down to – the resting membrane 
potential is calculated by the combined effects of 
concentration gradients times membrane permeability for 
each ion, and really just concerning Na and K.
V
m
= 61 log
P
K+
[K
+
]o + P
Na+
[Na
+
]o
P
K+
[K
+
]i +  P
Na+
[Na
+
]i
Formation of Membrane Potential
Here’s How it Works…
V
m
= 61 log
P
K+
[K
+
]
o
+ P
Na+
[Na
+
]
o
P
K+
[K
+
]
i
+  P
Na+
[Na
+
]
i
P
K+ 
= permeability for Potassium = 1
P
Na+
= permeability for Sodium = .04
[K
+
]
o
= concentration of Potassium outside the cell = 5
[K
+
]
i 
= concentraiton of Potassium inside the cell = 150
[Na
+
]
o
= concentration of Sodium outside the cell = 150
[Na
+
]
i
= concentration of Sodium inside the cell = 15
V
m
= 61 log
1(5)  + .04(150)
1(150) + .04(15)
= 61 log
5  + 6
150 + .6
= 61 log
11
150.6
V
m
= 61(log of .073) = 61 (-1.37) = -69mV +1mV (for the 
Na
+
/K
+
pump effect) = -70mV
Page 3


1
Agenda
• Membrane potentials – what they are
• Formation of membrane potentials
• Types and uses of membrane potentials
• The significance of membrane potentials
Membrane Potentials       What They Are
Membrane Potential
Any animal cell’s 
phospholipid bi-layer 
membrane and associated 
structures
A difference in electrical 
charge across (ECF – ICF) 
this membrane, representing 
potential energy.
Can also be called a transmembrane potential.
Formation of Membrane Potentials
• Requires a selectively permeable membrane
– Due to membrane components
• Force involved is electrochemical
– “Electro” due to the charges of the ions on either side 
of the membrane
– “chemical” due to the number and types of ions on 
either side of the membrane
– Main components?
•Na
+
& K
+ 
•Cl
-
•A
-
negatively charged anions
•H
+
(proton gradient) – specialized use
2
Formation of Membrane Potential
• Ion Concentrations (millimoles/liter)
-63mV
+122mV
-90mV
+60mV
E
ion
at 37
°
C
1 150 5 K
+
negligible 10 108 Cl
-
negligible .0001 1 Ca
2+
.04 15 150 Na
+
Permeability ICF ECF Ion
Formation of Membrane Potential
So, if we take those numbers and look graphically at what 
happens between Na
+
, K
+
and A
-
…
ECF
ICF
Concentration gradient for K
+
Electrical gradient for K
+
Concentration gradient for Na
+
Electrical gradient for Na
+
A
-
K
+
E
K
= -90mV
Na
+
E
Na
= +60mV
--- - - -- - - - - - - - - - - -
+    +    +        +     +      +    +     +     +       +      +   +     +        +    +       +     +    +           +
[K
+
]=5 mmole/L [Na
+
]=150 mmole/L
[K
+
]=150 mmole/L
[Na
+
]=15 mmole/L
Formation of Membrane Potential
• The cell membrane is about 40 times less permeable to 
Na
+
than K
+
, putting the resting potential closer to E
K
+
(which is -90mV)
• The equilibrium potentials of K
+
, Na
+
, Cl
-
and A
-
result in 
a membrane potential of -70mV
– This determined by the Goldman-Hodgkin-Katz equation
This equation boils down to – the resting membrane 
potential is calculated by the combined effects of 
concentration gradients times membrane permeability for 
each ion, and really just concerning Na and K.
V
m
= 61 log
P
K+
[K
+
]o + P
Na+
[Na
+
]o
P
K+
[K
+
]i +  P
Na+
[Na
+
]i
Formation of Membrane Potential
Here’s How it Works…
V
m
= 61 log
P
K+
[K
+
]
o
+ P
Na+
[Na
+
]
o
P
K+
[K
+
]
i
+  P
Na+
[Na
+
]
i
P
K+ 
= permeability for Potassium = 1
P
Na+
= permeability for Sodium = .04
[K
+
]
o
= concentration of Potassium outside the cell = 5
[K
+
]
i 
= concentraiton of Potassium inside the cell = 150
[Na
+
]
o
= concentration of Sodium outside the cell = 150
[Na
+
]
i
= concentration of Sodium inside the cell = 15
V
m
= 61 log
1(5)  + .04(150)
1(150) + .04(15)
= 61 log
5  + 6
150 + .6
= 61 log
11
150.6
V
m
= 61(log of .073) = 61 (-1.37) = -69mV +1mV (for the 
Na
+
/K
+
pump effect) = -70mV
3
Maintenance of Membrane 
Potential
• Without energy, the membrane potential would 
eventually be destroyed as
–K
+
leaks out the cell due to membrane leakage 
channels
• There are just more of the K
+
leakage channels than Na
+
, 
giving us the difference in membrane permeability
–Na
+
leaks in due to membrane leakage channels
•Na
+
/K
+
ATPase (Sodium-Potassium Pump) 
restores the balance pumping Na
+
out and K
+
back in.
Types and Uses of Membrane 
Potentials
• Resting membrane potential
– Just described at -70mV
• Threshold membrane potential
– The electrical change that causes specialized channels to cycle 
through open/close confirmations
– This occurs in mot excitable tissues at -55mV
• Action potentials
– This is a change in the membrane potential due to rapid influxes
and effluxes of ions (Na
+
and K
+
)
– Causes adjacent cell membrane to undergo same rapid change
– Continues on to end of the membrane
– Used for communication
• Graded potentials
– Change in membrane potential that is variable based on the rate 
of and location of stimuli on the membrane
– Used for integration
The Significance of Membrane 
Potentials
• Why do we care?
– What would happen if membrane potentials 
didn’t exist?
– What would happen if the membrane 
potentials were different? (higher or lower)
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