Cell membrane has the characteristic property to receive stimulus and convey the message through electrical signals, itself getting depolarized and repolarized.

1. Electrical Properties of Cell
Membrane
Presented by-
Rubina Roy
Assam University, Silchar

2. CONTENTS
• Introduction
• Membrane Potential
-Ion Channels
-Ion Pumps
- Sodium Potassium Pump
• Determination of Membrane Potential
• Action Potential
-All-Or-None Law
• Role of Cell Electrical Properties in Animal Body
- Transmission of Nerve Impulses
- Muscle Contraction & Relaxation
• Conclusion
• References

3. INTRODUCTION
• Cells are bounded by membranes which are composed of phospholipid bilayers.
• The phospholipid bilayer acts as a conductor to non polar molecules like oxygen, carbon
dioxide, nitrogen, benzene, and uncharged polar molecules like water, urea, glycerol.
• Charged polar ions like H+, Na+, K+, Cl-, HCO3
-, etc., and uncharged large molecules like
glucose, amino acids, nucleotides get trapped by the hydrophobic fatty acid chains acting
as an insulator.
• The positively charged ions are carried across the membrane by transport proteins.
• Membranes are highly impermeable to anions.

4. Membrane Potential
 The membrane potential is the difference in electrical charges between the extracellular
matrix and the cytoplasm of a cell. It is maintained by ion channels and ion pumps.
 At this resting state, the cytoplasm of cell has higher negative charge than the
extracellular matrix, and the membrane is sad to be polarized maintaining a dipole across
the membrane.
 In non-excitable cells, the membrane potential ranges from -20 mV to -200 mV.
 In case of excitable cells (neurons and muscle cells), the membrane potential is about -70
mV, and is called resting potential.

5. Ion Channels
• Ion channels are transport proteins which carry ions along the concentration gradient
across the cell membrane.
• Ion channels are of two types- voltage gated channels and ligand gated channels.
• Voltage gated channels open only in response to change in electric potential.
• There are 4 types of voltage gated channels- Na+ channels, Ca2
+ channel, K+ channel, Cl-
channel.
• Ligand gated channels open in response to a binding ligand.

6. Ion Pumps
• Ion pumps carry ions against the concentration gradient at the expense of energy.
• It is mediated by the carrier protein ATPase which carries the ions across the membrane
by hydrolysing ATP.
• There are 3 types of ATPases- P-ATPase, F-ATPase, V-ATPase.
• P-ATPase includes NA+ K+ ATPase, CA2
+ ATPase, which carry Na+, K+ and Ca2
+ ions,
• F-ATPase & V-ATPase carry H+ ions across the membrane.

7. Sodium Potassium Pump
 Also called Na+ K+ ATPase, is a transport protein which transports Na+ and K+ ions
across the membrane by hydrolysing ATP. It has high affinity for Na+ than K+.
 It is a heterodimer composed of 2 subunits- alpha subunit and beta subunit.

8. Determination of Membrane Potential
• At thermodynamic equilibrium, the membrane potential is equal to the potassium
equilibrium potential.
The magnitude of potassium potential is given by Nernst equation,
EK =
where, R= Gas constant= 1.987 cal/(degree mol)
T= Absolute temperature= 293 k at 20°c
Z= charge= 1
F= Faraday constant = 96,000 coulombs/(mol V)
[K+]o = concentration of K+ ions in the extracellular fluid
[K+]i = concentration of K+ ions in the intracellular fluid

9. Action Potential
• Action potentials are initiated by stimulus & generated by
Na+ & K+ voltage gated channels found.
• Depolarization is immediately followed by repolarization,
which is mediated by the voltage gated K+ channels and
voltage gated Cl- channels.
• Single stimulus with greater strength cannot carry the action
potential along the cells. Signal transmission requires a series
of successive stimuli which can depolarize the membrane upto
threshold potential to initiate an action potential. This is called
the All-or-none law.
• The gap period between repolarization and depolarization by
successive stimuli is called refractory period.

10. Transmission of Nerve Impulses

11. Action Potential in Muscle Contraction

12. Conclusion
• Membrane’s electrical properties are of utmost importance for the continuous
communication among different cells and tissues, normal functioning of all the
physiological processes, and maintaining body homeostasis and shape.
• Any mutation in the genes encoding the transport proteins carrying the ions across the
membrane, may lead to the disbalance in the electric potential between extracellular
fluid & cytosol, resulting in diseases like Cystic Fibrosis, Snowflake Vitreoretinal
Degeneration, Barter Syndrome, Alzheimer’s Disease, etc.
• These genetic hereditary diseases ca be treated by correction or replacement of the
mutated gene.

13. References
 Niebur, E. (2008). Electrical properties of cell membranes. Scholarpedia, 3(6),
7166.
 Zaydman, M. A., Silva, J. R., & Cui, J. (2012). Ion channel associated diseases:
overview of molecular mechanisms. Chemical reviews, 112(12), 6319-6333.
 Hübner, C. A., & Jentsch, T. J. (2002). Ion channel diseases. Human molecular
genetics, 11(20), 2435-2445.

14. THANK YOU