Membrane Physiology
Dr. A. R. Joshi
Professor of Physiology,
Bharati Vidyapeeth Medical College, Pune.
Structure of cell
Unit Membrane
(Fluid Mosaic Model)
•Ingredients: 1. Phospholipids & Cholesterol
2. Lipoproteins
3. Glycocalyx
Cell Membrane
Cell Membrane
Types of Channels
● Ligand gated channels
e.g. Na+ channels at N-M Junction
● Voltage gated channels
e.g. Ca++ channels on nerve membrane
Functions of cell membrane
• Protection
• Electrical property
• Transports across membrane
(Semipermeable )
• Cell to cell communication
• Movement and phagocytosis
Transports across cell membrane
Passive transports :
●Diffusion: - Simple diffusion
- Facilitated diffusion - Diffusion thro’ channels
●Osmosis
Transports across cell membrane…
● Active transports– Uniport– Symport (co-transport)– Antiport (counter-transport)
● Endocytosis & Exocytosis
Simple diffusion
Facilitated diffusion
Diffusion thro’ channel
Osmosis
Summary of ionic transport
Active Transport - Glucose
Active Transport – Na-K pump
Endocytosis & Exocytosis
Ionic Concentration ECF ICF
Na+ 142 mEq/l 10 mEq/l
K+ 3 to 5 mEq/l 140 mEq/l
Cl- 103 mEq/l 4 mEq/l
HCO3- 28 mEq/l 10 mEq/l
Ca++ 2.4 mEq/l 0.0001 mEq/l
Mg++ 1.2 mEq/l 58 mEq/l
PO4--- 4 mEq/l 75 mEq/l
SO4-- 1 mEq/l 2 mEq/l
Proteins 2 gm/dl (5mEq/l ) 16gm/dl (40 mEq/l )
pH 7.4 7
Resting Membrane Potential
• The difference in electric potential that exists across the cell membrane when cell is in resting state
• Developed due to K ions (-94mV)
Na ions (+ 8mV)
Na-K pump (- 4mV)
Measurement of RMP
Resting Membrane Potential
• Nernst’s equation:
RMP= +61 log ﴾Conc. of ions inside﴿ ﴾Conc. of ions outside ﴿
(Corrected by Goldman’s equation)
• RMP -Skeletal muscle –90mV
-Nerve fiber –90 mV
-Heart SA node –55mV
-Heart muscle fiber –90 mV
-Hair cells in inner ear – 150mV
Action potential
• Series of events occurring in RMP when cell is stimulated with adequate stimulus
• Events 1. Application of adequate stimulus 2. Depolarization (Na+ influx)
3. Repolarization (K+ efflux)
4. Hyperpolarization
5. Na+-K+ pump
Action Potential-Cardiac Muscle
Properties of action potential
• Propagation
(Impulse- self propagatory A.P.)
• All or none law
• Refractory period
(Short R.P. for skeletal muscle and nerve
Long R.P. for cardiac muscle)
Auto-rhythmicity by S.A. Node(Leaky sodium channels)
Cell to cell communication
• Mediators– Neurotransmitter– Local hormone
(either excitatory or inhibitory)
e.g. Neuromuscular transmission
Synaptic transmission
Neuromuscular junction
Drugs acting at Neuro-muscular Junction
● Cholinomimatic drugs- e.g. Pilocarpine
● Anti-cholinergic drugs-e.g.Atropine
● Competitive inhibitors- e.g. Scholine
● Anticholinesterases -e.g.Neostigmine
● Drugs regenerating cholinesterase- e.g.PAM
For Assistance in Physiology
• Dr. A.R. Joshi
Professor of Physiology
(mobile : 9423523322)
email:
