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:

aniruddharj@hotmail.com