action potential

MEMBRANE POTENTIAL &

SYNAPTIC TRANSMISSION

By- Ritam Choudhury,Rudradip Das

B.Pharm

INDEX

General introductionNeurone classification – Myelinated

and Non – Myelinated Special features of a neuroneResting Membrane PotentialAction PotentialNerst Equation Ionic distributionSynaptic transmissionConclusion

General Introduction

An impulse is initiated by stimulation of sensory nerve endings or by the passage of an impulse from another nerve.

Transmission of the impulse, or action potential is due to movement of ions across the nerve cell membrane.

Neurones are classified in two types-

Myelinated Neurone

Non MyelinatedNeurone

Special Properties of Neurons-

Excitability--Action Potential in Axons.

Conduction--Action Potential in Axons.

Transmission--Synapses, Electrical & Chemical.

Integration--Postsynaptic Cell.

Plasticity--Presynaptic Terminal and Postsynaptic Membrane.

Resting membrane potential-

An impulse is initiated by stimulation of sensory nerve endings. Transmission of the Impulse is due to the movement of ions acrossthe nerve cell membrane. In the resting state the nerve cell membrane is polarised due to differences in the concentration of ions across the plasma membrane . This means that there is a different electrical charge on each side of the membrane which is called the Resting membranePotential

o Action Potential-

Nernst Equation• Eion = 2.303 RT/ZF log [ion]o/[ion]in

• Eion = ionic equilibrium potential• Z= charge of ion• F= Faraday’s constant• T= absolute temperature (0Kelvin/-273°C) • R=Universal gas constant

The Nerst Equation relates the voltage across the membrane which is in equilibrium with the concentration of ions inside and outside the cell membrane.

Ion Inside Outside Cross PM

K+ 125 5 yes

NA+ 12 120 no

Cl- 5 125 yes

H2O 55,000 55,000 yes

Anion- 108 0 no

IONIC DISTRIBUTION

SYNAPTIC TRANSMISSION-

Stimulus Pre synaptic neurone

Depolarisation

Impulse Reach to Specific receptor on Pre synaptic membrane post synaptic neurons binds toCalcium ion entry Synaptic clept

Synaptic knob Release of neurotransmitter by exocitosis

Affinity of synaptic vessicle to bind with pre synaptic membrane

TO BE CONTINUED…..

POST SYNAPTIC NEURONE

Excitatory Neurotransmitter Inhibitory Neurotransmitter

Permeability to Na +

Repolarisation

Excitatory Post Synaptic Potential

Opening of k+/Cl- channel

Hyperpolarisation

Inhibitory Post Synaptic Potential

CONCLUSION-

The nervous system detects and responds to changes inside and outside the body. Together with the endocrine system, it controls many vital aspects of the body functions.

The nervous system consists of the brain , spinal cord, and peripheral nerves. The structure and organisation of the tissues that form these components enables rapid communication between different parts of the body.

References -Anne Waugh and Allison Grant, The Nervous System,139 – 183 ,Textbook of medical physiology,11th edition, Elsevier publishers,2007

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www.pharmainfo.net/impulse