Physiology of Synapse:- Excitatory synapses and Inhibitory synapses

Synapse is simply a junction between two neurons. There are two types of synapses in central nervous system.

·         Excitatory synapses

·         Inhibitory synapses

Excitatory synapses

Pre synaptic knob secretes as excitatory substance. (Ex: Acetyl choline, Noradrinalin, Gutamic acid)

Transmission:

Nerve impulse à pre synaptic knob releases acetyl choline (Ach)àAch diffuse across synaptic cleftàAch combine with receptor sites of post synaptic membraneàpermeability of post synaptic membrane changesà permeability to Na⁺ increases and Na⁺ enter the post synaptic knobà Excitatory post synaptic potential (EPSP) is obtainedàthreshold potential is reachedà action potential is formedà distribution of action potential

A combined EPSP depolarize the membrane to a threshold value to generate an action potential is known as summation. Summation can occur in two ways as temporal summation which is obtained by repeat discharge of single pre synaptic knob and spatial summation which is obtained by numerous pre synaptic knobs.

Inhibitory synapses

Pre synaptic knob secretes an inhibitory substance. (Ex: alpha butric acid and glycine)

This inhibitory synapses function in two ways as post synaptic inhibition and pre synaptic inhibition.

Post synaptic inhibition

Nerve impulseà pre synaptic knob release an inhibitory substance (GABA)àGABA diffuse across synaptic cleftà GABA binds with receptor sites on post synaptic membraneà permeability of post synaptic membrane changesà permeability to K⁺ and Cl^- ions increaseà K⁺ leaves and Cl^- ions enteràInhibitory post synaptic potential (IPSP) is obtainedà membrane hyperpolarizedà no action potential initiated

Pre synaptic inhibition

Nerve impulseà pre synaptic knob release inhibitory substancesàhyperpolarize the pre synaptic  excitatory membraneà prevent excitatory substances releasingà no excitation occurs on post synaptic membrane