SYNAPSE AND ITS PROPERTIES AND DETAILED OVERVIEW

Physiology mbbs first year

1. SYNAPSE AND ITS PROPERTIES DR SUMAN RAI

2. -: synapse :- Definition -- connection between 2 neurons . Synapses are neuron – neuronal junction through which information passes from one neuron to the other.

3. Types Anatomical classification — 1) Axo dendritic 2) Axo somatic 3) Axo axonic

4. Function classification Chemical synapse (impulse transmission through NT release ) Electrical synapse (impulse transmission through gap junction)

5. Functional anatomy of synapse 1) Pre synaptic neuron— Pre synaptic membrane Synaptic vesicles (contain NT) mitochondria Voltage gated ca +2 channel 2) Synaptic cleft 3) Post synaptic neuron – Post synaptic membrane Post synaptic receptors

6. Steps of synaptic transmission:- Action potential arrive at pre synaptic terminal Opening of voltage gated ca +2 channels Entry of ca +2 into pre synaptic terminal

7. Movement of synaptic vesicles towards presynaptic membrane . Release of neurotransmitter by calcium mediated exocytosis Binding of NT with receptors on past synaptic membrane .

8. Opening of ion channels (Na + ) Na + Influx leads to depolarized of membrane Generation of synaptic potential ( LP ) When synaptic potential reaches unto the firing level, Ap is generated.

9. -: properties of Synapses :- Synapse exhibit the following properties – 1) Law of one way conduction Synaptic impulse travels in one direction only i.e. from pre synaptic to postsynaptic neuron.

10. synaptic delay Time required for the impulse to be transmitted from pre to postsynaptic neuron is called synaptic delay.

11. 3) Law of Divergence & convergence Divergence- Information from one pre synaptic neuron Passes to many past synaptic neuron Convergence - Many pre synaptic neurons project to a single postsynaptic neuron

12. 4) Synaptic inhibition It prevents unnecessary spread of impulse. It is of two types 1 ) pre synaptic inhibition (Indirect inhibition) 2 ) postsynaptic inhibition (Direct inhibition)

13. Pre synaptic (indirect)— When pre synaptic neuron is inhibited by another separate neuron , terminating on it is K/as presynaptic inhibition. This is due to decreased release of Neurotransmitler from the Pre synaptic neuron

14. Post synaptic (direct) – When post synaptic neuron is directly inhibited by pre synaptic neuron through formation of IPSP This is due to release of inhibitory neurotransmitter from pre synaptic neuron .

15. 5) Summation summation means “Add –up” It is of 2 types 1 ) Temparal summation 2) spatial summation

16. Temporal summation When a single pre synaptic knob Is stimulated repeatedly . If 2 nd synaptic potential arrives the Recovery of 1 st synaptic potential. Past synaptic potential overlap in time . These potential summate temporally and Response increased

17. Spatial summation When many pre synaptic neurons (knobs) converging one past synaptic neuron are stimulated . If 2 or more separate inputs arrive simultaneously at the post synaptic neuron . Response evoked by all inputs become larger than their individual application.

18. 6) Occlusion When a presynaptic neuron ( A) fires 5 post synaptic neurons. discharge– 5 When another presynaptic neuron (B) fires separately another 5 post synaptic neurons . discharge- 5 5+5=10 ( by their individual firing of A & B )

19. When simultaneous firing of A & B 2 presynaptic neurons share their discharge zone ( common zone) Activation of 8 post synaptic neurons instead of 10 A+B = 8 (2 are occluded)

20. 7) Habituation and Sensitization Habituation – Synaptic transmission is decreased . • Repeated transmission of impulses. Prolonged inactivate of the ca +2 channels or decreased no. of synaptic vesicles . Gradual decrease of neurotransmitter release. deceased synaptic transmission

21. Sensitization Synaptic transmission is increased . when synaptic transmission is accompanied by a painful sensation . Opening of voltage gated ca +2 channels for longer period. Gradual increase of neurotransmitter release. increased synaptic transmission.

22. 8) Subliminal fringe- opposite of occlusion. 9) Synaptic plasticity-modification of impulse transmission.

23. THANK YOU