3. CNS
(SYNAPSE)

4. Synapse At the end of this lecture you should be able to ;
Synapse and its types
Properties of Synapses

5. The Synapse Junctional point between two neurons that
transmits impulse
from first to the
second Neuron.

6. Classification Anatomical Classification 1. Axo-Dendritic
(on the Basis of Communication )
1. Axo-Dendritic
2. Axo-Somatic
3. Axo-Axonic
4. Dendro-dendritic (amacrine cells in Eye)
PHYSIOLOGICAL Classification: (According to Nature)
1. Electrical
2. Chemical

8. Chemical synapse

9. Electrical synapse

10. Physiological Anatomy
Components
1. Presynaptic
terminal
3. Postsynaptic
membrane
2. Synaptic Cleft
Typical Anterior Motor
Neuron

12. Mechanism of Action of Neuro-transmitter on the Post-synaptic Membrane
Receptor Proteins have Two Components:
Binding Component
Ionophore Component
Anionic channel
a. Ion Channels {
Cationic channel
b. Second Messenger Activator

13. Second Messenger System in the Postsynaptic Neuron
G-Proteins; is Attached to Receptor Protein on its inner surface.
Three components of G-Protein.
1. Alpha - Activator
2. Beta & Gamma - attached to alpha component
On activation, ά-Component separates
from β & γ components
- is Free to perform the function specific for that particular Neuron.

14. Second Messenger System in the Postsynaptic Neuron

15. Functions Which Can be Performed By α-Component
Opening of specific Ion channel in the Postsynaptic Membrane.
Activation of Cyclic AMP
Activation of intracellular Enzymes.
Activation of Gene Transcription

16. Rapidly Acting Transmitters (Small Molecules)
Class-I Acetylcholine
Class-II. (Amines)
Adrenalin (Epinephrine)
Nor-adrenaline (Nor-Epinephrine)
Dopamin
Serotinin
Histamine
CLASS-III. ( Amino Acids)
Gamma Amino Butyric Acid (GABA)
Glutamate
Glycin
Aspartate
Class-IV- Nitrous Oxide
Class-V- Neuropeptides.
Substance-P, Enkephalin, Endorphins

17. Neurotransmitter Removal
Monoamine Oxidase

18. Properties of Synapses or Synaptic Transmission
1. One Way Conduction
2. Synaptic Delay.
minimum 0.5 m.sec
3. Excitation (EPSP)
Presynaptic
4. Inhibition-{
Postsynaptic

19. Excitation & Inhibition
Excitation: is carried out by:
1. Opening of Sodium Channels
2. Decreased conduction through K+ or Cl Channels.
3. Various changes in the metabolism of Postsynaptic Neuron
Inhibtion: Pre & Post Synaptic Inhibition
1. Opening of chloride Channels
2. Increase in K+ ion efflux by opening K+ Channels
3. activation of Enzymes which inhibit metabolism.
> By producing Hyperpolarization

20. Negative feedback inhibition of Spinal Motor Neuron via Inhibitory interneuron (Renshaw Cell) in the spinal cord
Renshaw Cell

21. Reciprocal Inhibition

22. Properties of Synapses
5. Synaptic fatigue :
Partially due to exhaustion of stores of neurotransmitter &
Probable two other factors include;
1. Progressive inactivation of postsynaptic receptors
2. Slow development of abnormal concentration of ions inside the postsynaptic neuronal cell.
Significance: Stabilization of Nervous system

23. Properties of Synapses
Spatial summation ( > one Neuron)
6. Summation {
Temporal summation
(Only One N repetitively)

24. Properties of Synapses
7. Facilitation

25. Properties of Synapses
8.Occlusion – Net Response < than the individual Presynaptic N
& Subliminal Fringe
Subliminal fringe is due to spatial summation.
Occlusion is due to Overlapping of the fibers.

26. Occlusion
The decrease in expected response due to pre synaptic fibers sharing post synaptic neurons is called occlusion

27. Properties of Synapses
9.Convergence
e.g on ά-motor N
CNS correlates ,summates
and sort different types of
Information.
10.Divergence
Amplifing type
Cortico spinal pathway

28. Divergence into multiple Tracts

29. Properties of Synapses
11.Recruitment. involving more & more neurons as the stimulus becomes stronger
11. After discharge.- Prolonged out put discharge after the incoming signal is over. Mechanism:
a. Synaptic after discharge (parallel Collaterals)
b. Reverberatory circuits

30. Properties of Synapses
. 13.Posttetanic Potentiation;
Production of enhanced postsynaptic potentials in response to stimulation. Due to accumulation of Ca++ in the Presynaptic Neuron.
14. Habituation;
Gradual Disappearance of response to a repeated benign stimulus is called Habituation. > Decrease Release of Ach > Decrease Intracellular Ca++. .

31. Properties of Synapses
Effect of Acidosis & Alkalosis:
Acidosis: Greatly depresses neuronal activity
Fall in pH from 7.4 to 7.0 > Comma ( Diabetic or Uremic )
Alkalosis: Greatly Increase Neuron Excitability
Hypoxia: > unconsciousness Within 3-7 seconds.
Drugs like Caffeine, theophyline & theobromine > Increase Excitability
Decrease in ca++ > Increased Excitability & Vice versa
Anesthetics > Increase in threshold for excitation