1. This document summarizes the structure and function of synapses in the central nervous system. It describes the basic anatomy of neurons and synapses, different types of synapses, and classification of synapses based on anatomy and physiology. 2. Key electrical events that occur at synapses are discussed, including the release and removal of neurotransmitters and the generation of postsynaptic potentials. Different types of synaptic inhibition are also outlined. 3. The document concludes by reviewing various properties of synapses, such as convergence, divergence, synaptic plasticity and their significance for neural integration and modulation in the nervous system.

1. CENTRAL NERVOUS
SYSTEM SYNAPSES
DR.AIESHA DURREBAR
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2. 2
 Physiological anatomy
1. Structure of neuron
2. Structure of synapse
3. Types of synapses
4. Classification of synapse
Electrical events at a synapse
Inhibition at synapse
Properties of synapse
OVERVIEW

3. STRUCTURE OF A NEURON
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4. STRUCTURE OF SYNAPSE
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5. 5
TYPE OF
SYNAPSE
SITE OF CONTIGUITY
PART OF PRESYNAPTIC
CELL
PART OF POST SYNAPTIC
CELL
AXO-
DENDRITIC
AXON DENDRITE
AXO- SOMATIC AXON SOMA
AXO-AXONAL AXON AXON
DENDRO-
DENDRITIC
DENDRITE DENDRITE
TYPES OF SYNAPSES

6. CLASSIFICATION OF SYNAPSES
ANATOMICAL CLASSIFICATION
TYPE I TYPE II
Axodendritic Axosomatic
Marked thickening of subsynaptic
membrane
Non continuous slight thickening in
subsynaptic membrane
Wide synaptic cleft=30nm filled with dense
ECF
Narrow synaptic cleft=20nm with not such
dense ECF
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7. 7
PHYSIOLOGICAL CLASSIFICATION
CHEMICAL SYNAPSE ELECTRICAL SYNAPSE
Transmission of impulse occurs due to liberation of
chemical mediator
Pre and post synaptic membranes come very close
to form gap junctions which act as low resistance
bridges through which ions pass with ease.
Most of the synaptic junctions Some of the junctions in lateral vestibular nucleus,
hippocampus and cerebral cortex
Signals transmitted only in one direction Signals transmitted in either directions
Sensitive to hypoxia Insensitive to hypoxia

8. ELECTRICAL EVENTS AT A SYNAPSE
 Resting membrane potential
 Release of neurotransmitters
 Development of postsynaptic potential
 Removal of neurotransmitter
 Genesis of action potential in post synaptic neuron
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9. RESTING MEMBRANE POTENTIAL
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• For Na+ = -61mV
• For K+ =-87mV
• For Cl- = +70mV

10. RELEASE OF NEUROTRANSMITTER
 Release sites
 Kiss and run discharge
 Dales phenomenon
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11. DEVELOPMENT OF POST SYNAPTIC
POTENTIAL
 EXCITATORY POSTSYNAPTIC
POTENTIAL (EPSP)
 INHIBITORY POST SYNAPTIC
POTENTIAL(IPSP)
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 SPATIAL SUMMATION  TEMPORAL SUMMATION

13. REMOVAL OF TRANSMITTER
SUBSTANCE
 Diffusion of transmitter substance outside the cleft.
or
 Enzymatic degradation of transmitter in the cleft. Eg:ACh
or
 Active reuptake of neurotransmitter back into presynaptic terminal.
Eg:NE
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14. GENESIS OF ACTION POTENTIAL
Soma as an integrator
Initial segment spike
Bell Magendie law; law
of dynamic polarity.
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15. SYNAPTIC INHIBITION
They are of two types
1. Postsynaptic inhibition
2. Presynaptic inhibition
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16. POSTSYNAPTIC INHIBITION
1. Direct inhibition
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17. 2. Indirect inhibition
 Refractory period
 Renshaw cell/negative feedback
inhibition-limit excitability.
APPLIED: Strychnine decreases
postsynaptic inhibition
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Ventromedial part of
anterior horn

18. PRESYNAPTIC INHIBITION
a. Reduces opening of Ca+ channels
directly.
b. Increases Cl- and/or K+ permeability
so that size of action potential
reaching excitatory ending is reduced
c. Direct inhibition of neurotransmitter
release.
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Example=Reciprocal inhibition:
APPLIED:
1. Convulsant drug picrotoxin-
decrease presynaptic inhibition
2. Barbiturates-increase presynaptic
inhibition

20. PROPERTIES OF SYNAPSE
1. Convergence and divergence
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3. Occlusion 4. Subliminal fringe
Significance:
1. Pattern in peripheral nerves are usually altered as they pass through synapses on the way to brain.
E.g.: referred pain.
1. The interaction between excitatory and inhibitory influences at the synapse required for integrating
and modulating activity of nervous system.

22. 4. Reverberation
5. After discharge
6. Acidosis and hypoxia
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23. 7. Synaptic plasticity
 Post tetanic potentiation
 Long term potentiation
 Low frequency depression
 Sensitization/ facilitation
 Habituation/ synaptic fatigue
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24. REFERENCES
1. TEXTBOOK OF PHYSIOLOGY,11TH EDITION, GUYTON AND
HALL
2. TEXTBOOK OF MEDICAL PHYSIOLOGY, INDU KHURANA
3. GANONG’S REVIEW OF MEDICAL PHYSIOLGY. 23RD
EDITION.
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25. THANK YOU
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