Synaptic Transmission

1. Dr. Geetanjali Purohit
Professor
Department of Physiology
Dr. M K Shah MCRC

2. PY 10.2 Describe and discuss the
functions and properties of synapse,
reflex, receptor

3. SLO’s
1. Describe the main morphologic features of
synapses.
2. Distinguish between chemical and electrical
transmission at synapses
3. Define convergence and divergence in
neural networks, and discuss their
implications.
4. Describe fast and slow excitatory and
inhibitory

4. S Y N A P S E
The junction where the axon of one neuron
(Presynaptic neuron) terminates on the dendrites,
soma or axon of another neuron (Postsynaptic
neuron)
Types of Synapses
Chemical Electrical and
Conjoint
Through Neurotransmitters
 Almost all synapses in
human C.N.S.
 Around 40 transmitters
 Through Gap junctions
 Only a few
 In smooth & cardiac
muscles.

6. Physiological classification of
Synapse
Chemical synapse Electrical synapse
Chemical mediators are released from pre
to post synaptic site
Pre and post membranes are close to each
other by a low resistance bridge–Gap
Junction through which ions pass
Seen in most of the synaptic junctions
Found at few locations like in lateral
vestibular nuclei, hippocampus and
cerebral cortex
Allows large number of synapses per
neurons and a large variety of
neurotransmitters. Helpful in the
processing of learning and memory.
Too many synapses on the same neuron
thus transmission is rapid and efficient.
Sensitive to hypoxia Insensitive hypoxia
Synaptic cleft is present
Cleft is replaced by low resistance bridge
Synaptic delay is observed No synaptic delay

7. Functional Anatomy and Transmission

8. Kiss and Run
discharge

9. ***Tetanus and botulinum toxins are acting on
synaptobravin and syntaxin and prevent the
NT discharge
Note: botulinum toxins is used for achlasia
cardia and the treatment of wrinkles

10. Electrical Events at Synapse:
Excitatory Postsynaptic Potentials (EPSP)
>Single stimulus of one synaptic knob
> After a synaptic delay of 0.5 ms
>Opening of voltage-gated Na+ channels
> A local and graded depolarizing potential
produced in PS membrane
> excitability to other stimuli is increased.

11. Electrical Events at Synapse: (contd.)
Inhibitory Postsynaptic Potentials: (IPSP)
>Single stimulation of some pre synaptic fibers
> Opening of Clˉ channels
> Influx of Clˉ
> Local hyperpolarizing potential
> Decreased excitability to other stimuli.

12. EPSP & IPSP

13. Summation
****When the algebraic sum of EPSP and IPSP reach 10–15 mV (firing
level), Action Potential results at the Axon Hillock.
1.Spatial summation: Activities in many
synaptic knobs at the same time.
2.Temporal summation: Repeated afferents
in a single knob causing new EPSP
before the decay of previous EPSP.

15. 1. Electrical synapse conducts impulse from one cell to another freely
due to the presence of which of the following component?
A.Neurotransmitter B.Chemicals C.Gap junction D.Tight junction
2. Which of the following causes rupture of synaptic vesical at the
presynaptic end of synapse?
A.Ca2+ influx B.Na+influx C.K+influx D.Ca2+efflux
3. Repeated afferents in a single knob causing new EPSP before the
decay of previous EPSP k/as .
a. Temporal summation b. spatial summation
c. Quantal summation d. none
4. Excitatory post synaptic potential EPSP occurs due to entry of
which of the following ion into the post-synaptic neuron?
A. Na+ ion B.Ca2+ ion C. K+ ion D. H+ ion
4. Inhibitory post synaptic potential IPSP occurs due to entry of which
of the following ion into the post-synaptic neuron?
A. Na+ ion B. Ca2+ ion C. Cl- ion D. H+ ion