SYNAPSES AND NEURONAL
INTEGRATION
DR. ZAHOOR ALI SHAIKH
LECTURE –10
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SNAPSES AND NEURONAL
INTEGRATION

A Neuron may terminate on one of THREE
structures:
1) MUSCLE
2) GLAND
3) ON ANOTHER NEURON – JUNCTION
BETWEEN TWO NEURON IS CALLED
SYNAPSE
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SYNAPSE

SYNAPSE – Junction between two neurons.
SYNAPSES
TWO TYPES
1) Electrical Synapses
2) Chemical Synapses
 Depending upon how the information is
transferred between TWO neuron.

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ELECTRICAL SYNAPSES
In electrical synapses, two neuron are connected
by Gap Junction which allow ions (charged
particles) to flow between the two cells .
Therefore Action Potential travels from one cell
to another.
 Electrical signals are rare in Human Nervous
System.

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ELECTRICAL SYNAPSES [CONT]

Example of Electrical Synapses
--- Pulp of tooth
--- Retina of the Eye
--- Cardiac Muscle
--- Smooth Muscle
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CHEMICAL SYNAPSES


In human CNS , most of the synapses are Chemical,
where chemical messenger transmits information
from one neuron to another .
WE WILL DISCUSS CHEMICAL SYNAPSE
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CHEMICAL SYNAPSE
A chemical synapse involves:
1) Pre-synaptic Neuron
2) Post-synaptic Neuron
 In chemical synapse, there is junction between
axon terminals of One Neuron known as ‘PreSynaptic Neuron’, and Dendrites or Cell body of
Second Neuron, known as ‘Post-Synaptic
Neuron’.

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CHEMICAL SYNAPSE

Mostly Dendrites or Cell body receive thousands of
synaptic inputs from axon terminals of many other
neurons
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ANATOMY OF CHEMICAL
SYNAPSE
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ANATOMY OF CHEMICAL
SYNAPSE
REMEMBER
 PRE-SYNAPTIC NEURON
 SYNAPTIC KNOB
 SYNAPTIC VESICLES
 NEUROTRANSMITTER
 SYNAPTIC CLEFT
 POST-SYNAPTIC NEURON

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ANATOMY OF CHEMICAL
SYNAPSE [CONT]
Pre-synaptic Neuron—It conducts the impulse
and ends in a slight swelling, the SYNAPTIC
KNOB.
 The synaptic knob contains SYNAPTIC
VESICLES.
 Synaptic vesicle store chemical messenger ,a
NEUROTRANSMITTER, that is synthesized by
pre-synaptic neuron.

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ANATOMY OF CHEMICAL
SYNAPSE [CONT]


SYNAPTIC CLEFT– Space between the pre-synaptic
and post-synaptic neuron.
POST-SYNAPTIC NEURON– it takes Action
Potential away from the synapse.
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SIGNAL TRANSMISSION ACROSS A
SYNAPSE
A Neurotransmitter carries the signals across
the synapse.
 HOW ?
By following mechanism
1. Action Potential reaches axon terminal of
presynaptic neuron.
2. Ca2+ channels open, Ca2+ enters synaptic knob
[presynaptic axon terminal].

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SIGNAL TRANSMISSION ACROSS A
SYNAPSE (CONT)
3. Neurotransmitter is released by exocytosis into
synaptic cleft.
4. Neurotransmitter binds with the receptors on
the synaptic membrane of post synaptic neuron.
5. Binding of neurotransmitter to receptors opens
the specific channel [Na+, K+, Cl-].
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SYNAPTIC DELAY

Transmission of electrical impulse [AP] by chemical
means from presynaptic neuron to post-synaptic
neuron takes time. It is called ‘Synaptic Delay’. It is
0.5 to 1 millisecond.
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TYPES OF SYNAPSE

1.
There are two types of Synapse:
1. Excitatory Synapse
2. Inhibitory Synapse
Excitatory Synapse
Here neurotransmitter released act
on receptors to open Na+ and K+ channels.
When Na+ enters, it causes small
depolarization [-70 to -60 mv]. It is called
‘Excitatory Post-Synaptic Potential’ [EPSP].
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TYPES OF SYNAPSE [CONT]
2. Inhibitory Synapse
Neurotransmitter released acts on
receptors and causes the opening of K+ or Clions. It causes Hyperpolarization [more negative
inside of post-synaptic neuron] when K+ leaves or
Cl- enters.
Therefore membrane is less excitable now. This
small hyperpolarization of post-synaptic cell is
called ‘Inhibitory Post-Synaptic Potential’ [IPSP].
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COMMON NEUROTRANSMITTERS
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‘IMPORTANT’


Glutamate – Most common excitatory
neurotransmitter in the brain. It causes EPSP.
GABA [Gamma amino butyric acid] – Most
common inhibitory neurotransmitter in brain. It
causes IPSP.
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NEUROTRANSMITTER REMOVAL FROM
THE SYNAPTIC CLEFT

1.
2.
3.
Neurotransmitters are quickly removed from the
synaptic cleft by various ways:
Inactivated by enzymes present on post
synaptic membrane.
Diffuse away from synaptic cleft.
Actively taken back into axon terminal.
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POST-SYNAPTIC POTENTIAL


EPSPs and IPSPs are graded potential [local].
They can be summated [added].
Types of Summation
1. Temporal Summation
2. Spatial Summation
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TEMPORAL SUMMATION


When single presynaptic neuron is stimulated
many times after short intervals, to summate
several EPSP, it is called ‘Temporal
Summation’.
Up to 50 EPSPs might be needed to bring postsynaptic membrane to threshold level.
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SPATIAL SUMMATION

When two or more excitatory neurons are stimulated
together at the same time, to get the action potential.
It is called Spatial Summation.
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CONVERGENCE AND DIVERGENCE
Convergence
On a given neuron, many other neurons
come and synapse on it. It is called
‘Convergence’.

Due to convergence input, a single neuron is
influenced by thousands of other cells.

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CONVERGENCE AND DIVERGENCE
[CONT]

Divergence
It refers to the branching of axon
terminals so that single cell synapses with many
other cells.
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‘IMPORTANT INFORMATION’
There are about 100 billion neurons in the brain.
 A single neuron maybe connected to 5000 to
10,000 other neurons.
 Brain is responsible for different activities like
sensations, movements of muscle, thought,
emotion, memory – all these depend on electrical
and chemical signaling between neurons along
wired neural pathways.

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WHAT YOU SHOULD KNOW FROM THIS
LECTURE
What is Synapse?
- Connection between two neurons
 What are types of Synapse?
- Electrical
- Chemical
 Chemical Synapse
- Presynaptic Neuron – Axon terminal (output unit)
- Postsynaptic Neuron – Dendrites or Cell Body (receiving or input unit)
 Anatomy of Chemical Synapse
 Mechanism of release of Chemical transmitter from the synaptic vesicles.
 Action of Chemical transmitter (neurotransmitter) on postsynaptic neuron
(dendrites of Cell Body)
 Excitatory and Inhibitory synapse depend on type of neurotransmitter – EPSP,
IPSP
 Most common excitatory neurotransmitter in brain – glutamate
 Most common inhibitory neurotransmitter in brain – GABA
 How chemical transmitter are removed at the synaptic cleft?
 Types of Summation
- Temporal – single presynaptic neuron stimulated many times after short
intervals
- Spatial – when two or more excitatory neuron stimulated same time to get AP

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THANK YOU
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