Synapses can be classified by the type of cellular structures serving as the pre- and post-synaptic components. ... The axon can synapse onto a dendrite, onto a cell body, or onto another axon or axon terminal, as well as into the bloodstream or diffusely into the adjacent nervous tissue.

1. Classification And Structure Of Synapses
Mechanisms Of Excitation Conduction In
A Chemical Synapse
Student name:
ALKOLBEE ALAA RADHI MUHSSIN
Lesson: Biochemistry of hormones
Prof.name: Nina kanunnikava
Yanka Kupala State University of Grodno

2. • Synapse is the junction between two
neurons. It is not an anatomical
continuation. But, it is only a
physiological continuity between two
nerve cells.
• CLASSIFICATION OF SYNAPSE:
Synapse is classified by two methods:
A. Anatomical classification
 B. Functional classification.

3. Anatomical Classification
• Usually synapse is formed by axon
of one neuron ending on the cell
body, dendrite or axon of the next
neuron. Depending upon ending of
axon,
synapse is classified into three types:
1. Axo-axonic synapse in which axon
of one neuron terminates on axon of
another neuron
2. Axo-dendritic synapse in which the
axon of one neuron terminates on
dendrite of another neuron
3. Axo-somatic synapse in which axon
of one neuron ends on soma (cell
body) of another neuron

4. Functional Classification
• Functional classification of synapse is on the basis of mode
of impulse transmission
1. Electrical Synapse: is the synapse in which the
physiological continuity between the presynaptic and the
postsynaptic neurons is provided by gap junction between the
two neurons.
2. Chemical synapse: Is the junction between a nerve fiber and
a muscle fiber or between two nerve fibers, through which the
signals are transmitted by the release of chemical transmitter

6. On The Basis Of Functions, Synapses Are Divided Into Two
Types:
1. Excitatory synapses: which transmit the impulses (excitatory
function)
-Excitatory Postsynaptic Potential:
Excitatory postsynaptic potential (EPSP) is the non propagated
electrical potential that develops during the process of synaptic
transmission.
2. Inhibitory synapses, which inhibit the transmission of
impulses (inhibitory function)
-Postsynaptic or Direct Inhibition:
Postsynaptic inhibition (IPSP) is the type of synaptic inhibition
that occurs due to the release of an inhibitory neurotransmitter
from presynaptic terminal instead of an excitatory
neurotransmitter substance. It is also called direct inhibition.
Inhibitory neurotransmitters are gammaaminobutyric acid
(GABA), dopamine and glycine

7. Chemical Synapse
• Terminal bouton is separated
from postsynaptic cell by
synaptic cleft.
• Neurotransmitter (NT) are
released from synaptic vesicles.
• Vesicles fuse with axon
membrane and NT released by
exocytosis.
• Amount of NTs released
depends upon frequency of
action potentials AP.

8. Synaptic Transmission
• Neurotransmitter NT release is rapid because many
vesicles form fusion-complexes at “docking site.”
• AP travels down axon to bouton.
• VG Ca2+ channels open.
◦ Ca2+ enters bouton down concentration gradient.
◦ Inward diffusion triggers rapid fusion of synaptic
• vesicles and release of NTs.
• Ca2+ activates calmodulin, which activates protein
kinase.
• Protein kinase phosphorylates synapsins.
◦ Synapsins aid in the fusion of synaptic vesicles.

9. Synaptic Transmission
• NTs are released and diffuse across synaptic cleft.
• NT (ligand) binds to specific receptor proteins in
postsynaptic cell membrane.
• Chemically-regulated gated ion channels open.
▫ EPSP: depolarization.
▫ IPSP: hyperpolarization.
• Neurotransmitter inactivated to end transmission.

10. Chemical Synapse
• EPSP (excitatory postsynaptic
potential):
▫ Depolarization.
• IPSP (inhibitory postsynaptic
potential):
▫ Hyperpolarization

11. Difference
Between
EPSP
and
IPSP
EPSP IPSP
EPSP: An EPSP is an electrical charge on the
postsynaptic membrane, which is caused by
the binding of excitatory neurotransmitters
and makes the postsynaptic membrane
generate an action potential.
IPSP: An IPSP is an electric charge on the
postsynaptic membrane, which is caused by
the binding of inhibitory neurotransmitters
and makes the postsynaptic membrane less
likely to generate an action potential.
EPSP is caused by the flow of positively-
charged ions.
IPSP is caused by the flow of negatively-
charged ions.
EPSP: EPSP is a depolarization. IPSP: IPSP is a hyperpolarization.
EPSP: EPSP brings the postsynaptic
membrane towards the threshold.
IPSP: IPSP takes the postsynaptic membrane
away from the threshold.
EPSP makes the postsynaptic membrane
more excited.
IPSP makes the postsynaptic membrane less
excited
EPSP facilitates the firing of an action
potential on the postsynaptic membrane.
IPSP lowers the firing of an action potential
on the postsynaptic membrane
EPSP is the result of the opening of the
sodium channels.
IPSP is the result of the opening of the
potassium or chloride channels.
EPSP is generated by the flow of glutamate
or aspartate ions.
IPSP: IPSP is generated by the flow of glycine
or GABA.

12. Acetylcholine (ACh) as NT
• ACh is both an excitatory and
inhibitory NT, depending on
organ involved.
▫ Causes the opening of
chemical gated ion channels.
• Nicotinic ACh receptors: Found
in autonomic ganglia and skeletal
muscle fibers.
• Muscarinic ACh receptors:
Found in the plasma membrane of
smooth and cardiac muscle cells,
and in cells of particular glands.

13. Acetylcholine (ACh) as NT
• Most direct mechanism. Ion
channel runs through
receptor.
▫ Receptor has 5
polypeptide subunits that
enclose ion channel.
▫ 2 subunits contain ACh
binding sites.
• Channel opens when both
sites bind to ACh.
▫ Permits diffusion of Na+
into and K+ out of
postsynaptic cell.
• Inward flow of Na+
dominates.
▫ Produces EPSPs

14. GABA (gamma-aminobutyric acid):
• GABA (gamma-aminobutyric
acid):
▫ major inhibitory NT in brain.
• Hyperpolarizes postsynaptic
membrane.
• Motor functions in cerebellum.
• After excretion – GABA
resorbed from synaptic cleft
(neurons or surrounding glial
cells); transport requires
presence of extracellular Na +
and Cl -

15. GABA (gamma-aminobutyric acid):
• The binding of GABA to
receptor.
-increases the flow of chloride
(CI-) ions in the postsynaptic cells
-raising its membrane
potential and inhibiting it.
• The binding of GABA to
receptors activates a second
messenger opening K+ channels.
• produce
• -Inhibitory Postsynaptic
Potential (IPSP) which
counteracts the excitatory
signals.

17. • Drugs such as Phenobarbital,
Valium, Librium, and other
sedatives bind themselves to
GABA receptors and enhance its
inhibitory effect on the Central
Nervous System.
• Amino acid is used at excitatory
synapses in the Central Nervous
System and is helpful in long
term potentiation or memory.
• Serotonin and histamine also
stimulate intestinal peristalsis.
Neurotransmitters react
differently to receptors in
different areas of the brain.
• So while it can cause an
excitatory effect in one area, it
can cause an inhibitory effect in
another.

18. Thank you