Synapses: basis of working of neuronal communication in CNS. Next pptx will show more. This one is the basics of synapses.

2. Synaptic transmission - I
By :- DR. ANJU JHA
MBBS, MD, PGDMCH

3.  Functional anatomy of a synapse.
 Process of synaptic transmission-
 Arrival of the message & release of neurotransmitter,
 development of excitatory postsynaptic potential,
 fate of neurotransmitter.
 generation of action potential,
 summation of postsynaptic potentials.

4.  The central nervous system contains more than 100
billion neurons.
 Cajal proposed neural doctrine.
 Waldayer coined the term neuron.
 Charles Sherington introduced the term Synapse.
 In Greek synapsis means conjuction.

5.  Impulses are transmitted from one nerve cell to
another cell at synapses.
 Synapses are the anatomic sites where the nerve cells
communicate with each other.
 There is no anatomical connections between two
neurons.
 They are connected only functionally.

8. Types of synapses
synapse
Chemical
Axo-
dendritic
Axo-
somatic
Axo-
axonic
Electrical

12. Structure of chemical synapse
 Synaptic Knob or button.
 Pre-synaptic membrane.
 Synaptic cleft.
 Post-synaptic membrane.

14. Synaptic Knob:
 The ends of the presynaptic fibers are generally
enlarged to form terminal boutons or synaptic
knobs.
 On average, each neuron divides to form over 2000
synaptic endings.
 The human central nervous system (CNS) has 1011
neurons.
 There are about 2 × 1014 synapses in human CNS.
 Synapses are dynamic structures, increasing and
decreasing in complexity and number with use and
experience.

15.  In the cerebral cortex, 98% of the synapses are on
dendrites and only 2% are on cell bodies.
 Each knob contains large number of mitochondria
and synaptic vesicles containing neurotransmitter.
 There are three kinds of synaptic vesicles:
Small, clear synaptic vesicles -contain
acetylcholine, glycine,GABA, or glutamate.
Small vesicles with a dense core that contain
catecholamines.
Large vesicles with a dense core that contain
neuropeptides.

16.  Pre-synaptic membrane: The axonal membrane
lining the synaptic knobs.
 Synaptic cleft: The presynaptic terminal is
separated from the postsynaptic neuronal soma by a
synaptic cleft having a width usually of 200 to
300Å.

17. Post synaptic membrane:
 Membrane lining the post synaptic process.
 It contains large number of receptor proteins which
protrude outwards in synaptic cleft.

18. Process of synaptic transmission
Sequence of events during synaptic
transmission:
 Release of neurotransmitter.
 Development of excitatory or inhibitory postsynaptic
potential.
 Removal of neurotransmitter from synaptic cleft.
 Development of action potential.

19. Nerve impulse travelling in a nerve fiber reaches to nerve terminal
Depolarization of synaptic knob occurs.
Voltage gated Ca++ channels present in pre synaptic membrane open up.
Ca++ ions from ECF of synaptic cleft enter in to pre-synaptic knob.
Rise in concentration of Ca++ stimulates the exocytosis of synaptic vesicles
Release of Neurotransmitter occurs
Release of Neurotransmitter
Released transmitter diffuses across the synaptic cleft
and
binds to post synaptic receptors.

20. Development of EPSP or IPSP
 Binding of neurotransmitter causes the opening of
channels through which ions can flow.
EPSP (Excitatory post synaptic potential):
 Most common excitatory neurotransmitter in CNS is
glutamate.
 After binding with receptors there is opening of
ligand gated Na+ channels.
 Increase in Na+ concentration in post synaptic
neuron there will be depolarization.

21. IPSP (Inhibitory post synaptic potential):
 It is hyperpolarization of the post synaptic
membrane.
 Inhibitory neurotransmitters in CNS are glycine and
GABA.
 There may be opening of K+ channels or opening of
Cl- channels.
 Exit of K+ or entry of Cl- makes the membrane
hyperpolarized.

24. Fate of neurotransmitter
Neurotransmitter released in synaptic cleft from
pre-synaptic terminal is soon inactivated by one of
three ways:
I. Diffusion of transmitter out of the cleft.
II. Enzymatic degradation of transmitter.
III. Actively transported back in to presynaptic
terminal.

26. Development of action potential
Development of action potential occurs from EPSP:
 Synaptic integration.
 Generation of the initial segment spike.
 Generation of propagated potential.

28. summation of postsynaptic potentials.
 EPSP is graded response.
 It does not follow all or none law like action
potential.
 It shows property of summation.
 Two types of summation :
 Temporal summation,
 Spatial summation.

29. Applied
 Poisoning by botulinum toxin (Botox) blocks
ACh release and results in a failure of
neuromuscular transmission.
 Botox injections have been used to treat dystonia,
a movement disorder characterized by involuntary
muscle contractions, and cosmetically to locally
block facial muscles that wrinkle the skin. Excessive
doses or systemic toxin delivery from contamination
during food canning can lead to death.