Electrical and chemical synapses differ in their mechanisms of signal transmission between neurons. Electrical synapses allow rapid direct transmission of electrical signals through gap junction protein channels, while chemical synapses are slower but transmit signals unidirectionally via the release of neurotransmitter vesicles into the synaptic cleft. Calcium ions play a critical role in the release of neurotransmitters at chemical synapses through their interaction with proteins like synaptotagmin and the SNARE complex that facilitate vesicle fusion with the presynaptic membrane.

1. SYNAPTIC
TRANSMISSION
DOMINA PETRIC, MD

2. TYPES OF SYNAPSES
Electrical synapses function by means of proteins
that form channels (gap junctions).
Chemical synapses work via the release the
packages of neurotransmitter (synaptic vesicles)
into the synaptic cleft.

3. QUORA.COM, ELECTRICAL SYNAPSE

4. ELECTRICAL SYNAPSES
• Allow very rapid communication of electrical signals
from one cell to another.
• Proteins that form gap junctions are called connexons.
• They aggregate to provide an aqueous channel that
allows for a current carrying molecule to pass directly
from the cytoplasm of one neuron to another neuron.
• This is the fastes way of communication of neurons.

5. ELECTRICAL SYNAPSES ARE USEFULL
WHEN:
It is important to synchronise a local population of
cells.
Synchronisation is important for example in
hypothalamus: synchronised release of the
hormone in enough quantity.

6. MOLECULES THAT PASS THROUGH
THE GAP JUNCTIONS:
calcium ions
(calcium
messanger system)
ATP
other ions

7. CHEMICAL SYNAPSES
• The principal type of synapses that are found in adult nervous
system.
• They can be dendrite-axon, axon terminal-cell body or axon
terminal-another axon terminal.
• Chemical synapses are four to five time slower than electrical
synapses.
• Chemical synapses are mostly unidirectional while electrical
signals are bidirectional.

8. CHEMICAL SYNAPSES
• Transmitter is synthesized and stored in vesicles.
• Action potential invades the presynaptic terminal.
• Depolarisation of presynaptic terminal causes the
opening of voltage-gated calcium channels.
• Influx of calcium ions through the channels.
• Calcium ions cause the vesicles to fuse with presynaptic
membrane.

9. CHEMICAL SYNAPSES
• Transmitter is released into the synaptic cleft via exocytosis.
• Transmitter binds to receptor molecules in postsynaptic
membrane.
• Opening or closing of postsynaptic channels.
• Postsynaptic current causes excitatory or inhibitory
postsynaptic potential that changes the excitability of the
postsynaptic cell.
• Removal of neurotransmitter by glial uptake or enzymatic
degradation.

10. CALCIUM IONS
Sudden rise of calcium
ions in presynaptic
terminal is critical for the
release of
neurotransmitter and the
generation of an action
potential in the
postsynaptic cell.

11. SYNAPTOTAGMIN
It is a molecule in the vesicular
membrane that binds to calcium.

12. SNARE COMPLEX OF PROTEINS
SNARE complex of proteins is
involved in snaring the vesicle
membrane to the cytoplasmic
face of the presynaptic terminal.

13. CLATHRIN
• Clathrin coats the vesicle membrane.
• Interacts with other proteins (for example dynamin
protein) and there is retreival of these membranes.
• Clathrin forms triskelion.
• Triskelion can associate with other molecules and
form a ring around the vesicular membrane.

14. LITERATURE
https://www.coursera.org/learn/medical-
neuroscience/lecture: Leonard E. White, PhD,
Duke University
Quora.com