1. SIGNAL TRANSMISSION AT
SYNAPSES
By: Mary Claire Butaya
BSPSYCH-3

2. What is a SYNAPSE?
• It is the site of communication of
neurons which consists of:
Sends the
signal
A. Presynaptic neuron (membrane)
B. Postsynaptic neuron (membrane)
Receives the
message

3. Types of Synapse
Action
A. Electrical Synapse potentials(impulses)
conduct directly between
adjacent cells through
GAP JUNCTIONS
B. Chemical Synapse Membranes are close
but do not touch with the
presence of SYNAPTIC
CLEFT

4. A. Electrical Synapse
- Transmission is DIRECT because of
gap junctions.
- GAP JUNCTIONS: contain a hundred or
so tubular connexons.
- Gap junctions are common in
visceral smooth muscle, cardiac
muscle, and the developing embryo.

6. B. Chemical Synapse
- Transmission is INDIRECT because of
synaptic cleft.
- SYNAPTIC CLEFT: a space of 20-50nm
that is filled with interstitial
fluid; separates the neurons.

7. Types of Chemical Synapses
• Axodendritic – axon to dendrite
• Axosomatic – axon to soma
• Axoaxonic – axon to axon

8. The PRESYNAPTIC NEURON converts an
electrical signal (nerve impulse)
into a chemical signal (released
neurotransmitter).

9. The POSTSYNAPTIC NEURON receives the
chemical signal and, in turn,
generates an electrical signal
(postsynaptic potential).

10. How a chemical synapse transmits a
signal
1. A nerve impulse (action potential)
arrives at a synaptic end bulb of a
presynaptic neuron.
2. the depolarizing phase of the
nerve impulse opens voltage-gated
Ca2+ channels; Ca2+ flows inward
through the opened channels.

12. 3. An increase in the concentration of
Ca2+ inside the presynaptic neuron is
the signal that triggers exocytosis
of some of the synaptic vesicles.
4. The neurotransmitter molecules
diffuse across the synaptic cleft
and bind to neurotransmitter
receptors in the postsynaptic
neuron’s plasma membrane.

14. 5. Binding of neurotransmitter
molecules to their receptors on
ligand-gated channels opens the
channels (inflow of ions).
6. POSTSYNAPTIC POTENTIAL: change in
membrane voltage. (as ions flow
through the opened channels, the
voltage across the membrane
changes.

16. 7. When a depolarizing postsynaptic
potential reaches threshold, it
triggers one or more nerve
impulses.

18. Excitatory and Inhibitory
Postsynaptic Potentials
• Excitatory: if the neurotransmitter
depolarizes the postsynaptic
membrane. (EPSP)
• Inhibitory: if the neurotransmitter
causes hyperpolarization of the
postsynaptic membrane. (IPSP)

20. Removal of Neurotransmitter
1. Diffusion
2. Enzymatic degradation
3. Uptake by cells

21. Spatial and Temporal Summation
• Spatial Summation
Results from buildup of
neurotransmitter released
simultaneously by SEVERAL
presynaptic end bulbs.

22. • Temporal Summation
Results from builup of
neurotransmitter released by
a SINGLE presynaptic end
bulb two or more times in
rapid succession.