Chemical Synapses (Bk. 2, Ch. 4)

Stages in synaptic transmission (§4.2):

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Referring to the diagram of a "typical" synapse:-

Diagram of chemical synapse
1. transmitter synthesis

2. storage in vesicles

3. depolarisation and Ca2+ influx

4. release of transmitter by exocytosis

5. diffusion in synaptic cleft

6. action on post-synaptic receptors

7. effect on post-synaptic cell

8. inactivation/reuptake



 
 

Receptor gated channels (§3.9. c.f. Voltage Gated Channels)

Binding with ligand (transmitter, hormone) causes opening of channels. The kind of receptors present define the effect of a transmitter.

There are many, many different transmitters (§4.5). They act on specific receptors ("lock and key").

Sometimes the same transmitter can have different effects, by acting on different receptor sub-types, e.g. - and - adrenoreceptors (both of which bind adrenaline and noradrenaline).
 

Summation (4.3)

Excitatory post-synaptic potentials (EPSP) - depolarisation.

Inhibitory post-synaptic potentials (IPSP) - hyperpolarisation.

Post-synaptic potentials may summate (add together) both temporally or spatially.

Temporal summation: summation of PSPs occurring at different times but at the same place.

Spatial summation: summation of PSPs occurring at the same time, but at different places on the cell

Temporal and spatial summation can occur simultaneously, and may involve both IPSPs and EPSPs. allowing the post-synaptic neuron to act as an information processor (an 'integrator').
 
 
 

Manipulation of synaptic function (§4.5)

Most stages in synaptic transmission (see above) can be affected by drugs.
The actions can either enhance or depress synaptic transmission, in various ways:
Synthesis of transmitter (1)
Ca influx (3)
Transmitter release (4)
Action of transmitter at receptors on post-synaptic membrane (6)
Breakdown, inactivation, reuptake of transmitter (8)


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