Layman's guide to synapses

What is synaptic transmission? How can it be used to influence information flow in neuronal circuits?
Synapses are so important because they regulate information flow in neuronal circuits. They achieve this by adapting the amplitude and frequency of transmission between neurons: At chemical synapses transmission occurs via translation of an electrical signal into chemical information and back into an electrical signals. Electrical signals are focal voltage changes migrating along the cell surface (yellow zig zag arrows). In the signal-sending (presynaptic) neuron incoming electrical signals trigger opening of calcium pores (voltage-gated calcium channels; green). Inflowing calcium (Ca2+) modifies certain presynaptic molecules which in turn mediate fusion of presynaptic vesicles. These vesicles contain and release a chemical substance (neurotransmitter; red dots) which diffuses across the synaptic cleft where it binds to postsynaptic receptors (red). These receptors translate the message back into an electrical signal by inducing ion currents across the membrane. Depending on the type of receptor channel the inflowing ions can be positively or negatively charged. This will determine whether transmission is excitatory or inhibitory (see next page).

This form of transmission seems complicated, but it allows regulation of the transmission process by blocking, facilitating or otherwise altering each single step of the procedure explained above. Such regulations are key features of functional nervous systems and their capability to learn and memorise.

Different synapse types use different transmitters and receptors. What are the implications? >>>