Layman's guide to synapses

The relevance of different synapse types

This page illustrates the difference between excitatory and inhibitory synapses, and the principle of how information of different synapse types can be integrated: In the shown example, the same postsynaptic terminal can be activated by excitatory transmission (A), but synchronous reception of inhibitory transmission can suppress this effect (C). This page demonstrates how synaptic integration functions at the subcellular level, whereas page 4 will show how this can be used to regulate activity of nerve cells in neuronal networks.

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The image shows a postsynaptic terminal (post) innervated by two presynaptic terminals (pre). The top one is of excitatory (Ex), the lower one of inhibitory nature (In). Of the different synaptic components only vesicles, neuro-transmitters and neurotransmitter receptors are shown (see page 2 for more details). The two terminal types use different transmitters and receptors (indicated by light and dark grey), mediating postsynaptic influx of positively or negatively charged ions, respectively. The colour code represents the voltage of the synaptic terminals relative to the extracellular milieu (which is defined as zero; white). Blue indicates negative and yellow positive voltages.
A) Transmitter release from the excitatory (Ex) presynaptic terminal induces influx of positively charged ions (plus on yellow ball) into the postsynaptic terminal causing a voltage reduction towards 0mV (white). If a certain threshold voltage close to 0mV is reached an actively propagated postsynaptic electrical message is ignited (yellow arrow). B) Transmitter release from the inhibitory terminal (In) induces influx of negatively charged ions (minus on blue balls) driving the voltage to minus 70mV (dark blue), thus further away from the threshold voltage. Consequently, no electrical message is induced. C) If both terminals release transmitter at the same time, the negatively charged ions buffer the effect usually induced by the positively charged ions. Therefore, since both synaptic responses are integrated in one common postsynaptic terminal, the threshold close to 0mV can not be reached and no postsynaptic electrical message is induced.
How are distinct synapse types used in neuronal networks? >>>