Chemical synapses are dependent onneurotransmitters. Their mode of action depends on the action potential change, which causes thecalcium channelsto open. That provides the influx of Ca2+ ions into the cell, which builds up apositive chargeinside the cell. This positive charge allows the synaptic vesicles to fuse with the cell membrane, releasing theneurotransmitters(in this case, acetylcholine) that were trapped inside the vesicles.

Acetylcholine是释放到synaptic cleft, and it binds to the receptor on the membrane of the postsynaptic cell. That allows the Na+ ions to flow inside the cell, which ultimately causes the muscle to contract.

Figure 1:电气和化学Synapses

After the neurotransmitter’s message is delivered, they detach from the receptors to be degraded, recycled, reabsorbed by presynapse (reuptake), or broken down by enzymes present in the synaptic cleft. This process can be affected by certaindrugsto influence reuptake or to mimic the presence of neurotransmitters, causing the cell to wrongly assume that the signal it's receiving is a natural chemical signal.

Activation of postsynaptic receptors leads to the opening or closing of ion channels in the cell membrane. This may be depolarizing(excitatoryneurotransmitters)—make the inside of the cell more positive—or hyperpolarizing (inhibitoryneurotransmitters):—make the inside of the cell more negative—depending on the ions involved.