Chemical synapses

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

Acetylcholine is released into the 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: Electrical and Chemical 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 certain drugs to 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( excitatory neurotransmitters)—make the inside of the cell more positive—or hyperpolarizing (inhibitory neurotransmitters):—make the inside of the cell more negative—depending on the ions involved.