Chemical Synapses

Chemical synapses are specialized sites where electrical signals from a presynaptic neuron are relayed by chemical messengers, known as neurotransmitters, to the postsynaptic cell to propagate an electrical impulse.

They consist of an axon terminal of a presynaptic cell, here a neuron, containing numerous neurotransmitter-filled synaptic vesicles, a postsynaptic cell, in this case, another neuron, with neurotransmitter receptors, and the synaptic cleft, a fluid-filled space between the two.

The unidirectional information transfer at a chemical synapse begins with the arrival of an action potential at the axon terminal of the presynaptic neuron. The resulting membrane depolarization triggers voltage-gated calcium channels to open, allowing calcium ions to rush in. This calcium surge causes the synaptic vesicles to fuse with the presynaptic membrane and release neurotransmitters into the synaptic cleft.

After diffusing through the synaptic cleft, the neurotransmitters bind to specific ion channels on the postsynaptic membrane. This binding opens specific ion channels, allowing appropriate ions to enter the postsynaptic cell and initiate excitatory or inhibitory responses.