A synapse is a junction between two neurons that allows nerve impulses to be transmitted chemically or electrically. In a chemical synapse, an action potential causes calcium ions to enter the presynaptic neuron, triggering vesicles filled with neurotransmitters like acetylcholine to fuse with the presynaptic membrane and release their contents into the synaptic cleft. These neurotransmitters then bind to receptors on the postsynaptic neuron, causing ion channels to open and generating a postsynaptic potential that may be excitatory or inhibitory. Acetylcholine is removed from the synaptic cleft by diffusion and enzymatic breakdown to terminate its effect and allow subsequent impulses to be transmitted.

2. Action potential

11. Acetylcholine (Ach)