How is propagation of action potentials terminated once the message has been sent/received?

An action potential is terminated when it reaches the synaptic terminal and voltage-gated calcium channels are activated. The action potential travels down the axon of the neuron to its terminal, which is the end of the axon where it meets the next neuron or target cell at a synapse. When the action potential reaches the synaptic terminal, it causes the voltage-gated calcium (Ca²⁺) channels in the terminal membrane to open.  The influx of calcium causes synaptic vesicles containing neurotransmitters to fuse with the terminal membrane, releasing their contents into the synaptic cleft. Neurotransmitter action is ended through enzymatic breakdown, reuptake, and diffusion. During breakdown, enzymes in the cleft degrade neurotransmitters. The neurotransmitters are then reabsorbed into the presynaptic neuron. Lastly, the neurotransmitters diffuse away from the synaptic cleft.