Neurons communicate with each other by releasing chemical messengers called neurotransmitters. Neurotransmitters are found at the end of a neuron axon, called the presynaptic terminal.

These chemicals are released in response to an electrical stimulation (the traveling action potential). Another neuron then detects the neurotransmitters by specific receptors at its postsynaptic membrane.

Activation of these receptors by an excitatory neurotransmitter causes Na+ channels to open, which starts of another action potential in the second neuron.
Activation by an inhibitory neurotransmitter stops the flow of action potential.

  • Examples of excitatory neurotransmitters are such as acetylcholine, glutamate, dopamine, epinephrine and norepinephrine.

  • An example of an inhibitory neurotransmitter is GABA.

To recap, an electrical flow that reaches the end of a neuron causes the release of neurotransmitters. A second neuron detects the neurotransmitter, which could cause an action potential to start and flow in the second neuron.

* Neurotransmitters are NOT taken up by the second neuron. They are either destroyed or recycled back to the presynaptic terminal of the first neuron, after release from the receptor on the second neuron.

* At the presynaptic terminal: When an action potential reaches the terminal, it opens up voltage-gated Ca2+ channels and causes Ca2+ ions to enter into the terminal of the neuron. Ca2+ then causes the synaptic vesicles to fuse with the presynaptic membrane, thus releasing the neurotransmitter into the synapse.

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