... onto. Neurotransmitters are usually small molecules and are packaged into small vesicles. When a neuron receives an action potential that travels along the axon reaching the synapse, the pre-synaptic membrane of the neuron becomes depolarized. This leads to the opening of calcium channels and an influx of calcium ions, which causes the vesicles to be released by exocytosis to the synaptic cleft and the neurotransmitter molecules are then free to bind to receptors that sits on the post-synaptic membrane of the neuron. Neurotransmitter receptors are commonly divided into two types: the ionotropic receptors and the metabotropic receptors. The first group of receptors is ligand-gated ion channels and its opening or closure of channel depends on the binding of neurotransmitters. The rate of transmission for ionotropic receptors is fast. The latter group passes on signals through second messengers such as G-proteins and they have slower neuromodulation. There are three major categories ...

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