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Chemical signaling between neurons is mediated by neurotransmitters, neuropeptides, hormones, neuromodulators, and many other types of signaling molecules. Many neurological diseases arise due to an imbalance in the brain's neurochemistry. For example, in Parkinson's Disease, there is an imbalance in the brain's level of dopamine.
Illustration of the major elements in chemical synaptic transmission. An electrochemical wave called an action potential travels along the axon of a neuron.When the wave reaches a synapse, it provokes release of a puff of neurotransmitter molecules, which bind to chemical receptor molecules located in the membrane of another neuron, on the opposite side of the synapse.
Artistic interpretation of the major elements in chemical synaptic transmission. An electrochemical wave called an action potential travels along the axon of a neuron.When the action potential reaches the presynaptic terminal, it provokes the release of a synaptic vesicle, secreting its quanta of neurotransmitter molecules.
Chemical synapses are characterized by the presynaptic release of neurotransmitters that diffuse across a synaptic cleft to bind with postsynaptic receptors. A neurotransmitter is a chemical messenger that is synthesized within neurons themselves and released by these same neurons to communicate with their postsynaptic target cells. A receptor ...
The axon leaves the soma at a swelling called the axon hillock and travels for as far as 1 meter in humans or more in other species. It branches but usually maintains a constant diameter. At the farthest tip of the axon's branches are axon terminals, where the neuron can transmit a signal across the synapse to another cell. Neurons may lack ...
Neurons expressing certain types of neurotransmitters sometimes form distinct systems, where activation of the system affects large volumes of the brain, called volume transmission. Major neurotransmitter systems include the noradrenaline (norepinephrine) system, the dopamine system, the serotonin system, and the cholinergic system, among others.
The two main chemical messengers of the sympathoadrenal system are norepinephrine and epinephrine (also called noradrenaline and adrenaline respectively). These chemicals are created by the adrenal glands after receiving neuronal signals from the sympathetic nervous system. The different physiological effects of these chemicals depend on the ...
Neuromodulation is the physiological process by which a given neuron uses one or more chemicals to regulate diverse populations of neurons. Neuromodulators typically bind to metabotropic, G-protein coupled receptors (GPCRs) to initiate a second messenger signaling cascade that induces a broad, long-lasting signal.