Neurotransmitters

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Neurotransmitters
Neurotransmitters are chemicals made by neurons and used by them to transmit signals to the other neurons or non-neuronal cells (e.g., skeletal muscle; myocardium, pineal glandular cells) that they innervate. The neurotransmitters produce their effects by being released into synapses when their neuron of origin fires (i.e., becomes depolarized) and then attaching to receptors in the membrane of the post-synaptic cells. This causes changes in the fluxes of particular ions across that membrane, making cells more likely to become depolarized, if the neurotransmitter happens to be excitatory, or less likely if it is inhibitory.
Neurotransmitters can also produce their effects by modulating the production of other signal-transducing molecules ("second messengers"messengers") in the post-synaptic cells (Cooper, Bloom and Roth 1996). Nine compounds -- belonging to three chemical families -- are generally believed to function as neurotransmitters somewhere in the central nervous system (CNS) or periphery. In addition, certain other body chemicals, for example adenosine, histamine, enkephalins, endorphins, and epinephrine, have neurotransmitter-like properties, and many additional true neurotransmitters may await discovery.

The first of these families, and the group about which most is known, is the amine neurotransmitters, a group of compounds containing a nitrogen molecule which is not part of a ring structure. Among the amine neurotransmitters are acetylcholine, norepinephrine, dopamine, and serotonin.
Acetylcholine is possibly the most widely used neurotransmitter in the body, and all axons that leave the central nervous system (for example, those running to skeletal muscle, or to sympathetic or parasympathetic ganglia) use acetylcholine as their neurotransmitter. Within the brain acetylcholine is the transmitter of, among other neurons, those generating the tracts that run from the septum to the HIPPOCAMPUS, and from the nucleus basalis to the CEREBRAL CORTEX -- both of whbasalis to the CEREBRAL CORTEX -- both of which seem to be needed to sustain memory and learning. It is also the neurotransmitter released by short-axon interneurons of the BASAL GANGLIA.
Norepinephrine is the neurotransmitter released by sympathetic nerves (e.g., those innervating the heart and blood vessels) and, within the brain, those of the locus coe...

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...d at the axon endings of motor neurons, where they stimulate the muscle fibers to contract. And they and their close relatives are produced by some glands such as the pituitary and the adrenal glands. In this chapter, we will review some of the most significant neurotransmitters.
Acetylcholine was the first neurotransmitter to be discovered. It was isolated in 1921 by a German biologist named Otto Loewi, who would later win the Nobel Prize for his work. Acetylcholine has many functions: It is responsible for much of the stimulation of muscles, including the muscles of the gastro-intestinal system. It is also found in sensory neurons and in the autonomic nervous system, and has a part in scheduling REM (dream) sleep.
The well-known poison botulin works by blocking acetylcholin, causing paralysis. The botulin derivative botox is used by many people to temporarily eliminate wrinkles --a sad commentary on our times, I would say. On a more serious note, there is a link between acetylcholine and Alzheimer's disease: There is something on the order of a 90% loss of acetylcholine in the brains of people suffering from that debilitating disease.

Bibliography

Biopsychology, pinel 2002

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