Neurochemistry

Communication between neurons occurs primarily at the level of synapses. The most common form of communication in the nervous system is through chemical synapses, which consist of presynaptic and postsynaptic components separated by a synaptic cleft. The presynaptic terminals contain synaptic vesicles, which are involved in the storage and release of neurotransmitters by the process of exocytosis. Complex mechanisms control the synthesis, vesicular storage, and release of neurotransmitters and regulate the availability of neurotransmitter at the level of the synaptic cleft. The effects of the neurochemical transmitter on its target are mediated by neurotransmitter receptors. Specific neurotransmitter systems are responsible for fast neuronal excitation or inhibition, while other neurotransmitter systems regulate the excitability of neurons in the nervous system. Abnormalities in neurochemical transmission are responsible for many disorders, including acute neuronal death, seizures, neurodegenerative disorders, and psychiatric diseases. Most importantly, neurochemical systems provide the target for pharmacologic treatment of these disorders. The aims of this chapter are to review the basis of neurochemical transmission and the distribution, biochemistry, and function of specific neurotransmitter systems.