Introduction

Abstract

Neurotransmission systems exist in all multicellular animals and enable inter-neuronal transmission at synapses and from nerve cells to effector organs such as skeletal muscles and glands. They are complex, comprising afferent nerves, containing the neurotransmitter, where it is synthesized and stored in vesicles, from which the transmitter is released in response to a nerve impulse. At the synapse, neuromuscular junction and autonomic effector organs, there are specialized receptors where binding of the neurotransmitter induces a response. There are many different neurotransmitters, including acetylcholine derivatives of adenine: adenosine 5′-triphosphate (5ʹATP) and cyclic adenosine monophosphate; aliphatic amino acids: glycine, glutamic acid (glutamate), aspartic acid (aspartate) and γ-aminobutyric acid (GABA), possibly β-alanine; and derivatives of aromatic amino acids: adrenalin, noradrenalin, dopamine, 5-hydroxytryptamine (5HT or serotonin) and histamine. Neurotransmission occurs in all multicellular animals and enables the transmission of information from neuron to neuron and from neurons to other tissues, including muscles and glands. The mechanisms underlying neurotransmission are complicated and include pre-junctional synthesis, storage and release of transmitter substances, as well as the release of transmitters in response to nerve impulses and their binding to receptors. Termination of transmission involves both the hydrolysis of transmitters and reuptake into pre-junctional nerve terminals.