Biomedical Engineering Reference
In-Depth Information
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Figure 6.1:
Voltages and concentrations of the synapse.
6.1 NEUROTRANSMITTERS
Neurotransmitters are the chemicals that relay electrical signals from the pre-synapse of one neuron
to the post-synapse of another neuron. There are approximately ten known neurotransmitter that are
classified in two different ways. The first classification is by molecular makeup where amino acids (e.g.,
glutamate, GABA), amines (e.g., epinephrine, dopamine, serotonin) and peptides (e.g., acetylcholine) are
the dominate types. However, there are many other molecules (e.g., vasopressin, neurotensin, insulin) and
ions (e.g., zinc) that can impact synapses indirectly and are sometimes considered neurotransmitters.The
second classification is by function, where some neurotransmitters induce depolarization (called
excitatory
transmitters
) and some induce hyperpolarizations (called
inhibitory transmitters
).The action of one type of
neurotransmitter may, however, be excitatory in one region of the nervous system while being inhibitory
in other regions. Furthermore, some neurotransmitters have other functional roles. For example, in a
developing brain, neurotransmitters can act to guide and strengthen synaptic connections.
6.2 THE PRE-SYNAPSE
The release of neurotransmitter at the pre-synapse is commonly modeled in one of three ways that vary
in complexity. The most complex is to model the binding of
Ca
2
+
, activation of the vesicle, and release
as separate steps. For example,
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