Читать книгу Abnormal Psychology - William J. Ray - Страница 78

In the chemical synapse, neurotransmitters play a critical role. Neurotransmitters transmit signals from one neuron to another (see Figure 2.8). It is also the case that psychotropic medications largely have their influence at the site of the synapse. To date, more than 100 different neurotransmitters have been identified. Neurotransmitters have been classified both in terms of structure and in terms of function. Most neurons utilize more than one type of neurotransmitter for their functioning.

neurotransmitters: chemicals released into the synaptic space that are involved in increasing or decreasing the likelihood for action potentials to be produced; they also maintain the communication across the synapse. Their presence or lack is related to particular psychopathological disorders

Regarding their structure, neurotransmitters can be classified in terms of size (Purves et al., 2013). This results in two broad categories. The first type is small molecule neurotransmitters such as glutamate, which is excitatory, and GABA (gamma-aminobutyric acid), which is inhibitory. They are often composed of single amino acids. These small molecule neurotransmitters tend to be involved in rapid synaptic functions.

Glutamate is considered to be the most important neurotransmitter in terms of normal brain function. In abnormal conditions, the firing of rapid glutamate neurons can lead to seizures in a number of areas of the brain. GABA is inhibitory, and drugs that increase the amount of GABA available are used to treat such disorders as anxiety. The second type of neurotransmitter in terms of size is larger protein molecules referred to as neuropeptides. These can be made up of 3 to 36 amino acids. Neuropeptides tend to be involved in slower, ongoing synaptic functions.

In terms of function, neurotransmitters can also be categorized into three broad groups (Nadeau, 2004). The first group includes those neurotransmitters such as glutamate and GABA that mediate communication between neurons. The second group includes those neurotransmitters such as opioid peptides in the pain system that influence the communication of information. The third group includes those neurotransmitters such as dopamine, adrenaline, noradrenaline and serotonin that influence the activity of large populations of neurons. For example, cocaine blocks the ability of a neuron to remove the neurotransmitter dopamine from the synapse, which increases the experience of addiction. (See Table 2.1 for a description of various neurotransmitters.)

Most medications used for treating mental illness influence the neurotransmitters at the synapses.

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