Give an account of how the monoamines act as transmitters and their roles in function in the brain

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Give an account of how the monoamines act as transmitters and their roles in function in the brain

The monoamines are a group of neurotransmitters which contain only one amino acid. Examples of monoamines include the catecholamines dopamine and noradrenaline, and serotonin. They allow signals in the brain to be transmitted across the synapse from one neuron to the next; from signals of wanting and reward, to the motor control of muscles. One neurotransmitter has different functions in different parts of the brain through the action of different receptors for the same neurotransmitter. Whilst there may be several receptor proteins responsible for different functions, each monoamine has specific receptor proteins which it binds to and is thus able to affect the behaviour of the target cell. The signal sent is attenuated by reuptake of the monoamines by the transporters of the cell from which the signal was released, as well as break down by enzymes (Torres, Gainetdinov & Caron, 2003).

Monoamines are mostly found in the limbic system; the primal brain areas which are responsible for basic needs, such as hunger and sex, as well as mood and emotion. In different areas of the brain monoamines have different functions, for example in the cortex dopamine plays a role in cognition; and in the hypothalamus it influences hormonal regulation. Noradrenaline and serotonin are very important in the regulation of mood and all antidepressants function by increasing neurotransmission of the monoamines.

Pharmacological drugs act on the function of the neurotransmitters in a variety of ways. Signals can be blocked (in the case of analgesics); using chemicals which impede the receptors in the target neuron. The reuptake of neurotransmitters from the extracellular space can be impeded (Torres, Gainetdinov & Caron, 2003) which increases the magnitude of the signal transmitted (for example antidepressants) or the volume of neurotransmitter itself can be increased (for example LSD is similar in structure to serotonin). This method of treatment of both physical and psychological disorders arises from the premise that many disorders originate in neurotransmission dysfunction, or are the result of adaptation of neural activity. Whilst indirect evidence for this position exists, for example from studies of rats which have been modified to have no reuptake transporters for transmitters; a singularly genetic origin of disorders such as schizophrenia and depression is precluded by psychological variables mediating symptoms.

The effects of neurotransmission are both immediate in that they allow signals to be transmitted in the brain; and occur over time as neurotransmitters mediate the regulation of genes which affects the function of the nerve cell, in particular behaviour of the receptors. For example, stress is believed to have an effect on gene expression through the increased transmission of certain neurotransmitters (Stahl, in press). This is an example of a means by which psychological factors can have a direct result on gene expression because of neurotransmission (Stahl, in press); which may provide a critical explanation for the interdependence of biological and psychological factors in the onset of diseases such as schizophrenia and bipolar disorder.

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Monoamine neurotransmission occurs at the synapse; the space between the end of one neuron and the start of the next. Monoamine transmitters are released from vesicles where they are stored at the synapses when they are stimulated by an action potential; an electrical signal which has been transmitted down the axon of the neuron. The molecules diffuse across the synapse and then bind with receptor sites on the target neuron. Each monoamine has a specific receptor on the target neuron, in fact some have several receptors which control different effects, for example some dopamine receptors influence emotion and others ...

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