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

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Introduction

Give an account of how the monoamines act as transmitters and their roles in function in the brain Before any detailed explanations of how monoamines act as transmitters and their prime functions in the brain, I feel it is appropriate to describe what transmitters are and outline their functions in the nervous system as well as the criteria needed for a transmitter. The definition of a neurotransmitter is "chemicals that are used to relay, amplify and modulate electrical signals between neurons". (wikipedia, 2006) Moreover, for these substances to be classified as a neurotransmitter, certain criteria must be met as follows. Firstly, it is synthesized when required endogenously at the pre-synaptic side of the cell and stored in vesicles. Secondly, an adequate amount can be released to cause a response on the post-synaptic neuron. Finally, an inactivation mechanism is required to terminate its effect upon cell. Neurotransmitters are agonists and may produce fast or slow sequence of events which could be either excitatory or inhibitory. The effect is largely determined by the receptors that the neurotransmitters bind onto. Neurotransmitters are usually small molecules and are packaged into small vesicles. When a neuron receives an action potential that travels along the axon reaching the synapse, the pre-synaptic membrane of the neuron becomes depolarized. ...read more.

Middle

The most common and recognizable symptom of Parkinson's disease is the shaky hands, where patients are less able to control their motor movement. The cause of the disease is principally understood as shortage of DA and death of DA neurons in nigrostriatal pathway. Evidentially DA has an affect on the basal ganglia motor loop which impinges on the brain to control our motor movements. The frontal lobes of the brain are the region responsible for most of the neurocognitive functions, where DA controls the information flow from other sections of the brain. Any disorder in this area can bring about reduced functions in memory and attention. As mentioned before, DA plays a role in regulation of prolactin secretion in which DA act as a neuroendocrine regulator to inhibit prolactin release from anterior lobe of pituitary gland. Receptors for DA include D1, D2, D3, D4 and D5 and D2 receptors are associated with sociability. Anxiety patients are found to have low D2 receptor binding. Other behavior disorders such as depression, schizophrenia and psychosis are related to DA system disruption. Treatment for these disorders often uses the blockade mechanism of the D2 receptors or blocking the reuptake of DA transmitters. Norepinephrine (NA) belongs to the catecholamine family, which are chemicals that are made from the amino acids tyrosine. ...read more.

Conclusion

For 5-HT1 receptors, the subdivision includes 5-HT1A, 5-HT1B and 5-HT1D. Generally with selected agonists binding to the receptors their functions in the central nervous system are inhibition of neuronal effects and behavioral effects for example, sleeping, and anxiety. But for 5-HT1D it has a role in cerebral vasoconstriction. At the 5-HT2A receptors it involves neuronal excitation which is the opposite of the 1A, B subtypes as well as learning. 5-HT2C receptors are responsible for secreting cerebral spinal fluid to the spinal cord for lubrication and other functions. The 5-HT3 receptors with a selection of specific drugs binding, it brings about anxiety plus neuronal excitation. For some of the other receptors of 5-HT, their roles in the nervous system are unclear and some are responsible for the gastrointestinal tract contraction and motility; vascular constriction or dilation. Clinically, 5-HT is used in the treatment of epilepsy and depression. Although histamine is the chemical that has many involvements physiologically in the human body, it also acts as a neurotransmitter. Four histamine receptors have been discovered ranging from H1-H4. However, only the H3 receptors are mainly engaged with the central nervous system. The cell bodies in the posterior hypothalamus release histamine and it plays a part in sleeping pattern modulation. Histamine releasing disorders are associated with inability of attention maintenance. Schizophrenia also has an association with low concentration of histamine in blood level. ...read more.

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