Detail and evaluate the role of any one of the neurotransmitters using examples of direct measurement and/or manipulation
All neurotransmitters are essential for the organisation of the body system, as they are chemicals through which neurons communicate. Neurons are specialised cells of the nervous system specialised cells that bring sensory information to the brain and perform other functional roles such as the processing of thoughts, actions, memories and behaviours (Martin, Carlson, Buskist, 2010). The communication between neurons is are essential to maintain these functions, which is why involvement of neurotransmitters concerning this process cannot be ignored. This essay will focus on the role of dopamine, a neurotransmitter in the central nervous system (CNS) that consists of the brain and the spinal cord. The psychological importance of dopamine in the human behavioural, emotional, cognitive and physical processes will be discussed, using examples of direct measurements and manipulations from ranges of empirical studies. Given the location of dopamine in the CNS, its main function relates to the organisation of the brain. So far, three major dopaminergic pathways have been discovered in the CNS. The first, mesolimbic pathway, runs from group of cell in the midbrain to other parts of the limbic system, nucleus accumenbens, amygdala and frontal cortex. The second, nigrostriatal pathway, consists of cells in the substantia nigra and basal ganglia, terminating in the corpus striatum. Lastly, the tuberohypophyseal system runs through the hypothalamus to the pituitary gland. The role of dopamine in relation to these pathways will be examined in the below paragraphs (Rang & Dale, 2007). It has been established that dopamine plays a critical role in the human behaviour processes. The imbalances of dopamine in the mesolimbic pathway has been linked to psychological disorders such as Attention Deficit Hyperactivity Disorder (ADHD) and schizophrenia, suggesting that the hyperactivity of dopamine in this pathway results to symptoms of hallucination and delusion in schizophrenia, as well as hyperactivity in ADHD patients (Laruelle & Abi-Dargham, 1999; Meisenzahl, Schmitt, Scheuerecker & Möller, 2007.). This suggestion was verified through the effect amphetamine, a drug that releases dopamine, had on rats in a study conducted by Ungerstedt (1968, as cited in Rang & Dale, 2007). Subsequent to the administration of the dopamine agonist, (amphetamine) rats began to show abnormal social interaction such as aggressive behaviours, withdrawal and gnawing. Besides, the fact that one of the treatments of schizophrenia entails the administration of dopamine antagonists – drugs that block the transmission of dopamine – highlights the role of dopamine in human behavioural processing (Rang & Dale, 2007). Furthermore, a positron emission tomography (PET) demonstrated the role of dopamine in the processing of emotion (Badgaiyan, Fischman & Alpert, 2009). A PET scan displays the location of a radioactive substance injected into the brain, tracing where a particular neurotransmitter is located and what activates it (Martin et al, 2010). Participants in this study were injected with a dopamine ligand, (a radioactive substance that binds to a dopamine receptor) followed by the presentation of a list of emotional connotations such fire and blood. Interestingly, the results of the study provided a first direct evidence of dopaminergic involvement in human emotional process, indicating that an alteration to the neurotransmitter in certain areas of the brain could cause impairment to the processing of emotional activity. The PET scan portrayed the increase of dopamine concentration in the amygdala pathway during the emotional task, representing dopamine’s role in relation to this pathway. The evidence presented in Badgaiyan et al, (2009) study supports the proposal that the inactivation of dopamine in the amygdala region of human brain leads...
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