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|a لقد ألقينا في هذا العرض نظرة عامة موجزه على الأساس البيولوجي للاعتماد على المواد النفسية. وتعمل المفاهيم التي حاولنا تلخيصها هنا بطريقة ما على فهم أسباب تعاطي بعض الأشخاص وأسباب اعتمادهم على المواد النفسية، كما يمكن أن تساعد في توجيهنا في تطوير العلاج الفعال واستراتيجيات الوقاية. ونحن نعتقد أن فهم بيولوجيا الاعتماد يعد أمرا حيويا لفهم السلوك الإدماني ولكنه، في نهاية المطاف، لا يمثل إلا جزء من القصة الكاملة.
|b The administration of drugs such as alcohol, nicotine, heroin or cocaineinvolves addiction. In order to understand how drugs affect us and why people continue to use them, we must first understand how they affect us biologically. The drugs of abuse and dependence with which we're interested all have their primary effects in the brain. They interact with cells within certain structures in the brain, and by so doing, they change our biological functions (like heart rate, blood pressure and sweating), how we feel and think (psychology) and how we act (behavior). Most drugs will also have actions in other parts of the body, but for the drugs of dependence, the brain is the most important site of action. A key point is that all the drugs of abuse produce a sought after or pleasurable effect; that is, they are rewarding to us in some way, either by providing a sought after positive effect or removing some form of discomfort. All the drugs of dependence will produce a positive emotional response by releasing a neurotransmitter called dopamine in the reward pathway, which is the part of our brain responsible for emotions. If those drugs can reach the brain quickly and effectively, because of either their chemical structure or how they are administered, then it is more likely that they will reinforce continued drug use and it is more likely that we may become dependent on that drug. After repeated use of a particular drug, our brain will adapt to its presence in such a way that we may only feel 'normal' when the drug is present. We may find that we need to use more and more of the drug to achieve the sought after effect, and we may experience depression, anxiety and a range of unpleasant physical symptoms when we try to stop using the drug. To understand the biological basis for these common effects of drugs of abuse, we must start by looking at what happens to the drug when it enters the body. We must consider how we take the drug - do we smoke it, inject it or drink it? These different routes of administration not only change how long it takes for us to feel the effect of the drug but also how intense those effects will be and how long they will last. Once administered, how does the drug reach the brain? These phases we call absorption and distribution. Finally, how does the amount of drug in our body change over time? The effects of the drug will eventually wane; the body will break down the drug molecules and remove it - these phases we call metabolism and excretion. All these stages of drug action affect patterns of drug use; how much we take, how often and how long is needed to recover from the effects. Within the brain, drugs mostly work on proteins namely receptors, enzymes, neurotransmitter carriers and ion channels. Receptors are protein molecules that recognize and respond to endogenous chemical compounds called neurotransmitters, which send messages between the cells in the brain. Individual classes of drugs bind only to certain receptors, while receptors only recognize certain classes of drugs. Drugs may either increase or decrease the activity of structures and pathways within the brain. Finally, if we take a drug on a continuing basis, the body will gradually adapt, leading to a reduction in the effect of the drug. This may possibly lead us to increase the amount and frequency with which we use the drug. Eventually we may find that we need to use the drug frequently just to feel 'normal'. These issues of tolerance and physical dependence on a drug are central to understanding the long-term abuse of drugs and addictive behavior.
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