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PS263 (139)
Chapter 15

Chapter 15--BIOPSYCH.docx

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Wilfrid Laurier University
Bruce Mc Kay

Chapter 15 Drug Addiction and the Brains Reward Circuits Chemicals that Harm with Pleasure151 Basic Principles of Drug Action Psychoactive drugsdrugs that influence subjective experience and behaviour by acting on the nervous system Drug Administration and Absorptiondrugs are usually administered in 1 of 4 ways 1Oral Ingestion The preffered route once swallowed the drugs dissolve in the fluids of the stomach and are carried to the intestine where they dissolve into the blood Some readily pass through the stomachdont need to reach the intestinealcoholso they take effect sooner2 main advantages of oral ingestion its ease and relative safetyDisadvantage unpredictability can be influenced by factors such as amount of food in stomach2InjectionEffects are strong fast and predictableTypically made subcutaneously SC into fatty tissue just beneath the skin intramuscularly IM into the large muscles or intravenously IV directly into veins preferreddelivers drugs directly to the brainmany addicts develop scar tissue infections collapsed veinstheres little opportunity to counteract the effects of overdose3InhalationAbsorbed into the bloodstream through the rich network of capillaries in the lungsie tobaccomarijuanaDisadvantages difficult to regulate the dosage and can damage the lungs if inhaled chronically Absorption Administered through the mucous membranes of the nose muth and rectumie cocaine through nasalDrug Prevention of the CNSOnvce a drug enters the bloodstream it is carries to the blood vessels of the CNSFortunately a protective filter called the bloodbrain barrier makes it difficult for dangerous bloodborne chemicals to pass from the vessels into neurons Mechanisms of Drug AddictionSome drugs act on the neural membranes of the CNS alcohol others act more specifically by binding to particular synaptic receptors by influencing synthesis transport release or deactivation of particular neurotransmitters or by influencing the chain of chemical reactions elicited in postsynaptic neurons by the activation of their receptors Drug Metabolism and EliminationMost drugs are terminated by enzymes synthesized in the liver which convert the active drugs to non active formsdrug metabolism Usually eliminates drugs ability to pass through lipid membranes so it cant penetrate the bloodbrain barrierSmall amounts are passed from the body in urine sweat feces breath and mothers milkDrug tolerance Drug tolerancestate of decreases sensitivity to a drug that develops as a result of exposure to itCan be administered in 2 ways 1 by showing the a given dose of the drug has less effect than it had before drug exposure 2 by showing that it takes more of the drug to produce the same effect 3 important points to remember about the specificity of drug tolerance 1Cross toleranceone drug can produce tolerance to other drugs that act by the same mechanism2Drug tolerance often develops to some effects of a drug but not to others Tolerance may develop to some effects while sensitivity to other effects increases Increased sensitivitydrug sensitization 3Drug intolerance isnt a unitary phenomenon there isnt a single mechanism that underlies all examples2 categories of change underlie drug tolerance 1Metabolic toleranceresults from changes that reduce the amount of the drug getting to its sites of action2Functional toleranceresults from changes that reduce the reactivity of the sites of action to the drugDrug Withdrawal Effects and Physical Dependence Withdrawal syndromean adverse physiological reaction triggered by sudden elimination after significant amount of a drug have been in the body for a long period of timeeffects are virtually always opposite to the initial effects of the drug Individuals who suffer withdrawal reactions when they stop taking s drug are said to be physically dependent Severity of withdrawal symptoms depends on the drug the degree of the proceeding exposure and the speed with which the drug is eliminated from the body
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