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Summary Block 4 The Human Body Problem 4
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Summary for Problem 4 in Block 4 of 1st year psychology
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Problem 4- Pinel 9E – Toates 3EPsychoactive drugs: drugs that influence subjective experience and behavior by acting on
the nervous system
Drugs are administered in 4 ways; the route od administration influences the rate at which
and the degree to which the drug reaches its sites of action in the body
1. Oral Ingestion: this is preferred for many drugs. Once they are swallowed, drugs
dissolve in the fluids of the stomach and are carried to the intestine to be absorbed
into the bloodstream. However, some drugs pass through the stomach wall like
alcohol and they show the effect sooner. Drugs that are not absorbed by the
digestive tract or get broken into inactive metabolites must take another route.
Advantages: ease and relative safety Disadvantages: can be influenced by the type or
amount of food you eat
2. Injection: this type is common for medical practice because the effects are strong,
fast and predictable. Injections can be made subcutaneously (into the fatty tissue
beneath the skin), intramuscularly (into large muscles), or intravenously (directly
into veins where they run beneath the skin). Many addicts prefer intravenous
because the bloodstream brings the drug directly to the brain. However, this speed
and directness could be dangerous because there is no opportunity to prevent an
overdose. Plus, addicts have scarred tissues, infections and collapsed veins.
3. Inhalation: absorbed through the rich network of capillaries in the lung. Nicotine,
marijuana and anesthetics are inhaled. But it’s hard to regulate the dosage precisely
and many substances damage the lungs
4. Absorption through mucous membranes: administered through nose, mouth or
rectum. For example, cocaine is snorted, but it damages the nasal membranes
When drugs enter the body, they are carried to the blood vessels of the central nervous
system. The blood-brain barrier makes it difficult many dangerous chemicals from the blood
vessels into the CNS neurons.
Mechanisms: Some drugs act diffusely on neural membranes throughout the CNS. Others:
- bind into particular synaptic receptors
- influence the synthesis transport, release and deactivation of neurotransmitters
- influence the chemical reaction chain in postsynaptic neurons by activating their
receptors
Elimination: Most drugs are terminated by enzymes synthesized by the liver.
Drug Metabolism: liver enzymes stimulate the conversion of active drugs into a non-active
form. Drug metabolism eliminates a drug’s ability to pass the lipid membranes of cells so
they can’t penetrate the blood-brain barrier.
Tolerance: decreased sensitivity to a drug that develops as a result of exposure. This can be
in two ways: by showing that a given dose has less effect that it had before exposure or by
showing it takes more of the drug to produce the same effect
3 important points:
- One drug can produce tolerance to other drugs that act by the same mechanism: This
is called cross tolerance
, - Drug tolerance often develops to some effects of a drug but not to the other effects.
In fact, sensitivity to some effects of the same drug might increase. This is called drug
sensitization.
- Tolerance doesn’t have a single mechanism that underlies all examples. Many kinds
of adaptive changes can occur in the body the reduce the effects of the drug.
Two categories of changes underlie drug tolerance:
- Metabolic tolerance: tolerance that result from the changes that reduce the amount
of drug getting to its sites of action
- Functional tolerance: tolerance that result from the changes that reduce the
reactivity sites of action
- Tolerance to psychoactive drugs is mostly functional. These can result from several
different types of neural changes: reducing the number of receptors, decreasing the
binding efficiency to existing receptors, diminish the impact of receptor binding on
the activity of the cell
Learning tolerance:
1. Contingent drug tolerance: develops only to drug effects that are actually
experienced. Most studies of contingent drug tolerance employ the before-after
design: two groups of subjects receive the same dosages and same series of test but
one group takes the drugs before the tests and the other group take the drugs after
the tests. The group that takes the drugs before the test/stimulation became tolerant
to the drug. It focuses on what the subjects do while they are under the influence of
the drug
2. Conditioned drug tolerance: tolerance effects are maximally expressed only when a
drug is taken in the same situation which it has previously been taken. Situational
specificity of drug tolerance: the effect is large, reliable and general. Addicts may be
particularly susceptible to effects of a drug overdose when the drug is taken in a new
context.
Addicts become tolerant when they repeatedly take their drug in the same
environment. (Siegel – 1982) They view each incidence of drug administration as a
Pavlovian conditioning trial.
Withdrawal Syndrome: after significant amounts of a drug have been in your body for a
period of time, it’s sudden elimination can trigger an adverse physiological reaction. The
effects of withdrawal are always the opposite of to the initial effects of the drug. People who
suffer withdrawal reactions when they stop a drug are physically dependent on that drug.
Longer exposure to greater doses has rapid elimination that cause greater withdrawal effect.
These effects may be produced by the same neural changes that produce tolerance (bc it’s
the opposite effect)
Drug Addicts: are habitual drug users who continue to use despite its adverse effects on
their health. They sometimes take drugs to prevent their withdrawal symptoms but that is
not the major motivating factor. Drugs are not the only substances to which humans get
addicted (gambling, food, internet etc.)
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