PSYC 2410 Chapter Notes - Chapter 15: Central Nervous System, Drug Metabolism, Opiate

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15.1- Basic Principles of Drug Action
- psychoactive drugs- drugs that induce subjective experienve and behavuour bgy
acting
on the nervous system
Drug Administration and Absorption
- four ways in which drugs are administered:
- 1) oral ingestion - preferred route of drug administration.
- Dissolve in stomach, carried to intestine where they are then absorbed into
the
bloodstream
- alcohol passes through the stomach,; take effect sooner
- two main advantages: 1) ease and 2) relative safetly
- disadvantage: unpredictability-absorption greatly influenced by other factor
such
as amount and type of food in stomach
- 2) injection- effects are strong, fast and predictable
- typically made subcutaneously (SC) (just beneath the skin, intramuscularly
(IM)
(into the large muscles) or intraveneously (IV) (directly into veins at points
where
they run justv beneath the skin)
- IV directs drug directly to brain; little or no opportunity to counteract the
effects of
an overdose or an impurity
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- 3) inhalation
- drugs can be absorbed into bloodstream by capillaries in the lungs
- two main shortcomings: difficult to recisely regulate the dose of inhaled
drugs and
many substances damage lungs if theuy are inhaled chronically
- 4) absorption through the mucous membvranes of the nose, mouth, or rectum
Drug Penetration of the Central Nervous System
- once drug enters bloodstream, it is carried into the CNS
- protective blood-brain barrier makes it difficult for dangerous chemicals to
get past
Mechanisms of Drug Action
- drugs such as alcohol and anesthetics act diffusely on on neural membranes
throughout
the CNS
- others bind to paticular synaptic receptors by influencing the suynthesis,
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 Elimination
- actions of most drugs are terminated by enzymes synthesized by the liver
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- drug metabolism - liver enzymes stimulate the conversion of active drugs to
nonactive
forms
- -eliminates a drug's ability to pass through lipid membranes of cells so that
it can no
longer penetrate the blood-brain barrier
Drug Tolerance
- drug tolerance- state of decreased sensitivity to a drug that develops as a
result of
exposure to it
- demonstrated in two ways: drug has less effect than it had before drug
exposure or by
showing that it takes more of the drug to produce the same effect
- drug tolerance is a shift in the dose-response curve( a graph of the
magnitude of
different doses of the drug)
- cross tolerance- one drug that can produce tolerance to other drugs that acts
by the same
mechanism
- drug tolerance often develops to some effects of a drug but not to others
- drug sensitization - increasing senstivity to a drug
- drug tolerance not a unitary phenomenon
- two categories of change underlie drug tolerance:
- metablic tolerance: results from changes that reduce the amount of the drug
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