How do psychoactive drugs
affect the nervous system?
What is the cliché image of a “stoner”?
• Confused?
• Low-ambition?
• Messed up?
• Why?
– We see the effects of
heavy drug use…
– What’s going on in
the body and brain?
Source:
http://blogs.tampabay.com/80s/2006/01/index.html
We’ve studied how the neurons work
• A stimulus makes the first neuron fire
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The message travels from neuron to neuron
“Pathway” in the system, and in the brain.
• Neurotransmitters
–
–
flow across the synapses
carry messages from one neuron to the next.
• Every neuron: all-or-nothing response
• After firing, neuron needs to recharge
–
Refractory period.
Source: http://thedea.org/theneuron.html
“Pleasure Pathway” in the brain
• Specific set of neurons
• When good things happen,
– Message travels along the same path in
your brain
– Connected to parts of brain regulating
behavior and memory
– Encourages repeat behavior
• The neurotransmitter involved:
DOPAMINE
“Drugs of choice” BYPASS the senses
• …and stimulate the Pleasure Pathway
• ALL DOCs stimulate release of dopamine
– Different drugs do other things as well
– They all have this in common.
• Explains part of the appeal: rush of pleasure
– Many people seek to repeat that feeling
• Pleasure pathway connected to parts of the brain that
manage behavior and memory…
So, what’s the problem?
• Artificial substances produce
overwhelming AMOUNT of dopamine
– And/ or, they block re-uptake
• Very large numbers of neurons fire
– No refractory period
• It exhausts the system
– Neurons exhaust their ability to
communicate.
Once the drugs are gone…
• Short-term: user feels the opposite of the drug
– “Rebound effect” while the neurons recover.
• Over time: the brain adapts
– Reduces the number of dopamine receptor sites
– Produces less dopamine
• Result: tolerance
– User needs larger dose to feel the pleasure rush.
• Maybe: Dependence
– User needs small doses just to function normally.
Source: http://www.askdrjones.com/?s=Carbohydrate+Craving
Dopamine does more than
communicate pleasure
• Dopamine stimulates communication along
two other pathways
– 1: hormonal regulation, nurturing behavior and
sensory processes
– 2: motor control
• Death of cells in this pathway result in Parkinson’s
Disease
Drugs affect other neurotransmitters
• Seratonin
– Sleep, regulation of body temperature, mood,
pain and appetite.
• Anti-depressant drugs block reuptake of seratonin
• GABA (antagonist) and Glutamate (agonist)
– Brain keeps these in balance, but depressants and
stimulants push them out of balance.
Drugs affect several parts of the brain
• Case study: alcohol. A depressant.
• Boosts GABA and dopamine.
– 1st to show depressed affects: cerebral cortex
• Judgment, strategy, thinking
• Your judgment is the first thing to go.
– Why do drunk people insist they can drive?
– Next to be affected: cerebellum
• Coordination
– Why can’t drunk people drive safely?
– Hippocampus
• Memory
– Large doses: the hindbrain
• Heart, breathing
Long-term effects of use
• Long-term, brain seeks “homeostasis”
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–
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BALANCE– your body’s natural level of activity.
Reduces # of receptor sites on your dendrites
Reduces amount of neurotransmitters produced
Changes last for some time
• Not clear when they become permanent.
• Numerous brain sectors show reduced activity
– Research: rats dependent on cocaine show sharply
reduced brain activity
• Even after 100 days with no drug
Silveri, 2010
Educational Purposes Only
Healthy Brain
20 yrs. Heroin Use
Decreased white matter, increased CSF (cerebrospinal fluid)
White matter is where the axon terminals, dendrites are-communication portion of the neurons.
ALL “drugs of choice”…
• Deliver a flood of dopamine… pleasure
– Alter judgment, inhibition, level of excitement
• Deliver a rebound effect once the drug is out
of the system
– Neurons need to recover from over-stimulation
– Person feels the opposite of the drug effect
• Pose the risk of long-term damage
– The dendrites and axon terminals change