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– 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”– 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

Healthy Brain 20 yrs. Heroin Use

Silveri, 2010Educational Purposes Only

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