Chapter 1. Psychoactive Drugs

1.1 Psychoactive Drugs

Psychoactive drugs alter perception, thinking, and mood. They do this by interfering with the normal activity of neurotransmitters, the brain's chemical messengers.

Depressants: Psychoactive drugs that reduce neural activity and slow body functions. Examples: Alcohol, barbiturates, opiates such as morphine or heroin.

Stimulants: Psychoactive drugs that excite neural activity and speed up body functions. Examples: Caffeine, nicotine, cocaine, amphetamines.

Hallucinogens: Psychoactive drugs that distort perception and may create hallucinations (false sensory experiences). Examples: LSD, marijuana (THC), mescaline.

On the next screens, we'll take a closer look at how some specific drugs influence neurotransmitter activity within a synapse.

1.2 Psychoactive Drugs

Most neural communication begins with the release of chemical neurotransmitters from the axon terminal. The axon terminal of this neuron has formed a synapse with the dendrite of another neuron. As you zoom in for a closer look, notice the receptors on that dendrite's membrane surface.

Inside the axon terminal, tiny sacs called synaptic vesicles hold the neurotransmitters.

When stimulated, the vesicles migrate toward the axon's presynaptic membrane, and release their neurotransmitters into the synaptic gap.

The neurotransmitters bind with specialized receptors on the postsynaptic membrane of the next neuron. Every receptor site as a lock, and a specific neurotransmitter type as a key that fits into and opens the lock.

1.3 Psychoactive Drugs

What happens to the neurotransmitters after they have served their purpose in sending the message to the next neuron? Normally, they are removed from the synapse in three ways:

Reuptake: The neurotransmitters pass back through the axon terminal membrane and reenter the synaptic vesicles, ready for the next release.

Breakdown: Enzymes disassemble the neurotransmitters into their component parts, so they can no longer bind with receptors.

Dispersal: Some of the neurotransmitters simply drift out of the synaptic region.

1.4 Psychoactive Drugs

Some psychoactive drugs bind directly to the receptors on the postsynaptic neuron, either activating those receptors or preventing them from being activated by neurotransmitters.

Nicotine (shown here in yellow) is an example of a drug that resembles the actual neurotransmitter so closely that it can bind to and activate the receptors in this synapse, enhancing the normal effect of the neurotransmitter.

Haldol (shown in blue) is similar enough to the actual neurotransmitter that it can bind to the receptors, but not similar enough to activate them. So Haldol reduces the normal effect of the neurotransmitter.

1.5 Psychoactive Drugs

Other psychoactive drugs do not bind to receptors, but instead increase the effectiveness of the normal neurotransmitters by blocking their reabsorption into the presynaptic membrane. Prozac is an example of a selective serotonin reuptake inhibitor (SSRI), which makes more serotonin available in the synapse.

Prozac (shown here in red) blocks the activity of proteins on the presynaptic membrane that normally recover the serotonin neurotransmitter molecules from the synaptic gap.

By slowing the serotonin reuptake process, Prozac keeps the serotonin molecules in the synaptic gap for an extended period of time, significantly increasing their mood-boosting effect.

1.6 Psychoactive Drugs

Other drugs increase the effectiveness of the normal neurotransmitters by blocking the enzymes that break the neurotransmitters down. Nardil is an example of a monoamine oxidase inhibitor (MAOI), which makes more neurotransmitters available in the synapse.

Nardil (shown here as red hoops) blocks the activity of enzymes that normally break down the neurotransmitter molecules into small pieces that cannot bind with the receptors.

By slowing the enzyme breakdown process, Nardil keeps the neurotransmitter molecules in the synaptic gap for an extended period of time, significantly increasing their effect.

1.7 Explain. Psychoactive Drugs

Psychoactive drugs alter the functioning of the brain by enhancing or inhibiting the normal activity of neurotransmitters, the brain's chemical messengers. Stimulants (such as caffeine, nicotine, cocaine, and amphetamines) excite neural activity and speed up body functions. Depressants (such as alcohol, barbiturates, and opiates) reduce neural activity and slow body functions. Hallucinogens (such as LSD and marijuana) distort perceptions and may produce hallucinations. In addition, other psychoactive drugs are used to treat specific psychological disorders. For example, antidepressant drugs (such as Prozac or Nardil) boost a person's mood, usually by increasing the availability of the neurotransmitter serotonin. Antipsychotic drugs (such as Haldol) suppress some of the bizarre behaviors of schizophrenia, usually by occupying some of the receptors for the neurotransmitter dopamine so that the dopamine molecules cannot bind with the receptors. Continued use of any psychoactive drug produces tolerance (requiring larger doses to produce the same effects), and may lead to physical or psychological dependence on the drug.

1.8 Question

1.9 Question

1.10 Question

1.11 Question

Choose the drug types appropriate to the scenario.

1.12 Question

Choose the drug types appropriate to the scenario.

1.13 Question

Choose the drug types appropriate to the scenario.