The main parts of the brain are the brainstem,
cerebellum, limbic system, diencephalon, and cerebral cortex.
Cortex. The upper part of the brain. This is
where higher levels of thinking, like logic and reason, cause and effect
of our actions, and understanding of conscious occur.
Cerebellum. At the back base of the brain. It represents
1/8th of the brain's mass and maintains our balance, posture and
coordinates skilled repetitive movements.
Brainstem. Connects brain and the spinal cord. It controls
many basic function, such as heart rate, breathing, eating, and
Limbic System. Sits on top of the brainstem and buried in the
center of the brain. It is the source of our emotions and motivations,
especially those linked to survival such as fear, anger, and sexuality.
The limbic system is also involved with feelings of pleasure associated
with survival such as eating and sex.
The limbic system represents a more evolutionary, primitive brain
structure. Drugs of abuse have powerful effects on us because the act
directly on the brainstem and limbic structures and override the more
thoughtful control of conscious thought and reason from the cortex.
The brain is made up of billions of nerve cells or neurons. They
consist of three parts.
- A cell body that directs all activities of the neuron
- Short fibers or dendrites that receive messages from other neurons
and send them to the central cell body.
- A long single fiber or axon, that transmits messages from the
central cell body to the dendrites for transmission to other neurons
or to body tissues such as muscles.
While there are many different types of neurotransmitters, each type
only binds to a specific, matching receptor -- like a key in a lock.
Once the chemical message carried by a neurotransmitter is received and
processed by the receiving nerve cell, the neurotransmitter is turned
off in one of two ways:
- It is broken down by an enzyme.
- It is reabsorbed back into the nerve cell that released it by a
transporter molecule. Transporter molecules reside in the cell
membranes of the axons that release the neurotransmitters.
Pleasure is a very powerful biological force for survival.
Life-sustaining activities, such as eating, activate a circuit of
specialized nerve cells devoted to producing and regulating pleasure.
One important chemical to this process is called dopamine.
Dopamine-containing neurons relay messages about pleasure through
their nerve fibers to nerve cells in a limbic system structure and
cortex. This pleasure circuit, know as the mesolimbic dopamine system,
spans the survival-oriented brainstem, the emotional limbic system, and
the frontal cerebral cortex.
Drugs that are addicting activate the brain's pleasure circuit by
interrupting how neurons communicate. Addiction is a biological,
pathological process that alters how the brain and its pleasure centers
Some drugs, like heroin and LSD, mimic the effects of a natural
chemical neurotransmitter. Others, like PCP, block receptors and
prevent neurons from communicating. Still others, like cocaine, block
the re-absorption of chemical neurotransmitters back into the neurons
that released them. Finally, some drugs, such as methamphetamine, cause
chemical neurotransmitters to be released in greater quantities than
Prolonged drug use changes the brain in fundamental and long-lasting
ways which affect the though patterns and behaviors of the user. At
some point, the change is so pronounced that the individual is no longer
able to control their drug use; it controls them. The effect of this
change is that a drug abuser is transformed into a drug addict, usually
before they are even aware of what is happening.