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Don't let anyone fool you, drug addiction is no fun. Mind-altering substances affect the way the brain works. Addicts experience intense cravings to continue to use drugs even when the consequences become extremely negative. Because brain chemistry is effected, the desire to use is no longer a matter of choice. Please click on the three links above to review how drug affect the brain.

[ Brain Structure ] [ Nerve Cells ] [ Effects of Drugs ]

Brain Structure

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 sleeping.  

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.

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Nerve Cells

The brain is made up of billions of nerve cells or neurons.  They consist of three parts.

  1. A cell body that directs all activities of the neuron
  2. Short fibers or dendrites that receive messages from other neurons and send them to the central cell body.
  3. 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:

  1. It is broken down by an enzyme.
  2. 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.
[ Brain Structure ] [ Nerve Cells ] [ Effects of Drugs ]
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Effects of Drugs

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 work.  

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 normal.

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.

[ Brain Structure ] [ Nerve Cells ] [ Effects of Drugs ]
[Brain Matters] [Brain Basics] [Addiction] [Hallucinogens] [Inhalants] [Marijuana] [Meth] [Nicotine] [Opiates] [Steroids] [Resources] [TNT Brain Matters] [Club TNT Home] [Madison Voices] [Breitlinks] [Business Ed] [Connect WCCF] [WCCF Home]
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2003-2006 Breitlinks, All Rights Reserved.  Some material for this page comes from the National Institute on Drug Abuse