Neurology
of Methamphetamine Use
When most people
think about the nervous system, they imagine the form and shape of the human brain.
However, the nervous system is actually much more than that. Together with the
spinal cord, the brain comprises the central nervous system. The peripheral
nervous system is all other nerve tissue in the body, including nerves leading
to and from the skin, muscles, blood vessels, and internal organs, brain, and
spinal cord. Methamphetamine use has many effects on both the central and
peripheral nervous systems.
Methamphetamine
Leads to Central Nervous System Malfunction
In humans, a thin
ring of tissue surrounding the central core of the brain governs much of
behavior and emotion. Within this central ring, several collections of neurons
and the connections between them are known together as the limbic system.
Eating a piece of
frybread feels good, making it highly likely that you will eat some frybread
again. Sex also creates great pleasure. The limbic system evolved over millions
of years to become stimulated by activities (such as eating, drinking fluids,
and having sex) that are important for survival of the individual and important
for survival of the species. However, methamphetamine use also stimulates the
limbic system.
Once activated by
a particular behavior (such as eating, sex, or methamphetamine use), the limbic
system uses pleasure as a reward, convincing the mind that whatever the body
just did was very good and should be repeated. In this way, the limbic system
motivates behaviors. To accomplish this feat, unique networks of cells in the
limbic system manipulate the rest of the brain.
Your limbic system
is composed of several networks of cellular connections called Diffuse
Modulatory Systems (DMS). When stimulated, a DMS creates a broad (diffuse)
signal throughout the brain, which controls (modulates) levels of brain
activity.
Classification of
a DMS is based on the type of neurotransmitter released by that system’s
neurons. In methamphetamine users, the dopamine system is the DMS most affected
by the drug and may lead to addiction [Link to Jace]. The norepinephrine and
serotonin systems also have a role during use of methamphetamine [Link to
Jace].
Methamphetamine
Deceives the Peripheral Nervous System
Concentrate for a
moment on your heartbeat. Imagine if you had to actively force, or
"tell" your heart to beat, much like you have to force your eyes to
read this sentence or tell your finger to click the mouse button. You wouldn't
accomplish much of anything if you had to perpetually concentrate on your heart
rate, breathing rate, or metabolism.
Your Autonomic
Nervous System (ANS) allows you to live each day without sacrificing
intellectual firepower on a task such as maintaining a steady cardiac rhythm.
The ANS works as a sort of cruise control for life-sustaining bodily functions
like heart rate and metabolism. Two different divisions of the ANS, the
sympathetic and parasympathetic divisions, determine whether your cruise
control speeds up or slows down.
When your bodily
functions have to speed up or become more active, like when confronted with a
physical threat or a compromising situation, the sympathetic division of the
ANS activates. Direct consequences of sympathetic stimulation include increase
in heart rate, inactivation of digestion, release of glucose from the liver for
immediate energy, constriction of blood vessels to increase blood pressure and
flow, sweating to eliminate excess water, relaxation of bladder muscles to
store urine, and stimulation of ejaculation. These changes prepare the body for
immediate action.
In humans, the
sympathetic division of the ANS uses only one neurotransmitter, called
norepinephrine. In comparison with norepinephrine, methamphetamine is an
analog, a molecule with a similar structure and function as another molecule.
Each time a user smokes, injects, or snorts methamphetamine, the drug fools the
organs controlled by the sympathetic division of the ANS into activation. Heavy
and frequent use of the drug leads to the weight loss, dilated pupils,
increased heart rate and increased blood pressure common in many
methamphetamine addicts.
Slowing down or relaxing
bodily functions is the responsibility of the parasympathetic division of the
ANS. Inducing the opposite effects of the sympathetic division, the
parasympathetic division activates digestion of food, lowers heart rate,
dilates blood vessels, and inhibits metabolism. Since acetylcholine is the
neurotransmitter used by the parasympathetic division, methamphetamine has no
direct effect on parasympathetic activation or inhibition.
Your nervous
system is crucial to survival. It produces your thoughts, feelings, and
emotions. The nervous system also allows you to react to critical situations
and controls your involuntary activities, such as digesting your food and
maintaining your heart rate. Methamphetamine use interferes with all of these
important aspects of nervous system function, making the user very likely to
one day appear in a treatment center, emergency room, or even, a morgue.