Effects of Substance Use
(why it makes you feel that way, why it never feels quite as good again, and why it's so hard to stop!)
Alcohol and drugs (even medications that might have been prescribed by a doctor) can negatively affect our minds, bodies, emotions, relationships and ability to meet responsibilities. First, some background information on how these substances work:
The brain is made up of billions of cells called neurons. A neuron has three parts: the cell body, which is in charge of the activities of the neuron; dendrites, short fibers that receive messages from other neurons and pass them on to the cell body; and an axon, a long single fiber that transmits messages from the cell body to the dendrites of other neurons. The end of the axon is called the axon terminal, where messages are constantly departing and returning. Different neurons are shaped differently, and are different sizes, but they usually have these three parts.
The way messages are transferred from the axon terminal of one nerve cell to the dendrites of another one is called neurotransmission. Although the axons of one neuron and the dendrites of another are close to one another, they do not physically touch. Instead, communication between nerve cells is achieved through the release of chemical substances, called neurotransmitters (because they transmit messages between neurons), into the space between them. This space is called a synapse.
The neurotransmitters are released from the axon terminal of one neuron, move across the synapse, and then bind to special molecules, called receptors, that are located within the cell membranes of the dendrites of the next neuron. This, in turn, stimulates or inhibits a response in the receiving neuron. So, neurotransmitters act as chemical messengers, carrying information from one neuron to another.
There are many different types of neurotransmitters, and each one has a different role to play in the way the brain functions. You have probably heard of some of them, like serotonin, which has been demonstrated to play a role in fighting depression. Each neurotransmitter has a very important job to do. Usually, the different types of neurotransmitters can only bind to a very specific matching receptor. So, when a neurotransmitter binds to its receptor, it’s like fitting a key into a lock, and the message is passed on to the new cell. Once this happens, the neurotransmitter is inactivated in one of two ways: it’s either reabsorbed back into the neuron that released it and re-released, or it’s reabsorbed and broken down by an enzyme. The reabsorption, also called reuptake, is accomplished by what are known as transporter molecules. These molecules pick up specific neurotransmitters from the synapse and carry them back across the cell membrane and into the axon. Then, the neurotransmitters are available to be used again or are broken down.
The Pleasure Circuit:
Pleasure is a very powerful biological force for our survival. If you do something pleasurable, your brain is wired in such a way that you tend to do it again. Life-sustaining activities, like eating, activate a circuit of specialized nerve cells devoted to producing and regulating pleasure. One important set of these nerve cells, which uses a neurotransmitter called dopamine, sits at the very top of the brainstem. These dopamine-containing
neurons relay messages about pleasure through their nerve fibers to neurons in a limbic system structure called the nucleus accumbens. The limbic system is involved in many of our emotions and motivations, particularly those that are related to survival, such as fear, anger, and sexual behavior. It’s also involved in feelings of pleasure, like those experienced from eating and sex, and it’s involved in memory.
Still other fibers reach to a related part of the frontal region of the cerebral cortex. This is the most highly developed part of the human brain and is responsible for thinking, perceiving, and producing and understanding language. It’s also involved in vision, hearing, touch, movement and smell.
So, the pleasure circuit, which is known as the mesolimbic dopamine system, spans the survival-oriented brainstem (heart rate, breathing, eating, sleeping), the limbic system (emotions and memory), and the frontal cerebral cortex (decision-making, problem solving, planning).
All drugs that are addicting can activate the brain’s pleasure circuit.
This means that no matter what your drug of choice is, or how much of it you have been consuming, all of these parts of your brain have been affected. Dopamine receptors are typically stable; however, sharp (and sometimes prolonged) increases or decreases in dopamine levels can downregulate (reduce the numbers of) or upregulate (increase the numbers of) dopamine receptors. This can lead to temporary or permanent impairment in several areas.
Typically, we begin to question whether our substance use is a problem only after others begin to insist that it is. “Denial,” or a genuine inability to appreciate just how bad things have gotten, is a common symptom of how alcohol and other substances affect our brain. These substances literally impair our ability to perceive ourselves accurately by changing the structure and function of our brain.
The symptoms commonly seen by others (and often minimized by the person experiencing denial) include deteriorating physical health, tolerance for the substance, withdrawal symptoms when the substance is discontinued, reduced functioning at work or school, social or interpersonal problems, and a general inability or refusal to stop using the substance even after experiencing negative consequences.
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