Skip to Main Content

HNSC Undergrad Dept | HNSC Graduate Dept | Library

HNSC 3162 Biological Concepts in Public Health (Cai)

Professor Patricia Cai OER

Topic 1: General Introduction to Mental Illness

Learning Objectives:

learning outcomes icon.

By the end of this section, you will be able to:

  • define mental health.
  • recognize the risk factors for mental illness.
  • recognize the characteristics of a variety of common mental illnesses.


Mental Health external link.

two hands icon

What is mental health?

Mental health includes our emotional, psychological, and social well-being. It affects how we think, feel, and act. It also helps determine how we handle stress, relate to others, and make healthy choices.1 Mental health is important at every stage of life, from childhood and adolescence through adulthood.

stethescope icon

Why is mental health important for overall health?

Mental and physical health are equally important components of overall health.  For example, depression increases the risk for many types of physical health problems, particularly long-lasting conditions like diabetesheart disease, and stroke. Similarly, the presence of chronic conditions can increase the risk for mental illness.2

hourglass icon

Can your mental health change over time?

Yes, it’s important to remember that a person’s mental health can change over time, depending on many factors.  When the demands placed on a person exceed their resources and coping abilities, their mental health could be impacted. For example, if someone is working long hours, caring for a relative, or experiencing economic hardship, they may experience poor mental health.

icon showing numerical phrases 1 in 5

How common are mental illnesses?

Mental illnesses are among the most common health conditions in the United States.

  •  More than 1 in 5 US adults live with a mental illness.
  • Over 1 in 5 youth (ages 13-18) either currently or at some point during their life, have had a seriously debilitating mental illness.5
  • About 1 in 25 U.S. adults lives with a serious mental illness, such as schizophrenia, bipolar disorder, or major depression.6

puzzle pieces

What causes mental illness?

There is no single cause for mental illness. A number of factors can contribute to risk for mental illness, such as

  • Adverse Childhood Experiences, such as trauma or a history of abuse (for example, child abuse, sexual assault, witnessing violence, etc.)
  • Experiences related to other ongoing (chronic) medical conditions, such as cancer or diabetes
  • Biological factors or chemical imbalances in the brain
  • Use of alcohol or drugs
  • Having feelings of loneliness or isolation

Citation: Psych2Go (May 9, 2020) 10 Common Mental Illnesses Crash Course (13:46)
  • What defines mental illness?
  • What are the common characteristics of all anxiety disorders?
  • Would defines personality disorder?
  • What are some common symptoms of attention deficit disorder?
  • Give examples of other traumatic events that pose risks for the post traumatic stress disorder.
  • What's the difference between not being happy with your body and having an eating disorder?

Knowledge Check:

Topic 2: Substance Abuse and Addiction

Learning Objectives:

learning outcomes icon.

By the end of this section, you will be able to:

  • define substance abuse and addiction.
  • recognize the symptoms and causes of substance use disorder.
  • summarize how substance use disorder is diagnosed and its treatment options.
  • describe the basic cellular components of a neuron.
  • explain the concept of synapse.
  • explain the mechanism of drug addiction.


Substance use, abuse, and addiction external link.

Substance abuse is a pattern of compulsive substance use marked by recurrent significant social, occupational, legal, or interpersonal adverse consequences, such as repeated absences from work or school, arrests, and marital difficulties.

Addiction is a state of psychological or physical dependence (or both) on the use of alcohol or other drugs. The term is often used as an equivalent term for substance dependence and sometimes applied to behavioral disorders, such as sexual, internet, and gambling addictions.

Substance Use Disorder external link.

What is substance use disorder?

Substance use disorder is the medical term used to describe a pattern of using a substance (drug) that causes significant problems or distress. This may be missing work or school, using the substance in dangerous situations, such as driving a car. It may lead to substance-related legal problems, or continued substance use that interferes with friendships, family relationships, or both. Substance use disorder, as a recognized medical brain disorder, refers to the use of illegal substances, such as marijuana, heroin, cocaine, or methamphetamine. Or the misuse of legal substances, such as alcohol, nicotine, or prescription medicines. Alcohol is the most common legal drug associated with substance use disorder.

Substance (drug) dependence (Addiction)

Substance dependence is the medical term used to describe use of drugs or alcohol that continues even when significant problems related to their use have developed. Signs of dependence include:

  • Tolerance to or need for increased amounts of the drug to get an effect
  • Withdrawal symptoms that happen if you decrease or stop using the drug that you find difficult to cut down or quit
  • Spending a lot of time to get, use, and recover from the effects of using drugs
  • Withdrawal from social and recreational activities
  • Continued use of the drug even though you are aware of the physical, psychological, and family or social problems that are caused by your ongoing drug use
What substances are associated with substance use disorder? Substances frequently include:
  • Alcohol
  • Marijuana
  • Prescription medicines, such as pain pills, stimulants, or anxiety pills
  • Methamphetamine
  • Cocaine
  • Opiates
  • Hallucinogens
  • Inhalants
What causes substance use disorder?

Cultural and societal factors determine what are acceptable or allowable forms of drug or alcohol use. Public laws determine what kind of drug use is legal or illegal. The question of what type of substance use can be considered normal or acceptable remains controversial. Substance use disorder is caused by multiple factors, including genetic vulnerability, environmental stressors, social pressures, individual personality characteristics, and psychiatric problems. But which of these factors has the biggest influence in any one person cannot be determined in all cases.

What are the symptoms of substance use disorder?

The following are the most common behaviors that mean a person is using or misusing drugs or alcohol. But each person may have slightly different symptoms. Symptoms may include:

  • Using or drinking larger amounts or over longer periods of time than planned.
  • Continually wanting or unsuccessfully trying to cut down or control use of drugs or alcohol.
  • Spending a lot of time getting, using, or recovering from use of drugs or alcohol.
  • Craving, or a strong desire to use drugs or alcohol.
  • Ongoing drug or alcohol use that interferes with work, school, or home duties.
  • Using drugs or alcohol even with continued relationship problems caused by use.
  • Giving up or reducing activities because of drug or alcohol use
  • Taking risks, such as sexual risks or driving under the influence.
  • Continually using drugs or alcohol even though it is causing or adding to physical or psychological problems.
  • Developing tolerance or the need to use more drugs or alcohol to get the same effect. Or using the same amount of drugs or alcohol, but without the same effect.
  • Having withdrawal symptoms if not using drugs or alcohol. Or using alcohol or another drug to avoid such symptoms.

The symptoms of substance use disorder may resemble other medical problems or psychiatric conditions. Always consult your doctor for a diagnosis.

How is substance use disorder diagnosed?

A family doctor, psychiatrist, or qualified mental health professional usually diagnoses substance use disorder. Clinical findings often depend on the substance, the frequency of use, and the length of time since last used, and may include:

  • Weight loss
  • Constant fatigue
  • Red eyes
  • Little concern for hygiene
  • Lab abnormalities
  • Unexpected abnormalities in heart rate or blood pressure
  • Depression, anxiety, or sleep problems
Treatment for substance use disorder

Specific treatment for substance use disorder will be determined by your doctor based on:

  • Your age, overall health, and health history
  • Extent of the symptoms
  • Extent of the dependence 
  • Type of substance you are using
  • Your tolerance for specific medicines, procedures, or therapies
  • Expectations for the course of the condition
  • Your opinion or preference

A variety of treatment (or recovery) programs for substance use disorder are available on an inpatient or outpatient basis. Programs considered are usually based on the type of substance. Detoxification (if needed, based on the substance) and long-term follow-up management or recovery-oriented systems of care are important features of successful treatment. Long-term follow-up management usually includes formalized group meetings and psychosocial support systems, as well as continued medical supervision. Individual and family psychotherapy are often recommended to address the issues that may have contributed to and resulted from the development of a substance use disorder.

How do neurons communicate? Synapse (NIH) external link.

Cellular Level

Neurons: In the simplest sense, the neuron consists of a cell body, axons, and dendrites. 

Cell Body: The cell body contains the nucleus and is the site of metabolic activity. Most of the neurotransmitters that will eventually be released at the synapse are synthesized here.

Dendrites: These are small projections from the cell body that serves a receptive role in the physiology of the neuron. They receive incoming signals from other neurons and relay them to the cell body, where the signals are integrated, and a response will be initiated. 

Axons: Generally, the outflow tract of the neuron. It is a cylindrical tube that is covered by the axolemma and is supported by neurofilaments and microtubules. The microtubules will help to transport the neurotransmitters from the cell body down to the pre-synaptic terminal, where they will be released. 

Synapses: The synapse itself is the site of transmission from the pre-synaptic neuron to the post-synaptic neuron. The structures found on either side of the synapse vary depending on the type of synapse:


Anatomy & Physiology by Lindsay M. Biga et al. book's Figure 12.2.2 – Parts of a Multipolar Neuron: The major parts of the neuron are labeled on a multipolar neuron from the CNS.


The human brain is made up of approximately 86 billion neurons that “talk” to each other using a combination of electrical and chemical (electrochemical) signals.

The places where neurons connect and communicate with each other are called synapses. Each neuron has anywhere between a few to hundreds of thousands of synaptic connections, and these connections can be with itself, neighboring neurons, or neurons in other regions of the brain. A synapse is made up of a presynaptic and postsynaptic terminal.

The presynaptic terminal is at the end of an axon and is the place where the electrical signal (the action potential) is converted into a chemical signal (neurotransmitter release). The postsynaptic terminal membrane is less than 50 nanometers away and contains specialized receptors. The neurotransmitter rapidly (in microseconds) diffuses across the synaptic cleft and binds to specific receptors.

The type of neurotransmitter released from the presynaptic terminal and the specific receptors present on the corresponding postsynaptic terminal is critical in determining the quality and intensity of information transmitted by neurons. The postsynaptic neuron integrates all the signals it receives to determine what it does next, for example, to fire an action potential of its own or not.

Figure 3. The Synapse


Anatomy & Physiology by OpenStax College book's Figure 3. The Synapse. The synapse is a connection between a neuron and its target cell (which is not necessarily a neuron). The presynaptic element is the synaptic end bulb of the axon where Ca2+ enters the bulb to cause vesicle fusion and neurotransmitter release. The neurotransmitter diffuses across the synaptic cleft to bind to its receptor. The neurotransmitter is cleared from the synapse either by enzymatic degradation, neuronal reuptake, or glial reuptake.

Citation: Alila Medical Media. (Sep 10, 2014) Mechanism of Drug Addiction in the Brain, Animation.(4:15)

Understanding Drug Use and Addiction Drug Facts external link.

Many people don't understand why or how other people become addicted to drugs. They may mistakenly think that those who use drugs lack moral principles or willpower and that they could stop their drug use simply by choosing to. In reality, drug addiction is a complex disease, and quitting usually takes more than good intentions or a strong will. Drugs change the brain in ways that make quitting hard, even for those who want to. Fortunately, researchers know more than ever about how drugs affect the brain and have found treatments that can help people recover from drug addiction and lead productive lives.

Citation: National Institute on Drug Abuse (NIDA/NIH). (Sep 20, 2022) Why are Drugs so Hard to Quit? (3:57)

What happens to the brain when a person takes drugs?

Most drugs affect the brain's "reward circuit," causing euphoria as well as flooding it with the chemical messenger dopamine. A properly functioning reward system motivates a person to repeat behaviors needed to thrive, such as eating and spending time with loved ones. Surges of dopamine in the reward circuit cause the reinforcement of pleasurable but unhealthy behaviors like taking drugs, leading people to repeat the behavior again and again.

As a person continues to use drugs, the brain adapts by reducing the ability of cells in the reward circuit to respond to it. This reduces the high that the person feels compared to the high they felt when first taking the drug—an effect known as tolerance. They might take more of the drug to try and achieve the same high. These brain adaptations often lead to the person becoming less and less able to derive pleasure from other things they once enjoyed, like food, sex, or social activities.

Long-term use also causes changes in other brain chemical systems and circuits as well, affecting functions that include:

  • learning
  • judgment
  • decision-making
  • stress
  • memory
  • behavior

Despite being aware of these harmful outcomes, many people who use drugs continue to take them, which is the nature of addiction.

Why do some people become addicted to drugs while others don't?

No one factor can predict if a person will become addicted to drugs. A combination of factors influences risk for addiction. The more risk factors a person has, the greater the chance that taking drugs can lead to addiction. For example:

  • Biology. The genes that people are born with account for about half of a person's risk for addiction. Gender, ethnicity, and the presence of other mental disorders may also influence risk for drug use and addiction.
  • Environment. A person’s environment includes many different influences, from family and friends to economic status and general quality of life. Factors such as peer pressure, physical and sexual abuse, early exposure to drugs, stress, and parental guidance can greatly affect a person’s likelihood of drug use and addiction.
  • Development. Genetic and environmental factors interact with critical developmental stages in a person’s life to affect addiction risk. Although taking drugs at any age can lead to addiction, the earlier that drug use begins, the more likely it will progress to addiction. This is particularly problematic for teens. Because areas in their brains that control decision-making, judgment, and self-control are still developing, teens may be especially prone to risky behaviors, including trying drugs.
Can drug addiction be cured or prevented?

As with most other chronic diseases, such as diabetes, asthma, or heart disease, treatment for drug addiction generally isn’t a cure. However, addiction is treatable and can be successfully managed. People who are recovering from an addiction will be at risk for relapse for years and possibly for their whole lives. Research shows that combining addiction treatment medicines with behavioral therapy ensures the best chance of success for most patients. Treatment approaches tailored to each patient’s drug use patterns and any co-occurring medical, mental, and social problems can lead to continued recovery.

More good news is that drug use and addiction are preventable. Results from NIDA-funded research have shown that prevention programs involving families, schools, communities, and the media are effective for preventing or reducing drug use and addiction. Although personal events and cultural factors affect drug use trends, when young people view drug use as harmful, they tend to decrease their drug taking. Therefore, education and outreach are key in helping people understand the possible risks of drug use. Teachers, parents, and health care providers have crucial roles in educating young people and preventing drug use and addiction.

Points to Remember

  • Drug addiction is a chronic disease characterized by drug seeking and use that is compulsive, or difficult to control, despite harmful consequences.
  • Brain changes that occur over time with drug use challenge an addicted person’s self-control and interfere with their ability to resist intense urges to take drugs. This is why drug addiction is also a relapsing disease.
  • Relapse is the return to drug use after an attempt to stop. Relapse indicates the need for more or different treatment.
  • Most drugs affect the brain's reward circuit by flooding it with the chemical messenger dopamine. Surges of dopamine in the reward circuit cause the reinforcement of pleasurable but unhealthy activities, leading people to repeat the behavior again and again.
  • Over time, the brain adjusts to the excess dopamine, which reduces the high that the person feels compared to the high they felt when first taking the drug—an effect known as tolerance. They might take more of the drug, trying to achieve the same dopamine high.
  • No single factor can predict whether a person will become addicted to drugs. A combination of genetic, environmental, and developmental factors influences risk for addiction. The more risk factors a person has, the greater the chance that taking drugs can lead to addiction.
  • Drug addiction is treatable and can be successfully managed.
  • More good news is that drug use and addiction are preventable. Teachers, parents, and health care providers have crucial roles in educating young people and preventing drug use and addiction.

Knowledge Check:

Topic Sources