Mental illnesses are brain disorders. Trying to understand the “why” behind an illness or the “how” behind medication requires caregivers to know some detail about how the brain works. For example: What’s a neurotransmitter? What are synapses? And what’s the difference between serotonin and dopamine?

This basic overview, which answers those questions, comes from material on the National Institute of Mental Health’s website. The site contains lots of information to answer your questions about the complexities of mental illness.

NIMH research shows that mental illnesses can be related to changes in the anatomy, physiology and chemistry of the nervous system. When the brain malfunctions, symptoms of mental illness start to appear.

Neurons are the basic working unit of the brain and nervous system, each enclosed by a cell membrane. These highly specialized cells conduct messages. Each neuron has three main parts:

• A cell body with a nucleus (containing DNA and information the cells needs for growth and repair) and cytoplasm, the substance filling the cell where all the chemicals and small structures named cell organelles reside.
• Dendrites that branch off from the cell body and are the neuron’s point of contact for receiving chemical and electrical signals (called impulses) from other nearby neurons.
• Axon that send impulses and extend from the cell body to meet and deliver impulses to another neuron.

Synapses are tiny gaps between neurons where the impulses or messages move from one neuron to the other as chemical or electrical signals.

The brain continues to mature at least until a person is in his 20s. As scientists learn more about brain development, they can see what goes wrong when a person develops a mental illness. One of the mysteries of schizophrenia, for example, is why it often occurs for the first time when a person is in his late teens or early 20s. Many believe scientists will find the secret as they learn more the processes in the brain at that time.

What can go wrong in the brain?

Every cell contains a complete set of DNA, with all the information inherited from our ancestors. As we grow, we create new cells, each with a copy of the DNA. Sometimes the copying process goes wrong, resulting in a gene mutation.

Scientists also study epigenetics, which looks at how environmental factors, such as sleep, diet and stress, can influence our genes. Unlike gene mutations, epigenetic changes don’t change the DNA code. They affect how a gene turns on or off to produce a specific protein.

The role of neurotransmitters

All that we do depends on neurons communicating with each other through electrical impulses and chemical signals. Neurons activate with small differences in electrical charges, called action potentials. The ions (atoms with unbalanced charges) concentrate across the cell membrane and travel very quickly along the axon. (It’s a bit like dominoes falling.)

When the action potential gets to the end of the axon, most neurons release a neurotransmitter, or a chemical message, that crosses the synapse and binds to receptors in the next neuron’s dendrites. So neurotransmitters are key to sending chemical messages between neurons. In mental illness and other conditions like Parkinson’s disease, this process doesn’t work correctly.

Important neurotransmitters include:

• Serotonin controls functions including mood, appetite and sleep. People with depression usually have lower levels of serotonin. Some medications that treat depression block the recycling, or reuptake, of serotonin by the sending neuron. So more serotonin stays in the synapse for the receiving neuron to obtain. This medication, called selective serotonin reuptake inhibitor (or SSRI) causes more normal mood functioning.
• Dopamine controls movement and aids the flow of information to the front of the brain, where thought and emotion take place. Low levels of dopamine can result in Parkinson’s disease, which affects the person’s ability to move and causes tremors, shaking and stiffness. Some research suggested that having too little dopamine in the thinking and feelings sections of the brain could play a role in schizophrenia and attention deficit hyperactivity disorder.
• Glutamate is the most common neurotransmitter. When it is releases, the chances that the neuron will fire increase. So it enhances the electrical flow among brain cells. It also may be involved in learning and memory. Problems in making or using glutamate have been linked in autism, obsessive compulsive disorder, schizophrenia and depression.

Regions of the brain

Many neurons working together form a circuit. And many circuits working together form specialized brain systems. Research into the causes of mental illness tend to focus on these regions:

• Amygdala activates the “fight-or-flight” response to confront or flee from a situation. Scientists are studying the amygdala’s involvement in anxiety disorders, including post-traumatic stress disorder and phobias.
• Prefrontal cortex is where the brain’s executive functions are. These include judgment, decision making and problem solving. The prefrontal cortex also works in short-term memory and retrieves long-term memory. It helps to control the amygdala during stressful events. Research shows the people with post-traumatic stress disorder and attention deficit hyperactivity disorder have reduced activity in the prefrontal cortex.
• Anterior cingulate cortex has many roles, including controlling blood pressure and heart rate. It also helps us respond when we sense a mistake, feel motivated, stay focused on a task and manage emotional reactions. Reduced activity or damage in this area is linked to attention deficit hyperactivity disorder, schizophrenia and depression.
• Hippocampus helps create and file memories. When it is damaged, the person can’t create new memories. However, the person can still remember past events and learned skills, as well as carry on a conversation, because those activities are in different parts of the brain. The hippocampus may be involved in mood disorders through its control of a major mood circuit called the hypothalamic-pituitary-adrenal axis.

No one expects caregivers to become brain scientists, but having a general understanding of the brain will help when learning about medicines and research. The more knowledge we have, the better.