Like a fast-moving relay race, neurotransmitters are the vehicle by which messages travel from one nerve cell to another in the brain. They affect mood, memory and our ability to concentrate, as well as several physical processes. When these chemical messengers are disrupted, the message may go right back to the transmitter or be lost altogether. When considering mental illness, the result of interrupted neurotransmitters can be depression or even a tendency toward drug and alcohol dependency. Though the brain has billions of nerve cells, they don\u2019t actually touch \u2013 thus the job of neurotransmitters to bring messages back and forth. Because neurotransmitters can impact a specific area of the brain, including behavior or mood, their malfunctions can cause effects ranging from mood swings to aggression and anxiety. Many neurotransmitters exist in the brain, but those most studied in relation to mental disorders are dopamine, acetylcholine, GABA, noradrenaline (norepinephrine) and serotonin. Understanding the way neurotransmitters function in the brain could lead to better treatments for mental disorders. Normally, nerve impulses move along the brain through axons , long cellular structures \u2013 until they land at a presynaptic membrane. These membranes house the neurotransmitters that will be sent out into free spaces, or synaptic clefts, so that they can be collected by receptors of another neuron. The neuron that collects the neurotransmitter then internalizes it and the nerve impulse can keep moving forward with the message. If serotonin or norepinephrine movement is interrupted, depression or anxiety disorders can result, as these hormones (also called neurotransmitters) regulate things like mood, appetite and concentration. For patients with depression, the neurotransmitters may return to their original location (the presynaptic membrane) instead of sending the right message produced by the serotonin to a neuron. Medications for depression can help stop these hormones from returning to their original location, a process called reuptake. The result is that broken signals are repaired; there is more serotonin activity; and reduced symptoms for depression. Dopamine is another neurotransmitter linked to mental illness, such as schizophrenia, characterized in part by emotional disturbances, but certain medications can help reduce the symptoms. Attention-deficit\/hyperactivity disorder (ADHD) is also believed to be a result of interrupted passages of dopamine or norepinephrine. Tiredness, high levels of stress and poor motivation are also linked to low dopamine. Additional mental illnesses, such as personality disorders and social disorders, are believed to be caused by the interrupted transfer of neurotransmitter messages. In patients with drug or alcohol addictions, the gamma-aminobutyric acid, or GABA, receptor may be affected. This neurotransmitter slows the speed of nerve impulses and causes muscles to relax. Interestingly, people with vitamin deficiencies may be more likely to experience disrupted, lacking or ineffective neurotransmitters. Amino acids are the building blocks of neurotransmitter production, but amino acids can\u2019t be generated without first taking in a broad range of vitamins and minerals. Diets that are too low in protein may also contribute to impaired neurotransmitter function. A combination of good nutrition, prescription medications or antidepressants, exercise and psychotherapy are recommended to increase neurotransmitter production and encourage a smooth flow of these critical chemicals in the brain.