When a person suffers from an anxiety disorder, it can feel like his body is raging out of control. It makes sense, then, to consider the biological factors underlying anxiety. Biology alone does not explain why anxiety disorders occur. Anxiety disorders probably arise from a combination of additional factors, including environment, development and individual psychology, according to the National Institute of Mental Health (NIMH).
Genetics
The NIMH has sponsored a number of twin studies on anxiety disorders that have shown genetics to play a role in anxiety disorders. Not all anxiety disorders may be strongly genetically determined, however. The U.S. Surgeon General reports that panic disorder may be an example of a disorder with a strong genetic basis. Nonetheless, scientists remain unsure of the exact role of genes in the expression of anxiety and specific "anxiety genes" have not been located.
Brain Variations
According to the NIMH, two parts of the brain may be problematic in anxiety disorders: the amygdala and the hippocampus. Both structures are part of the limbic system, the emotional system of humans, according to the U.S. Surgeon General. The amygdala is responsible for telling higher-level areas of the brain when there is a threat in the environment. Some emotional memories seem to be stored in the amygdala, the NIMH reports. When the amygdala uses these memories to send out signals of threat when none exist, specific phobias may occur. The hippocampus, a brain structure vital for storage of new memories, may play a role in PTSD. The hippocampus tends to be smaller in people who were in war or abused as children, according to the NIMH. Stressed animals show this same hippocampal size difference, reports the U.S. Surgeon General. Research is ongoing to determine how this size difference may relate to the expression of PTSD.
Neurotransmitters
The U.S. Surgeon General reports that five major neurotransmitters are involved in anxiety disorders: gamma-aminobutyric acid (GABA), norepinephrine, serotonin, cholecystokinin and corticotropin-releasing hormone (CRH). CRH and norepinephrine act as stress hormones in the body, while the other neurotransmitters mentioned serve a calming function. Chronic stress may affect the balance of these neurotransmitters, resulting in anxiety disorders, according to the Cleveland Clinic. Drug treatment targeting each of these neurotransmitters has been explored, with varying success.
