When a neuron (nerve cell) is activated, an electrical signal travels down the axon and releases a neurotransmitter. The neurotransmitter carries a chemical message across the synaptic cleft, attaches to a receptor on the receiving neuron, and transmits an excitatory or inhibitory message. Feedback mechanisms serve as regulators for the neurons sending the messages, and a reuptake transporter protein returns the neurotransmitter back across the synapse to the sending neuron after the job is completed. At times this complex system develops problems that manifest clinically as psychiatric disorders, including anxiety disorders. Problems with neurotransmission may include receptor hypersensitivity or hyposensitivity, deficient neurotransmitter release, and reuptake occurring too quickly [3].

As mentioned previously, anxiety occurs as a normal adaptive response to a threat and may be accompanied by increased autonomic (sympathetic and parasympathetic) activity [17]. The autonomic nervous system controls involuntary function of the internal organs and is involved in the fear response [3]. Abnormal anxiety with physiological activation has been shown to include somatic concerns. For example, studies have shown that a history of anxiety disorders is associated with an increased risk for coronary heart disease, including sudden cardiac death, compared to a history without anxiety problems [17].