During acute stress, which branch of the autonomic nervous system is activated to trigger the fight-or-flight response?

• A. Sympathetic
• B. Parasympathetic
• C. Somatic
• D. Central

Answer: (A)

During acute stress, the fight-or-flight response is driven by the sympathetic branch of the autonomic nervous system. This system rapidly readies the body for action by increasing heart rate and the force of contraction, bronchodilating airways, dilating pupils, releasing glucose from the liver, and redirecting blood toward skeletal muscles while dialing down nonessential functions like digestion. The sympathetic signals originate in the thoracic and lumbar regions, with preganglionic neurons releasing acetylcholine onto postganglionic neurons that secrete norepinephrine, and the adrenal medulla releasing epinephrine (adrenaline) into the bloodstream to amplify the response. In contrast, the parasympathetic branch promotes rest and digestion, the somatic system governs voluntary skeletal muscle control, and the central nervous system refers to the brain and spinal cord rather than a branch of the autonomic system.