Which autonomic system mediates the fight-or-flight response increasing heart rate and contractility?

• A. Parasympathetic Nervous System
• B. Somatic Nervous System
• C. Sympathetic Nervous System
• D. Enteric Nervous System

Answer: (C)

The fight-or-flight response is mediated by the sympathetic nervous system, which primes the heart for rapid action by increasing both heart rate and the force of contraction. This happens as sympathetic nerves release norepinephrine onto beta-adrenergic receptors on the sinoatrial and ventricular myocytes, boosting chronotropy (rate) and inotropy (contractility). The adrenal medulla can release epinephrine, further amplifying these effects. In contrast, the parasympathetic system slows heart rate and reduces contractility, while the somatic and enteric systems control voluntary muscles and gut function, respectively. So the sympathetic nervous system is responsible for the described heart changes.