Final answer:
The parasympathetic system decreases HR and promotes rest and digest, while the sympathetic system increases HR during fight-or-flight responses, maintaining homeostasis.
Step-by-step explanation:
The parasympathetic and sympathetic systems regulate heart rate (HR) and cardiac output (CO) through the two paired cardiovascular centers of the medulla oblongata. The sympathetic system, associated with the fight-or-flight response, increases HR by releasing norepinephrine onto the heart cells which bind to adrenergic receptors, causing faster depolarization. In contrast, the parasympathetic system, epitomizing rest and digest functions, decreases HR by releasing acetylcholine (ACh) onto heart cells that bind to muscarinic receptors, leading to hyperpolarization and a slower heart rate.
Normally, the heart operates under parasympathetic tone, maintaining a resting HR around 60-80 bpm. The sympathetic system can raise the HR during stress or exercise to about 120-140 bpm. Homeostasis, the balancing act between these two systems, ensures the body appropriately responds to various stimuli with appropriate changes in HR and CO to maintain optimal function.
The parasympathetic and sympathetic systems regulate heart rate (HR) and cardiac output (CO). The sympathetic system increases heart rate, while the parasympathetic system decreases heart rate. The sympathetic system stimulates activity via sympathetic nerves, which release norepinephrine and bind to adrenergic receptors, causing the heart to depolarize faster and increase heart rate. The parasympathetic system, on the other hand, stimulates the release of acetylcholine, which binds to muscarinic receptors and hyperpolarizes the heart cells, slowing down the heart rate.