Final answer:
The sympathetic system increases heart rate and contraction strength, while the parasympathetic system decreases heart rate, maintaining balance and homeostasis.
Step-by-step explanation:
The sympathetic and parasympathetic systems exert opposing effects on the heart. The sympathetic system acts as an accelerator, increasing the heart rate and the strength of cardiac contractions via the release of neurotransmitters like norepinephrine (NE) which binds to adrenergic receptors. This results in enhanced cardiac output, especially during activities like exercise. On the other hand, the parasympathetic system functions like a brake, decreasing the heart rate through the release of acetylcholine (ACh), which binds to muscarinic receptors and causes hyperpolarization of the cardiac muscle cells. Thus, it promotes a restful state with lower energy expenditure. The balance between these two systems is vital for maintaining homeostasis and the body's ability to respond to different physiological demands.