Final answer:
The sympathetic nervous system acts as a cardioaccelerator, increasing heart rate and contraction force, while the parasympathetic nervous system acts as a cardioinhibitory, slowing the heart rate. These systems work through the cardiac plexus and adjust heart activity via sympathetic and parasympathetic stimulation in response to the body’s needs.
Step-by-step explanation:
The influence of the sympathetic and parasympathetic nervous systems on the heart is a crucial aspect of cardiovascular regulation. The sympathetic nervous system acts as a cardioaccelerator, enhancing heart rate (HR) and the force of contraction through the release of norepinephrine (NE), which stimulates depolarization and contraction. Conversely, the parasympathetic nervous system serves as a cardioinhibitory agent, slowing down the HR by releasing acetylcholine (ACh) and causing hyperpolarization, which inhibits contraction. These two divisions work through a network known as the cardiac plexus to maintain a balanced heart function in response to the body's changing needs.
During rest, parasympathetic tone predominates, maintaining a normal resting HR at approximately 60 to 80 bpm, lower than the innate rhythm of the sinoatrial (SA) node which would otherwise set the pace at about 100 bpm. During stress or exercise, sympathetic stimulation is increased, which can raise the heart rate to 120-140 bpm, increasing cardiac output and blood flow to meet the body's demands.
The autonomic nervous system adapts the heart's activity via various receptors that respond to different physiological conditions, enabling appropriate adjustments to the balance of sympathetic and parasympathetic stimulation.