EVERYDAY SCIENCE

Detailed explanation-1: -At the beginning of exercise, your body removes the parasympathetic stimulation, which enables the heart rate to gradually increase. As you exercise more strenuously, the sympathetic system “kicks in” to accelerate your heart rate even more.

Detailed explanation-2: -The sympathetic nervous system releases norepinephrine (NE) while the parasympathetic nervous system releases acetylcholine (ACh). Sympathetic stimulation increases heart rate and myocardial contractility.

Detailed explanation-3: -The sympathetic nervous system (SNS) has a wide variety of cardiovascular effects, including heart-rate acceleration, increased cardiac contractility, reduced venous capacitance, and peripheral vasoconstriction.

Detailed explanation-4: -At rest, heart rate is dominated by the parasympathetic nervous system activity. Parasympathetic control occurs via muscarinic acetylcholine receptors that decrease the sinoatrial pacemaker activity by inhibiting the pacemaker current and activating an inwardly rectifying potassium channel in the pacemaker cells.