MICROANATOMY

Detailed explanation-1: -The parasympathetic nervous system (PNS) releases the hormone acetylcholine to slow the heart rate. Such factors as stress, caffeine, and excitement may temporarily accelerate your heart rate, while meditating or taking slow, deep breaths may help to slow your heart rate.

Detailed explanation-2: -The high-frequency components of heart rate variability are associated with vagus nerve/parasympathetic effect, whereas the low-frequency components are due to sympathetic and parasympathetic activation.

Detailed explanation-3: -Parasympathetic activation (vagus nerve) exerts an inhibitory action on the heart: it slows conduction from the sinus node, leading to bradycardia, and reduces conduction via the atrioventricular node.