GENERAL HISTOLOGY

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: -Parasympathetic control of the heart via the vagus nerve is the primary mechanism that regulates beat-to-beat control of heart rate. Additionally, the vagus nerve exerts significant effects at the AV node, as well as effects on both atrial and ventricular myocardium.

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.

Detailed explanation-4: -The sympathetic nervous system releases norepinephrine (NE) while the parasympathetic nervous system releases acetylcholine (ACh). Sympathetic stimulation increases heart rate and myocardial contractility.