MEDICAL PHYSIOLOGY

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: -In contrast, parasympathetic stimulation decreases heart rate and constricts the pupils. It also increases secretion of the eye glands, increases peristalsis, increases secretion of salivary and pancreatic glands, and constricts bronchioles.

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: -In the heart, parasympathetic stimulation of M2 receptors causes decreased heart rate and velocity of conduction through the AV node. In the vasculature, parasympathetic stimulation of M3 receptors leads to vasodilation. In the lungs, parasympathetic stimulation of M3 receptors leads to bronchoconstriction.