The baroreceptors in the carotid sinus sense this increase in blood pressure and relay the information to the cardiovascular centres in the medulla oblongata.
In order to maintain homeostasis, the cardiovascular centres activate the parasympathetic nervous system.
Via the vagus nerve, the parasympathetic nervous system stimulates neurons that release the neurotransmitter acetylcholine (ACh) at synapses with cardiac muscle cells.
Acetylcholine then binds to M2 muscarinic receptors, causing the decrease in heart rate that is referred to as reflex bradycardia.
[citation needed] The M2 muscarinic receptors decrease the heart rate by inhibiting depolarization of the sinoatrial node via Gi protein-coupled receptors and through modulation of muscarinic potassium channels.