Explain how a rise in blood pressure results in a decrease in the rate of heartbeat.

Baroreceptors detect the rise in blood pressure in the aorta, they send impulses to the cardiovascular centre. Then, impulses are sent via parasympathetic nerves to the SAN. This triggers the release of ACh, this decreases the frequency of impulses to the AVN. As a result the rate of atrial and ventricular contraction is lower, so the "heartbeat" is slower.