Explain how increased blood CO2 leads to an increased heart rate

The high CO2 rate is detected by chemoreceptors in the aorta. The chemoreceptors send impulses to the medulla in the brain. The medulla then sends impulses along sympathetic neurons to the sinoatrial node in the heart. The neurons release noradrenaline which binds to receptors on the sinoatrial node. This binding causes the sinoatrial node to send impulses at a faster rate, therefore increasing heart rate.