1. SAN generates electrical impulses that cause cardiac muscle to contract
2. the rate at which the SAN fires is unconsciously controlled by medulla oblongata
3. stimuli are detected by internal receptors
1. pressure receptors, baroreceptors, in aorta or carotid arteries, stimulated by blood pressure
2. chemical receptors, chemoreceptors, in aorta, carotid arteries or medulla, stimulated by O2 and CO2 levels and pH
4. electrical impulses from receptors are sent to medulla along sensory neurones
5. medulla processes the information and sends impulses along sympathetic neurones (increases heart rate) or parasympathetic neurones (decreasing heart rate), part of autonomic nervous system