Control of heart rateAQA A-Level Biology: Mind map

Exam questions on Control of heart rate

1. A mammalian heart is removed from the body and placed in warm, oxygenated saline solution. All the nerves to it have been cut. The heart continues to beat rhythmically for several minutes.
   Explain why the wave of excitation is carried by Purkyne tissue down the septum to the apex of the heart before it spreads upwards through the ventricle walls.2 marks
2. A volunteer holds her breath for 30 seconds. During this time the carbon dioxide concentration of her blood rises and her heart rate increases from 70 to 85 beats per minute.
   Explain how the rise in carbon dioxide concentration leads to the increase in her heart rate.2 marks
3. Physiologists investigate how the autonomic nervous system controls the heart rate of an anaesthetised mammal at rest. With all nerves intact, the resting heart rate is 90 beats per minute. When the parasympathetic nerve to the sinoatrial node (SAN) was cut, the rate rose to 110 beats per minute. When the sympathetic nerve to the SAN was cut instead, the rate fell to 80 beats per minute. When both nerves were cut, the heart continued to beat at 100 beats per minute.
   The blood pressure of this mammal suddenly rises. Describe how pressure receptors lead to a return of the heart rate towards normal.3 marks