Control of Resting Heart Rate
Laura Armstrong
Teacher
Recall Questions
This topic requires prior knowledge of heart structure. You can test your knowledge on this below.
Which blood vessels supply the heart muscle with oxygenated blood?
The coronary arteries.
What is the function of the SAN in the heart?
It initiates the electrical impulses that control the heart’s contraction. It is known as the heart’s pacemaker.
Where is the SAN located?
In the wall of the right atrium.
Topic Explainer Video
Check out this @LauraDoesBiology video that explains control of resting heart rate or read the full notes below. Once you've gone through the whole note, try out the practice questions!
The SAN and Myogenic Control
- The Heart is myogenic: it can contract without external stimulation.
- The sinoatrial node (SAN), located in the wall of the right atrium, initiates a wave of electrical activity at regular intervals.
- This causes both atria to contract simultaneously.
Sequence of Normal Heartbeat
- The SAN initiates a wave of electrical activity / an electrical impulse.
- Impulse spreads across atria, causing atrial systole (contraction).
- Impulse is delayed at the AVN to allow full atrial emptying.
- The impulse can only pass from atria to ventricles via the AVN as there is a layer of non-conducting tissue between the atria and the ventricles.
- AVN passes impulse down the Bundle of His in the septum and into Purkyne fibres.
- This causes ventricular systole, starting at the apex (base of heart) and spreading up over the ventricle walls.
- The impulse spreads upwards over the walls of the ventricles to make sure they are empty of blood and that blood is moved up into the arteries.
(Under resting conditions a normal, steady heart rate is around 70 bpm).
Key Terms
- SAN (Sinoatrial Node): Natural pacemaker that initiates the heartbeat.
- Myogenic: Muscle contraction that originates within the muscle itself.
- Atrial Systole: Atrial contraction.
- Ventricular Systole: Ventricle Contraction.
- Purkyne Fibres: Specialised, rapid-conducting cells in the heart's ventricular walls.
No answer provided.
Exam Tips
In questions about the control of heart rate at rest include the role of:
The SAN, The AVN, The bundle of His and the Purkyne fibres.
You may have to explain why the ventricles contract from the apex up.
No answer provided.
Describe how the heart rate is controlled at rest. (5 marks)
- SAN releases (wave of) electrical activity / electrical impulse.
- Atria contract (at the same time).
- Accept systole for ‘contract’.
- AVN relays/passes electrical activity after a (short) delay.
- (Via) bundle of His and Purkyne tissue.
- Ventricles contract (at the same time from bottom upwards).
- Accept systole for ‘contract’.
Practice Question
Try to answer the practice question from the TikTok on your own, then watch the video to see how well you did!