LGS A-Level OCR Biology - Unit 3 - The cardiac Cycle, Heart Action Coordination, and ECGs
Electrical signals in the heart begin at the SAN, causing the atria to contract. The impulse then passes to the AVN, which delays the signal before sending it down the bundle of His. The signal travels to the apex and spreads through Purkyne fibres, triggering coordinated contraction of the ventricles.
Outline the movement of electrical signals through the heart
wave of depolarisation begins at SAN causes atria to contract
wave of depolarisation travels to AVN
AVN imposes slight delay before stimulating the bundle of His
AVN stimulates bundle of His
Bundle of His splits into two branches and conducts the wave of excitation to the apex
at apex Purkyne fibres spread out through ventricular walls
spread of excitation triggers the contraction of ventricles
Key Terms
Outline the movement of electrical signals through the heart
wave of depolarisation begins at SAN causes atria to contract
wave of depolarisation travels to AVN
AVN imposes slight delay before sti...
Why can the wave of depolarisation not travel directly to the ventricles?
There is a ring of non-conducting tissue between the atria and ventricles
Why is it important that the AVN imposes a slight delay?
Ensures the atria contract before the ventricles
- all atrial blood empties into ventricles before the ventricles contract
What does AVN stand for?
Atrial-ventricular node
What does SAN stand for?
Sino-atrial node
Why do ventricles contract from the apex up?
blood needs to be moved upwards
- ensures complete emptying of ventricles
Related Flashcard Decks
Study Tips
- Press F to enter focus mode for distraction-free studying
- Review cards regularly to improve retention
- Try to recall the answer before flipping the card
- Share this deck with friends to study together
| Term | Definition |
|---|---|
Outline the movement of electrical signals through the heart | wave of depolarisation begins at SAN causes atria to contract wave of depolarisation travels to AVN AVN imposes slight delay before stimulating the bundle of His AVN stimulates bundle of His Bundle of His splits into two branches and conducts the wave of excitation to the apex at apex Purkyne fibres spread out through ventricular walls spread of excitation triggers the contraction of ventricles |
Why can the wave of depolarisation not travel directly to the ventricles? | There is a ring of non-conducting tissue between the atria and ventricles |
Why is it important that the AVN imposes a slight delay? | Ensures the atria contract before the ventricles - all atrial blood empties into ventricles before the ventricles contract |
What does AVN stand for? | Atrial-ventricular node |
What does SAN stand for? | Sino-atrial node |
Why do ventricles contract from the apex up? | blood needs to be moved upwards - ensures complete emptying of ventricles |
What is the effect on the heart of the sympathetic nerve releasing noradrenaline? | Heart rate increases |
What is the effect on the heart of the vagus nerve releasing acetyl choline? | Heart rate decreases |
What does ECG stand for? | Electrocardiogram |
What does an ECG show? | Shows the spread of electrical excitation through the heart as a way of recording what happens when it contracts |
What are is the x axis on an ECG? | Time |
What are is the y axis of an ECG? | Electrical potential (mV) |
What does the P wave on an ECG show? | Depolarisation of atria in response to SAN triggering the atria to contract |
What does the QRS wave on an ECG show? | Ventricular systole wave of depolarisation in ventricle walls ventricles contract AV valve closes |
What does the T wave on an ECG show? | -ventricles relax |
How can heart rate be measured using an ECG? | -heart rate is time between peaks (R) |
What is the cardiac cycle? | The sequence of events that occur in the heart during one heartbeat |
What occurs during atrial diastole? | Both atria and ventricles are relaxed blood enters the right atrium via the vena cava and the left atrium via the pulmonary vein atria fill with blood AV valves are closed pressure in atria increases as they fill with blood semi-lunar valves are closed |
What occurs during atrial systole? | atria contract contract almost simultaneously atrial pressure higher than ventricular pressure so AV valves open the semi-lunar valves are still closed |
What occurs during ventricular systole? | ventricles fill with blood and contract AV valves close so blood isn’t forced back into the atria semilunar valves open with forces blood into the aorta/pulmonary artery |
What occurs during ventricular diastole? | pressure in the aorta and pulmonary artery increases ventricles relaxed semi-lunar valves close to prevent backflow |
What causes the heart sounds? | Blood hitting the heart valves |
What causes the ‘lub’ sound? | Blood hitting AV valves as ventricles contract |
What causes the ‘dub’ sound? | Backflow of blood hitting the semilunar valves |
When does the 'lub' sound happen? | During ventricular systole |
When does the 'dub' sound happen? | During ventricular diastole |
What happens when ventricular pressure is greater than atrial pressure? | AV valve closes as systole is entered |
Why do the semilunar valves open? | Because pressure in the aorta is lower than pressure in ventricles |
Why do the semilunar valves close? | The pressure in the aorta is greater than in the ventricles |
Why do AV valves open? | Atrial pressure is greater than ventricular pressure |
Why does ventricular pressure increase after the closing of the AV valve? | Due to the thicker ventricle wall |
As the ventricles contract what happens to the ventricular volume and pressure? | Volume decreases | Pressure increases |
What is arrhythmia? | An abnormal rhythm of the heart |
What is bradycardia? | The heart beats more slowly than normal rhythm |
What is Tachycardia? | A fast heart rate (pver 100bpm) |
What is ecotopic heartbeart? | Extra heartbeats that are out of the normal rhythm |
What is atrial fibrilation? | Abnormal rhythm of the heart when the atria beat very fast and incompletely |
How are ECGs measured? | electrodes stuck on skin measure electrical differences in the skin signal fed into machine which produces an ECG |