The cardiac cycle, heart action coordination, and ECGs Flashcards Preview

OCR A level biology > The cardiac cycle, heart action coordination, and ECGs > Flashcards

Flashcards in The cardiac cycle, heart action coordination, and ECGs Deck (38):
1

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

2

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

3

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

4

What does AVN stand for?

Atrial-ventricular node

5

What does SAN stand for?

Sino-atrial node

6

Why do ventricles contract from the apex up?

-blood needs to be moved upwards
-ensures complete emptying of ventricles

7

What is the effect on the heart of the sympathetic nerve releasing noradrenaline?

Heart rate increases

8

What is the effect on the heart of the vagus nerve releasing acetyl choline?

Heart rate decreases

9

What does ECG stand for?

Electrocardiogram

10

What does an ECG show?

Shows the spread of electrical excitation through the heart as a way of recording what happens when it contracts

11

What are is the x axis on an ECG?

Time

12

What are is the y axis of an ECG?

Electrical potential (mV)

13

What does the P wave on an ECG show?

Depolarisation of atria in response to SAN triggering the atria to contract

14

What does the QRS wave on an ECG show?

-Ventricular systole
-wave of depolarisation in ventricle walls
-ventricles contract
-AV valve closes

15

What does the T wave on an ECG show?

-ventricles relax

16

How can heart rate be measured using an ECG?

-heart rate is time between peaks (R)

17

What is the cardiac cycle?

The sequence of events that occur in the heart during one heartbeat

18

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

19

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

20

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

21

What occurs during ventricular diastole?

-pressure in the aorta and pulmonary artery increases
-ventricles relaxed
-semi-lunar valves close to prevent backflow

22

What causes the heart sounds?

Blood hitting the heart valves

23

What causes the 'lub' sound?

Blood hitting AV valves as ventricles contract

24

What causes the 'dub' sound?

Backflow of blood hitting the semilunar valves

25

When does the 'lub' sound happen?

During ventricular systole

26

When does the 'dub' sound happen?

During ventricular diastole

27

What happens when ventricular pressure is greater than atrial pressure?

AV valve closes as systole is entered

28

Why do the semilunar valves open?

Because pressure in the aorta is lower than pressure in ventricles

29

Why do the semilunar valves close?

The pressure in the aorta is greater than in the ventricles

30

Why do AV valves open?

Atrial pressure is greater than ventricular pressure

31

Why does ventricular pressure increase after the closing of the AV valve?

Due to the thicker ventricle wall

32

As the ventricles contract what happens to the ventricular volume and pressure?

Volume decreases
Pressure increases

33

What is arrhythmia?

An abnormal rhythm of the heart

34

What is bradycardia?

The heart beats more slowly than normal rhythm

35

What is Tachycardia?

A fast heart rate (pver 100bpm)

36

What is ecotopic heartbeart?

Extra heartbeats that are out of the normal rhythm

37

What is atrial fibrilation?

Abnormal rhythm of the heart when the atria beat very fast and incompletely

38

How are ECGs measured?

-electrodes stuck on skin
-measure electrical differences in the skin
-signal fed into machine which produces an ECG