Heart

Question 1

What are the layers of the heart? (6)

Answer 1

Pericardium
Parietal pericardium
Pericardial space
Viseceral pericardium/ epicardium
Myocardium
Endocardium

Question 2

What supplies parasympathetic stimulation to the heart?

Answer 2

Vagus nerve (CN X) (innervates atria)

Question 3

What neurotransmitter is involved in the parasympathetic stimulation of the heart?

Answer 3

ACh (acetylcholine)

binds to muscarinic receptors

Question 4

What does parasympathetic stimulation of the heart cause? (3)

Answer 4

• Decreased heart rate
• Decreased force of contraction
• Decreased cardiac output

Question 5

What supplies sympathetic stimulation to the heart?

Answer 5

Postganglionic fibres innervate the entire heart

Question 6

What neurotransmitter and hormone are involved in the sympathetic stimulation of the heart?

Answer 6

Adrenaline

Noradrenaline

Question 7

What does sympathetic stimulation of the heart cause? (3)

Answer 7

• Increased heart rate
• Increased force of contraction
• Increased cardiac output

Question 8

Where does the initial depolarisation signal arise from in the heart?

Answer 8

SA node (conducting-system cells) located in RA

Question 9

Describe the path of depolarisation in the heart

Answer 9

1. SA node
2. AV node
3. Bundle of HIS
4. RBB/ LBB
   5 Purkinje fibres

Question 10

What mechanisms allow atrial contraction to fully complete before ventricular depolarisation begins?

Answer 10

Propagation of AP through the AV node is relatively slow

Ring of non-conducting tissue separates atria and ventricles

Question 11

What forms the majority of the thick filament?

Answer 11

Myosin

Question 12

What is myosin comprised of?

Answer 12

Two heavy pp chains

Four light pp chains

Question 13

What is the structure of myosin?

Answer 13

Two globular heads

Long intertwined tail

Question 14

What do globular myosin heads contain?

Answer 14

ATP binding site

Actin binding site

Question 15

What forms the majority of the thin filament?

Answer 15

Actin

tropomyosin and troponin

Question 16

What is the structure of actin?

Answer 16

Two intertwined helical chains (made of polymerised actin monomers)

Question 17

What is tropomyosin?

Answer 17

Long molecule that OVERLIES myosin binding sites on actin

Question 18

What is troponin?

Answer 18

On Ca2+ binding, troponin changes shape, dislocating tropomyosin and exposing myosin binding sites on actin

Question 19

What enables contraction to occur?

Answer 19

The movement of tropomyosin exposing myosin binding sites on actin

Question 20

What is a sarcomere?

Answer 20

Two successive Z-lines

Question 21

How is Ca2+ released in response to an AP in cardiac muscle?

Answer 21

Ca2+ enters through L-channels in T-tubules

Binds to ryanodine receptors on SARCOPLASMIC RETICULUM which releases more Ca2+

Question 22

How is Ca2+ released in response to an AP in skeletal muscle?

Answer 22

AP induces DHP receptors (in T-tubules) to pull open ryanodine receptors allowing Ca2+ release

Question 23

Why is the plateau phase important? (2)

Answer 23

Prevents tetany in case of recurrent stimuli

Allow the heart to fill (only happens during relaxation)

Question 24

Describe the 5 stages in generation of an AP in cardiac myocytes

Answer 24

0 - influx of Na+
1 - efflux of K+ through transient K+ channels
2 - influx of Ca2+ through L-type Ca2+ channels and efflux of K+
3 - efflux of K+
4 - Na+/K+ ATPase and open K+ channels

Question 25

Describe the 3 stages in generation of an AP in nodal cells

Answer 25

4 - declining K+ permeability, Na+ influx through F-type Na+ channels, Ca2+ influx through T-type Ca2+channels 0 - Ca2+ influx through L-type Ca2+ channels 3- L-type Ca2+ channels close, K+ channels open

Question 26

What are the main stages of AP generation (including relevant numbers)

Answer 26

``` 0 = depolarisation 1 = partial repolarsation 2 = plateau 3 = repolarisation 4 = reestablishing resting potential (polarised) ```

Question 27

Why is it the SA node that determines the pace of the heart?

Answer 27

SA nodal cells brought to threshold more rapidly than AV nodal cells, therefore, have a higher inherent depolarisation rate

Question 28

What does the P wave of an ECG show?

Answer 28

Atrial depolarisation

Question 29

What is shown by the PR interval?

Answer 29

Time taken for atria to depolarise and electrical activation to get through to AVN

Question 30

What does the QRS complex show?

Answer 30

Ventricular depolarisation

Question 31

What is shown by the T wave?

Answer 31

Ventricular repolarisation

Question 32

What does each small square represent on an ECG graph?

Answer 32

40ms (milliseconds)

Question 33

What does each big square represent on an ECG graph?

Answer 33

0.2s

Question 34

What occurs during systole?

Answer 34

Ventricular contraction | Blood ejection

Question 35

How long does systole last?

Answer 35

0.3s

Question 36

What occurs during diastole?

Answer 36

Ventricular relaxation | Blood filling

Question 37

How long does diastole last?

Answer 37

0.5s

Question 38

What is isovolumetric contraction? (3)

Answer 38

Pressure increases Fixed volume All valves are CLOSED

Question 39

Where is the tricuspid valve located? (what is it also known as?)

Answer 39

RA and RV | aka R atrioventricular valve

Question 40

Where is the bicuspid valve located? (what is it also known as?)

Answer 40

LA and LV | aka L atrioventricular valve, mitral valve

Question 41

What is isovolumetric relaxation? (3)

Answer 41

Pressure decreases Fixed volume All valves are CLOSED

Question 42

What is diastasis?

Answer 42

No net movement of blood into ventricles | Pressure between atria and ventricle equalises

Question 43

What is end-systolic volume?

Answer 43

Amount of blood remaining in ventricles after systole/ diastole Aka preload

Question 44

What is end-diastolic volume?

Answer 44

Amount of blood remaining in ventricles after diastole

Question 45

What is preload?

Answer 45

Volume of blood in ventricles just before contraction

Question 46

What is afterload?

Answer 46

Arterial pressure the ventricles have to overcome during contraction

Question 47

What is Starling’s law? (5)

Answer 47

``` Increase venous return Increase preload (EDV) Increase sacromere stretch Increase force of contraction Increase SV and therefore CO (even if HR constant) ```

Question 48

What increases stroke volume? (3)

Answer 48

Increased preload Increased sympathetic input Decreased afterload

Question 49

Give examples of muscular arteries

Answer 49

Aorta | Pulmonary artery

Question 50

What 2 factors facilitate venous return?

Answer 50

- Respiratory pump | - Skeletal muscle pump