Cardiac Action Potentials And ECGs

Question 1

What determines direction of flow?

Answer 1

Pressure
Valves

Question 2

Deoxygenated blood pathway to oxygenated blood to body

Answer 2

Deoxygenated blood is pumped by the right ventricle into the lungs via the pulmonary arteries to become oxygenated
Then returns to the heart to be pumped around the body but the left ventricle (the wall of the LV is thicker)

Question 3

Direction of flow through the heart is controlled by. Two factors:

Answer 3

Pressure+valves
Pressure increases as the chamber of the heart contract and blood will want to flow from high to low pressure
Pressure is almost mostly responsible for opening and closing of valves which help to direct the flow of blood

Question 4

Systole vs diastole

Answer 4

Systole : contraction
diastole : relaxation

Question 5

Cardiac cycle and times

Answer 5

Atrial systole begins 0-100msec

Atrial systole ends, atrial diastole begins 100-370 msec
Ventricular systole- first phase
Ventricular systole- second phase

Ventricular diastole -early 370-800 msec
Ventricular diastole -late

Question 6

What happens at atrial systole?

Answer 6

Atrial contraction forces small amount of additional blood into relaxed ventricles

Question 7

What happens at ventricular systole: first and second phase?

Answer 7

First phase= ventricular contraction pushes AV valves closed but does not create enough pressure to open semilunar valves
Second phase= as ventricular pressure rises and exceeds pressure in arteries the semilunar valves open and blood ejected

Question 8

What happens at ventricular diastole - early and late

Answer 8

Early- ventricles relax pressure in ventricles drops; blood flows back against cusps of semilunar valves and forces them closed. Blood flows into relaxed atria
Late- all chambers are relaxed. Ventricles fill passively

Question 9

Isovolumetric contraction

Answer 9

Right when atriole diastole begins, ventricular contracting = av valves close but then there is a short period where pressure increases in ventricles as they contract but there is no movement of blood

Question 10

Is there a positive or negative charge inside cell?

Answer 10

More negative charge

Question 11

Chemical gradient in cells established by?

Answer 11

Na/K ATPase
High K inside and low outside
High Na outside and low inside

Question 12

In resisting state explain Na/K ATPase

Answer 12

Relatively impermeable to Na, but there is some movement of K
Facilitated by so called potassium ‘leak’ channels= electrical gradient

Question 13

Equilibrium potential of an ion is?

Answer 13

The membrane potential at which the electrical and chemical forces acting on that ion are in balance and there is no net movement of the ion

Question 14

Membrane potential of K and Na

Answer 14

K= -90 mV
Na= +60 mV

Question 15

Depolarisation is when?

Answer 15

Membrane potential becomes more positive than resting membrane potential

Question 16

Repolarisation is when?

Answer 16

The membrane potential is in a depolarised state and returns back to resting

Question 17

Why does cardiac action potential have a longer duration than typical neuronal action potential?

Answer 17

This is because of the plateau phase due to Ca2+ entry

Question 18

Phases in cardiac AP+ how long does it last roughly?

Answer 18

Phases 1-4
200 ms

Question 19

Cardiac action potential: phase 0

Answer 19

Depolarisation caused by opening of Na channels

Question 20

Cardiac action potential: phase 1

Answer 20

Transient repolarisation
At this phase Na channels inactivate
K channels open and membrane starts to repolarise (as the positively charged K leave the cell)

Question 21

Cardiac action potential: phase 2

Answer 21

Plateau phase where Ca 2+ channels open Ca enters the cell
K+ still open
No net movement of charge as flow of these two ion’s balance out (both +tive)

Question 22

Cardiac action potential: phase 3

Answer 22

Ca channels close and K+ are open
Membrane repolarisation as the k+ ions leave the cell

Question 23

Calcium influx =

Answer 23

Contraction
Calcium binds to troponin

Question 24

When Ca2+ enters the cell during cardiac AP what happens? Effect -linked to contraction

Answer 24

Binds to troponin which is attached to tropomyosin which causes conformational change in tropomyosin and exposes myosin binding site on the actin fibre
Allowing it to interact with actin and we get cross bridge formation = initiates contraction

Question 25

Action potentials are what type of signals?

Answer 25

Electrical

Question 26

Action potentials initiate where? And pathway

Answer 26

In SA node and spread around the heart in the cardiac conduction system
Electrical signal reaches cardiomyocytes in atrial and ventricles= spread to those contractile cells = no AP in these cells

Question 27

Muscle cells /cardiomyocytes are functionally coupled to other muscle cells by? Benefit?

Answer 27

Intercalated discs with gap junctions= allow spread of electrical activity to pass from cell to cell
When reached individual cell = initiates AP with associated Ca2+ influx so contraction

Question 28

The AP looks different (regional changes) in the heart why?

Answer 28

Due to regional differences in ion channels in different parts of the heart

Question 29

Initiating region of electrical impulse

Answer 29

SINOATRIAL NODE SAN

Question 30

Delay node to enable ventricular filling?

Answer 30

Atrioventricular (AV) node

Question 31

Bundle branches define:

Answer 31

Electrical conductance pathways through left and right myocardium, include bundle of HIs

Question 32

Purkinje fibres:

Answer 32

Specialised cardiac myocardium-like cells that are responsible for translating electrical impulse into contractile force

Question 33

Resting membrane potential depolarised at around?

Answer 33

-60mV

Question 34

SA node fires about ? How many times?

Answer 34

80-100 times per minute to initiate the heart beat

Question 35

Threshold potential around?

Answer 35

Between -50 and -55 mV

Question 36

Impulse conduction through the heart steps:

Answer 36

1. Electrical activity initiates in the SA node
2. Spreads out through the right atria to AV node and also across to left atria (note= spread of depolarisation and AP firing in atrial cardiomyocytes)
3. When it reaches AV node 100msec delay. Atria contract
4. Impulse travels along interventricular septum down the bundle branches and into purkinje fibres
5. Distributed by purkinje fibres and relayed throughout ventricular myocardium. Atria contraction completed. Ventricular contraction begins =225m sec

Question 37

When electrical activity reaches AV node there is 100msec delay why?

Answer 37

Allows the atria to contract before the ventricles

Question 38

ECG measure?

Answer 38

The electrical activity in the heart
Records atrial and ventricular depolarisations and repolarisations

Question 39

Atrial depolarisation on ECG?

Answer 39

P wave
Spread of electrical activity in atria

Question 40

Ventricle depolarisation in ECG?

Answer 40

QRS complex
Spread of electrical activity into the ventricles

Question 41

Ventricular repolarisation in ECG?

Answer 41

T wave
Return of resting membrane potential in the ventricles

Question 42

We can study ECGs to detect?

Answer 42

Abnormalities in the electrical conduction system
Cardiologists analyse specific intervals and segments to study and diagnose specific abnormalities in cardiac function

Question 43

The p WAVE initiates before?

Answer 43

Atrial systole

Question 44

QRS complex initiates before?

Answer 44

Ventricular systole

Question 45

T wave occurs ?

Answer 45

At the end of ventricular systole before ventricular diastole
=spread of repolarisation which represents recovery phase of the cardiac AP to allow myocytes to relax

Question 46

When do AV valves open? And close?

Answer 46

When atrial pressure is higher than ventricular pressures + close when pressure gradient reversed

Question 47

When do semilunar valves open and close?

Answer 47

Open when ventricular pressure is higher than aortic/pulmonary pressure and close when pressure gradient reversed