Cardiac impulse

Question 1

What is Audtorhythmicity?

Answer 1

The heart is capable of beating by itself, it does not need any external stimuli.

Question 2

Where does the heart beat initiate from?

Answer 2

Excitation of the pacemaker cells in the Sino-Atrial node initiates the heart beat.

Question 3

Where is the SA node located?

Answer 3

The upper right atrium, close to where the Superior Vena Cava enters.

Question 4

What is Sinus Rhythm?

Answer 4

It is when the heart is controlled by the SA node.

Question 5

What is the Pacemaker Potential?

Answer 5

It is the slow depolarisation of the membrane potential towards a threshold.

Question 6

What causes the depolarisation in the pacemaker potential?

Answer 6

Decrease in k+ efflux
Na+ and K+ influx (funny current)
Transient Ca++ influx (t type channels)

Question 7

What occurs once the pacemaker potential has reached the threshold?

Answer 7

The rising phase of Action Potential

Question 8

What causes the rising phase of action potential?

Answer 8

Long lasting l type Ca++ channels causing a Ca++ influx.

Question 9

What is the falling phase of action potential caused by?

Answer 9

Inactivation of l type Ca++ channels (efflux)

Activation of K+ channels (efflux)

Question 10

How does the electrical impulse of the SA node reach the AV node?

Answer 10

Cell-to-cell conduction

Question 11

What is the pathway of the impulse once it reaches the AV node?

Answer 11

AV node
Bundle of His
Left and Right Branches
Purkinje Fibres

Question 12

What is the AV node composed of?

Answer 12

Specialised cardiac cells

Question 13

Where is the AV node located?

Answer 13

The base of the right atrium just above the junctions of the atria and ventricles

Question 14

Why is the AV node the only electrical point of contact between the atria and ventricles?

Answer 14

The fibrous links do not allow action potential to pass through.

Question 15

Where does the spread of excitation arise from?

Answer 15

Cell to cell interactions via gap junctions and some internodal pathways.

Question 16

What does the delayed conduction in the AV node allow for?

Answer 16

Allows for the atria to contract (systole)

Question 17

What do the bundle of His and purkinjie fibres allow for?

Answer 17

The rapid spread of action potential to the ventricles.

Question 18

What is the resting membrane potential in cardiac cells before the are excited?

Answer 18

-90mV

Question 19

What phase is the rising phase of action potential in the cardiac muscle cells and what is it caused by?

Answer 19

Phase 0 and it’s due to a fast Na+ influx.

Question 20

What is Phase 1?

Answer 20

The closure of Na+ channels and transient K+ efflux

Question 21

What is Phase 2?

Answer 21

Mainly Ca++ influx (Plateau phase)

Question 22

What is Phase 3?

Answer 22

The closure of Ca++ channels and K+ efflux (falling Phase)

Question 23

What is Phase 4?

Answer 23

Resetting the membrane potential

Question 24

What is the plateau phase of the action potential?

Answer 24

Membrane potential maintained near the peak of the action potential for a few 100 milliseconds. It is a unique characteristic of contractile cardiac cells.
It is due to the influx of Ca++ through l type channels.

Question 25

What causes the falling Phase of the action potential?

Answer 25

Inactivation of Ca++ channels and activation of K+ channels (efflux)

Question 26

What influences heart rate?

Answer 26

The autonomic nervous system

Question 27

What noes the sympathetic nervous system do to heart rate?

Answer 27

Speeds it up

Question 28

What does the parasympathetic nervous system do to heart rate?

Answer 28

Slows it down

Question 29

What is the parasympathetic supply to the heart?

Answer 29

The vagus nerve

Question 30

What does the vagal tone do?

Answer 30

Slows the intrinsic heart rate from 100 to resting of 70

Question 31

What is a normal resting heart rate?

Answer 31

60-100bpm

Question 32

What is Bradycardia?

Answer 32

When the HR is below 60 bpm

Question 33

What is Tachycardia?

Answer 33

When the HR is above 100 bpm

Question 34

What does Vagal stimulation do?

Answer 34

Slows the heart and increases AV nodal delay

Question 35

How does Acetylcholine act?

Answer 35

Through muscarinic M2 receptors

Question 36

What is Atropine?

Answer 36

A competitive inhibitor of acetylcholine

Question 37

When would atropine be prescribed?

Answer 37

In extreme bradycardia to speed up the heart

Question 38

What does stimulating the vagal nerve do in terms of the rate of firing?

Answer 38

The rate of firing slows The cell Hyperpolarises and it takes longer to reach the threshold The slope of the pacemaker potential decreases (flattens) It has a negative chronotropic effect

Question 39

What is a negative chronotropic effect?

Answer 39

Slows the HR

Question 40

What do the cardiac sympathetic cells supply?

Answer 40

The SA and AV nodes and the myocardium

Question 41

What do the cardiac sympathetic cells do?

Answer 41

Increase the HR and decreases AV nodal delay | Increases force of contraction

Question 42

What does noradrenaline act through?

Answer 42

B1 adrenoceptors

Question 43

What impact does the stimulation of the cardiac sympathetic cells have?

Answer 43

The slope of the pacemaker potential increases (steep) Threshold is reached quicker The frequency of action potentials increases Positive chronotropic effect

Question 44

What is a positive chronotropic effect?

Answer 44

Increase in HR

Question 45

What is an RCG?

Answer 45

An electrocardiogram

Question 46

What is an ECG a record of?

Answer 46

The depolarisation and repoalrisation of the cycle of cardiac muscle obtained from the skin surface

Question 47

What are the electrodes places on the skin surface (Standard Limb Leads)

Answer 47

Lead 1- RA/LA Lead 2- RA/LA Lead 3- LA/LL

Question 48

How many standard limb leads are there?

Answer 48

3

Question 49

What limb remains earthed in an ECG

Answer 49

Right leg

Question 50

In an ECG what does P indicate?

Answer 50

Atrial depolarisation

Question 51

In an ECG what does the QRS complex show?

Answer 51

Ventricular depolarisation (masks atrial repolarisation

Question 52

In an ECG what does T indicate?

Answer 52

Ventricular repolarisation

Question 53

In an ECG what does the PR interval show?

Answer 53

The AV nodal delay

Question 54

In an ECG what does the ST segment show

Answer 54

Ventricular systole

Question 55

In an ECG what does TP interval show?

Answer 55

Diastole

Question 56

Why does the ECG not pick up atrial repolarisation?

Answer 56

It is masked by atrial repolarisation and is so small it cannot he detected by the skin