Chapter 18.5 Electrical Conduction-Cardiovascular System

Question 1

What does conduction consist of?

Answer 1

specialized cardiac muscle tissue that generates and distributes action potentials

Question 2

What are components of conduction system?

Answer 2

Sinoatrial (SA) node (pacemaker)
Atrioventricular (AV) node
Atrioventricular (AV) bundle (bundle of His)
Right and left bundle branches, and
Purkinje fibers

Question 3

What is meaning of automaticity in relation to cardiac muscle tissue?

Answer 3

It means Cardiac muscle tissue contracting on its own in absence of neural or hormonal stimulation

Question 4

What are part of heart’s conducting system and is also known as?

Answer 4

cells responsible for initiating and distributing stimulus to contract, which are also known as cardiac conduction system or nodal system.

Question 5

What is SA NODE called

Answer 5

Pacemaker

Question 6

What does SA Node initiate?

Answer 6

Initiates AP(Action Potential) ~100 times faster than any other region in conducting system

Question 7

What is SA Node influenced by?

Answer 7

Influenced by neurotransmitters and hormones

Question 8

What can ANS (sympathetic and parasympathetic) modify but does not establish?

Answer 8

Can modify HR(Heart Rate), but does not establish heart’s fundamental rhythm

Question 9

Where is SA node located and how does it contribute to conduction system?

Answer 9

Located at RA(Right Atrium) wall, inferior to SVC(superior vena cava) opening.
And AP(Action Potential) spontaneously arises and then conducts to both atria so that they finish contracting at same time

Question 10

Where is AV NODE located and how does it contribute to conduction system?

Answer 10

Located at Interatrial septum, inferior to coronary sinus and AP slows considerably, allowing for atria to empty

Question 11

Where is AV Bundle (Bundle of His) located and how does it contribute to conduction system?

Answer 11

Located at Interventricular septum and it is Only site where AP can conduct from atria to ventricles

Question 12

How do Right and Left Bundle Branches contribute to conduction system?

Answer 12

Extend through interventricular septum towards apex

Question 13

Where is Purkinje Fibers located and how does it contribute to conduction system?

Answer 13

Originate near apex, extends upwards and AP rapidly conducts from apex to remainder of ventricular myocardium

Question 14

What is heart innervated by?

Answer 14

innervated by both sympathetic and parasympathetic nerve fibres

Question 15

What does SNS innervate?

Answer 15

entire heart muscle and node cells which release NE

Question 16

What does Parasympathetic system innervate?

Answer 16

node cells which releases primarily acetylcholine

Question 17

What happens when there is reduction in potassium permeability?

Answer 17

Fewer K+ ions move out of cell when membrane potential is negative

Question 18

How do voltage-gated sodium channels in SA node contribute to depolarization?

Answer 18

They open when membrane potential is negative (-60mV), allow positively charged Na+ to move into cell which end up leading to depolarization

Question 19

As membrane depolarizes, what does calcium channels opening allow?

Answer 19

Allow further influx of positively charged ions (Ca2+) and e SA node cells to reach threshold level;causes action potential

Question 20

What does Electrocardiogram (ECG) record

Answer 20

electrical changes that accompany heartbeat

Question 21

What is charge of Resting Membrane Potential?

Answer 21

negative, so change towards positive =depolarization occurring

Question 22

What are 3 Waves identified on ECG

Answer 22

P Wave (~0.08 sec), QRS Complex (~0.12 sec), and T Wave (~0.16 sec)

Question 23

What does P wave represent in electrocardiogram (ECG), and what happens after it?

Answer 23

Represents depolarization from SA node through atria and Atrial contraction follows

Question 24

What does QRS complex represent in electrocardiogram (ECG), and what happens after it?

Answer 24

Represents Ventricular depolarization and is followed by
ventricular contraction

Question 25

What occurs at T Wave?

Answer 25

Ventricle repolarization begins to occur

Question 26

What does single cardiac cycle include?

Answer 26

all of events associated with one heartbeat

Question 27

What would systole and diastole mean?

Answer 27

Systole = Contraction (ejection)
Diastole = Relaxation (filling)

Question 28

What happens during atrial systole and ventricular filling in cardiac cycle, and how does it relate to ECG waveform?

Answer 28

Blood flow from body to atria to ventricles and AV valves open; SL valve closed.
At same time, Firing of SA node = atrial depolarization-P wave
and Atrial systole pushes rest of blood into ventricles (P to Q(RS))

Question 29

What happens during Ventricular Systole in cardiac cycle, and how does it relate to ECG waveform?

Answer 29

Ventricular depolarization – QRS Wave,
Ventricular contraction begins; AV valve closes –“lub”,
Small “isovolumetric contraction” – all valves are closed,
and Opening of SL valve

Question 30

What happens during Ventricular Diastole in cardiac cycle, and how does it relate to ECG waveform?

Answer 30

Ventricular repolarization – T wave,
Ventricles relax (diastole),
SL valve close “dub”, All valves closed - isovolumetric relaxation,
and AV valves open

Question 31

What is Arrhythmias?

Answer 31

Irregular heart rhythm due to defect in conduction system

Question 32

What happens during arrhythmias?

Answer 32

SA node disrupted

Question 33

What would be causes of arrhythmias?

Answer 33

Coronary artery disease – atherosclerosis
– Hypertension
– Myocardial infarction
– Hyperthyroidism
– Defective heart valves
– Stress
– Drugs and chemicals