PPT 2 EXAM 3: conduction, ECG and cardiac cycle

Question 1

name the 4 main structures of the heart that perform cardiac conduction + explain functions

Answer 1

1) Sinoatrial node (pacemaker) : SA
- initiates electrical impulse

2) Atrioventricular node : AV
- pauses the impulse
*depolarization??
3) Atrioventricular bundle: AVB
- conducts the impulse down to the apex
- also called the ‘Bundle of His’

4) Purkinje fibers: (PK subban)
- spread the impulse to contractile cells of the ventricles

Question 2

order the steps of cardiac conduction (6)

Answer 2

1) resting conduction system

2) SA node initiates eletrical impulse: it spreads across atria, then they contract

3) AV node delays the impulse while atria finish their contraction

4) impulse travel through AV bundle and Purkinje fibers

5) Impulse spreads across ventricles from the apex UPWARD (to ensure it spreads correctly AND to provent blood backflow)

6) Ventricles contraction starts at the apex and moves upward

Question 3

CARDIAC MUSCLE
name the main 3 components of the cardiac muscle.

Answer 3

1) Contractile cells
2) Conducting cells
3) intercalated discs

Question 4

explain what contractile cells are (3)

Answer 4

• 99% of the cardiac muscle
• electrically conductiv
• they contract

Question 5

explain what conducting cells are (5)

Answer 5

• 1% of the cardiac muscle
• electrical conduction system ***mainly
• they initiate and propagate the action potential
• under the influence of the nervous and endocrine systems
• they are also autorythmic

Question 6

explain what intercalated discs are (4)

Answer 6

• they hold cells together with 2 junctions: desmosomes and gap junctions
• they allow electricity to flow through all heart cells= SYNCHRONOUS CONTRACTION
• they have the ability to depolarize and repolarize

(- contributes to the striated marks of the heart)

Question 7

Intercalated discs:
Differentiate desmosomes from gap junctions

Question 8

Explain the CARDIAC CYCLE: differentiate systole and diastole

Answer 8

• it starts with contraction of atria
• it ends with ventricular relaxation

CONTRACTION = systole
- atria syst: blood enters ventricles
then
- ventricular syst: blood enters arteries

RELAXATION = diastole
- the heart chambers fill with blood (from pulmonary veins) since it is the time at which lowest pressure

Question 9

what is a heart rate?

Answer 9

it’s the number of cardiac cycles per min
ex: 60 bpm= 60 cycles per min