Cardiac Cycle

Question 1

P wave -

Answer 1

Depolarization of atrial myocardium

Question 2

QRS-complex -

Answer 2

Depolarization of ventricular myocardium

Question 3

T-wave -

Answer 3

Repolarization of ventricular myocardium

Question 4

Sinoatrial (SA) node

Answer 4

• located in the right atria, medial to the opening of the superior vena cava.
• generates cardiac action potentials spontaneously, which allows the heart to beat spontaneously and independently of nerves.
• generates cardiac action potentials at a greater frequency than other cardiac muscle cells
• activation leads to excitation along the internodal tracts towards the left atrium and AV node. This results in atrial contraction.

Question 5

Atrioventricular (AV) node and bundle of His

Answer 5

• the AV node is located medial to the right ventricular valve
• action potentials are propagated slowly through these areas compared to the rest of the hearts conduction system
• ventricular depolarization precedes ventricular contraction
• the propagation delay allows atrial contraction to be completed, and the ventricles to fill with blood before ventricular contraction begins

Question 6

Bundles of His

Left and right bundle branches

Answer 6

• the electrical condition pathway divides at the interventricular septum form the left and right bundle branches.
• the branches descend to the apex of each ventricle
• at the ventricle apex, the bundle branches divide repeatedly for distribution throughout the ventricular walls
• ventricular depolarization precedes ventricular contraction

Question 7

Purkinje fibers

Answer 7

• the terminal branches of the bundle branches become Purkinje fibres, cardiac muscle fibre that have structural modifications
• these modifications allow action potentials to travel more rapidly than they would in cardiac muscle tissue
• the Purkinje fibers are found toward the endocardial surface. Thus, electrical activity at any level travels outward towards the epicardial surface