Conducting System Of The Heart

Question 1

What is the cardiac conduction system

Answer 1

Collection of nodes and specialised conduction cells that initiate and coordinate contraction of the heart muscle

Question 2

Heart conduction

Answer 2

Sequence of electrical events during one full contraction of the heart muscle
An excitation signal (an action potential) created by the sinoatrial (SA) node
The wave of excitation spreads across the atria causing the, to contract
Upon reaching the atrioventricular (AV) node, signal is delayed
It is then conducted to the bundle of His, down the interventricular septum
The bundle of His and Purkinje fibres spread the wave impulses along the ventricles causing them to contract

Question 3

Sinoatrial (SA) node

Answer 3

Collection of specialised pacemaker cells located in upper wall of right atrium at the junction where superior vena cava enters
Can spontaneously generate electrical impulses. Wave of excitation created by SA node spreads via gap oss both atria resulting in atrial contraction (atrial systole) with blood moving from atria into the ventricles
Rate at which SA node generates impulses influenced by autonomic nervous system

Question 4

Sympathetic nervous system and the SA node

Answer 4

Increases firing rate of SA node, thus increases heart rate

Question 5

Parasympathetic nervous system and SA node

Answer 5

Decreases firing rate of SA node and decreases heart rate

Question 6

Atrioventricular node

Answer 6

After electrical impulses spread across atria, they converge at the atrioventricular node located within the atrioventricular septum near opening of coronary sinus
AV node acts to delay impulses by approx 120ms to ensure atria have enough time to fully eject blood into ventricles before ventricular systole
Wave of excitation passes from atrioventricular node into atrioventricular bundle

Question 7

Atrioventricular bundle (bundle of His)

Answer 7

Continuation of specialised tissue of AV node, transmits electrical impulse from AV node to Purkinje fibres of ventricles
Descends down membranous part of interventricular septum before dividing into bundles

Question 8

Atrioventricular bundle - right bundle branch

Answer 8

Conducts the impulse to purkinje fibres of the right ventricle

Question 9

Atrioventricular bundle - left bundle branch

Answer 9

Conducts the impulse to the purkinje fibres of the left ventricle

Question 10

Purkinje fibres

Answer 10

Sub-endocardial plexus of conduction cells
Abundant with glycogen and have extensive gap junctions
Located in subendocardial surface of ventricular walls, able to rapidly transmit cardiac action potentials from atrioventricular bundle to myocardium of ventricles
Rapid conduction allows coordinated ventricular contraction (ventricular systole) and blood moved from right and left ventricles to pulmonary artery and aorta respectively