**A&P 2 Unit 16 & 18 (Lab) [The Heart, Part 2] Flashcards
Sinoatrial (SA) Node
- The heart’s natural pacemaker, with fastest rate of depolarization (100/min)
- Right atrium near opening of SVC
Atrioventricular (AV) Node
- Lower right atrium
- Medial to tricuspid valve
- AV node briefly delays the impulse
Atrioventricular (AV) Bundle
- Pathway between AV node and bundle branches
- Creates the only electrical connection between the atria and ventricles through a non-conducting fibrous “skeleton”
Bundle Branches (Right & Left)
Two branches through the interventricular septum towards apex
Purkinje Fibers
Conduct the impulse from apex, superiorly, in the outer ventricular walls
Internodal Pathways
- Located in the walls of the atria.
- Links the SA node to the AV node.
- Function: Distributes the action potential to the contractile cells of the atria.
Two Features Allow the Depolarizations to Spread Rapidly
- Gap junctions
- Branching Cardiac Fibers
Explain the role of gap junctions in the spread of depolarization in the myocardium.
They directly connect the cytoplasm of two cells, which allows various molecules and ions to pass freely between cells.
Summary of depolarization through the conduction system and muscle
- SA node depolarizes
- Electrical activity goes rapidly to AV node via internodal pathways
- Depolarization spreads more slowly across atria. Conduction slows through AV node.
- Depolarization moves rapidly through ventricular conducting system to the apex of the heart.
- Depolarization wave spreads upward from the apex.
The atria and ventricles are two separate bundles of muscle, separated by an internal fibrous septum
- The atria contract as a unit.
- After a brief delay in the AV node, the impulse spreads to the ventricles.
- The ventricles contract as a unit (while the atria relax).
Electrocardiogram (ECG, EKG)
The ECG records the heart’s electrical activity (pacemaker cells and contractile cells)
- Electrodes at the skin surface detect the directions of depolarizations and repolarizations
- The instrument (electrocardiograph) records and displays the data from pairs of different electrode combinations. Each combination is called a Lead.
- There are 12 Leads, each providing a different electrical view of the heart
P Wave
Atrial depolarization:
- Begins when SA node fires
- Depolarization travels through atria
- Atria contract
QRS Complex
Ventricular depolarization:
- Depolarization reaches the ventricles
- Through bundle branches, Purkinje fibers
- Ventricles contract
- Atria repolarize during QRS (hidden wave)
T Wave
Ventricular repolarization:
- As T wave peaks, ventricles are relaxing
Auscultation
The technique of listening to body sounds
Stethoscope
Detects and amplifies body sounds (heart, lungs, GI tract)
Diaphragm (Stethoscope)
- Flat, broad side
- Used most often in heart auscultation
- Light pressure – for higher-pitched sounds
- Heavier pressure – for lower-pitched sounds
Bell (Stethoscope)
- Smaller, concave side
- Detects low-pitched sounds