Electrical System of the Heart Flashcards
How does the heart’s electrical system develop?
During embryonic development, some cells become autorhythmic
An inherent and rhythmic ______ activity is the force behind the heart’s continuous beating, but it is regulated by _________ (___).
Electrical
Hormones (ANS)
What is the “pacemaker” of the heart?
SA Node
What does SA Node stand for?
Sinoatrial node
Where is the SA node?
Medial to the opening of the superior vena cava
The SA node has an inherent rate of ___ bpm, but “____ ____” holds the HR to__-__ bpm
100
Vagal Tone
70-80
The normal heartbeat triggered by the SA node is called ______ ______.
Sinus rhythm
Signal goes from the SA node to…
Both Atria
AV node stands for?
Atrioventricular node
Where is the AV node?
In lower interatrial septum, above tricuspid valve
What does the AV act as?
This node acts as an electrical gateway to the ventricles
What happens to the electrical impulse at the AV node?
At AV node, impulse is delayed .1 seconds, allowing the atria to respond and complete their contraction before the ventricles contract
The AV bundle is also called the …
Bundle of His
Where is the bundle of His?
Superior part of interventricular septum
What is the only electrical connection between the atria and ventricles?
Bundle of His/AV bundle
The AV bundle forks into __ branches. Called…?
2
Right and Left Branches
Where are the right and left branches? Where do they go?
Both in interventricular septum
They descend towards the apex of the heart, continuing to separate ventricles
What are Purkinje fibers?
Nerve like processes that arise from the lower bundle branches and turn upwards to spread throughout the ventricular myocardium
Purkinje fibers are _______ ______ cells to conduct signal rapidly. The network is more elaborate in the ____ ventricle.
large diameter
Left
The electrical signal comes first to the papillary muscles, then the ventricle from _____ _____.
Purkinji fibers
In the heart, signals pass from cell to cell via…
Gap junctions and intercalated discs
What is an EKG?
Electrocardiogram- Detects the conduction of action potentials through the myocardium during the cardiac cycle
What does an EKG do? How does it work?
This gives a wealth of information about heart function
The cardiac cycle produces electrical currents that can be measured at the surface of the body
What is the P wave?
Atrial depolarization-Onset of atrial contraction
During the P wave, where is electrical current I the heart?
Spreads from SA node through atria
What is the QRS complex?
Ventricular depolarization (atrial repolarization hidden here) Onset of ventricular contraction
Why does the QRS complex have a complex waveform?
Due to different sizes of the two ventricles and different lengths for them to depolarize
What is the T wave?
Ventricular repolarization
Repolarization is slower than _____________.
Depolarization
Describe the T wave in regards to the QRS complex.
The T wave is more spread out and lower in amplitude than the QRS complex
What is the P-Q interval? How long does it take?
Atria contract and begin to relax
This is the time it takes for the signal (impulse) to travel from SA to AV nodes ~.16 sec
What is the Q-T interval? How long does it take?
Ventricles contract and begin to relax, 0.38 seconds
What is the S-T segment?
Ventricles ejecting blood
What is the cardiac cycle? What EKG letters describe the cardiac cycle?
Repetitive pumping process, all events PQRST
1 complete contraction and relaxation of all 4 heart chambers
How long is the cardiac cycle?
About .8 seconds in a normal adult; .25-.3 seconds in a newborn
Can be 1.0 seconds or more in an athlete
