Heartbeat Flashcards
What does SA Node stand for?
Sinoatrial node
What is a heartbeat?
A single contraction of the heart
What is the ‘lub dub’ of a heartbeat?
2
The contraction of the atria
The contraction of the ventricles
How many types of cardiac muscle cells are there?
Two types
What are the two types of cardiac muscle cells?
Conducting system (internal wiring)
Contractile cells (muscle)
What does the conducting system do?
Controls and coordinates heartbeat
What does the contractile cells do?
Produce contractions that propel blood
What are the three main types of waves on an ECG trace?
P wave
QRS complex
T wave
What does a P wave indicate?
Depolarisation of the atria
What does a QRS complex indicate?
Ventricle depolarisation/excitation
What does a T wave indicate?
Ventricular repolarisation
What does an ECG measure?
Electrical activity of the heart (recorded on the surface)
What may an ECG identidy?
An area of tissue damage
What is depolarisation?
The signal for excitation
What is repolarisation?
The signal for relaxation
Why is co-ordinated contraction of the chambers of the heart needed?
To ensure correct timing of blood flow
What brings about co-ordinated contraction?
2
The conduction system (internal wiring)
Contractile muscle cells (myofibres)
What does AV node stand for?
Atrioventricular node
Where does the electrical activity of the heart start?
The pacemaker/SA node
What is the pathway for electrical activity in the heart?
5
Pacemaker/SA node
Atrial muscle
AV node (at the same time)
Along conduction pathway in ventricles
Across the ventricle muscle
How are muscle cells of the heart interconnected?
They are interconnected at intercalated discs
What allows excitation to spread from one muscle cell to another?
Cardiac myofibres
What happens when one part of a muscle sheath becomes excited?
All other myofibers in the sheath depolarise
What are sheaths of muscle also called?
Syncytia
Name the two syncytia of the heart.
Atrial syncytium
Ventricular syncytium
Why is a fibrous layer needed between the two syncytia?
To ensure the depolarisation of the atria does not spread to the ventria except at the AV node
Why can it be said that the heart tissue uses autorhythmicity
Because the heart tissue contracts rhythmically in the absence of neural and hormonal stimuli
List the five parts that make up the conduction system of the heart.
SA node/pacemaker
AV node
Bundle of His
Branch bundles
Purkinje fibres
What happens when the excitation reaches the AV node?
There is a delay
Why is a delay needed at the AV node?
To allow the atria to contract fully before the ventria depolarise and contract
Why is atrial contraction needed first?
To top up the ventria
What is an abnormally slow heart rate called?
Bradycardia
What is an abnormally fast heart rate called?
Tachycardia
What is bradycardia?
Abnormally slow heart rate
What is tachycardia?
Abnormally high heart rate
What is an ectopic pacemaker?
4
Abnormal cells
Generate high rate of action potentials
Bypass conducting system
Disrupt ventricular contractions
