Download Coordination of the cardiac cycle. ECG

Coordination of cardiac cycle
- ensures coordinated contractions of
all 4 chambers of heart
(prevents fibrillation – atria and
ventricles contracting at different
frequencies)
Heart muscle = cardiac muscle
• Myogenic – can generate its own contractions (will contract and relax in rhythm
even out of the body)
Intercalated discs
(junctions of muscle cells)
Connective tissue and blood
capillaries between muscle
fibres
Cardiac muscle
fibre
nucleus
striations
Coordination of cardiac cycle
- structures involved
Vena cava
Aorta
Sinoatrial node (SAN)
Atrioventricular node (AVN)
Right atria
Right ventricle
Left atria
Purkyne fibres
Left ventricle
Stimulating the heart to contract
Identify each of the following
• Patch of tissue that initiates heartbeat by sending
waves of excitation over atria wall (pacemaker)
• Patch of tissue at the base of atrium/top of septum
of heart where wave of excitation is delayed and
which conducts electrical excitation from atria to:
• specialised muscle fibres in septum which conduct
electrical excitation from AVN down septum to apex
(base) of ventricles
Identify each of the following
• Patch of tissue that initiates heartbeat by sending waves of
excitation over atria wall (pacemaker) SAN sinoatrial node
• Patch of tissue at the base of atrium/top of septum of heart
where wave of excitation is delayed and which conducts
electrical excitation from atria to septum AVN
atrioventricular node
• specialised muscle fibres in septum which conduct
electrical excitation from AVN down septum to apex (base)
of ventricles Purkyne fibres
This diagram shows the timing of the wave of excitation as it passes
across the surface of the heart. An ELECTRO-CARDIOGRAM (ECG)
shows this electrical activity.
The different phases of an ECG
The electrocardiogram
- graph showing electrical activity of cardiac muscle (atria and
ventricles) during a cardiac cycle
P = excitation of atria
(atrial systole)
QRS = excitation of
ventricles (ventricular
systole)
T = diastole
Tachycardia
Bradycardia
Ectopic heartbeat
Fibrillation