Summary OCR A/AS-Level Biology 3.2.6 Coordination of the Cardiac Cycle

Coordination of The
Cardiac Cycle
Myocytes (myogenic cells) = polarised cells that initiate their own contraction
Purkyene tissue = muscle fibres that conduct the wave of excitation


 Myocytes have a slight charge across their membrane (polarised)
 Allows them to be affected by the wave of excitation
 When the charge is reversed, they become depolarised
 Depolarisation occurs in the sino-atrial node (SAN) in the right atrium
 SAN is controlled by the nervous system
 Membrane around the node allows charge to be maintained:
o Positive inside
o Negative outside
 Caused by ions building up
 During depolarisation, positive ions move outside
 Repolarisation is when ions move to even the charge across the membrane



Atrial Systole
 SAN sends a wave of electrical activity through the atria (wave of excitation)
 As the wave of excitation passes through the atrial walls, they contract in synchrony
 Non-conductive tissue between chambers prevent ventricles from contracting



Ventricular Systole
 Electrical wave reaches atrio-ventricular node (AVN) which relays the wave down the
inter-ventricular septum (IVS) through purkyene tissue
 As the wave of excitation passes through the ventricular walls, they contract in
synchrony from the bottom upwards