cells in SAN depolarise - become electrically excited. This triggers a wave of electrical excitation across the atria causing them to contract.
SAN's wave of electrical excitation cant pass into ventricles as atria and ventricles are separated by a layer of non-conducting tissue.
Atrioventricular node
located between atria
detects electrical excitation passing over atria and after a short delay then transmits excitation into the pukyne fibres which causes the ventricles to contract from the apex upwards.
Why do ventricles contract from the apex upwards?
It ensures that the maximum volume of blood is pumped out of the ventricles.
Why is there a slight delay before AVN's transmission?
It ensures that ventricles contract after the atria.
Bundle of his connects to the AVN and is loads of Purkyne fibres bundled together.
