Controlling The Cardiac Cycle Flashcards
Why can muscle cells in heart contract without input from nervous system
Due to myogenic contraction, sinoatrial node can initiate depolarisation
How does heart contract
-depolarisation initiated in sinoatrial node (SAN) which acts as pacemaker and is in wall of right atrium at top
-depolarisation spreads through atria causing atrial systole
-cannot spread directly to ventricles due to region of non conductive tissue between them
-SAN passes the electricity to atrioventricular node
-AVN passes the wave of electricity down the septum down the nerves of the bundle of His, slight delay here so ventricles don’t contract before atria fully empty
-electricity passed up ventricular muscle by Purkyne fibres which allows ventricles to contract bottom up allowing them to fully empty pushing blood up into aorta and pulmonary artery
How are nodes depolarised
Positively charged ions (calcium ions) move out of nodes
How is electrical activity in heart detected
ECG
What does p wave show
Controlled by SAN depolarising causing atrial systole
What does QRS complex show
AVN depolarised causing ventricular systole
What does t wave show
Diastole
What is fast heart called and what looks like on ECG
Tachycardia, smaller distance between beats
What is atrial fibrillation and what looks like on ECG
Atria beating more frequently than ventricles, no clear P waves seen as SAN constantly firing, irregular beats
What is slow heart rate called and what does it look like on ECG
Bradycardia, greater distance between each beat
What is y axis on ECG
Voltage
