Structure of the heart

Left ventricle has thicker, more muscular walls than the right ventricle. Needs to contract more powerfully to pump blood all th way round body. Right side only needs to pump to lungs (nearby)

Ventricles have thicker walls than atrium as need to push blood out of body whereas atrium only needs to go short distance into ventricles

Atrioventricular valves link atrium to ventricle to stop blood flowing backwards into atrium when ventricle contracts.

Semi-lunar valves link ventricles to pulmonary artery/aorta to stop blood flowing back into heart when ventricles contract

Cardiac muscle is 'myogenic'- can contract and relax without receiving signals from nerves. This pattern of contractions controls regular heartbeat.  Process starts in sino-atrial node (SAN) in wall of right atrium. SAN like a pace maker- sets rhythm of heartbeat by sending regular wavs of electrical activity to atrial walls. Causes left and right atrium to contract at same time.  Band of non-conducting collagen prevents wave being passed on directly from atrium to ventricles. Instead waves passed from SAN to atrioventricular node (AVN) AVN responsible for passing waves of electrical activity onto the bundle of His. BUT there's a slight delay before AVN reacts to ensure ventricles contract after atria have emptied. Bundle of His- group of muscle fibres responsible for conducting waves of electrical activity to finer muscle fibres in right&left ventricle walls (Purkyne fibres) These fibres carry waves of electrical activy into muscular walls of right&left ventricles causing them to contract simultaneously from bottom up.

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