How is an electrical impulse transmitted through the heart?

Contraction of the heart is myogenic meaning it initiates from within the heart muscle itself (myo=muscle, genic= created). Therefore, no extra nerves need to signal the heart to contract which is important as the heart needs to contract continuously and rhythmically. 

The heart has it's own conduction system to ensure each of the 4 chambers contract in a way to ensure all blood is pumped efficiently to either the lungs or the rest of the body.

1. An electrical impulse originates in the specialised pacemaker cells of the sinoatrial node (SAN) which sits just above the atria, which have unique electrical properties.

2. A wave of electrical activity spreads across both left and right atria so they contract together

3. The electrical impulse converges on another group of cells in between the atria and ventricles, the atrioventricular node (AVN) which delay conduction of the impulse into the ventricles. This allows the atria to contract completely before contraction of the ventricles begins.

4. The electrical impulse then travels down the Bundle of His, conducting fibres which run between the 2 ventricles, towards the apex of the heart.

5. From the apex, the impulse travels up through purkinjie fibres into the left and right ventricles. This ensures the contraction of the ventricles starts from the bottom upwards, so blood is ejected upwards into either the aorta (left side) or the pulmonary artery (right side).

This system is crucial, as shown by the fact that if this conduction system becomes disrupted in an arrhythmia, the ability of the heart to contract efficiently may be compromised. This is a potential cause of heart failure (insufficient blood output by the heart).

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