ACTION POTENTIAL OF HEART

 

The entire circulatory system revolves around the heart, which relies on being able to function from electrical signals that travel through the muscles. In mammals, the signals that are sent come from the heart itself; because of this, the heart is able to function and beat on its own without the use of signals from the brain. These signals in the heart originate in the Sino-Atrial Node (SA node). This structure within the heart is composed of “pacemaker cells” which are responsible for producing an Action Potential that will then travel through the rest of the heart. An action potential is the electrical impulse that initiates the contraction of these muscle cells. The signal sent by the SA node initially travels through the myocardial cells, which causes the heart muscle to contract. It then continues on to the Atrioventricular Node (AV node), where the muscle contraction concludes. The electrical signal now passes into the Bundle of His, and then to the Purkinje Fibers; the signal is now able to spread to the rest of the ventricles of the heart which allows both ventricles to contract at the same time. Action potentials that cause these signals are able to travel through the muscle cells so easily due to the fact that adjacent cells are joined by intercalated discs that allow for the flow of ions from cell to cell; action potentials are spread through the intra and extracellular flow of currents and ions. The same way you can measure electricity and voltage in a battery circuit presented in a physics lab, the heart’s electrical activity can be measured using an electrocardiogram or EKG. The action potentials you can measure within the heart vary from cell type to cell type. Upon analyzing a graph, it seems that ventricular action potential has a plateau period unlike what you would find in a nervous or skeletal muscle reading. The action potential at the SA node has no measured resting membrane potential because it is never actually at rest. 

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QRS Complex

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Before P wave 

- Action potential produced at the SA node 

- Wave not shown because by the time electrical signal reaches skin it is not detectable 

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P wave

- Action potential is at the atrium and traveling down to the AV node, bundle of his, and lastly the purkinje fibres

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QRS 

- Action potential in the ventricles 

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T wave 

- Ventricles re-polarize 

 

When Action Potential Goes Wrong 
 

Bradycardia

 

• The action potential is too slow causing slow heart rate

• Less than 60 BPM

 

Tachycardia

 

• The action potential is too quick causing fast heart rate

• Higher than 100 BPM 

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