Question

Describe the path of the conductive pathway associated with the cardiac cycle beginning with the sinoatrial (SA) node. Please indicate the electrocardiogram letter (P,Q,R,S, or T) that corresponds to the particular part of the conducting pathway.

Answer 1

Answer-

According to the given question- Heart have the capability to maintain the proper amount of blood circulation with the help of muscle cells present in it and with the its ability to pump the blood continuously and rhythmically. Cardiac muscle made up of contractile units known as sarcomeres. Cardiac muscle are involuntary with two types of cardiac muscle one is  contractile cells (99 % of total cells) and another is specialized cardiac cells which are responsible for regulating the contractile cells.   Cardiac action potential are transmitted between the different types of specilized cells present in the heart or myocardium which  signal the muscle fibers to contract.

Cardiac conduction system-

• Consist of Sinoatrial node, or SA node, which are present in the right atrium also close to the superior vena cava entrance. Sinoatrial node is called natural pacemaker of the heart which are responsible for initiating the heartbeat and also responsible for determining the rate of  heart . The Impulse in the form of electrical signal which are generated in SA node started to spread in both the atria simultaneously and due to which they stated to contract.
• The atrioventricular node, or AV node also present in the opposite side of  SA node in the same right atrium, close to the atrioventricular valve. this AV node responsible for electrical signal in the ventricles. when AV node gets the signal It delays the  electrical impulses for some times to pass to the ventricles to ensure that the all blood present in the atria should have ejected in the ventricles before the start of contraction of ventricles
• The signal from the SA node received by AV node which pass it to atrioventricular bundle or AV bundle also known as  bundle of His which are divided into left and right bundle to pass the electrical impulses to Purkinje  fibers, which are responsible for spreading the impulse to whole part of ventricular myocardium.
• The impulse activity of heart is observed in the graph called electrocardiogram or ECG . The ECG is generally a recorded form of the action potential which are generated by the both SA nodes, AV Nodes and the cells that are present in the heart myocardium.
• The segment of ECG or wave of ECG denotes a single phenomenon or event of cardiac cycle. During the start of the impulse when the artria have blood completely filled its  SA node fires a signal in the form of electrical signal which pass through the atria and due to which the artria gets depolarize , this artrial depolarization are represented by P wave on electrocardiogram.
• After the contraction of Atria or in other term called atrial systole the signal pass to the AV nodes after some interval which is about 100 mili seconds represented as P - Q segment on electrocardiogram. P - Q segment is the travel time of signal from SA node to AV node.
• Then after getting signal from the SA Node, the AV Node fired which are represented as Q-R-S segment in the electrocardiogram and causes  the depolarization of ventricles.
  • Q wave -  depolarization of interventricular septum.
  • R wave - depolarization of the ventricles main mass
  • S wave - ventricular depolarization at the heart base.
• The repolarization of arteria also happened at the same time during the ventriclular depolarization i.e. during the Q-R-S segment
• The S-T segment is observed in the electrocardiogram are the time when the  ventricles contract and blood is pump from the ventricles.
• T wave - represents the repolarization of ventricles.

These can be represnted as follows.

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R-wowe T-Wave Pave p- a s s -T segment segment P wave wave R wave a I wave Artrial defalarization Depolarization of Interventricular seftum ventricle main mass ventricular depolarization at Heat mannen base I wave - ventricles repolarization