Test: Electrocardiogram & Circulatory Pathways (NCERT) - NEET MCQ

• Each peak in the ECG is identified with a letter from P to T that corresponds to a specific electrical activity of the heart.
• The P- wave represents the electrical excitation or depolarization of the atria.
• The QRS complex represents the depolarization of the ventricles which initiates the ventricular contraction.
• The contraction starts shortly after Q and marks the beginning of the systole.
• The T- wave represents the return of the ventricles from excited to a normal state or repolarization.
• The end of the T-wave marks the end of systole.

So, the correct option is 'Time delay in A-V node'.

The QRS complex represents the depolarisation of the ventricles, which initiates the ventricular contraction. By counting the number of QRS complexes that occur in a given time period, One can determine the rate of heart beat of an individual.

1. The T-wave in an ECG represents ventricular repolarization, not excitation of ventricles.
2. The heart rate is determined by the number of QRS complexes in a given time period, not the sum of P and T waves.
3. The P-wave represents atrial depolarization, and its end does not mark the end of systole.
4. In a standard ECG, a person is connected to the machine with three electrical leads for basic monitoring, which is correct.

A normal electrogram (ECG) is composed of a ‘P’ wave, a QRS wave (complex), and a T wave. The ‘P’ wave is a small upward wave that represents electrical excitation or atrial depolarization which leads to contraction of both the atria. QRS wave (complex) begins after a fraction of a second of the P wave. It begins as a small downward deflection (Q) and continues as a larger upright (R) and triangular wave, ending as a downward wave (S) at its base. It represents ventricular depolarization. The ‘T’ wave is dome-shaped which represents ventricular repolarization. The potential generated by the recovery of the ventricle from the depolarization state is called the repolarization wave. The end of the ‘T’ wave marks the end of the systole.

In a standard ECG, the P wave is a small upward wave that represents depolarisation of atria which leads to contraction of both atria.

The labelled parts '1' and '4' are aorta and left ventricle respectively, which carry oxygenated blood. Left ventricle receives oxygenated blood from left auricle which received it from pulmonary veins and this oxygenaed blood then moves into the aorta to be supplied to the whole body.

Pulmonary circulation is the movement of blood between heart and lungs. During this pathway deoxygenated blood entering the right atrium, moves into the right ventricle From here it moves through the pulmonary arch into the lungs for oxygenation. Then from lungs oxygenated blood moves into the left atrium through pulmonary veins.

Systemic circulation is the movement of the blood between heart and rest of the body (tissues) and the back to the heart. The oxygenated blood moves from the left auricle into the left ventricle. From here the blood moves into the aorta which ultimately divides into arteries that carry oxygenated blood to various tissues in the body. From the tissues deoxygenated blood is carried by the veins into the right atrium via superior vena cava and inferior vena cava.

'A' is vena cava that carries deoxygenated blood
'B' is aorta that carries oxygenated blood
'C' is pulmonary artery that carries deoxygenated blood
'D' is pulmonary vein that carries oxygenated blood.

To measure a standard ECG, a patient is connected to the machine with three electrical leads-one to each wrist and one to the left ankle. It continuously monitors heart activity.