Question

In an ECG, the T wave is

a. caused by ventricular depolarization and ventricular contraction

b. atrial contraction

c. caused by ventricular repolarization

d. known as the pacemaker potential

The normal pathway followed by cardiac action potential is to begin in the SA node and then propagate

a. to AV bundle fibers and Purkinje fibers

b. to internodal fibers → AV bundle fibers → AV node → Purkinje fibers

c. to internodal pathways → AV node → AV bundle fibers and Purkinje fibers

d. all of the above

an increase in heart rate could result from

a. an abnormal rapid firing of the purkinje fibers

b. decrease in the amount of myosin and troponin fibers in the muscle

c. an increase in the parasympathetic nerve activity to the heart

d. an increase in sympathetic nerve activity to the heart

Answer 1

1. Caused by ventricular repolarisation

• ECG represent electrical activity of heart (not mechanical).
• P wave - depolarisation of atria
• QRS complex - depolarisation of ventricle
• T wave - repolarisation of ventricle

2.  internodal pathways → AV node → AV bundle fibers and Purkinje fibers

• SA node is knobs as pacemaker of heart.
• SA node -> internodal pathway and atrial conducting fiber --> AV Node --> AV bundle fiber --> right and left bundle branches --> Purkinje fiber

3. Increase in sympathetic nerve activity to heart

• Sympathetic system increase heart rate and parasympathetic system decrease heart rate.

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