Answer: Tetanic (continuous) contraction of the heart (ensures rhythmic pumping).
- A Blood from flowing backward through the semilunar and AV valves
- B Tetanic (continuous) contraction of the heart (ensures rhythmic pumping)
- C Autonomic nerve signals from the vagus and sympathetic trunk from reaching the SA node
- D Excessively rapid filling of the ventricles during diastole
Correct answer: B. Tetanic (continuous) contraction of the heart (ensures rhythmic pumping)
Explanation: The refractory period of cardiac muscle cells prevents tetanus. The heart must relax between beats to fill with blood for the next contraction.
A single ECG cycle: the P wave marks atrial depolarisation (contraction signal), the large QRS complex marks ventricular depolarisation, and the T wave marks ventricular repolarisation (recovery) before the next cycle begins.
Concept context
Blood, lymph, the heart, the cardiac cycle, blood pressure, and ECG. High NEET weightage.