95. What are the three steps of the 'wave of excitation'?
Answer: D
The three steps of the 'wave of excitation' are the excitation of the atrium, the excitement of the ventricle, and the relaxing of the ventricle.
These three steps describe the sequential electrical changes in the heart that lead to its contractions and relaxations, as described in the extract.
A) The discharge from the SA node, the peak ECG, and the excitement of the ventricle.
This option inaccurately describes the steps involved in the wave of excitation. While the discharge from the SA node is involved, the peak ECG is not a step but rather a result of the process, and it fails to mention the relaxation phase of the ventricles.
B) The excitement of the ventricle, the relaxing of the ventricle, and the systemic neural response.
This option is incorrect as it misrepresents the steps. It omits the important initial step of atrial excitation and incorrectly adds the systemic neural response, which is not part of the wave of excitation steps described in the extract.
C) The contraction of the atrium, the relaxation of the atrium, and the contraction of the ventricle.
This choice is partially correct but does not accurately reflect the sequence of steps in the wave of excitation. It misses the critical phase of ventricular relaxation and misrepresents the roles of contraction and relaxation in the correct order.
D) The excitation of the atrium, the excitement of the ventricle, and the relaxing of the ventricle.
This option correctly outlines the three steps of the wave of excitation as stated in the extract. It accurately captures the sequence of events as electrical impulses spread through the heart muscle, leading to atrial excitation, ventricular excitement, and finally, ventricular relaxation.
Conclusion
Option D is definitively correct as it accurately describes the three steps of the wave of excitation in the heart. The other options either misrepresent the steps or include extraneous information that does not pertain to the sequence outlined in the extract. Understanding these steps is crucial for recognizing how the heart functions electrically, which is vital for diagnosing any potential abnormalities.