Reyes, Charles Jourdan F. January 14, 2013
V BS Biology Bi183.1 Section A
Exercise 1: Baseline Data
Figure 1. Force (N), ECG (mV) and heart rate (bpm) of the pithed frog.
Figure 2. Force (N) per unit time (s) of the pithed frog.
Figure 3. ECG (mV) per unit time (s) of the pithed frog.
Table 1. Time between QRS and the start of ventricular contraction(s).
1. Observe the heart and describe its behavior. Is this behavior consistent with what is shown in the data above?
Yes. The heart of the frog rhythmically contracts and relaxes. This behavior is supported by the general fluctuations observed force values and the consistent patterns of the ECG occurring in regular intervals.
2. Explain the basis for the delay between the atrial and ventricular contractions.
The said delay is mainly caused by the A-V node and its adjacent conductive fibers, causing an overall delay of 0.13 second (Guyton and Hall 2006). Conduction in the transitional, nodal, and A-V bundles is dampened by the decreasing number of gap junctions along the pathway of conduction, creating great resistance against the conduction of excitatory ions from one fiber to another. This ensures that the atria completely empty blood into the ventricles before ventricular contraction occurs.
3. Describe the relationship between the ECG QRS complex and the beginning of ventricular contraction. What is the physiological significance of this relationship?
A typical electrocardiogram normally exhibits P, Q, R, S, and T waves, all of which represent electrical voltages produced by the heart. The QRS waves occur as a result of the electrical depolarization of the right and left ventricles, an event that triggers ventricular contraction and the subsequent rise in ventricular pressure. This complex is used to determine the axis of the ECG (Guyton and...