Ex 6
Activity 1: Recording Baseline Frog Heart Activity (p. 75)
2. 62 bpm
Activity 2: Investigating the Refractory Period of Cardiac Muscle (pp. 75–76)
3. It is possible to induce an extrasystole in the relaxation part of the cardiac cycle.
4. The heart can not be tetanized by multiple stimuli.
Tetanization would make the heart ineffective as a pump.
Activity 3: Examining the Effect of Vagus Nerve Stimulation (p. 76)
5. Vagal stimulation initially decreased heart rate and force of contraction, and then caused
the heart beat to stop for a brief period before returning to a relatively normal contraction
state after vagal escape initiates.
Activity 4: Assessing the Effect of Temperature (pp. 76–77)
2. Cold Ringer’s solution decreased heart rate.
(Various answers depending on students’ predictions.)
5. Warm Ringer’s solution increased heart rate.
51 bpm at 5° C; 70 bpm at 32° C
Increasing the temperature causes an increase in heart rate.
Activity 5: Assessing the Effect of Pilocarpine (pp. 77–78)
5. 46 bpm
Pilocarpine mimics vagal stimulation and slows the heart.
Activity 6: Assessing the Effect of Atropine (p. 78)
4. 71 bpm
The heart rate should increase.
When atropine blocks the effect of acetylcholine, the effect is to allow the sympathetic
neurotransmitter to bind to cardiac muscle tissue, thus increasing heart rate.
Atropine and pilocarpine are antagonistic in their action.
Activity 7: Assessing the Effect of Epinephrine (p. 78)
4. 80 bpm
Epinephrine increases the heart rate and force of contraction.
Epinephrine mimics the effects of the sympathetic nervous system.
Activity 8: Assessing the Effect of Digitalis (p. 78)
4. 42 bpm
Digitalis slows and steadies the heart.
Activity 9: Assessing the Effect of Various Ions (p. 79)
6. Calcium increases the strength of contraction; probably induces spasticity.
• The heart rate does not stabilize until 23°C Ringers solution is applied.
• The heartbeat is irregular, speeding up at times, slowing down at others.
Sodium decreases the strength and rate of contraction.
• The heart rate does not stabilize until 23°C Ringers solution is applied.
• The heartbeat is irregular, speeding up at times, slowing down at others.
Potassium weakens cardiac contractions.
• The heart rate does not stabilize until 23°C Ringers solution is applied.
• The heartbeat decreases considerably at first, then becomes erratic—alternately
speeding up and slowing down.
Yes, all three ions may induce arrhythmias.
These answer should help u answer the review sheet as the questions from the review sheet come from the activities if not please state the specific questions from the review sheet that u need answers to.
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