Frog Heart Activity Recording Experiment

Frog Heart Activity Recording Experiment

# Objective

The experiment aims to:

• Observe and record the activity of the frog’s heart, including the atrial systole, ventricular systole, and complete diastole phases.

• Demonstrate the role of the autonomic nervous system in regulating heart activity by stimulating the vagus nerve.

• Investigate the cyclical refractory period of the myocardium through induced extrasystole.

# Materials

• Frog

• Ringer’s solution

• Dissecting table

• Spinal cord probe

• Large and small scissors, forceps with teeth, forceps without teeth

• Vagus nerve

• Heart activity recording machine

• Induced electric current

# Procedure

1. Spinal cord disruption:

• Hold the frog with your left hand, with your thumb holding the frog’s head at a right angle to the body.

• Hold the probe with your right hand, puncture the skin at the point between the skull joint and the first vertebra (forming an equilateral triangle with the two eyes).

• Puncture the spinal cord until the frog’s hind legs straighten.

2. Exposing the frog’s heart:

• Place the frog on its back in the middle of the dissection table.

• Use forceps to lift the thoracic skin and cut it off with large scissors.

• Clip onto the xiphoid process, lift the chest wall and cut off a triangular piece of muscle to expose the heart.

3. Recording normal heart activity:

• Use the heart activity recording machine to record the frog’s heart activity.

• The graph will show three phases: atrial systole, ventricular systole, and complete diastole.

4. Stimulating the vagus nerve:

• Expose the vagus nerve (located across the bright triangular muscle, two small fibers on top running parallel, the larger fiber below with a red blood vessel).

• Use an electric current to stimulate the vagus nerve.

• Observe and record any changes in heart rate.

5. Inducing extrasystole:

• Use an induced electric current to stimulate the frog’s heart ventricle at different stages: ventricular systole and diastole.

• Observe and record the changes in the graph.

6. Analyzing the heart’s automatic nodes:

• Tie a string in two locations: between the sinus venosus and the atrium, and between the atrium and the ventricle.

• Observe and record the changes in heart rate at each string tie location.

# Results

• Cardiac cycle: Includes three phases: atrial systole, ventricular systole, and complete diastole.

• Role of the autonomic nervous system: Stimulation of the vagus nerve (parasympathetic) slows down the heartbeat.

• Cyclical refractory period of the myocardium: When extrasystole is induced, the heart only responds to stimulation during diastole, not during systole.

• Analyzing the automatic nodes: The sinus node (similar to the sinoatrial node in humans) is the primary pacemaker, while other nodes have the ability to spontaneously generate impulses but with decreasing frequency from top to bottom.

# Significance

• The experiment helps understand the mechanism of heart function, including the cardiac cycle, the role of the autonomic nervous system, and the refractory period of the myocardium.

• The experiment helps understand the structure and function of the heart conduction system, including the automatic nodes.

• The experiment provides basic knowledge of cardiac physiology, which has applications in the diagnosis and treatment of cardiovascular diseases.

# Notes

• The experiment should be conducted carefully, following animal ethics regulations.

• The frog should be handled gently, avoiding injury.

• After the experiment is finished, the frog should be disposed of properly.

# Additional questions

• Explain why the frog’s heart does not respond to stimulation during systole?

• What is the function of Ringer’s solution in the experiment?

• Compare the heart conduction system in frogs and humans?

• Explain why a compensatory pause is necessary after inducing extrasystole?

• List some common cardiovascular diseases in humans.