1. Prepare the live frog by pithing so that it will have no feelings or movements when its muscle is removed. To do this, follow these steps:
a. Hold the frog securely in one hand so that its legs are extended downward.
b. Position the frog's head between your thumb and index finger.
c. Bend the frog's head forward at an angle of about 90° by pressing on its snout with your index finger (fig. 19.4).
d. Use a sharp probe to locate the foramen magnum between the occipital condyles in the midline between the frog's tympanic membranes.
e. Insert the probe through the skin and into the foramen magnum, and then quickly move the probe from side to side to separate the brain from the spinal cord.
f. Slide the probe forward into the braincase, and continue to move the probe from side to side to destroy the brain.
g. Remove the probe from the braincase, and insert it into the spinal cord through the same opening in the skin.
h. Move the probe up and down the spinal cord to destroy it. If the frog has been pithed correctly, its legs will be extended and relaxed. Also, the eyes will not respond when touched with a probe.
A n anesthetizing agent, tricaine methane sulfonate, can be used to prepare frogs for this lab. This procedure eliminates the need to pith frogs.
2. Remove the frog's gastrocnemius muscle by proceeding as follows:
a. Place the pithed frog in a dissecting tray.
b. Use scissors to cut through the skin completely around the leg in the thigh.
c. Pull the skin downward and off the leg.
d. Locate the gastrocnemius muscle in the calf and the calcaneal tendon (Achilles tendon) at its distal end.
e. Separate the calcaneal tendon from the underlying tissue, using forceps.
f. Tie a thread firmly around the tendon (fig. 19 5).
g. When the thread is secure, free the distal end of the tendon by cutting it with scissors.
h. Attach the frog muscle to the recording system in the manner suggested by your laboratory instructor (see figs. 19.1 and 193).
i. Insert the ends of the stimulator wires into the muscle so that one wire is located on either side of the belly of the muscle.
Keep the frog muscle moist at all times by dripping frog Ringer's solution on it. When the muscle is not being used, cover it with some paper toweling that has been saturated with frog Ringer's solution.
Before you begin operating the recording system and stimulator, have the laboratory instructor inspect your setup.
Was this article helpful?
This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.