Frog Heart Lab Report

Towards the end of the 19th century, one of the great mysteries challenging scientists was how the billions of nerve cells that make up the human nervous system communicate with each other and how the stimulation of a nerve was transmitted to the effector organ from the nerve ending. Most neurophysiologists thought that it occurred through direct transmission of the stimulation wave from the nerve cell to the effector organ or to another nerve cell; many of them defending the idea that signaling across synapses is electrical, just like the propagation wave along the axon during an action potential.
However, there was ample evidence to argue against such a simple picture of neuronal communication. Scientists had observed that there was a unidirectional

Still in his nightgown, he conducted the experiment using two beating frog hearts, each in its own chamber. The main advantage of using frog hearts was that vertebrate cardiac muscle continues to contract even when it is removed from the body for a few hours. The first heart was still connected to the vagus nerve and placed in saline solution; the second heart was denervated. Electrical stimulation of the vagus nerve caused the first heart to slow down. The second heart, which was is still in another chamber, was unaffected. The saline solution from the first heart was then applied to the second heart. After a delay, the second heart also slowed down as if it's vagus nerve had been stimulated as well. The saline solution had taken on characteristics capable of causing changes in the behavior of the second heart mirroring the activity that had been seen by the nerve stimulation of the first heart. The results from this simple yet ingenious experiment led Loewi to hypothesize that there was a substance created by the electrical stimulation of the vagus nerve that caused the first heart to slow down. The fact that the substance could then be transferred to the second heart via saline solution and cause the second heart to also slow down made Loewi confident that the substance was a chemical. Loewi called the proposed chemical "vagusstoff," which meant "vagus substance" in German. The chemical was later identified and named acetylcholine by Sir Henry Dale. Loewi would also go on identify noradrenaline through his original experimental design with the two frog hearts, but this time stimulating the sympathetic nerves to the heart instead of the vagus nerve, which increased the heart rate. In 1936, Otto