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The Schwann Cell And Action Potential

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What you will see and hear in this presentation is the development of Myelin in the peripheral nervous system. And the propagation of the Action Potential along a Myelinated Axon. This multimedia presentation will be most helpful if you already have a good understanding of the Schwann Cell and the electro-chemical process of the Neuron, called the Action Potential. The Schwann Cell forms a protective covering around the Axon. Schwann Cells start to develop in the embryo and continue to increase the wrapping around the Axon through childhood. This development increases the thickness of the wrappings which peaks in adolescence. This is why teenagers have such quick responses. The Schwann Cell contains the typical cell organelles and cell membrane structure. However, notice as the Schwann Cell surrounds the Axon... that the Nucleus and other organelles are squeezed to the outside wrapping of the cell. This outer wrapping of the Schwann Cell is called the Neurolemma. The inner lining is made up of layers upon layers of cell membrane. This inner wrapping is called the Myelin Sheath. You will recall that the cell membrane, called the Fluid Mosaic Model is made up of a bi-layer of lips integrated with proteins. The thicker the Myelin, in other words the more layers of cell membrane making up the Myelin the more advantageous it is to the Axon. One advantage, is the regeneration of severed Axons. Another advantage is an increase in the speed of the propagation of the Action Potential along the Axon. The rest of this presentation will concentrate on the increased speed of Action Potentials down the length of the Mylenated Axon. Here is the Neuron. You can see the repeated Schwann Cell membrane forming the Myelin. Note that there is a small space between the Schwann Cell's, where the Axon is not covered by the Neuroglial Cell. These spaces are called Nodes of Ranvier. From what you already know, Action Potentials occur at the Axon Hillock and continue to be repeated away from the cell body much like dominoes falling one after another. An Action Potential starts on a polarized membrane which is negative seventy (-70). A stimulus causes the Sodium Gates to open slightly and Sodium starts to trickle into the cell. If the cell reaches negative sixty (-60) or threshold, the Sodium Gates open wide and Sodium floods in. Bringing the inside of the Axon to positive 30 (+30) . At this point, the Sodium Gates close and Potassium Gates open. Potassium starts to pour out of the cell. This allows the Neuron to become polarized again. Then the Sodium Potassium pump starts to actively transport Sodium out and Potassium back into the Neuron. First we will look at the propagation of the Action Potential in the Unmyelinated Axon. Propagation is the repeating of Action Potentials down the Axon. The Action Potential is repeated, because as the Sodium comes in it diffuses to adjacent areas within the Axon. As the Sodium increases in this area. Threshold is reached. Sodium Gates open wide Sodium rushes in causing depolarization and an Action Potential. As the Sodium enters this area it diffuses through the Axoplasm and another Action Potential is created. This continues down the length of the Axon. Now look at the Myelinated Axon. The same process applies to the Myelinated Axon. An Action Potential develops and as the Sodium comes in it diffuses through the Cytoplasm of the Axon. It continues to diffuse through the portion of the Axon wrapped in Myelin. The increased Sodium concentration reaches the Node of Ranvier. Increases the Axoplasm to negative sixty (-60) and depolarization occurs. The Sodium Gates open wide, Sodium floods in, and we have an Action Potential. Again, the Sodiums diffuse through the Axoplasm reaching the next Node. An Action Potential develops, the process is continued down the Myelinated Axon, passing from Node to Node. Compare the Unmyelinated Axon with the Myelinated Axon. You can see the Action Potential reach the end of the Myelinated Axon more rapidly than the Unmyelinated Axon. The speed of the propagation is faster going from Node to Node than Action Potentials that develop adjacent to the previous Action Potential.

Video Details

Duration: 5 minutes and 6 seconds
Country: Russia
Language: English
Views: 394
Posted by: the_june on Jan 30, 2011

I don't know who did this but THANK YOU SOOOO MUCH!

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