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Lecture 4

Lecture 4.doc

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Robert Gerlai

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Lecture 4: Test: Focus on what we covered in class. 50 % scantron type – mcqs, t/f 50 % sa. Electricty - movement of electrons. Electron – negatively charged subamotic particle. Works like a wave and a particle at the same time. Atoms are sometimes asymmetrical. Electrons can spend most of their time in one part rather than other parts, thereby creating a charge. What surrounds the cells, plasma membrane, semi-permeable. Bio-lipid layers. Inside the cells membrane is hydrophobic, and outside is hydrophilic. Extracellular layer, and intracellular layer. Protein channels that allow ions to go through. Channels can be closed or open. Resting potential – 65 mV on average. Difference in charge across the membrane, inside is more negative that outside. More potassium in the inside and more sodium on the outside, the proteins inside create the negative charge. Proteins shed protons – ie hydrogen atom that is positively charged, so proteins are negatively charged. Number of sodium ions outside is more than potassium ions in the inside, therefore the net charge is more negative. This charge difference is facilitated by the sodium/potassium pump. The channel transfers 3 sodium ions to the outside and two potassium to the inside. ATP is used in the process, phosphorylation – energizing the protein channel, the ATP contains phosphate groups that have bonds that can easily be broken and charge the channel. Electric signals reach a particle area, it opens voltage gated sodium channels, they are membrane potential sensors as well. In a wet environment charge is not conducted well, but myelin sheath make it possible, this is possible through glial cells. The message gets recreated at each node when the action potential moves. There is passive conductance but not efficient due to wet environment. More negative charge so its like a magnet, but sodium moves in from passive conductance due to concentration gradient – more sodium outside then inside, diffusion force. Once the charge reaches a threshold like + 40 mV, the channel close because the bio-chemical features of the channel senses the threshold, the diffusion force and the electric force, make the potassium ions move from inside to outside. Initial phase of action potential is done through passive conductance, then once it reaches a small threshold of depolarization, and then sodium channels open and a surge of sodiums come in. Once the threshold is reached the action potential will trigger, it will fire with the same altitude and same shape – width of the bell, once it is triggered – all or none. The properties of biological sensors determines the all or none phenomenon, the coordinated action and the how they sense action potential is how you get the shape of the action potential and all or none phenomenon. Channels open and close in a coordinated measure, which takes time, an active process. Schwan cell or glial cell – myelin sheath wraps itself around the cell membrane. The nodes of ranvier are the regions where cell membrane is naked – this is where the action potential is regenerated. In the myelin sheath the action potential moves passively, and decays because there are all kinds of things in the cell membrane that hinder the speed of electro
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