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Week%203%20-%20Teacher - BIPN 100 Dr Fortes Lecture 4...

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BIPN 100 Chris Childers Dr. Fortes Winter 09 Lecture 4 – January 12 th Lecture 5 – January 14 th Lecture 6 - January 16 th Graded Potentials Action Potentials Action Potential Mechanism & Gating Refractory Periods Action potential conduction Glial Cells Synapses EPSPs / IPSPs Receptors Vessicle Packaging Action Potentials vs. Graded Potentials Graded Potential Action Potential Ligand? (Electrical, chemical etc.) Electrical Only Decays with distance Propogation? Maintains maximal potential Both Hyperpolarizing? Depolarizing? Depolarizing Only No Refractory Period? Summation? No No Threshold? Yes Summation How is a stronger signal conveyed? Quicker Diagram an action potential on the following graph… Na+, K+ and Cl- channels have two different kinds of gates. What are they? And how do they factor into the shape of the action potential we just drew? How do they effect the refractory period of action potentials? Voltage gated receptors – positively charged amino acid helix; upon electrical stimulation the positively charged amino acids will move with respect to the electrical stimulus Gating mechanisms – most of these channels have two gates: 1. Opening gate – “Activation Gate” 2. Intracellular protein that can block the channel from the intracellular side – “Inactivation Gate” - This applies to Na+, K+ and Ca2+ channels - The K+ and Ca2+ inactivation gates are very slow - The Na+ inactivation gate is fast
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BIPN 100 Chris Childers Dr. Fortes Winter 09 Mechanism… - Threshold is reached when incoming Na+ is greater than outgoing K+ - Once threshold is reached, the conductance of Na+ is greatly increased (100 or 1000 fold increase). - One would think that the potential would then change to the Na+ equilibrium potential, but the inactivation gate closes before it reaches this level. - The hyper-polarization occurs because the K+ channel gate is very slow. - Both Na+ and K+ channels open because of the threshold potential but K+ channels open and close much slower. Gating….
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Week%203%20-%20Teacher - BIPN 100 Dr Fortes Lecture 4...

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