Neurobiology week of Jan 25
Neurobiology week of Jan 25 BIO 467
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This 2 page Class Notes was uploaded by Mikayla Huber on Wednesday January 27, 2016. The Class Notes belongs to BIO 467 at Arizona State University taught by Dr. Newbern in Fall 2016. Since its upload, it has received 31 views. For similar materials see Neurobiology in Biology at Arizona State University.
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Date Created: 01/27/16
Jan 25: Voltage-dependent membrane permeability Todays Goals • Understand how changes in ionic current contribute to action potential generation and propagation. • Know the principles underlying the voltage/current clamp technique. • Be able to explain how an action potential is propagated down an unmyelinated and myelinated axon Action potential phases Rising Overshoot Falling Undershoot Voltage clamp Allows experimenters to control a neuron’s voltage and measure the changes in the current Current clamp Allows experimenters to control the neuron’s ion current and measure the changes in voltage *These clamps allowed the scientists Hodgkin and Huxley to determine that membrane permeability is voltage dependent. Ionic current Iion = g ion (V –mE ) ion I = ionic current g = membrane conductance V = membrane potential E = equilibrium potential for the specified ion * V – E is the electrochemical driving force acting on the ion *The relationship between ion current and Membrane potential during an action potential depends on: Activation of Na conductance, activation of K conductance and rapid inactivation of + Na conductance. Neurons themselves are poor transmitters, so they periodically regenerate the signal at Nodes of Ranvier (concentrated areas of Na channels between the pieces of myelin sheaths) Conduction velocity The action potential’s rate of transmission Saltatory conduction A current only flows across the neuronal membrane at the nodes Jan 27: Ion Channels and Transporters Todays Goals • Understand what “patch clamping” is and how it helped prove Hodgkin and Huxley’s theories • Know the basic structural components of ion channels and transporters • Be familiar with different subfamilies of ion channels and some of their diverse effects Patch Clamping A glass pipette with a minute opening is brought into close contact with the target cell. Suction is applied until a gigaOhm seal is formed and no ions flow between the pipette and the membrane. All flowing current from ion channel opening enters the pipette. A high sensitivity amplifier records the minute amount of current. Provided the first direct evidence for voltage-sensitive, ion-selective channels. Voltage gated ion channel structure They are integral membrane proteins that repeatedly cross the membrane. They contain a pore region that regulates ions passing through a selectivity filter present in the pore walls. Some have a voltage sensor that is positively charged with amino acids. Various ion channel activation Voltage activated Ligand activated Stretch activated Heat activated *Many known toxins effect ion channels Peptide toxins block K channels Ex: Bees – apamin Wasps – dendrotoxin Scorpions – charybdotoxin
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