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Lecture 5

Lecture 5 - Membrane Transport and Action Potential - January 22.docx

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BIOL 2021
Patricia Lakin- Thomas

January 22, 2013 Lecture 5: Chapter 11 – Gated Ion Channels Mechanically Gated  Ear for soundwaves  Auditory hair cells  Convert mechanical stimuli into electrical stimuli  Microvilli are sterocilia  Sound makes pressure waves and the stereocilia tilt and that pulls on the filament, pulling ion channels o Action potential Membrane Potential  Voltage – difference in electrical charge across a membrane  PM in all cells have potential  Animal cells: -20 – -120 mV  100mV = 1/100 000 K+ in cytosol  No measurable concentration changes Causes of Potential in Animal Cells  Electrogenic = causes membrane potential  Na+/K+ ATPase = 10% of potential o 3 Na+ : 2 K+  90% comes from K+ leak channels o Open K+ channel o Allows equilibration across the channel Nernst Equation (Panel 11-2)  What’s the voltage at equilibrium  Electrical:  Chemical: ( )  K+ inside = 140 mM, K+ outside = 5mM o V = -89mV Membrane Potential Uses:  Active Transport  Signal Transduction (Neurons) Neuron Anatomy  Dendrites, axons, terminal branches  Signals in one direction only  Previous cells axon terminals  synapse  dendrite  axon  terminals  synapse ... Synapse  Ends don’t touch, they “meet” at a synapse o Space between is synaptic cleft  Presynaptic cell, synaptic cleft, post synaptic cell  Signal is a neurotransmitter o Fusion event o Binds to ligand gated ion channels (ligand is the neurotransmitter) Transmitter Gated Ion Channels  Open transiently  Change permeability of membrane  Selective for ligand/ion  Example: Acetylcholine – gated: o Allow Na+ into th
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