6 Overview_of_Excitability.pptx

Overview of Excitability 1 A Simple Reflex 2  There are 2 forces that act on ions 1. Concentration Gradient aka chemical gradient, diffusion) Move from high to low concentrations, ”down the gradient” 2. Electric Gradient aka charge gr...

Overview of Excitability 1 A Simple Reflex 2  There are 2 forces that act on ions 1. Concentration Gradient aka chemical gradient, diffusion) Move from high to low concentrations, ”down the gradient” 2. Electric Gradient aka charge gradient, electricity) Opposite charges attract Same charges repel 3 Membrane Potential Membrane potential: voltage across the neuronal membrane at any moment Membrane potential describes the potential inside the cell, compared to outside More neg charges lined up inside cell (left), more pos 4 charges lined up outside the Distribution of Ions Some ions are distributed unevenly across the membrane: K+ more concentrated inside Na+, Ca2+, and Cl- more concentrated outside 5 Ions cross the membrane through transmembrane proteins 1) Channels (passive transport, diffusion)  Move ions down their gradients 2) Pumps (active transport, requires energy)  Move ions up (or against) gradients 6 The Action Potential 7  During the action potential, proteins in the membrane will open, to allow different ions to pass through the membrane. The ions pass through the membrane by diffusion, moving down gradients. Na+ and K+ are the main ions involved. Movement of which ion, in which direction mediates the increase in membrane potential (“rising phase”)? Movement of which ion, in which direction mediates the decrease in membrane potential (“falling phase”)? 8 Action Potential Initiation 9 Action Potential Propagation 10 Synaptic transmission 11 Flipped Class: Ions, Biomolecules, and Water What are ions? What are the major types of biomolecules? How do ions and biomolecules interact with water? What is a concentration gradient? Preparation for class on Wednesday Read Bear, Connors, and Paradiso Chapter 3, pp. 57-9, 64-70 View Khan Academy videos on Canvas Complete Problem Set 2 12