W9 Membrane Potential, Action Potential 1 & 2 (Ferrari) PDF

Equilibrium & Membrane Potentials Thomas Ferrari, PhD [email protected] Ross University School of Medicine Office Hours: see Canvas calendar for times https://teach.webex.com/meet/tferrari Objectives 1) 2) 3) 4) 5) 6) 7) 8) Define the concepts of electrochemical equilibrium and equilibrium...

Equilibrium & Membrane Potentials Thomas Ferrari, PhD [email protected] Ross University School of Medicine Office Hours: see Canvas calendar for times https://teach.webex.com/meet/tferrari Objectives 1) 2) 3) 4) 5) 6) 7) 8) Define the concepts of electrochemical equilibrium and equilibrium potential at given internal and external ion concentrations. Write the simplified Nernst equation, and indicate how this equation accounts for both the chemical and electrical driving forces that act on an ion. Based on the Nernst equation, predict the direction that an ion will take when the membrane potential a) is at its equilibrium potential b) is ‘higher’ than the equilibrium potential, or c) is ‘less than’ the equilibrium potential. List values in a typical excitable cell for ENa+, EK+, ECl-, and ECa++. Explain how the resting membrane potential is generated and understand the basis of membrane potential in reference to the Goldman-Hodgkin-Katz equation. Predict how changes in K +, Na+, or Clwould change the membrane potential. Understand how the activity of voltage-gated K+, Na+, or Ca++ channels generates an action potential and the roles of these channels in each phase of the action potential (threshold, depolarization, overshoot, repolarization, hyperpolarization). Understand electrotonic conduction, list some types of graded potentials, and differentiate between properties of graded potentials and action potentials. Differentiate between the properties of electrotonic conduction, conduction of an action potential, and salutatory conduction. Identify regions of a neuron where each type of electrical activity may be found. Contrast the mechanisms by which an action potential is propagated along both non-myelinated and myelinated axons. Predict the consequences on action potential propagation in the early and late stages of demyelinating diseases such as multiple sclerosis. Electrochemical Equilibrium and Equilibrium Potentials Equilibrium Potential (a.k.a. Electrochemical Equilibrium) *For negative ions like chloride this is flipped to Ci Co Resting Membrane Potentials Resting Membrane Potential is not Affected by Extracellular Sodium You need to know what this equation means, but you do not have to use it for calculations Net Driving Force (DF) DF = Vm - Ei Graded Potentials Graded Receptor Potentials • Receptors for sensory systems need to code intensity • Stimulus strength determines size of graded potential • Graded (receptor) potential produces #/frequency of APs This process is called sensory transduction – turning different kinds of stimuli into APs in the nervous system. Electrotonic Conduction Electrotonic Conduction is: • Passive • Local • Graded i.e., Graded Potentials, Local Potentials, Receptor Potentials, Generator Potentials, Post-Synaptic Potentials, Pacemaker Potentials, Passive Conduction Microelectrode Recording Electrically Excitable Cells: • Neurons • Muscle Electrically excitable means the cell can generate graded and/or action potentials Action Potentials The same size stimulus that reaches threshold and creates the first AP may not reach threshold for a 2nd AP. Due to refractory period and Ohm’s law: V = IR Voltage = Current X Resistance So a lower R (which is the same as saying a higher P) results in less voltage change. Voltage-Gated Sodium Channel accounts for absolute refractory period Electrical Events in Excitable Cells Action Potential Propagation This is great, but it means a LOT of channels, pumps all along the axon Myelination is the Solution to Energy and Speed Issues Membrane resistance ? Membrane permeability ? Demyelinating Diseases Disrupt Saltatory Conduction Action potential propagation frequency will decrease as disease progress, e.g., if healthy neuron is 100 AP/sec this frequency will decrease...90, then 80, etc.