PSIO 5th Edition Lecture 33Outline of Last Lecture AUTONOMIC NERVOUS SYSYEMOutline of Current Lecture I. Neurophysiology: Resting Membrane PotentialII. BioelectricityIII. Resting Membrane PotentialIV. ManipulationCurrent LectureObjective:1. Describe the normal concentration and electrical gradients for Na+ and K+ that exist across the membrane of all cells2. Predict what will happen to the membrane potential of a cell is the permeability of the membrane increases or decreases for Na+ of K+.3. Compare and contract the characteristics of leak-channels and voltage-gated, chemically-gated, and mechanically-gated channels.Neuronal Tissue: Two Types of CellsA. Nerve Cells (Neurons)Involved in the generation and interpretation of Electrical Signals B. Glial Cells (Neurolgia) Support neuronal cell activity“Bioelectricity” - Resting membrane potential – Baseline electrical condition of ALL cells; depends on 2 parameters A. Transmembrane Ion Gradients ( Na+ and K+)B. Membrane Permeabilty to those ions- Action potential“Resting Membrane Potential” - A- = negatively charged proteins and phosphate- Ion Gradients- Na, K-, ATPase develops and maintains steady state ion gradients for ALL cells- PermeabilityIntracellular (cytoplasm)Extracellular:1. Pumping creates ionic gradient for K+2. K+ leaks out down its concentration gradient so that the inside of the cells becomes more negative3. Now two kinds of forces push/pull on K+ “Resting Membrane Potential”2 opposing forces – Chemical and ElectricalChemical pushes K+ out and Electrical pulls K+ inChemical and Elecrical forces for K+ are nearly in balance – outwardly directed K+ gradient results in an inside-negative electrical potentialThe Electrical potential difference (PD) is measured in Volts ( -0.05 volts to -0.1 volts)K+ dominated inside negative membrane potential is a characteristic of ALL cells at restModulation of the membrane potential- changes in the membrane permeability can produce large changes in the membrane potentialMembrane permeability = open channels to an ion (K+ or Na+) for that ion Regulation of channel mediated ion permeability allows cells to generate electrical signalsKeys to manipulation of Membrane Potential: 1. Maintain (stable) Na+ and K+ gradients (Na,K,ATPase)2. Vary the activity of specific ion channelsManipulation of membrane Permeability- Ion Channels1. Integral membrane proteins2. Channels can be open or closed3. Some channels are routinely open4. Some channels have their open states regulated a. Chemically ligand-gated channels open when a signal molecule binds to the channel protein (ACh)b. Mechanically gated channels – open when membrane gets stretched c. Voltage gated channels – open when membrane potential gets less negative
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