Electrical Signals NeuronsThings to rememberFigure 8-1 (General organization of nervous system)Fig 8-2,8-3,8-4 (Parts and general types of neurons)Fig 8-5, 8-6 (Types and functions of glial cells)Nature of neuronal signalsNeurons and muscle cells have electrical properties that are used to communicate information (generate signals)ALL Living cells generate an electrical potential difference (Vm) across their plasma membranes (membrane potential)Unlike most cells, neurons also generate signals, consisting of brief changes in Vm (membrane potential)Signals make everything possible- Two typesResponses to a stimulusLowering of the membrane potentialPositive = upinside of cell is positiveNegative = downinside of cell is negative1. Graded local signalsGraded- Amplitude varies with the strength of the stimulusLocal- signal generated in one place on the membrane, the amplitude decreases as it moves away from that one place. All or non regenerative signals (action potential)All or none = once you give a threshold stimulus, then it will be really positive really fast and this is called the action potential. All or none because if you give at least a threshold stimulus the action potential will always be the same sizeRegenerative = As it spreads away, the amplitude does not decay with distance, keeps regenerating itselfVm when one ion is permeableWhere do membrane potentials come from?- 2 conditions1. Unequal distribution of an ion across the membrane2. Plasma membrane must be permeable to the ionsrates of movement continue until they are equal and opposite (equilibrium)Nernst equation for K+ = Equilibrium potential(high concentration inside and low outside)diffuses out down its concentration gradient and in down its electrical gradientIf neuron: membrane will be negative inside if only permeable to K+E(K)= 61log([K]o/[K]i) mVNernst Equation for Na+ = Equilibrium potential(low concentration inside cell and high outside)diffuses in down concentration gradient and out down its electrical gradientIf neuron: membrane will be positive inside if only permeable to Na+E(Na)= 61log([Na]o/[Na]i) mVVm when several ions are permeableGoldman Hodgkin-Katz EquationWhat if more than one ion is permeable? Consider 3: Na+,Cl-, and K+K+ close to -90mV, Na+ close to 50 or 60mV, and Cl- is negativeDepends on the permeability of each ion (P), the more permeability the more effect it has2. Depends on the relative concentrations [] of each ionVm= 61log {(P(K)[K+]out +P(Na)[Na+]out +P(Cl)[Cl-]in)/(P(K)[K+]in + P(Na)[Na+]in + P(Cl) [Cl-]out)} mVIf the permeability of a specific ion is very low then the term essentially drops out because it wont have much effect on the membrane potentialCell controls membrane potential by varying the permeability of these three ionsSomething to remember***If the permeability for a particular ion increases the membrane potential will change, tending to move toward the equilibrium potential for that ion ***** IMPORTANTIon leakage and Na+/K+ pumpsFor a typical cell, both K+ channels and Na+ channels are open, so for the typical cell: Neither ion is in equilibriumIf Vm = -70 mV, neither ion is in equilibrium so Na+ leaks in, K+ leaks outNa+/K= pumps counteract ion leakage, maintaining gradients and VmWhat is the force making the ion move???When not at equilibrium there is a net force, the difference between the potential of the membrane and the ions equilibrium potential: THE DRIVING FORCEFor Na+: -70-60 = -130mV (inward) netFor K+: -70 +90 = +20 mV (outward) netVm - E(ion) = Driving Force (for cations, negative is inward, and positive is outward)To fix this, the sodium potassium pump maintains the ionic distribution of ions across the membrane by pumping Na+ out and pumps K+ in. Requires ATPNeurons have a lot of Na+/K+ pumps in their membranesso they need a lot of ATP*Babies need this: they are very active and continuously growing so they need a lot of calories to keep up with the ATP need in their brains*Phylogeny of V-gated ion channelsVoltage gated ion channels1. Simplest ion channel-2 transmembrane segmentsFound in prokaryotes and potassium channel called the inwardly rectifying potassium channel (Kir)2. Addition of 4 more transmembrane segments6-membrane motif structuremost channels todayK+ channelsMany different kinds3. Voltage gated sodium and calcium channelsone single protein that contains 4 subunitsEarly Ca2+ channels diverged into two types- by amount of depolarization required to open channel1. High voltage activated (HVA)Separated into two types1. L typesensitive to set of drugs that block the Ca2+ channels (dihydropyridine)important in heartstop raise in blood pressure2. Non L typenot sensitive to this drug (dihydropyridines)2. Low voltage activated (LVA)4. Sodium Channels (most recent)many typesVoltage-gated Na+ channel (Na-v)Big alpha subunit with 4 transmembrane subunitsPore is down middle of each subunitBISC 307L 1st Edition Lecture 4Current Lecture Electrical Signals Neurons- Things to remembero Figure 8-1 (General organization of nervous system)o Fig 8-2,8-3,8-4 (Parts and general types of neurons)o Fig 8-5, 8-6 (Types and functions of glial cells)- Nature of neuronal signalso Neurons and muscle cells have electrical properties that are used to communicate information (generate signals)o ALL Living cells generate an electrical potential difference (Vm) across their plasma membranes (membrane potential)o Unlike most cells, neurons also generate signals, consisting of brief changes inVm (membrane potential)o Signals make everything possible- Two types Responses to a stimulus Lowering of the membrane potential Positive = upinside of cell is positive Negative = downinside of cell is negative 1. Graded local signals- Graded- Amplitude varies with the strength of the stimulus- Local- signal generated in one place on the membrane, the amplitude decreases as it moves away from that one place . All or non regenerative signals (action potential)- All or none = once you give a threshold stimulus, then it will be really positive really fast and this is called the action potential. All or none because if you give at leasta threshold stimulus the action potential will always be the same size- Regenerative = As it spreads away, the amplitude does not decay with distance, keeps regenerating itself - Vm when one ion is permeableo Where do membrane potentials come from?- 2 conditions 1. Unequal distribution of an ion across the