Slide 1We study how the brain makes mind and behaviorLesions and Stimulation…Brain and CNS are made of cells: NeuronsSlide 5A) Purkinje Cells, B) Granule CellsOr…….http://www.youtube.com/watch?v=ifD1YG07fB8&feature=relatedAs we were saying…What’s a “potential?”All cells have a resting potential.Irritable cells…..Slide 13In the next lecture or two….Slide 15Slide 16Slide 17Slide 18OK, here’s a new situation. What’s different? What forces?Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25You should note that there is a relationship between Fc and Fe…NERNST EQUATION with GOLDMAN EXTENTION : Derivation:It is noted that this applies when only permeable ion is K+This Nernst Equation….The Equilibrium Potential of Na+..Back to the neuron…Slide 32Here are the results…Why the discrepancy??The rest of the discrepancyis due to the… 2)The whole storyMeasuring Neuronal VoltagesBetter for fast things (spikes)….Slide 39Hodgkin ExperimentOne stimulation of + 10 mV, a depolarization…You always see the overshoot…4 stimulations….. (Bucking Currents)Voltage Gated Ion Channels.Hodgkin Cycle (inner wheel)Why doesn’t it inevitably lead to a spike?Inner wheel PLUS Outer wheelThe outer wheel …Slide 49Theory of the Action potential--Hodgkinhttp://www.afodor.net/HHModel.htmEvidence:…as in these experiments.Well this is nice…In other words…Remember this?Slide 57Superscientists don’t exist…but Analog amplifiers do……In other words…An Experiment with a voltage clamp or current injectorThis PROVES even the dynamic parts of Hodgkin-Huxley Model:Strength-Duration CurvePsychology 312-1 Physiological Basis of [email protected] study how the brain makes mind and behaviorMETHODS (in oversimplification terms): 1.Lesions (Ablation): Oldest Method; 2 ways: a) Natural: Take them as they come (bullet holes, tumors; “Neuropsychology”.) b) You do it: chemicals, electricity (cheap). 2. Stimulation: “the opposite of lesions.” Again, electrical or chemical. 3. Recording: a)Imaging (PET, fMRI), b)Electrophysiology (EEG, ERP from neuron populations, or from single neurons)Lesions and Stimulation…….. Assume that single structures are responsible for single behavior patterns or psychological functions. This is the height of naiveté, to wit……... “Structure A is substrate for anger.” Ergo…a) If you lesion it, no more anger, as in lobotomy. (Usually no more lots of other stuff too.)b) If you stimulate it, you get a guy angry..Jose Delgado did the reverse….. http://www.youtube.com/watch?v=6nGAr2OkVqEBrain and CNS are made of cells: NeuronsOf course, real neurons come in all shapes & sizes, like the following:Drawing by Santiago Ramón y Cajal of neurons in the pigeon cerebellum. (A) Denotes Purkinje cells, an example of a multipolar neuron. (B) Denotes granule cells which are also multipolar.A) Purkinje Cells, B) Granule CellsOr…….http://www.youtube.com/watch?v=ifD1YG07fB8&feature=relatedThe job of the nervous system is to transmit information from neuron to neuron, and to a target organ like a muscle which initiates behavior.As we were saying…The job of the nervous system is to transmit information from neuron to neuron, and to a target organ like a muscle which initiates behavior.This happens by action potential (“spike”) propagation down a neuron, and, usually, via synaptic transmission to another neuron.What’s a “potential?”The name implies the ability to do work…electrical work, the ability to move charged particles from one level of potential to another, lower level.All cells have a resting potential. That is, a relatively constant difference in electrical potential across the cell membrane. Say +30 mV inside vs. – 10 mv outside.This is where they spend most of their lives…at rest..it’s a good life. “Irritable” tissue—muscle cells or nerve cells--- are differentIrritable cells…..…..occasionally show sudden fast changes in cell membrane potential, before recovering the resting level. In neurons, these changes are called “impulses” or action potentials, and they propagate from cell body to end of neuron.Here is a neuron membrane passing from rest to action and back to rest…In the next lecture or two….….we will consider how the resting neuronal membrane potential and the action potential are generated. To do this, we need to do some thought experiments…OK, first, let us note that there are 3 passive phenomena mainly influencing the situation within a neuron:(Passive means life is irrelevant to these phenomena.)1. Membrane (semi-) permeability. 2. Chemical or concentration forces: Particles tend to move away from high and to low concentration.3. Electrical forces. + “likes” – and “dislikes” +. – “likes” + and “dislikes” –OK, now, back to those thought experiments……Consider a beaker of water divided by a semi-permeable membrane into 2 compartments, and I put a teaspoon of a monovalent salt into the left compartment. What does the salt ”want to” do? What forces are at work?OK, the concentration forces drive ions to the right. No problem, both positive and negative ions can go through, so do. Now what forces act?..So another pair go through, which puts system at balance or electrochemical equillibrium…with no difference in potential(=voltage)across the membraneOK, here’s a new situation. What’s different? What forces?OK, only the cation can get through in the first instant. It does. Let’s now analyze forces and predict next moment.The anion “wants to” follow the cation but is too big. (Good example of semipermeability.) What are forces now , and can we predict next moment?We now have electrochemical equilibrium (There is still Fc but balanced by Fe) but with a residual voltage across the membraneIn the previous slide, the one permeable little cation is said to be:at its Equilibrium Potential.This is the voltage across the membrane at which the electrical and chemical forces on the ion are in balance. Fc + Fe = 0 orFe = -FcThe situation (figure) in a resting neuron is more complicated: Given this situation what are forces on K+, the most permeable cation?More complicated because more ions are involved, and they together affect electrical and chemical forces.You should note that there is a relationship between Fc and Fe……i.e., the