BIOL 3800 1st Edition Lecture 6Outline of Last Lecture I. NeuronsA. Major players in Nervous SystemB. Communicate via electrical and Chemical SignalsC. Most Electrically ExcitableD. All Neurons and Glial Cells (supporting cells) make up nervous systemE. 3 Important Reasons Thoroughly StudiedII. Neuronal Structure and FunctionA. 2 Ways to Differentiate Neuronal RegionsB. Neuron StructureC. Little Correlation Between Neuronal Complexity and PhylogenyIII. Transmission of Signals in Single NeuronA. Spike-Initiating ZoneB. Physiological BehaviorIV. Transmission of Signals Between NeuronsA. Afferent fibersB. InterneuronsC. SynapsesD. Effector NeuronsE. Neuronal Circuit: Afferent, Interneurons, EfferentF. Presynaptic/Postsynaptic NeuronsG. Neuronal CircuitV. Organization of Nervous SystemA. Sensory NeuronsB. Motor NeuronsC. SomataD. Glial CellsOutline of Current Lecture I. Membrane ExcitationA. Voltage (electric potential)B. How we Measure Membrane PotentialsC. Electrical Properties of MembranesD. Role of Ion ChannelsII. Passive Electrical Properties of Membrane These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.A. CapacitatorB. Membrane Resistance and ConductanceIII. Types of Membrane PotentialsA. 3 Types of Membrane PotentialsIV. Other Things to KnowA. BrainB. Membrane PotentialC. Nernst and Goldman EquationsCurrent LecturePhysical Basis of Neuronal Function III. Membrane ExcitationA. Voltage (electric potential) 1. found in plasma membrane all animal cells2. Electrically excitable cells like neurons & muscle fibers can respond to change by producing AP’s3. Measure of membrane potential: potential difference across membrane (in Volts)B. How we Measure Membrane Potentials1. A.L. Hodgkin & A. F Huxley (1940’s and 1950’s): measured membrane potentials via experiment with giant squid2. Oscilloscopesa. The vertical displacement of a beam of electrons given off by cathode ray tube and this tool amplifies and plots the amplitude of the electrical signal producedb. Computer takes over this job now and can group data together to be compared easierc. Insert cathode ray through plasma membrane creates resting potential Vrest (steady inside neg potential when no AP’s or postsynaptic events happening)i. Resting state cytoplasm isopotential (same potential everywhere)ii. potential difference provides energy that moves ions across membraneiii. Electric field across plasma membrane largeC. Electrical Properties of Membranes1. Excitable cells have passive and active electrical properties2. Hyperpolarization: when negative interior of cell becomes more negative3. Depolarization: when diminished potential diff. across cell because more positive charge within cell (opening voltage gated Na+ channels)4. Threshold potential: value of membrane potential at which an AP triggered 50 % of timei. Different for every neuron and depends on density of voltage gated Na+ channels at axon hillockD. Role of Ion Channels1. Most membrane channels ion selective meaning only certain can cross membrane2. Electrochemical gradient drive ions through channels3. Some channel only open in response to change in cells called (i.e) voltage-gated channels 4. Passive electrical responses that are associated with K+ channels AKA “leak channels” mainly responsible for maintaining resting potential5. Ligand gated channels: channels that open when neurotransmitters bind to protein receptors on cell surfaceII. Passive Electrical Properties of MembranesA. Capacitator1. Can store energy as separated charges made when two conductors separated by and insulator (i.e lipid bilayer)B. Membrane Resistance and Conductance1. Lower resistance of membrane more ions will cross2. Relationship b/w current resistance and steady-state voltage = Ohm’s lawi. Ohm’s law says Voltage drop made across membrane by current through that membrane directly proportional to current X resistanceof membraneV=ΔI X R3. Do not self propagateIII. Types of Membrane PotentialsA. 3 Types Membrane Potentials1. Resting potential a. Nothing happening “nonexcited” resting state b. Vrest b/w -20 and -100mVc. 2 factors i. presence of open ion channels that have selective permeabilityii. Unequal distribution of ions maintained by active transport which allows membrane potential to be established2. Graded potentiali. Synaptic potentialsii. Receptor potentials3. Action Potential (AP) “something happening” “suprathreshold” because goes above thresholdIV. Other Things to KnowA. Brain1. In humans brain cell is 2% of body weight and 20% total energyB. Membrane Potential 1. When thinking of membrane potential and you see -70 and -80 don’t think -80 smaller ignore neg. sign pay attention to magnitudeC. Nernst and Goldman Equations1. Nernst equation states equilibrium potential dependant on:a. Tempb. Charge on ion that is able to go through membranec. Ratio of ionic conc. on both sides of membrane2. Goldman Equation is like Nernst but includes relative permeability of each ion speciesa. Important to know how to use Nernst and Goldman