Learning Objectives Organization of the Nervous System Electrical Signaling Chemical Signaling Networks of Neurons that Convey Sensation Networks for Emotions & Behavior or Motor Systems

Evaluations: 5 Exams plus a Final Each exam including the final is worth 100 Points. The exams are multiple choice, matching,True/False. BRING TO EACH EXAM A 100 QUESTION SCANTRON. EXTRA CREDIT: Extra credit question (s) will only be available on Exam 5 and will be based on assigned outside reading listed above and will be worth 25 points. Grading: Total Possible Points 500 A= >90% B= >80% C= >70% Students with an “A” grade after 5 exams are exempt from the final. Students taking the final exam can drop the lowest grade on Exams 1-5 or a missed exam.

Policy on Grading If you have a question about an incorrect answer, –Note it on your score sheet –At the end of the course if the points you think were mistakingly deducted would bring your grade up to the next letter grade, come see me then –If a question was universally missed by all I will consider giving you points for it.

Week 4 Tues1-31Electrical Signalling: Membrane Potential Thurs2-2Nernst & Goldman Equations Ch 3 Week 5 Tues2-7Action Potential Ch 4 Thurs2-9Ion Channels: Voltage Gated Week 6 Tues2-13Exam 2 Thurs Chapter 3 and 4 Matthew and ONLINE BEAR’S 3 rd Edition Chapters

Electrical Properties of Neurons & Excitable Cells Resting Membrane Potential Equilibrium Potential of an Ion Nernst & Goldman Equations

Ion Inside Outside Cross PM K+1255yes NA+12120no Cl-5125yes H2O55,000 yes Anion-1080no

Clinical significance of resting membrane potential Jack Kevorkian kills patients with potassium sulfate depolarizes cardiac and neuronal membranes Die from heart failure, hearts stops beating because the resting membrane potential is not sufficiently negative

Generation of Vr Selective permeability of neuron membrane Unequal distribution of ions across membrane Action of ion pumps Largely due to potassium since no open channels for sodium Slow leak for Na is rectified by the Na/K ATPase that pumps out 3 Na for 2 K

Plasma Membrane Maintains the separation of ions and charges Lipid bilayer is non polar and does not allow polar or charged molecules to cross C. Ernest Overton: showed that non-polar molecules crossed PM but polar molecules did not.

Selective Permeability The ability of membrane to select which ions or small particles can move through freely while restricting passage of others Restriction is due to lipid bilayer Selective passage is due to membrane proteins, selective ion channels and transporters, exchangers

Membrane Potential The difference in charge across the plasma membrane. Written as Vm Generated by movement of ions across the membrane where the ionic concentrations of the intracellular and extracellular fluid are different Inside the plasma membrane is always negative with respect to outside the plasma membrane at rest

Resting Membrane Potential Membrane potential at which neuron membrane is at rest, ie does not fire action potential Written as Vr

Ion Movement Concentration gradient Charge gradient –Together referred to as the electrochemical driving force Action of ion pump

Electrochemical Gradient Exerts force on ions and determines its movement Based on concentration of ion inside/outside Based on charge of the ion and charge of the pm This determines the driving force on an ion in any instant of time

Equilibrium potential Membrane Potential (potential difference across the plasma membrane) at which the net flow of an ion type = zero The number of ions moving into the cell = the number of ions moving out of the cell for a particular species of ion

Equilibrium Potential of An Ion The membrane potential at which the net driving force propelling the ion in = the net driving force proplling the ion out. Written E ion ; E Na, E Cl, E K

Nernst Equation E ion = RT/zF log [ion] o /[ion] in E ion = ionic equilibrium potential Z= charge of ion F= Faraday’s constant T= absolute temperature at R= gas constant Simplifies to 58 mV

Nernst Equation Variables Assumes that membrane is permeable to that ion As temperature increases the diffusion increases As charge on the molecule increases, it decreases the potential differences needed to balance diffusion forces.

E Na E na = 61.54mV log [Na]o/[Na]i E Ca = 30.77mV log [Ca]o/[Ca]i C Cl = mV log [Cl]o/[Cl]i

Resting Membrane Potential Membrane potential at which neuron membrane is at rest, ie does not fire action potential Written as Vr

Goldman Equation Em= RT/F ln Pk[K]o+Pna[Na]o+PCl[Cl]i Pk[K]I+Pna[Na]I+PCl[Cl]o Also known as the constant field equation because it assumes that electrical field of the membrane potential is equal across the span of the membrane

Membrane Permeability Membrane is 50 more permeable to K than to Na b=P na /P k =0.02 c=P Cl /P k The membrane is so impermeable to Chloride that you drop it from the equation

Em= mV log [K]o+b[Na]o [K]I+b[Na]I Should equal depending in initial given concentrations: -60 to -100 mV

Goldman Equation Em= RT/F ln Pk[K]o+Pna[Na]o+PCl[Cl]i Pk[K]I+Pna[Na]I+PCl[Cl]o Also known as the constant field equation because it assumes that electrical field of the membrane potential is equal across the span of the membrane