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Ch03
 

Ch03

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    Ch03 Ch03 Presentation Transcript

    • THE NEURAL MEMBRANE AT REST
    • ELECTRICAL PROPERTIESSimple reflex : information needs to be quickly transmitted to the CNS and backInformation is transmitted through action potentials (change in the electrical properties of themembrane)Cells able to generate an AP have excitable membraneAt rest, these cells have a inside negative electrical charge (resting membrane potential) thatbecome positive during the AP
    • CYTOSOLIC AND EXTRACELLULAR FLUIDWater is the key ingredient in intracellular and extracellular fluidKey feature – uneven distribution of electrical charge (O has a net negativecharge)Ions are atoms or molecules with a net electrical charge dissolved in the waterSalz for example is a crystal of Sodium (Na+) and Chloride (Cl-)Monovalent Ion: Difference between protons and electrons =1,Divalent Ion: Difference between protons and electrons =2,cation (+), anion (-)When the crystal breaks down spheres ofhydration -layer of water are attracted to the ionThe orientation of the water molecules isdetermined by the valence of the ion
    • IONS INVOLVED IN CELLULAR PHYSIOLOGY Sodium Calcium + 2+Potassium Chloride + -
    • THE PHOSPHOLIPID MEMBRANEHydrophilic: Dissolve in water due to uneven electrical charge (e.g., salt,proteins, carbohydrates)Hydrophobic: Does not dissolve in water due to even electrical charge (e.g., oil,lipids in general) The Phospholipid Bilayer Hydrophilic HydrophobicResting and Action potentials depend on special proteins that are inserted in themembrane
    • THE PROTEINProteins are molecules assembled by combination of different amino acids (20 types) Central alpha carbon R group Amino group Carboxyl group
    • THE PROTEIN STRUCTURE Peptide bondPrimary Tertiary Secondary Quaternary
    • CHANNEL PROTEINSIon ChannelsThey form a pore through the membrane that hydrophilicis ion selectiveThey can be opened and closed (gated)by changing in the local microenvironmentof the membrane hydrophobicIon PumpsFormed by membrane spanning proteinsUses energy from ATP breakdownNeuronal signaling
    • THE MOVEMENT OF IONSDiffusion: movement of ion due to concentration levelsDissolved ions tend to distribute evenly by following down concentration gradientConcentration gradient = difference of concentration of an ion across the membraneElectricityElectrical current (I, measured in Amperes) represents ion movement.It’s regulated by1) electrical conductance (g, measured in Siemens) or electrical resistance (R, measured in Ω): ability (or inability) of an electrical charge to migrate from one point to another2) electrical potential (V, measured in volts): difference in chargebetween cathode and anode
    • THE MOVEMENT OF IONSElectrical current flows across the membrane byOhm’s law relationshipI =gV or I =V/R Membrane potential: Voltage across the neuronal membrane. The resting potential is typically -65 mV …let’ see why…
    • EQUILIBRIUM POTENTIALExample 1 Equilibrium is reached when diffusional and electricalExample 2 forces are equal and opposite (equilibrium potential, Eion)
    • MEMBRANE POTENTIALIn the membrane ions have different concentration between inside and outside,and this gradient is established by action of ionic pumps, that use energy inorder to move ions against concentration forces Membrane permeability determines membrane resting and action potentials
    • MEMBRANE POTENTIAL Membrane permeability determines membrane resting and action potentialsMembrane rest potential is determined by the higher number of K vs. Na channelsopen (resting potential close to Ek potential)