1 October 2010 Test # 1 Monday See Test 1 Study topics on website See supplemental powerpoint on EPI and NE posted to powerpoint folder. Today in class Ionic basis of resting membrane potential Role of sodium potassium ATPase Ionic basis of action potential Action potential conduction Lab next week: Measuring AP CV 1QQ # 11 for 8:30 class
1. Membranes of neuronal dendrites and cell bodies a) b) c) d) e) Have voltage-gated ion channels Conduct electrical signals decrementally Are myelinated Receive synapses from other neurons Have a resting membrane potential near -70 mV. 2. Dorsal root ganglia
a) b) c) d) e) Have astrocytes Have oligodendrocytes House the cell bodies of sensory neurons House the cell bodies of autonomic neurons are part of the efferent pathway to muscle cells. 1QQ # 11 for 9:30 class 1. Membranes of neuronal dendrites and cell bodies
a) b) c) d) e) Have ligand-gated ion channels Conduct electrical signals non-decrementally Are myelinated Have graded potentials Have a resting membrane potential near -70 mV. 2. Ventral roots a)
b) c) d) e) Have astrocytes Have oligodendrocytes House the cell bodies of sensory neurons House the cell bodies of autonomic neurons are part of the efferent pathway to muscle cells. S1 Fig. 06.10e
Equilibrium potential = Nernst potential = diffusion potential Predict the change in membrane potential if K+ were added to the extracellular fluid. E ion+ = 61/Z log ([conc outside]/ [conc inside]) E K+ E K+ 5 mM = 61/1 log (5/150)
= -90 mV 150 mM 50 mM K+ When the electrostatic force that impedes diffusion of K+ is exactly equal to the driving force favoring diffusion based on a concentration gradient. the membrane potential reaches an equilibrium at which the voltage is called Nernst Potential or Equilibrium Potential. So which compartment corresponds to intracellular fluid? S2
The Nernst Equation If the membrane is permeable to ONLY ONE ion species and you know the concentrations on both sides of the membrane, use the Nernst Equation to calculate the membrane potential. Nernst potential for X = 61/Z log [Outside ] / [Inside] Now consider a situation in which only Na+ is permeable. Fig. 06.11
S3 Fig. 06.11a S4 Fig. 06.11b S5 Fig. 06.11c S6
Fig. 06.11d S7 Equilibrium potential for Na+ Fig. 06.11e E Na+ = 61/1 log (145/15) E Na + = +60 mV 145 mM Predict the
change in membrane potential if Na+ were added to the extracellular fluid. 15 mM Extracellular Intracellular So, given these concentrations of Na+ and a membrane permeable only to Na+, use Nernst equation to calculate
what the membrane potential would be. At the equilibrium potential, no net movement of Na+ because driving forces (concentration and electrical) are exactly equal and opposite. S8 Electrical and concentration gradient driving forces for Sodium and Potassium Size and Direction of Arrows
show driving forces! What would happen to membrane potential if suddenly PNa became very great? The Goldman Equation!
Why is resting membrane potential closer to EK than ENa? How does the membrane potential change if 1) permeability to sodium increases 2) Permeability to potassium increases S9 The Goldman Hodgkin Katz Equation
If you know the concentrations of ALL permeable ions and their relative permeabilities, you can calculate the membrane potential using the GHK Equation. S 10 At RMP, some Na+ leaks in, some K+ leaks out. S 11 Na+ K+ ATPase maintains the concentration gradients across
cell membranes Animation of the Pump What would happen to membane potentials and concentrations of Na+ and K+ if cells didnt have this pump? S 12 Animations of the Origin of Resting Membrane Potential Animation of Resting Membrane Potential (single ion) Origin of Resting Membrane Potential and intracellular recording
YouTube animation of Na-K-ATPase, Sodium Co-transporter, and K Leak channels S 13 S 14 Which ion moving in which direction (into or out of cell) is responsible for depolarization and overshoot? Which ion moving in which direction (into or out of cell) is responsible
for repolarization and hyperpolarization? Increase PNa+ Increase PK+ Can the membrane potential go more negative than -90 mV? S 15
Leak Channels Gated Channels .. Ligand-gated .. Mechanically-gated .. Voltage-gated Electrogenic SodiumPotassium ATP-ase maintains concentrations across membrane Graded potentials are conducted decrementally for only a few millimeters, die out over distance and time, and are proportional
to the size of the stimulus. 3 Na+ 2K+ S 16 Open Na+ channels, Na+ goes _____ Open K+ channels, K+ goes _____ S 17
Graded potentials are conducted no more than 2mm Insect bites foot (stimulus). Sensory neuron produces graded potential in proportion to intensity of the stimulus. How is signal conducted to the brain? S 18
Types and locations of Ion Channels Sensory neuron Leak Channels Gated Channels .. Ligand-gated .. Mechanically-gated .. Voltage-gated Interneurons & Motoneurons Intracellular Recording Electrode
End of Material For Test # 1 Begin Material For Test # 2 S 19 What happens when the membrane is depolarized by more than about 15 mV? Analogy of shutter release pressure on a camera, either
trips shutter or not. Action potentials are all or nothing. How is the intensity of a stimulus encoded by action potential if all action potentials have the same size (amplitude)? S 20 S 21
Rising Phase Falling Phase Relative permeabilities Duration of AP Refractory periods absolute RP relative RP Why does the peak of the
action potential not reach ENa? Properties of V-gated Na and K channels account for the shape of the action potential and the refractory periods. S 22 To reset from inactivated state to closed state, membrane must repolarize.
Open at -55 mV Membrane must repolarize to reset Na+ Channels to be capable of opening again. Compare and contrast voltagegated Na and K channels based on time to open and duration of open time. S 23 What accounts for the afterhyperpolarization?
Explain the shape of the action potential based on the properties of Voltage-gated sodium and potassium channels (when and how long each type opens and closes.) S 24 S 25
Who Cares? Novacaine, lydocaine, xylocaine, All block voltage-gated Na+ channels Prevent action potentials, so stimulus does not result in an action potential in sensory neurons which would convey that information to the brain where person would be conscious of the stimulus!
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