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Electrical and concentration gradient driving forces for Sodium and Potassium

S 8. What would happen to membrane potential if suddenly P Na became very great?. The G-H-K Equation!. Electrical and concentration gradient driving forces for Sodium and Potassium. Why is resting membrane potential closer to E K than E Na ?.

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Electrical and concentration gradient driving forces for Sodium and Potassium

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  1. S 8 What would happen to membrane potential if suddenly PNa became very great? The G-H-K Equation! Electrical and concentration gradient driving forces for Sodium and Potassium Why is resting membrane potential closer to EK than ENa? Size and Direction of Arrows show driving forces! How does the membrane potential change if 1) permeability to sodium increases 2) Permeability to potassium increases

  2. S 9 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.

  3. 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+ Can the membrane potential go more negative than -90 mV? Increase PK+ Increase PK+ How do ions get across the membrane? Ion channels!

  4. S 3 Types and locations of Ion Channels Sensory neuron Leak Channels Gated Channels ….. Ligand-gated….. Mechanically-gated ….. Voltage-gated w/ LGCs and MGCs Intracellular Recording Electrode or Stimulating Electrode Interneurons & Motoneurons w/ LGCs w/ VGCs

  5. S 4 Expanded on next slide What happens when the membrane is depolarized by more than about 15 mV? Action potentials are all or nothing. Analogy of shutter release pressure on a camera, either trips shutter or not. How is the intensity of a stimulus encoded by action potential if all action potentials have the same size (amplitude)?

  6. S 5 Relevance of the GHK equation Changes in membranepermeability produce changes inmembrane potential via the openingand closing of ion channels!

  7. S 6 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 voltage-gated Na and K channels based on time to open and duration of open time.

  8. S 7 Voltage-gated Na+ channel Tetrodotoxin from ovary of Puffer fish, used in Japanese sushi (fugu) scienceblogs.com/.../upload/2006/03/channel.jpg

  9. S 8 What types of ion-channels are labeled in this neuron in red? TTX with red fluorescent marker

  10. S 9 Relative permeabilities Duration of AP Refractory periods absolute RP relative RP RisingPhase FallingPhase 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.

  11. S 10

  12. S 11 Natural ways to Initate an Action Potential Graded depolarization in cell body reach threshold at axon hillock Unstable membrane potential cycles: pacemaker potentials in pacemaker cells of heart, smooth muscles of gut, and medullary neurons for respiratory rhythm. Graded depolarization in in receptive membranes of sensory neurons reach threshold for AP at trigger zone. i.e. nociceptors and stretch receptors.

  13. S 12 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!

  14. S 13 Questions About Action Potential Conduction: How does an action potential move along the axon? Why doesn’t the amplitude get smaller with distance? Why is the conduction of an action potential unidirectional? What is the absolute refractory period and what is going on with voltage gated sodium channels that accounts for the absolute refractory period? What is the relative refractory period and what is going on with voltage gated sodium channels that accounts for the relative refractory period? Axon Hillock Axon

  15. S 14 In unmyelinated axons, action potential must be generated at each point along the membrane, a relatively slow process that involves influx of Na+ which sets up positive feedback cycle. In myelinated axons, action potential must be generated only at the nodes of Ranvier, which allows AP to be conducted much faster and with fewer ions moving, and thus less energetically expensive.

  16. S 1 The Questions: How does an action potential move along the axon? Why doesn’t the amplitude get smaller with distance? Why is the conduction of an action potential unidirectional? Axon Hillock ofinterneuron or efferent neuron Axon Trigger Zone of Sensory Neuron

  17. Saltatory Conduction S 3 What’s at theend of an axon? Figure 6.23 AP CV (up to 100 m/s) Location of channels Energy Requirements Axon diameter Clustering of V-gated channels at Nodes of Ranvier Reminder: influx of Na+ is very quickly followed by efflux of K+ (not shown above)

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