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Gated Ion Channels

Gated Ion Channels. A. Voltage-gated Na + channels. 5. generation of AP dependent only on Na +. repolarization is required before another AP can occur. K + efflux. Gated Ion Channels. A. Voltage-gated Na + channels. 6. positive feedback in upslope.

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Gated Ion Channels

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  1. Gated Ion Channels A. Voltage-gated Na+ channels 5. generation of AP dependent only on Na+ repolarization is required before another AP can occur K+ efflux

  2. Gated Ion Channels A. Voltage-gated Na+ channels 6. positive feedback in upslope a. countered by reduced emf for Na+ as Vm approaches ENa b. Na+ channels close very quickly after opening (independent of Vm)

  3. Gated Ion Channels B. Voltage-gated K+ channels 1. slower response to voltage changes than Na+ channels 2. gK increases at peak of AP

  4. Gated Ion Channels B. Voltage-gated K+ channels 3. high gK during falling phase decreases as Vm returns to normal channels close as repolarization progresses

  5. Gated Ion Channels B. Voltage-gated K+ channels 4. hastens repolarization for generation of more action potentials

  6. Does [Ion] Change During AP? A. Relatively few ions needed to alter Vm B. Large axons show negligible change in Na+ and K+ concentrations after an AP.

  7. Potential Transmission A. Electrotonic 1. graded 2. receptor (generator) potentials

  8. Potential Transmission a.  stimulus, then  ∆ Vm b. electrical signal spreads from source of stimulus c. problem: no voltage-gated channels here d. signal decay “passive electrotonic transmission”

  9. Potential Transmission A. Electrotonic 3. good for only short distances 4. might reach axon hillock - that’s where voltage-gated channels are - where action potentials may be triggered

  10. Potential Transmission B. Action potential 1. propagation without decrement 2. to axon terminal

  11. Synaptic Transmission

  12. Synaptic Transmission A. Presynaptic neuron 1. neurotransmitter (usually) 2. synaptic cleft

  13. Synaptic Transmission B. Postsynaptic neuron 1. bind neurotransmitter 2. postsynaptic potential (∆ Vm) 3. may trigger action potential on postsynaptic effector

  14. Synaptic Transmission C. Alternation of graded and action potentials

  15. Intraneuron Transmission A. All neurons have electrotonic conduction (passive) B. Cable properties 1. determine conduction down the axon process 2. some cytoplasmic resistance to longitudinal flow 3. high resistance of membrane to current “but membrane is leaky”

  16. Intraneuron Transmission C. Nonspiking neurons 1. no APs 2. local-circuit neurons 3. still release neurotransmitter 4. vertebrate CNS, retina, insect CNS 5. are very short with increased Rm

  17. Intraneuron Transmission A. All neurons have electrotonic conduction (passive) B. Cable properties 1. determine conduction down the axon process 2. some cytoplasmic resistance to longitudinal flow 3. high resistance of membrane to current “but membrane is leaky”

  18. Intraneuron Transmission C. Nonspiking neurons 1. no APs 2. local-circuit neurons 3. still release neurotransmitter 4. vertebrate CNS, retina, insect CNS 5. are very short with increased Rm

  19. Intraneuron Transmission D. Propagation of action potentials 1. ∆ Vm much larger than threshold - safety factor

  20. Intraneuron Transmission D. Propagation of action potentials 2. spreads to nearby areas - depends on cable properties - inactive membrane depolarized by electrotonically conducted current

  21. Intraneuron Transmission D. Propagation of action potentials - K+ efflux behind region of Na+ influx

  22. Intraneuron Transmission D. Propagation of action potentials 3. unidirectional a. refractory period b. K+ channels still open

  23. Intraneuron Transmission D. Propagation of action potentials 4. speed a. relates to axon diameter and presence of myelin b.  axon diameter,  speed of conduction

  24. Intraneuron Transmission E. Saltatory conduction 1. myelination a.  Rm ,  Cm b. the more layering, the greater the resistance between ICF and ECF

  25. Intraneuron Transmission E. Saltatory conduction c. charge flows more easily down the axon than across the membrane

  26. Intraneuron Transmission E. Saltatory conduction 2. nodes of Ranvier a. internodes (beneath Schwann cells or oligodendrocytes) b. nodes are only exit for current c. only location along axon where APs are generated

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