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1QQ# 13 for 10:30

1QQ# 13 for 10:30. Why is action potential conduction velocity slower in a non-myelinated axon compared to a myelinated axon? In what ways do voltage-gated Na+ channels differ from voltage-gated K+ channels?. 1QQ# 13 for 11:30.

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1QQ# 13 for 10:30

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  1. 1QQ# 13 for 10:30 • Why is action potential conduction velocity slower in a non-myelinated axon compared to a myelinated axon? • In what ways do voltage-gated Na+ channels differ from voltage-gated K+ channels?

  2. 1QQ# 13 for 11:30 • Why are myelinated axons considered more energy-efficient that non-myelinated axons? • In what ways do voltage-gated Na+ channels differ from voltage-gated K+ channels?

  3. S 7 Figure 6.27 Most neurotransmitters are synthesized in the axon terminal. Exceptions: Peptide NTs originate in cell body, move in vesicles by fast orthograde axonal transport to axon terminal. Vesicle release proportional to Ca++ influx (High f AP leads to residual Ca++ in terminal) • Fates of neurotransmitters: • Bind to receptor on Post-synaptic cell • Diffusion away from synapse • Enzymatic degradation e.g. Acetylcholinesterase (AChE) and Monoamine Oxidase (MAO) • Uptake by astrocytes • Reuptake into presynaptic terminal (e.g. SSR) Tetanus toxin & Botulinum toxin disrupt SNARE function.

  4. Size of PSP is Variable! S 8 Who Cares? Presynaptic Facilitation Presynaptic Inhibition Figure 6.33 Mechanism: vary Ca++ entry in presynaptic terminal B.

  5. S 1 Unidirectional Release, diffusion, binding, Post-synaptic Receptor Types: Inotropic or Metabotropic Figure 6.25 Classification: Excitatory (closer to threshold for AP) Or Inhibitory (stabilizes or hyperpolarizes)

  6. Types of Ligand-Gated Receptors S 2 = ACH = Acetylcholine Inotropic receptor Metabotropic receptor Agonist = Nicotine Agonist = Muscarine Antagonist = Curare Antagonist = Atropine Types of Acetylcholine Receptors so named for agonist: Nicotinic AChR and Muscarinic AChR

  7. S 3 Priority by proximity To axon hillock!

  8. S 4 Figure 6.28 Some ion Channels that allow flux of Na+ and K+ simultaneously e.g. nicotinic Acetylcholine Receptor (nAChR) EPSPs :which ion moving in which direction? Duration of PSP vs AP Synaptic delay

  9. S 5 Figure 6.29 IPSPs :which ion moving in which direction? Some IPSPs result in no change in membrane potential by opening Chloride channels that stabilize membrane potential at resting value (Nernst Potential for Cl- = -70mV) or in cells that actively transport Cl- out. EK+

  10. S 6 Figure 6.31 Summation and Synaptic Integration Different times Different locations Challenge question: Suppose each IPSP hyperpolarizes by 5 mV and each EPSP depolarizes by 5 mV. If 4 inhibitory synapses are active at the same time, how many excitatory synapses must be active simultaneously to exceed threshold (-55 mV) if the resting membrane potential is -70mV?

  11. S 7 Synapses named for NT used: -ergic Examples: Cholinergic Adrenergic Serotonergic GABAergic Peptidergic

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