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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

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

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?


Figure 6 27

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.


Figure 6 33

Size of PSP is Variable!

S 8

Who Cares?

Presynaptic Facilitation

Presynaptic Inhibition

Figure 6.33

Mechanism: vary Ca++ entry in presynaptic terminal B.


Figure 6 25

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)


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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


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S 3

Priority by proximity

To axon hillock!


Figure 6 28

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


Figure 6 29

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+


Figure 6 31

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?


1qq 13 for 10 30

S 7

Synapses named for NT used: -ergic

Examples:

Cholinergic

Adrenergic

Serotonergic

GABAergic

Peptidergic


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