1QQ# 13 for 10:30

1. Why is action potential conduction velocity slower in a non-myelinated axon compared to a myelinated axon?

2. In what ways do voltage-gated Na+ channels differ from voltage-gated K+ channels?

1QQ# 13 for 11:30

1. Why are myelinated axons considered more energy-efficient that non-myelinated axons?

2. In what ways do voltage-gated Na+ channels differ from voltage-gated K+ channels?

Figure 6.27

Vesicle release proportional to Ca++ influx (High f AP leads to residual Ca++ in terminal)

Fates of neurotransmitters:1)Bind to receptor on Post-synaptic cell2)Diffusion away from synapse3)Enzymatic degradation e.g. Acetylcholinesterase (AChE) and Monoamine Oxidase (MAO)4)Uptake by astrocytes5)Reuptake into presynaptic terminal (e.g. SSR)

S 7Most 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.

Tetanus toxin & Botulinum toxin disrupt SNARE function.

Figure 6.33Presynaptic FacilitationPresynaptic Inhibition

Who Cares?

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

Size of PSP is Variable!

S 8

Figure 6.25UnidirectionalRelease, diffusion, binding,Post-synaptic Receptor Types: Inotropic or Metabotropic

Classification:Excitatory (closer to threshold for AP)OrInhibitory (stabilizes or hyperpolarizes)

S 1

Inotropic receptor Metabotropic receptor

Types of Acetylcholine Receptors so named for agonist:Nicotinic AChR and Muscarinic AChR

Types of Ligand-Gated ReceptorsS 2

Agonist = Nicotine Agonist = Muscarine

Antagonist = Curare Antagonist = Atropine

= ACH = Acetylcholine

Priority by proximityTo axon hillock!

S 3

Figure 6.28

EPSPs :which ion moving in which direction?Duration of PSP vs APSynaptic delay

Some ion Channels that allow flux of Na+ and K+ simultaneouslye.g. nicotinic Acetylcholine Receptor (nAChR)

S 4

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+

S 5

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?

S 6

Synapses named for NT used: -ergic

Examples:CholinergicAdrenergicSerotonergicGABAergicPeptidergic

S 7