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Ch. 5 Synaptic transmission

Ch. 5 Synaptic transmission. Electrical synapse. Chemical synapse. 雙向 快速. Electrical synapse: to synchronize electrical activity among populations of neurons (hypothalamus). crayfish. 小龍蝦. ATP, c-AMP. Chemical synapse. AP voltage-dependent Ca 2+ channels.

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Ch. 5 Synaptic transmission

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  1. Ch. 5 Synaptic transmission Electrical synapse Chemical synapse 雙向 快速

  2. Electrical synapse: to synchronize electrical activity among populations of neurons (hypothalamus) crayfish 小龍蝦 ATP, c-AMP

  3. Chemical synapse AP voltage-dependent Ca2+ channels

  4. Quantal transmission at neuromuscular synapses • End plate potential (EPP) • spontaneous changes occur in muscle cell mambrane miniature end plate potentials (MEPPs): occur even in the absence of stimulation, block by curare (ACh receptor blocker) • EPP = summation of MEPPs Low Ca2+ EPP fluctuations

  5. 假說：these “quantal” fluctuations suggest that EPPs are made up of individual units, each equivalent to a MEPP • 驗證：independent occurrence of unitary events (Poisson statistics): predict the distribution of EPP amplitudes • 結論：presynaptic AP causes a postsynaptic EPP because it synchronizes the release of many transmitter quanta

  6. Release of transmitters from synaptic vesicles: one synaptic vesicle is one MEPP Fusion of synaptic vesicles with the presynaptic membrane 4-AP 會影響 AP 的 duration-> Ca2+

  7. Dock: two membranes become tightly associated with each other prime: active fusion of the membranes

  8. The role of Ca2+ in transmitter secretion • 有五種實驗證明 nerve terminal 有 voltage dependent Ca2+ channels 存在：(1)Na+ channels blocker (2) voltage clamp experiment 如圖所示 (3)Ca2+ imaging 如下圖 (4) 直接打入 Ca2+(5) Ca2+ chelators • The purpose of AP is to activate Ca2+ channels • -latrotoxin triggers Ca2+ independent exocytosis Ca2+ channel blocker 鎘 Block Na+ & K+ channels

  9. Fura-2 在 presynaptic neuron 打入 Ca2+ Ca2+ chelators

  10. Synaptotagmin: Ca2+ sensor, bind to neurexins NSF & SNAP: common proteins in fusion, 與 SNARE 結合 (SNAP receptors 包括 synaptobrevin, syntaxin& SNAP-25)

  11. Toxins that affect transmitter release • Clostridial toxins (梭狀芽孢桿菌毒素), botulism (肉類桿菌中毒), tetanus (破傷風) • botulinum toxin & tetanus toxin: cleave synaptobrevin, syntaxin & SNAP-25 • female black widow spider: -latrotoxin triggers Ca2+-independent exocytosis, bind to neurexins

  12. Ch. 6 Neurotransmitters • The utility cycle of all neurotransmitters: (1) synthesized & packaged (2) release & binding (3) removed or degraded • classified into tow broad categories: (1) small-molecule NMs (2) neuropeptide

  13. What defines a neurotransmitter? • 1926, Otto Loewi Vagus nerve Heart rate Heart rate “vagus substance” ACh

  14. Criteria that define a substance as a neurotransmitter: Box A 斜體字

  15. The comparisons of neurotransmitters to hormones Action at a distance vasopressin, oxytocin, can be as a hormone and as a NM

  16. Two major categories of neuro-transmitters (1)small-molecule neurotransmitters: ATP, AMP (2) peptide neurotransmitters

  17. 請任舉兩個實驗證明 nevre terminal 具有 voltage- dependent Ca2+ channels。 請說明 Otto Loewi 證明神經傳導物質存在的實驗。

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