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

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Presentation on theme: "Ch. 5 Synaptic transmission Electrical synapse Chemical synapse 雙向 快速."— Presentation transcript:

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) ATP, c-AMP crayfish 小龍蝦

3 Chemical synapse AP voltage-dependent Ca 2+ 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 Ca 2+ 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-> Ca 2+

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

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

9 Fura-2 Ca 2+ chelators 在 presynaptic neuron 打入 Ca 2+

10 Synaptotagmin: Ca 2+ 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 Ca 2+ - 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 1926, Otto Loewi What defines a neurotransmitter? Vagus nerve 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

18 請任舉兩個實驗證明 nevre terminal 具有 voltage- dependent Ca 2+ channels 。 請說明 Otto Loewi 證明神經傳導物質存在的實驗。


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