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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 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


18 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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