Upload
allan-longbottom
View
241
Download
5
Embed Size (px)
Citation preview
Ch. 5 Synaptic transmissionElectrical synapse Chemical synapse
雙向快速
Electrical synapse: to synchronize electrical activity among populations of neurons (hypothalamus)
ATP, c-AMP
crayfish 小龍蝦
Chemical synapse
AP
voltage-dependentCa2+ channels
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 MEPPsLow Ca2+
EPP fluctuations
• 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
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+
Dock: two membranes become tightly associated with each other
prime: active fusion of the membranes
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
Block Na+ & K+ channels
Ca2+ channel blocker鎘
Fura-2
Ca2+ chelators
在 presynaptic neuron 打入 Ca2+
Synaptotagmin:Ca2+ sensor, bind to neurexins
NSF & SNAP:common proteins in fusion, 與SNARE 結合 (SNAP receptors 包括 synaptobrevin, syntaxin& SNAP-25)
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
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
• 1926, Otto Loewi
What defines a neurotransmitter?
Vagus nerve
Heart rate
Heart rate
“vagus substance” ACh
Criteria that define a substance as a neurotransmitter: Box A 斜體字
The comparisons of neurotransmitters to hormones
Action at a distancevasopressin, oxytocin, can be as a hormone and as a NM
Two major categories of neuro-transmitters
(1)small-moleculeneurotransmitters: ATP, AMP
(2) peptideneurotransmitters
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。