第三區(qū)段-16學(xué)時神經(jīng)發(fā)育與干細(xì)胞2012級

1、干細(xì)胞與神經(jīng)系統(tǒng)發(fā)育Haixia Lu MD, PhDProfessor of NeurobiologyInstitute of NeurobiologyE-mail: Tel: Xian Jiaotong University college of medicineIII-SNSXian Jiaotong University college of medicineIII-SNSReferences:其它：Advanced experimental medicine and biology chapter 2: Anteroposterior Regionalization of the B

2、rain: Genetic and Comparative AspectsNeuroscience - exploring the brain, Second editionWikipedia （維基百科）and Pubmed 1.呂國蔚 主編醫(yī)學(xué)神經(jīng)生物學(xué)，第2版，高等教育出版社2.壽天德 主編神經(jīng)生物學(xué)，第2版，高等教育出版社3.朱曉峰 主編神經(jīng)干細(xì)胞基礎(chǔ)與應(yīng)用，第1版，科學(xué)出版社4.李云慶 主編神經(jīng)科學(xué)基礎(chǔ)，第2版，高等教育出版社5.齊建國 主編神經(jīng)科學(xué)擴(kuò)展，第1版，人民衛(wèi)生出版社前期有關(guān)“神經(jīng)系統(tǒng)發(fā)育”的課程內(nèi)容1. 人胚早期發(fā)育 人體生物學(xué)緒論區(qū)段2. 神經(jīng)系統(tǒng)的胚胎發(fā)育 感覺器官與

3、中樞神經(jīng)系統(tǒng)區(qū)段Morphological development of nervous systemCellular development of Nervous systemStem cell (SC) & Neural stem cell (NSC)Xian Jiaotong University college of medicineIII-SNSPart IPart IIPart IIINeural Dysplasia (神經(jīng)發(fā)育異常) ？Neural Dysplasia (神經(jīng)發(fā)育異常) 1. 與骨性結(jié)構(gòu)發(fā)育異常相關(guān)（顱骨，脊柱） 神經(jīng)管閉合缺陷：如顱骨裂、顯性或隱性脊柱裂李云慶

4、主編神經(jīng)科學(xué)基礎(chǔ)，第2版，高等教育出版社Neural Dysplasia (神經(jīng)發(fā)育異常) 顱骨和脊柱畸形： 如狹顱癥、小頭畸形、枕大孔區(qū)畸形、 寰樞椎脫位、寰椎枕化、頸椎融合、 小腦扁桃體下疝等Acrocephaly （尖頭畸形）Scaphocephaly （舟狀頭畸形）Brachycephaly （園頭畸形）Plagiocephaly （斜頭畸形）園頭畸形舟狀頭畸形小頭畸形尖頭畸形李云慶 主編神經(jīng)科學(xué)基礎(chǔ)，第2版，高等教育出版社1. 與骨性結(jié)構(gòu)發(fā)育異常相關(guān)（顱骨，脊柱）Neural Dysplasia (神經(jīng)發(fā)育異常) 1. 與骨性結(jié)構(gòu)發(fā)育異常相關(guān)（顱骨，脊柱） 腦室發(fā)育畸形：如中腦導(dǎo)水管

5、閉鎖、第四腦室正中孔以 以及外側(cè)孔閉鎖、CSF循環(huán)障礙導(dǎo)致先天性腦積水李云慶 主編神經(jīng)科學(xué)基礎(chǔ)，第2版，高等教育出版社Neural Dysplasia (神經(jīng)發(fā)育異常) 2. 神經(jīng)組織發(fā)育缺陷 頭顱增大：如腦積水、腦積水性無腦畸形、巨腦畸形 腦皮質(zhì)發(fā)育不全：如腦回增寬、腦回狹小、腦葉萎縮型硬化和 神經(jīng)細(xì)胞異位 先天性腦穿通畸形（congenital porencephalia）：由于局部腦皮 質(zhì)發(fā)育缺陷，腦室向表面開放如漏斗狀，可雙側(cè)對稱發(fā)生 無腦畸形：大腦完全缺如，顱蓋和頭皮缺失，生后不久死亡 胼胝體發(fā)育不全：胼胝體完全或部分缺失，常伴腦積水、小頭畸形和 顱內(nèi)先天性脂肪瘤等，臨床可無癥狀或表

6、現(xiàn)癲癇或智能低下李云慶 主編神經(jīng)科學(xué)基礎(chǔ)，第2版，高等教育出版社腦穿通畸形李云慶 主編神經(jīng)科學(xué)基礎(chǔ)，第2版，高等教育出版社李云慶 主編神經(jīng)科學(xué)基礎(chǔ)，第2版，高等教育出版社Neural Dysplasia (神經(jīng)發(fā)育異常) 3. 腦性癱瘓：表現(xiàn)為先天性運(yùn)動功能異常4. 神經(jīng)外胚層發(fā)育不全：神經(jīng)皮膚綜合癥神經(jīng)皮膚綜合征所包括的疾病已知有20余種，臨床上常見的有神經(jīng)纖維瘤病、結(jié)節(jié)性硬化、腦一面血管瘤?。簧僖姷挠幸撂偕販p少癥、小腦視網(wǎng)膜血管瘤病等。均屬于神經(jīng)系統(tǒng)遺傳性疾病。 李云慶 主編神經(jīng)科學(xué)基礎(chǔ)，第2版，高等教育出版社Xian Jiaotong University college of med

7、icineIII-SNSPart I壽天德 主編神經(jīng)生物學(xué)，第2版，第8章Morphological development of nervous system呂國蔚 主編醫(yī)學(xué)神經(jīng)生物學(xué)，第2版，第9章（中樞）神經(jīng)系統(tǒng)的形態(tài)發(fā)育 Ectoderm - neural tube - brain and spinal cord Establishment of neural axis: anterior-posterior and dorsal-ventral relation The common characteristics of neural development -from Hydra

8、to HumanNotochord(脊索)-mesodermThe entire nervous system arises from the ectodermHydra 水螅Zebrafish（斑馬魚）昆蟲 insect Neurulation in vertebrates results in the formation of the neural tube, which gives rise to both the spinal cord and the brain. 脊椎動物的神經(jīng)外胚層細(xì)胞形成神經(jīng)管（最終形成大腦和脊髓）的過程，稱為神經(jīng)胚化Neurulation (神經(jīng)胚化)*Par

9、t I神經(jīng)系統(tǒng)的形態(tài)發(fā)育Neurulation包括三個階段 2) the neural folds 神經(jīng)褶 (day 20-21)Part I神經(jīng)系統(tǒng)的形態(tài)發(fā)育 1) the neural plate 神經(jīng)板 (day 18-19) 3) the neural tube 神經(jīng)管 最終形成腦和脊髓 (day 22-26) Part I神經(jīng)系統(tǒng)的形態(tài)發(fā)育 1) the neural plate 神經(jīng)板 (day 18-19) The notochord（脊索） induces the formation of the central nervous system (CNS) by signalin

10、g the ectoderm germ layer（外胚層）above it to form the thick and flat neural plate. 來自中胚層的脊索刺激其上方的外胚層不斷變厚，形成神經(jīng)板 Part I神經(jīng)系統(tǒng)的形態(tài)發(fā)育外胚層細(xì)胞不斷增多，中間部位向下凹陷，形成一條溝，稱之為神經(jīng)溝，也稱神經(jīng)褶 2) the neural folds 神經(jīng)褶 (day 20-21)Part I神經(jīng)系統(tǒng)的形態(tài)發(fā)育3) the neural tube 神經(jīng)管 最終形成腦和脊髓 (day 22-26) The neural plate folds in upon itself to form

11、 the neural tubes（神經(jīng)管）, which will later differentiate into the spinal cord（脊髓） and the brain（腦）, eventually forming the central nervous system. Part I神經(jīng)系統(tǒng)的形態(tài)發(fā)育神經(jīng)嵴（neural crest）原始腦泡神經(jīng)管背側(cè)的細(xì)胞群與神經(jīng)管分離，形成前后走行的細(xì)胞區(qū)帶。最終形成PNS的感覺神經(jīng)元、自主神經(jīng)節(jié)節(jié)后神經(jīng)元以及肌細(xì)胞、骨與軟骨細(xì)胞、黑素細(xì)胞等Part I神經(jīng)系統(tǒng)的形態(tài)發(fā)育初級神經(jīng)胚化和次級神經(jīng)胚化Different portions of

12、 the neural tube form by two different processes, called primary and secondary neurulation, in different species.不同物種，不同部位的神經(jīng)管形成的過程不同1）Primary Neurulation初級神經(jīng)胚化2）Secondary Neurulation 次級神經(jīng)胚化The neural plate creases inward until the edges come in contact and fuse.neural foldneural tubePart I神經(jīng)系統(tǒng)的形態(tài)發(fā)育

13、1）Primary Neurulation2）Secondary Neurulation Neural tube forms by hollowing out of the interior of a solid precursor.Secondary Neurulation occurs in the posterior section of most animals but it is better expressed in birds. Cranial neuropore anlage brain原基anlage spinal cordCaudal neuroporeCNSThe neu

14、ral tube formation神經(jīng)孔體節(jié)Neural tubes from both primary and secondary neurulation eventually connect.Spina bifida (脊柱裂) ：the open ends of the neural tube fail to close 部位特點(diǎn)，功能影響 Ectoderm - neural tube - brain and spinal cord Establishment of neural axis: anterior-posterior and dorsal-ventral relationX

15、ian Jiaotong University college of medicineIII-SNSPart IMorphological development of nervous system神經(jīng)系統(tǒng)的形態(tài)發(fā)育壽天德 主編神經(jīng)生物學(xué)，第2版，第8 章呂國蔚 主編醫(yī)學(xué)神經(jīng)生物學(xué)，第2版，第9章神經(jīng)系統(tǒng)的形態(tài)發(fā)育I. Anterior-posterior regionalization of brain（頭-尾軸）-advanced experimental medicine and biology, chapter 2:Anteroposterior Regionalization of

16、the Brain: Genetic and Comparative Aspects 1) otd/Otx and ems/Emx genes - involve in specification of the anterior brain2) Hox genes - involve in the differentiation of the posterior brain3) Pax genes - involve in the development of the anterior/ posterior brain boundary zone 上述基因?qū)偻春谢颍╤omeobox gen

17、e），是控制發(fā)育的主要基因，對動物的器官發(fā)生和細(xì)胞分化調(diào)控起關(guān)鍵作用。 Part Iotd/Otx and ems/Emx genesHox (homeotic) genesPax genesPax基因家族編碼的蛋白是一組極為重要的轉(zhuǎn)錄調(diào)控因子,在胚胎發(fā)育的器官形成中扮演重要角色,其主要功能包括:調(diào)控細(xì)胞增殖、促進(jìn)細(xì)胞自我更新、誘導(dǎo)前體細(xì)胞定向轉(zhuǎn)移 Hox 基因在胚胎發(fā)育中的表達(dá)水平對于組織和器官的形成具有重要的調(diào)控作用。該類基因的突變，就會在胚胎發(fā)育過程中導(dǎo)致某一器官異位生長，即本來應(yīng)該形成的正常結(jié)構(gòu)被其他器官取代了。 同源盒基因（homeobox gene）之一，最早發(fā)現(xiàn)與果蠅的頭部發(fā)育有

18、密切的關(guān)系Sonic hedgehog (Shh): is a key player in patterning the ventral axis 2) Bone morphogenic proteins (Bmp) and Wnt family members: play an important role in patterning the dorsal axis 3) Other factors: Fibroblast growth factors (FGF) and Retinoic Acid (RA) provide positional information to the neu

19、ral progenitor cellsXian Jiaotong University college of medicineIII-SNSII. Dorsal-ventral patterning of neural tube（背-腹軸）Part I神經(jīng)系統(tǒng)的形態(tài)發(fā)育Shh secreted from the floor plate creates a gradient along the ventral neural tube. Shh functions in a concentration-dependent manner to specify ventral neuronal fa

20、tes. V0-V3 represent four different classes of ventral interneurons, and MN indicates motor neurons.Xian Jiaotong University college of medicineIII-SNS中間神經(jīng)元V1,V2,V3底板細(xì)胞運(yùn)動神經(jīng)元Xian Jiaotong University college of medicineIII-SNSXian Jiaotong University college of medicineIII-SNSPart IICellular developme

21、nt of nervous system細(xì)胞神經(jīng)發(fā)育細(xì)胞確定呂國蔚 醫(yī)學(xué)神經(jīng)生物學(xué)，第9章，第2節(jié)神經(jīng)細(xì)胞的發(fā)育細(xì)胞增殖細(xì)胞遷移突觸形成軸突延伸不完善，不準(zhǔn)確Part IICellular development of nervous system細(xì)胞神經(jīng)發(fā)育1. Development of neural progenitors 神經(jīng)前體細(xì)胞的發(fā)育2. Neural progenitors differentiate into neuron and glia 神經(jīng)前體細(xì)胞分化為神經(jīng)元和膠質(zhì)細(xì)胞3. Neural cell migration 神經(jīng)細(xì)胞遷移4. Neuronal axons e

22、xtension 神經(jīng)元軸突延伸5. Synapse formation 神經(jīng)突觸形成6. Neural network 神經(jīng)網(wǎng)絡(luò)形成OutlineXian Jiaotong University college of medicineIII-SNSPart II細(xì)胞神經(jīng)發(fā)育1. Development of neural progenitors 神經(jīng)前體細(xì)胞的發(fā)育-細(xì)胞增殖神經(jīng)前體細(xì)胞 neural progenitorsNeural tube-MSCNeural-epitheliaMSC： multipotent stem cellneural tubeVentricular zoneMa

23、ntle layer Neuroblastneural tubePseudostratified epithelium(假復(fù)層上皮) Xian Jiaotong University college of medicineIII-SNSCell processes extension while cell body stay in ventricular zone (G1，細(xì)胞發(fā)出突起)During the synthesis of DNA, cell body migrate away from ventricular zone (S，細(xì)胞向表層移動) After the synthesis

24、, cell body move back to ventricular zone along its process(G2，細(xì)胞核返回)Cell process retract (突起縮回)Cell division（細(xì)胞分裂）Cell proliferation Xian Jiaotong University college of medicineIII-SNSNeural-epitheliaCell proliferation - a characteristic of the choreography of cell proliferationXian Jiaotong Univer

25、sity college of medicineIII-SNSCell divisionCell proliferation - The fate of the newly formed daughter cellsDaughter cells cleaved vertically from the precursor remain in the ventricular zone to divide again and again.This mode of cell division predominates early in development expand the population

26、 of neuronal precursorA = A + AXian Jiaotong University college of medicineIII-SNSCell proliferation - The fate of the newly formed daughter cellsDaughter cells cleaved horizontally from the precursor, one migrates away to take up its position in the cortex, where it will never divide again. The oth

27、er daughter remains in the ventricular zone to undergo more division.Ventricular zone precursor cells repeated this pattern until all of the neurons of the cortex have been generated. This mode predominates later in development neuronal precursorA = A + BXian Jiaotong University college of medicineI

28、II-SNSCell proliferation-How does the cleavage plane during cell division determine the cells fate?Xian Jiaotong University college of medicineIII-SNS -The distribution of cell constituents in precursor cells:植物極動物極the gene expression is regulated by its transcription factorsNotch-1 “unopposed” by n

29、umb, activates the gene expression that the cell to cease division and migrate away from the ventricular zone.Xian Jiaotong University college of medicineIII-SNSCell proliferation - How does the cleavage plane during cell division determine the cells fate? - The distribution of cell constituents in

30、precursor cells:Part II細(xì)胞神經(jīng)發(fā)育2. Neural progenitors differentiate into neuron and glia 神經(jīng)前體細(xì)胞分化為神經(jīng)元和膠質(zhì)細(xì)胞fate decisionNeuroblastsNeuronsGliaXian Jiaotong University college of medicineIII-SNSNeuronal differentiation 神經(jīng)元分化 Differentiation of the neuroblast into a neuron begins with the appearance of ne

31、urites sprouting off the body (axon and dendrite at first). 開始于突起的形成NeuronsNeuroblasts The differentiation is programmed well before the neuroblast arrives at its final resting place. 邊分化邊遷移Xian Jiaotong University college of medicineIII-SNS神經(jīng)細(xì)胞分化的影響因素Cell fate:geneExtracellular factorsnicheCell rec

32、eptors(Notch-numb, BMP, Wnt, Noggin)Different factors work on different level:CytokinesDNARNAsiRNAShort distance: cell-cell influence through Notch and Delta Long distance: follistatin, noggin, chordin and BMP Hans Spmann and Hilde MangoldOrganiser 組織者 Xian Jiaotong University college of medicineIII

33、-SNS Long distanceHans Spmann and Hilde MangoldP144右圖Xian Jiaotong University college of medicineIII-SNSOrganiser 組織者 Long distanceNeural progenitor in the center（Dark Green）inhibits the surrounding neuroectodermal cells (Light Green) to have vertical cleavage，consequently differentiated into epider

34、mal cells (White). Cell differentiationXian Jiaotong University college of medicineIII-SNS Short distanceNotch and Delta Progenitor with high level Delta and low level Notch expression（Green）stop its neighbor cells expressing AS-C and Delta genesXian Jiaotong University college of medicineIII-SNSCel

35、l differentiation Short distanceNotch and Delta Notch plays important role in differentiation of progenitors Normal Notch- Notch+ Xian Jiaotong University college of medicineIII-SNSCell differentiation Short distanceNotch and Delta neural tubeVentricular zoneMantle layerNeuroblastneural tubeCell mig

36、rate away from ventricular zone（VZ）Xian Jiaotong University college of medicineIII-SNSPart II神經(jīng)細(xì)胞發(fā)育3. Neural cell migration 神經(jīng)細(xì)胞遷移 - Inside-out development of the cortex - The first group of cells migrate to cortical plate(皮質(zhì)板), from VZ that form subplate (板下區(qū)) Xian Jiaotong University college of me

37、dicineIII-SNS3. Neural cell migration 神經(jīng)細(xì)胞遷移較早分化的較大神經(jīng)元先遷移并形成最內(nèi)層，依次順序向外；而較晚分化的較小神經(jīng)元則通過已形成的層次遷移并形成其外側(cè)新的層次；故不論皮質(zhì)的什么區(qū)域，其最內(nèi)層總是最早分化，而最外層則最后分化。Cell migrationAdultMLEGLEPLIGLIPLMFLXian Jiaotong University college of medicineIII-SNSThis shows neuroblasts climbing along the thin processes of the radial glia r

38、oute to the cortical plate, which forms just under the marginal zoneCell migrationHowever in cerebellum, granular cell migration is differentEGLMLPLIGLNeuoblasts in EGL will migrate back and form IGL after birthMLIGLXian Jiaotong University college of medicineIII-SNSCell migrationPart II細(xì)胞神經(jīng)發(fā)育4. Neu

39、ronal axons extension 神經(jīng)元軸突延伸4). Chemoattraction and chemorepulsion （向化性效應(yīng)）1). Growing axon （軸突生長）2). Fasciculation （簇生，自發(fā)性收縮）3). Axon guidance and guidance cues （軸突延伸引導(dǎo)）1). Growing axon （軸突生長）The growing tip of a neurite is called a growth cone （生長錐）, which is specialized to identify an appropriate

40、 path for neurite elongation.Growth cone in culture- probe the environment, moving in and out of the lamellipodia- takes hold of the substrate and pull the advancing GC forward 絲足板足Xian Jiaotong University college of medicineIII-SNSCell adhesion molecules (CAMs)“highway” 2). Fasciculation （簇生，自發(fā)性收縮）

41、粘附分子的一種Xian Jiaotong University college of medicineIII-SNS3). Axon guidance and guidance cues （軸突延伸引導(dǎo)）Target cellExtracecular molecularsSpecial bindingSecond messengerFunction changes of microbubules and actin within growth coneControlling growth cone extendingGuidance cues: chemoattraction and acti

42、ns concentrate in forepart of a GC chemorepulsion and actins disappear in forepart of a GCMembrane receptorsXian Jiaotong University college of medicineIII-SNS4). Chemoattraction and chemorepulsion （向化性效應(yīng)） Netrin spurs the axon growth toward the midlineThe receptors of Netrin and Slit are be regulat

43、ed in varying from one side of the midline to other pull Slit chase the axon away the midlinePushXian Jiaotong University college of medicineIII-SNSModel (chemical synapse ) Definition of synapse Classify of synapse Structure of synapse Synapse formation *Xian Jiaotong University college of medicine

44、III-SNSPart II細(xì)胞神經(jīng)發(fā)育5. Synapse formation （神經(jīng)）突觸形成1) Definition of synapseIn the nervous system, a synapse is a structure that permits a neuron to pass an electrical or chemical signal to another cell 突觸： 神經(jīng)系統(tǒng)中允許神經(jīng)元傳遞電信號或化學(xué)信號給其它細(xì)胞的特殊結(jié)構(gòu)；神經(jīng)元之間以及與其它細(xì)胞間的特化的細(xì)胞連接Synapses are essential to neuronal function:

45、 neurons are cells that are specialized to pass signals to individual target cells, and synapses are the means by which they do so. In many synapses, the presynaptic part is located on an axon, but some presynaptic sites are located on a dendrite or soma. Xian Jiaotong University college of medicine

46、III-SNSSynapse formation 神經(jīng)突觸形成 2) Classify of synapseThere are two fundamentally different types of synapsechemical synapseelectrical synapseXian Jiaotong University college of medicineIII-SNSSynapse formation 神經(jīng)突觸形成 In a chemical synapse, the presynaptic neuron releases a chemical called a neurotr

47、ansmitter that binds to receptors located in the postsynaptic cell, usually embedded in the plasma membrane. In an electrical synapse, the presynaptic and postsynaptic cell membranes are connected by channels that are capable of passing electrical current, causing voltage changes in the presynaptic

48、cell to induce voltage changes in the postsynaptic cellChemical synapseElectrical synapseXian Jiaotong University college of medicineIII-SNS3) Structure of synapseXian Jiaotong University college of medicineIII-SNSSynapse formation 神經(jīng)突觸形成 Structure of synapseSynaptic vesicleNeurotransmitterVoltage g

49、ated ion channelReuptake pumpPostsynaptic densityReceptorAxon terminalDendriteSynaptic cleftStructureEM:Xian Jiaotong University college of medicineIII-SNS4) Synapse formation *(1) Genesis of connection (突觸形成-細(xì)胞間聯(lián)系的建立) (2) Elimination of cell and synapse (細(xì)胞和突觸數(shù)量減少) (3) Activity-dependent synaptic r

50、earrangement (活動依賴性突觸重排) (4) Synapse plasticity (突觸可塑性)與兒童發(fā)育過程中極其相似Xian Jiaotong University college of medicineIII-SNS 生長錐與適宜的細(xì)胞接觸； 神經(jīng)遞質(zhì)釋放增加； 突觸前膜與靶細(xì)胞粘附增強(qiáng)； 其它競爭突觸被異突觸壓抑； 受體在突觸后膜堆積； 新受體在突觸后膜合成并插入； 接頭外受體消除Synapse formation 神經(jīng)突觸形成 (1) Genesis of connection 突觸形成-細(xì)胞間聯(lián)系的建立The 3 phases of Synapse formation

51、 Pathway selection path When the growth cone comes in contact with its target, a synapse is formed.Which cell should link with?Target selection structureAddress selection cellWhere the axon should go?Axon extensionTarget cellExtracecular molecularsSpecial bindingMembrane receptorsXian Jiaotong Unive

52、rsity college of medicineIII-SNSThese three phases depend on :Direct cell-to-cell contact contact between cells and extracellular secretions of other cellcommunication via action potentials and synaptic transmission The 3 phases of Synapse formation Pathway selection pathTarget selection structureAd

53、dress selection cellTarget cellExtracecular molecularsSpecial bindingMembrane receptorsXian Jiaotong University college of medicineIII-SNS(1) Genesis of connection 突觸形成-細(xì)胞間聯(lián)系的建立 When the growth cone comes in contact with its target, a synapse is formed. The details of mechanisms of synapse formation

54、 in the CNS are still not clear yet - Most of the data comes from studies of the neuromuscular junction 1. The GMN terminal secretes agrin, (Ca+ entry into the GC triggers neuro- transmitter release and changes in the cytoskeleton adhere to its post- synapse partner) 2. Agrin interacts with MuSK in

55、the muscular cell membrane. 3. The clustering of Ach receptors in the postsynaptic membrane via the action of rapsyn (like a shepherd to gather the receptors at the synapse)Ca+Neuromuscular junction.Xian Jiaotong University college of medicineIII-SNSA process known as Programmed cell death (PCD). Ma

56、tching inputs with targets by selective cell death.The input neurons (突觸前) will compete with one another for limited quantities of trophic factors produced by the target neurons.Cell death (2) Elimination of cell and synapse 細(xì)胞和突觸數(shù)量減少Xian Jiaotong University college of medicineIII-SNSEach neuron (突觸

57、后) can receive on its dendrites and soma a finite number of synapses called synaptic capacity （突觸容量） A useful model system for the study of synaptic elimination: effect of postsynaptic AChR, basal membrane of muscular fibril on neuromuscular synaptic elimination.Changes in synaptic capacity哺乳動物出生后開始

58、進(jìn)行精細(xì)動作的產(chǎn)生Xian Jiaotong University college of medicineIII-SNS(2) Elimination of cell and synapse 細(xì)胞和突觸數(shù)量減少(3) Activity-dependent synaptic rearrangement 活動依賴性突觸重排Synaptic segregation（突觸分離）Xian Jiaotong University college of medicineIII-SNSThroughout the developing nervous system, competition between a

59、xons causes the permanent removal of some synaptic connections -Wen-Biao Gan and Jeff W. Lichtman. Synaptic Segregation at the Developing Neuromuscular Junction. Science, 1998: 282( 5393). 1508-1511 Synaptic segregation（突觸分離）The two input neurons in one eye (top) fire at the same time. This is suffi

60、cient to cause the top LGN target neuron to fire but not the bottom one. This is the same situation that the two input neurons in the other eye (bottom) are active simultaneously, causing the bottom target neuron to fire.Over time, neurons that fire together wire together. Notice also that input cel