Nerve.ppt

1、Nervous Tissue and cell,ZHU YONG HONG(朱永红） Deparement of histology and embryology,1. Introduction 2. Neurons (1). Classifications (2). Structures A. Cell Body B. Processes: (Dendrites, Axon) 3. Synapses (1). Chemical synapses (2). Electrical synapses 4. Glial Cells 5. Nerve Fiber Organization(1). Ne

2、rve fibers: myelinated or unmyelinated fibers (2). Nerves 6. Nerve Endings (1). Sensory nerve endings (2). Motor Endings (Myoneural junctions),1. Introduction,Two basic systems of internal communication and physiological homeostasis in the body: the endocrine and the nervous systems. 10-100 billion

3、neurons in human central nervous system Central Nervous System (brain and spinal cord) Peripheral Nervous System (nerves and ganglia),Nervous Tissue,Cellular Elements Neuron (Nerve Cell) Neuroglial Cells central neurglia: astrocyte, oligodendrocyte, microglia and ependymal cell peripheral neuroglia:

4、 Schwann cell in nerve and gaglion, satellite (capsular) cell in ganglion Intercellular Substance: extremly sparse,Conformatin of nervous tissue neuron and neuroglial cell CNS soma of nerve cells locates (neurons) ganglion,nervous pathway Processes of (in CNS) neurons locates spreads all over (perip

5、heral nerve) Nerve cell is a structure and function unit of nervous system, which is also called neuron. neurons are specialized to receive, integrate, and transmit electrochemical messages.,Neuroglial cells play a role in structural and nutritional support of neurons, electrical insulation, and enh

6、ancement of impulse conduction velocity.,2. Neuron,Two special properties: Irritability (the ability to respond to a stimulus). Propagation of impulses (the ability to conduct impulses). Cell body/perikaryon (5-150 m dia) Axon (myelinated or unmyelinated) with terminals and synaptic junctions Dendri

7、tes - receive input Variety of neuron shapes: multipolar, bipolar, pseudounipolar,Morphology categories,Functional Categories,(1). Classifications,99% of neurons are interneurons,1.1 Classification of neurons,Classification according to function of neuron 1.感觉神经元 sensory neuron 接受刺激，传向中枢。 2.运动神经元 mo

8、tor meuron 传出神经冲动 3.中间神经元 interneuron 联络,Classification according to function of neuron,sensory neuron motor meuron interneuron,Nucleus: large, euchromatic, prominent nucleolus, usually center of soma Nissl bodies: clumps of RER Golgi complex and mitochondria Neurofilaments and microtubules Inclusio

9、ns: melanin (rare) Cell membrane has specialized receptive areas, the subsynaptic membranes of synapses.,Perikaryon (Cell Body) In gray matter and ganglia,(2). Structures,Nissl bodies: basophil, concentration of granular ER. In cell body and dendrites,Neurofilaments: a variety of intermediate filame

10、nt - are bundle into neurofibrils visible after silver impregnations in the cytoplasm. Skeleton and transportation,Dendrites树突,May be highly branched and tapered Contain mitochondria, microtubules, and granular ER. Receptive surface for synaptic junctions Tens of thousands of synapses on large dendr

11、ites Dendritic spines（树突棘） integrate the excitatory influences and modify their responses and morphology in learning,inputs from over 200,000 other cells,Purkinje cell of cerebellum,Axons轴突,1 axon projects from cell body,long and thinner Axon hillock, axolemma and axoplasm,*Membrane is the axolemma（

12、轴膜）, at its terminal/synapse which holds vesicles. *May or may not be myelinated around the axolemma, sometimes recurrent back to near the soma.,*Has mitochondria, neurofilaments, microtubules, travelling vesicles, and, in some neurons, secretion droplets, in the axoplasm.,*Can be meter long,*Contai

13、ns axoplasm flowing from the axon hillock（轴丘）.,*The initial segments,the triggering of the action potential,retrograde transportation,anterograde transportation,Target tissue,Axon transportation,3. Synapses (Chemical)突触,Synapses are specialized axon terminal contacts to dendrites and cell bodies, an

14、d functionally polarized to transfer excitation one way.,Axodendritic synapse Axosomatic synapse Axoaxonic synapse,Structure of synapse,Types of synapse,LM:the axon terminal form bulbous swelling or terminal bouton.,cleft,receptors,1.presynaptic element presynaptic membranesynaptic vesicles with neu

15、rotransmitter, e.g., serotonin, acetylcholine, dopamine, etc. dense projectionsynapsin Imitochondria,SER, microtubule,microfilament. 2.synaptic cleft 15-30nm 3.postsynaptic element receptor,Action potentials travel down the axon of the neuron to its end, the axon terminal(synaptic knob).,The synapti

16、c knob opens Ca2+ channels in the plasma membrane. The influx of Ca2+ triggers the exocytosis of some of the vesicles. Their neurotransmitter is released into the synaptic cleft. The neurotransmitter molecules bind to receptors (ion channels) on the postsynaptic membrane.,Initiation of AP,Glia or ne

17、uroglia: named from the Greek word for glue. CNS: astroglia, oligodendroglia, microglia and ependyma PNS: Schwann cell, satellite Only nuclei visible without special stain,4. Neuroglia,FUNCTIONS OF NEUROGLIA (1) Structural support (especially the astrocytes in the CNS) (2) Participation in the blood

18、-brain-barrier (astrocytes) (3) Formation of the myelin sheath of axons (4) Isolation of junctional surfaces of synapses (5) Repair processes following damage or injury to nerves.,Astrocytes,Protoplasmic astrocytes: large, star-shaped with many processes, may attach to blood vessels; have filaments

19、and microtubules; common in grey matter. Fibrous astrocytes: have more filaments and glycogen, and lie in the white matter. Glial scar at injury,pedicles,Oligodendrocytes,Smaller than astrocytes; plump cell body with fairly dense cytoplasm and a darker round nucleus and fewer, shorter processes than

20、 an astrocyte; common in white matter, but some are perineuronal. Myelin forming cell of CNS Damaged in multiple sclerosis,Amyotrophic Lateral Sclerosis(A.L.S ),Microglial Cells,Smallest, nucleus of heterochromatin Short processes; phagocytic Originate from monocytes,Ependymal Cells,Line ventricles

21、of CNS Cuboidal shape Some are ciliated,5. Nerve Fiber Organization,#Smaller axons unmyelinated. #Larger axons Myelinated by Schwann cells or oligo dendrocytes,The long process of axon or dendrite enveloped by glia cell,The Schwann cells plasmalemma winds and wraps around the axon.The layers of memb

22、rans unite and form mylin.,The membrane propagates the action potential.,insulator,nodes of Ranvier.,internode,Myelin sheath around the axolemma is interrupted at regular intervals to leave the axolemma bare at nodes of Ranvier.,EM reveals myelin to have lamellae with alternate dark and light lines,

23、 apparently concentric around the axon.,Schmidt-Lanterman clefts: In each internode of myeline sheath, Schwann cell cytoplasm penetrates ,separations of the myelin lamellae, constituting the incisures of Schmidt-Lantermann, perhaps giving the myelin some flexibility and aiding molecular turnover.,Ne

24、rve fibers Nerve bundles nerve,Peripheral Nerve,Peripheral Nerve,Epineurium: several layers of fibroblasts with collagen in between,Nerve bundle,Endoneurium: reticular fibers, fibroblasts and collagen,Perineurium: 2-3 layers of fibroblast-like cells with some collagen,Free nerve endings Meissners co

25、rpuscles: tactile mechanoreceptors found in dermal papilla. Pacinian corpuscles: mechanoreceptors common in the dermis of thick skin. Neuromuscular spindle,6. Nerve Endings,Efferent nerve endings (motor),Afferent nerve endings (sensory),Motor unit,Unencapsulated endings,Encapsulated endings,Free ner

26、ve endings: sensory endings in deep layers of epidermis and papillary layer of dermis; responsive to pain, temperature, movement (associated with hair follicles).,Tactile (Meissner) corpuscle: ovoid, a stack of flattened cells (modified Schwann cells) intertwined with nerve endings and surrounded by

27、 a CT capsule; papillary layer of the skin (e.g., fingertips); responsive to touch; Lamellar (Pacinian) corpuscle: big, round or oval, the nerve ending and concentric layers of flat cells; hypodermis, mucous membranes; responsive to pressure;,Muscle spindle: a double tapered object, lying between an

28、d among myofibers, is an important proprioceptor, the device for body position,tactile input, joint movement, etc., to determine how much tension is being generated by the myofibers; to then report that back to the CNS.,Neuromuscular junction,Motor end plates or neuromuscular junctions are specializ

29、ed structures at the ends of motor axons and are the sites of innervation of skeletal muscle fibers.,Motor unit: A single motor nerve and all the muscle fibers it innervates.,The sarcolemma is depressed into a trough and invaginates into many small secondary synaptic clefts. It has ACh receptors. Th

30、e swollen ending of the axon lies in the trough.,(c) The axon terminal has Mt, and vesicles (d) Schwann cells cover the axon and its terminal bag.,Reflex arcs: The peripheral receptors are connected to peripheral effectors in a neuronal network. 1. Stimulation of the receptor 2. An impulse via affer

31、ent sensory nerve enters the spinal cord. 3. Interneurons connect with cell body of motor neuron. 4. Motor neuron transmits the efferent impulse to an effector (motor end plate) which responds to the impulse.,Degeneration and Regeneration,If axon cut, distal part degenerates In PNS distal part will

32、regenerate If cut too close to cell body, cell body may die CNS axons do not regenerate well,神经系统常用的研究方法 1.形态学方法 束路追踪法:轴浆运输法,变性法,神经元质膜荧光染色(DiI) 免疫组织化学法: 原位杂交 其他如:受体定位,神经系统功能活动形态定位法.,2.生理学方法 神经递质释放量的测定 推免灌流、脑透析术、脑片 突触体、抗体微探针 神经递质的功能测定 微电泳、抗体微量注射、生物测定 行为学方法 经典条件反射 操作式条件反射,3.电生理学方法 电生理常用仪器 阴极射线示波器 生物电发

33、大器 电子刺激器 储存和分析电生理实验结果的仪器 细胞外记录 拉制和充灌玻璃微电极的方法 金属微电极广泛应于神经、肌肉细胞外记录 多管微电极用于检验药物或激素对单个神经元的作用,具有特种用途的其他类型微电极 细胞外电位的波形因记录细胞的不同而异 细胞内记录 脑内电刺激 刺激电极、刺激参数、刺激电极尖端定位 顺行冲动记录法 顺行冲动细胞外记录法方法较易进行 顺行冲动细胞内记录法获得的信息量较大 逆行冲动记录法 逆行冲动具有相对恒定的潜伏期 逆行冲动能跟随高频电刺激 碰撞实验是鉴定逆行冲动的可靠指标 电压钳 通过细胞内微电极向细胞内输入电流,电压钳是一个负反馈系统 钠离子和钾离子的电导可由其过膜电流计算得出 斑片钳 斑片钳技术可从分子水平研究细胞膜离子通道的功能 斑片钳放大器是具有高增益