北大神經(jīng)生物學(xué)課件-2神經(jīng)元和神經(jīng)膠質(zhì)細(xì)胞神經(jīng)元

1、北大神經(jīng)生物學(xué)課件2神經(jīng)元和神經(jīng)膠質(zhì)細(xì)胞神經(jīng)元One of the Cajals many drawings of Brain circuityThe letters label the different elements Cajal identified in an area of the human cerebral cortex that controls voluntary movement.Neurons: Excitable cells “wiring” “Signal Senders”Neuroglia: Support, Nurturing, InsulationCellul

2、ar ComponentsNerve CellsNeuronsNeurogliaCell body (soma; perikaryon) Axon : only one (branches are collaterals; terminals are end feet)Dendrites : much shorter; one or more than one; branch extensively into dendritic treesStructure of NeuronsAxon Hillock(Axonal end feet)The Axon and Axon Collaterals

3、Cell Body (Soma): Life SupportProtein SynthesisSingle Nucleus, RER (Nissl Bodies)Axon: Longest process transmits messages away from cell bodyDendrites: Multiple processes off cell body receive messagesNeurons Structure & Function Neurons are similar to other cells in the body in some ways such as:1.

4、 Neurons are surrounded by a membrane. 2. Neurons have a nucleus that contains genes. 3. Neurons contain : What are inside of a neuron?Nucleus NucleolusMicrofilaments/NeurotubulesEndoplasmic Reticulum (ER) Mitochondria Golgi ApparatusNissl BodiesOthersDendrites :dendrite treeAxon :axon hillock (axon

5、 origination)axonal transport systeminitial segment (first myelin sheath)action potential generationmyelin sheath Axon and DendritesAxonsDendritesTake information away from the cell bodyTake information to the cell bodySmooth surfaceRough surface (dendritic spines)Generally only 1 axon per cellUsual

6、ly many dendrites per cellNo ribosomeHave ribosomesCan have myelinNo myelin insulationBranch further from the cell bodyBranch near the cell bodyDifferences between Axons and DendritesNeuron Classification by ShapeMultipolar: “multi-” many processesMajority: Single axon, many dendrites (motor neuron

7、and interneuron)Bipolar: “bi-” 2 processes Found in some sensory organs (retina, taste, smell, inner ear neuron) Unipolar (pseudo-unipolar): “uni -” 1 process (with branches)Sensory afferent neurons (dorsal root ganglia)Classification of Neurons by MorphologyClassification of Neurons by Axon LengthG

8、olgi type I NeuronsLong axons (longest from the cortex to the tip of spinal cord, 50-70 cm)Golgi type II NeuronsShort axons (shortest axons terminate only a few micron from cell body, interneurons)Amacrine NeuronsAn unusual cell type, lack axonsSensory neuron from receptor to CNS; receive stimuli an

9、d transmit afferent impulses to CNSInterneurons communicating between neurons; form circuits in the CNSMotor neuron from CNS to effector cells; deliver efferent impulses out through the PNS to the effectors to carry out the actions directed by the CNSFunctional Classification of NeuronEXCITABLE Memb

10、rane: Able to regulate the movement of ions (charges) across and along membrane SIGNAL TRANSDUCTIONDO NOT Replicate: Damaged cells cannot be replaced!Important Features of NeuronsAction PotentialFour Functional Regions of Model NeuronsImpulse transmission : electrical chemical Morphology : axodendri

11、ticaxonsomaticaxoaxonicdendrodendriticClassification of Synapsessynapse4Vesicles release NeurotransmittersChemical synapse :presynaptic knob (presynaptic component)synaptic vesiclessynaptic cleftpostsynaptic membrane (postsynaptic component)Electrical synapse :gap junctionsSynapse StructuresTypes of

12、 synapseDis-tanceCytoplasmic continuityUltrastruct-ural componentAgent of trans-missionSynaptic delayDirection of trans-missionElectrical3.5 nmYesGap-junction channelIon currentVirtually absentUsually bidirectionalChemical20-40 nmNoPresynaptic vesicle and active zone; postsynaptic receptorsChemical

13、transmittersSignificant: at least 0.3 ms; usually 1-5 ms or longerUni-directionalDistinguishing Properties of Electrical and Chemical SynapsesAt a chemical synapse, neurons transmit information across a cleft. Small Molecule Neurotransmitter SubstancesAcetylcholine (ACh); Dopamine (DA); Norepinephri

14、ne (NE); Serotonin (5-HT); Histamine Amino AcidsGamma-aminobutyric acid (GABA); Glycine; Glutamate; AspartateNeuroactive Peptides - partial list!Bradykinin; beta-endorphin; calcitonin; cholecystokinin; enkephalin; dynorphin; insulin; gastrin; substance P; glucagon; secretin; vasopressin; oxytocin, e

15、tc. List of Some NeurotransmittersAxonal transport : intracellular communicationBidirectional mechanism :anterograde transport retrograde transport Classified by transport rates :slow transport system (0.2 to 1 mm/day) fast transport system (200 to 400 mm/day)Axonal Transport SystemsHitching a Ride

16、on “Retrorail”Membranes of organelles involved in synaptic transmission are returned to the cell body for reuse or degradationNucleusCytoskeleton(Anterograde transport)ComponentRate (mm/day)Structure and compositionFast transportAnterograde200-400Small vesiculotubular structures, neurotransmitters;

17、membrane proteins and lipidsMitochondria50-100MitochondriaRetrograde200-300Lysosomal vesicles and enzymesSlow transportSCb2-8Microfilaments, metabolic enzymes, clathrin complexSCa0.2-1Neurofilaments and microtubulesMajor Rate Components of Axonal Transport1. Neurons have specialized projections call

18、ed dendrites and axons. Dendrites take information to the cell body and axons take information away from the cell body2. Neurons communicate with each other through an electrochemical process3. Neurons contain some specialized structures (like synapses) and chemicals (like neurotransmitters)4. Nissl

19、 Bodies 5. DO NOT Replicate: Damaged cells cannot be replaced!Neurons differ from Other CellsNeuron :Supporting cells :CNS : neuroglia (glia)PNS : Schwann cells and satellite cellsFunctions :physical supportelectrical insulationmetabolic exchangeblood-brain barrierComposition of Nervous TissueTypes

20、and Functions of GliaName of Glial CellFunctionAstrocyte (Astroglia)Star-shaped cells that provide physical and nutritional support for neurons: 1) clean up braindebris; 2) transport nutrients to neurons; 3) hold neurons in place; 4) digest parts of dead neurons; 5) regulate content of extracellular

21、 space MicrogliaLike astrocytes, microglia digest parts of dead neurons.Oligo-dendrogliaProvide the insulation (myelin) to neurons in the central nervous system.Satellite CellsPhysical support to neurons in the peripheral nervous system.Schwann CellsProvide the insulation (myelin) to neurons in the

22、peripheral nervous system.Neuroglia in the CNSAble to replicate!Importance in nervous system function is VASTLY underestimated!Evidence is mounting: Nurturing roleSignaling role (Memory?)InflammationPainMany more to come!Neuroglia: Distinguishing FeaturesPresence of tight junctions between the endot

23、helial cellsOne of the notable features of endothelial cells in comparison to other cell is the lack of pinocytic vesiclesSelective permeability to molecules based on their molecular weight and lipid solubilityPresence of specific markersRich in two enzymes: gamma glutamyl transpeptidase (GGTP) (for

24、 amino acid transport) and alkaline phosphatase (transport of phsopahte ions) used as marker for BBB.Others: glucose transporter (GLUT-1); endothelial barrier antigen (EBA; unknown function) and antigen recognized by the MRC OX-47 monoclonal antibody (important for cell-to-cell adhesion); transferri

25、n receptor (transport of ferric ions).Properties of Blood Brain BarriersBBB1. Neurons have TWO processes called axons and dendrites. Glial cells only have ONE. 2. Neurons CAN generate action potentials. Glial cells CANNOT, however, do have a resting potential. 3. Neurons HAVE synapses that use neurotransmitters. Glial cells do NOT have chemical synapses. 4. Neurons do NOT continue to divide. Glial cells DO continue to divide. 5. There are many MORE (10-50 times more) glial cells in the brain compared to the num