Chapter 2: Neurons and Glia
Chapter 2: Neurons and Glia NEUROSC 3000 - 020
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NEUROSC 3000 - 020
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This 12 page Class Notes was uploaded by Victoria Gonzalez on Monday September 28, 2015. The Class Notes belongs to NEUROSC 3000 - 020 at Ohio State University taught by Robert Boyd in Summer 2015. Since its upload, it has received 16 views. For similar materials see Introduction to Neuroscience in Neuroscience at Ohio State University.
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Date Created: 09/28/15
Chapter 2 Neurons and Glia Victoria Gonzalez Learning objectives 0 Understand the basic structure of the neuron and how they are idenU ed Explain the basic structure and function of the synapse Understand how neurons are classi ed 0 Describe the basic structure and function of different types of glia 1 Neurons and glia intro a Approximately an equal amount of neurons and glia 85 billion b Neurons sense changes in the environment and communicate the changes to other neurons i Perform most information processing in brain ii 001005 mm wide 40200x smaller than a tip of pencH c Glia or glial cells contribute to brain functions by insulating supporting and nourishing neighboring neurons i They suspend neurons in their appropriate locations d There are more neurons in the cerebellum and cerebral cortex e It is dif cult to quantify the exact number of cells need microscope 2 Early studies of neurons a Neurons couldn t be studied until late 17th century with microscope b To study the brain the brain needs to be sliced thinly with a microtome i To do this the brain needs to be hardened xed This was done with formaldehyde in the 19th century c A normal brain is creamcolored so cells cannot be seen i Nissl stain labels the nuclei of all cells and the neuron s nissl bodies made of rough endoplasmic reticulum 1 There is far more RER in neurons than any other cell a Distinguishes between neurons and glia b Enables histologists to study the arrangement of neurons in different parts of the brain 2 By Franz Nissl 1894 ii Golgi stain shows the structure of a neuron but can t tell you how many golgi there are 1 The golgi stain changed the way we view neurons 2 Stains all parts of a neuron but not all neurons 3 Revealed that neurons have axons one can be long and dendrites many usually short 4 Revealed that cell body aka soma perikaryon is only a small part of the neuron 5 By Camillo Golgi 3 Is the nervous system an exception to the cell theory No a Schwann 1839 proposed cell theory saying that all tissues are made of cells b Goli thought that neurites of different cells are fused together to form a continuous network the brain is an exception to the cell theory c Cajal argued that neurons are not continuous with each other they communicate by contact not continuity d Neuron doctrine idea that cell theory also applies to neurons i Not cleared up until the 19505 when looked at with an electron microscope 4 Neuron structure a Soma cell body similar to many other cells i 20 micrometers pm in size b Nucleus is 510 pm i Nucleus contains DNA 1 Transcription DNA to RNA 2 Splicing mRNA is formed by removing the introns and joining the extrons 3 Translation mRNA to proteins c Ribosomes protein synthesis through translation i Rough endoplasmic reticulum bound with ribosomes 1 Proteins made here are transported to the membrane of the cell or to another cell ii Free ribosomes 1 Proteins made here are destined to reside within the cell s cytosol d Smooth endoplasmic reticulum regulates internal concentrations of substances e Golgi apparatus an organelle that sorts and chemically modi es proteins that are destined for delivery f Mitochondrion site of ATP production through the kreb s cycle and the electron transport chain i The brain is 2 of our body weight but uses 20 of our energy 9 Neuronal membrane i 5 nanometers thick ii Many proteins are embedded in the membrane iii Protein composition varies form soma axons and dendr es iv The function of neurons cannot be understood without understanding the structure and function of the membrane and associated proteins h Cytoskeleton U39lbUUNl l 6 7 ii 1 U1gtUU omen Neur other P P FPUNE i m long i Axon 1 2 3 Synapse i j Microtubules involved in axoplasmic transport 20 nm in diameter 350 um in length Polymer of many tubulin proteins Not static move around Associated with other proteins microtubule associated proteins MAPs a Tau proteins are abnormal in dementia associated with Alzheimer s disease Axial polar Long range tracks Micro laments 5 nm in diameter same thickness as cell membrane Made up of two thin strands of actin polymers Numerous in neurites Not static Run longitudinally and are closely associated with the membrane Seen at synaptic terminals Axial and radial polar Shorter than microtubules and neuro laments Short range tracks o laments called intermediate laments in cells 10 nm 100 um in length medium sized Strong Maintain neuronal shape These tangle in Alzheimer s Axial no polarity Space lling mutants lacking neuro laments have slow conduction Axons transfer information over a long distance 1 mm to components Axon hillock beginning of the axon connected to the soma Axon proper middle of the axon Axon bouton axon terminal the end of the axon a Terminal arbor short branches at the end of the axon Axon collaterals axon branching vi vii viii ix 1 Recurrent collaterals axon branches that return to communicate with the same cell that gave rise to the axon or dendrites of neighboring cells Axons are only found in neurons Axons are different from the soma 1 No RER few ribosomes proteins originate in soma 2 Proteins in the membrane differ from those in the soma Axon diameter is variable 1 um to 25 um 1 The speed of a nerve impulse depends on axon diameter 2 Thicker axons have faster nerve impulses Presynaptic neuron axon terminal and post synaptic neuron dendrite or soma are divided by synaptic cleft no direct contact Many drugs and chemicals act at the synapse Synaptic transmission mediated by chemical neurotransmitter Malfunctions here are responsible for many mental disorders When a neuron makes synaptic contact with another cell it is said to innervate that cell k Dend rites vi vii viii Dendritic tree collection of branches that extend from soma Come in different shapes in sizes Dendrites can be receiving input from thousands of different neurons 10005 of synapses Some dendrites are covered with spines 1 Spines are plastic they change structure depending on the type and amount of synaptic input There are ribosomes on dendrites lots of protein synthesis Dendrites contain microtubules fewer micro laments When learning occurs the structure of the dendrites changes Unusual changes in spines have been shown to occur in the brains of individuals with cognitive impairments i39uclteus Nuclea ug A quot 39 Membrane 39 icrmubulle DE dFWiIE39E x f R ughEH Ile Bandy quot Pal rribammes Ri hammzea E lg i apparatus 1 N gigmug J Synaptic vestiges I Synapse Mum 39 Synaptlccile Ammi ermiirual quot Nude Uif Ha n39ariazr 7 l MpgIan Sheath Ethwann ceIiII Nucleus Edmwnntelll un llamEnl Miizrutubulle Exam quot 5 Axonal transport a Wallerian degradation after axons are cut axon distal to injury dies i Early clue that transport occurs Slow axoplasmic transport cytosolic proteins 110 mmday i By Weiss he tied up an axon and let materials accumulate then cut the tie and traced materials Fast axoplasmic transport membrane bounded organelles and associated proteins are carried in vesicles 1000 mmday Anterograde transport materials move down from soma to axon terminal i Proteins are walked down microtubules with the help of kinesin using ATP Retrograde transport materials move up the axon from the terminal to the soma i Proteins are transported down microtubules with help of dynein fast 50250 mmday Fast and slow differ due to time cargos actually spend moving i Slow transport moves stops moves stops ii Fast transport keeps moving continuously Retrograde transport can be used to trace synaptic connchons i Inject HRP enzyme into animal brain ii Two days later after retrograde transport HRP appears on all neurons are receiving transmission from that neuron iii Can be used for retrograde or anterograde connchons 1 For anterograde mapping radioactive amino acids are used iv Helps to map out connections in the brain 6 DNA Microarrays one method used to identify unique gene expression in different brains or in different regions of the same brain a b Brains with a disorder are compared to normal brains One brain s mRNA is tagged with a green tag the other s is tagged with a red tag c mRNA from both brains are mixed d When brain one s mRNA is more expressed the mix will turn red When brain two s mRNA is more expressed the mix will turn green f When the two brain s mRNA is equally expressed it will turn yellow 7 Neural Speci cation a Cell types are de ned by neuronspeci c combination of genes with each member more broadly expressed b Many genes expressed in neurons are expressed in non neural cells as well i The key is the combination of genes 8 Classi cation of neurons efforts began with the Golgi stain a Number of neurites axons and dendrites i Unipolar one neurite found in sensory ganglia ii Bipolar two neurites retina olfactory bulb iii Multipolar many neurites many synapses most n e U l O n S 3 xiiA l tuf i I l I j 139 T V nanquoti Ill If I 39l 39139 HH39HFEIH lllll l Iallilkj39i Unipolar Bipolar Multipolar Ensign Neuron Interneumnil Wetoneurnn b Shape of dendritic tree i Pyramidal cells triangle shaped 1 Dendrites extend all along axon Almost pine shaped 2 Extended communication throughout ii Stellate cells star shaped 1 Circular dendritic tree 2 More local communication iii Spiny neurons have spines 1 All pyramidal cells 2 Some stellate cells iv Apinous neurons do not have spines 1 Some stellate cells i Brami 5 a Neurotransmitter v Neurons generally make only one neurotransmitter vi Neurons are classi ed by the neurotransmitter they make 1 Afferent coming into the brain arriving 10 2 Efferent going away from the brain exiting 11 b Connectivity vii Primary sensory neurons 1 From receptors to CNS viii Motor neurons 1 CNS to muscle ix lnterneurons 1 Form connections with other neurons 2 Most neurons t into this category Multiplalr MEI mumquot EEHEW new Intern Elli hung Ellen L i ll Ln Rerl bur 2 cell 1 IV quot quot i tell F lnhe al by E39EH39EIQ NEIE Iquot aanwier KENquoti L 39x l a M garElli n shea l I l Bennall l Neuron branch a f muscle 1 synapse r i a aquot 39 if A 39 D 391En l ECETH I 39Peas p Amen terminals Hus l tarmijn ls c Axon length x Golgi type 1 neurons projection neurons 1 Extend between brain regions 2 Long axons 3 Mainly pyramidal cells xi Golgi type 2 neurons local circuit neurons 1 Connect to neurons in vicinity 2 Short axons 3 Mainly stellate cells 12 9 Glia thought to be supportive of neuronal functions can act as stem cells support synapse formation a About the same number of glia as neurons 85 billion of each b Astrocytes i Most numerous glia ii Look kind of like a star iii Packed tightly between neurons lling the spaces iv Regulate synaptic transmission v Secrete proteins that help form neuron structure c Myelinating glia i Oligodendrocytes 1 Brain and spinal cord 2 Myelinate several axons ii Schwann cells 1 Peripheral nervous system 2 Myelinate single axons one Schwann cell is responsible for every inetrnode region iii Make myelin which increases conduction velocity iv Provide vital metabolic support for axons v Involved in multiple sclerosis d Ependymal cells i Line ventricles ii Direct cell migration during development e Microglia i Remove debris phagocytosis ii Release cytokines iii May be activated in response to stroke or brain trauma iv May also be involved in pruning or re ning circuits
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