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Chapter 2

Chapter 2 - Neurons and Glia

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Janelle Leboutillier

Chapter 2Neurons and Glia 5785IntroductionAll tissues and organs in the body consist of cells The specialized functions of cells and how they interact determine the functions of organsWell focus on structure of different types of cells that differ based on structure chemistry and functionGlia outnumber neurons by tenfoldNeurons are the most important cells for unique functions of the brain IT is the neurons that sense changes in environment communicate these changes to other neurons and command body responses to the sensationsGliaglial cells are thought to contribute to brain function mainly by insulating supporting and nourishing neighbouring neuronsThe Neuron DoctrineScientists have had to overcome several obstacles The first was small size most cells range form 001005 nm in diameter th In the 19 century scientists discovered how to hardenfix tissues by immersing them in formaldehyde and developed special device called microtome to make very thing slicesThese technical advances spawned field of histologythe microscopic study of structure of tissuesThe final breakthrough of neurohistology was the introduction of stains that could selectively colour some but not all parts of the cells in brain tissues th One was introduced by German neurologist Franz Nissl in late 19 centurybasic dyes would stain nuclei of all cells and also stain clumps of material surrounding the nuclei of neuronsNissl bodies and the stain is Nissl stain useful for distinguishing neurons from glia and it enables histologists to study the arrangement or cytoarchitectures of neurons in different parts of the brain cytocellThe Golgi StainItalian histologist Camillo Golgi discovered that by soaking brain tissue in silver chromate solution called Golgi stain a smallof neurons became darkly coloured in entiretyThe Golgi stain shows that neurons have at least 2 distinguishable parts central region that contains cell nucleus and numerous thin tubes that radiate away from the central regionThe swollen region contain cell nucleus has several interchangeable names cell body soma and perikaryonThe thin tube that radiate from somas care neuritis and are of 2 types axons and dendritesThe cell body usually gives rise to single axon uniform diameter throughout length branches extend at right angles Axons act like wires that carry the output of the neuron Dendrites rarely extend more than 22 mmNeurohistology The gain in brain is mainly in the stainCajals ContributionSpanish contemporary of Golgi who used it to greatest effect is Santiago y Cajal a skilled histologist and artist who learned about Golgis methods in 1888 Cajal used the Golgi stain to work out the circuitry of many regions of the brain Golgi and Cajal drew completely opposite conclusions about neurons Golgi stated that neurites of different cells are fused together to form a continuous reticulumnetwork The brain is an exception to the cell theory which states that the individual cell is the elementary functional unit of all animal tissues Cajal stated that the neurites of different neurons are not continuous w one another and must communicate by contact not continuityThis idea that the neuron adhered to the cell theory came to called the neuron doctrine Cajal and Golgi shared the Nobel prize in 1906 but were rivals foreverFinal proof of the neuron doctrine came from the development of the electron doctrine in the 1950sfinally possible to show that the neurites of different neurons are not continuous with one another
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