1 - LS2:ReviewChapter44; 1 , Chemicalsginals...

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LS 2: Review Chapter 44; Neurons and Nervous System 1) Nervous system made of billions of neurons, which communicate through Electrical and  Chemical sginals. Soma -cell body, contains nucleus and most cell organelles. (140mm diameter) Where  protein synthesis occurs. Dendrites -extension from soma, receptive sites for chemical signals. Axon Hillock        Integrates information collected by dendrites and initiates action potential. Axon-  neuron has ONLY 1 axon, generate (axon hillock) and conduct signals away from  soma; Abundant microtubules for transport. Also known as Nerve Fibers. Axon Terminals - synapse with target cell. Contain neurotransmitters filled vesicles. Glial   Cells -   not   excitable,   do   not   transmit   electrical   signal;   help   in   nutrient   supply,  physical support, consume foreign particles, insulate axons. (10:1) Wrap around the axons of neurons, covering them with concentric layers of  insulating plasma membrane . 1) Oligodendroctes - produce Myelin (the covering for axons) in CNS (brain +  spinal cord) Can produce myelin to wrap around multiple axons for insulation. 2) Schwann Cells - produce Myelin in PNS (sensory cells). Produce myelin to  rap around 1 axon.
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3) Nodes of Ranvier : are gaps in myelin sheaths along axon. 4) Myelin   Speeds   Up   Action   Potential/   Saltatory   Conductance :     Action  potentials do not travel along all axons at the same speed. They travel faster  in myelinated (100m/sec) than in nonmyelinated (2m/sec) axons, and in large- diameter   axons   vs   small   diameter   axons.   Squid   has   giant   axon,   but  vertebrates use myelin insulation. (200 times smaller diameter) (“leaky hose” 
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