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Unformatted text preview: LS 2: Review Chapter 45; Neurons and Nervous System 1) Nervous system made of billions of neurons, which communicate through Electrical and Chemical signals. 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- 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 neurotransmitter filled vesicles. Glial Cells- not excitable, do not transmit electrical signal; help in nutrient supply, physical support, consume foreign particles, insulate axons. Axon Hillock : High concentration of VGSC; Integrates signal from dendrites and soma, where Action Potential is initiated. . 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. 3) Glia include Schwann cells and oligodendrocytes, both of which generate myelin sheets on axons. Glia also include astrocytes , which support neurons metabolically and contribute to the bloodbrain barrier. Microglia , help in immune defense. 4) Nodes of Ranvier : are gaps in myelin sheaths along axon. (high concentration of sodium voltage gated channels) 5) 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 vertebrates use myelin insulation....
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This note was uploaded on 10/26/2011 for the course LS 2 taught by Professor Pires during the Spring '08 term at UCLA.
- Spring '08