Physiology 3120 Lecture Notes - Axon Hillock, Saltatory Conduction, Schwann Cell

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Propagation of action potentials: generally, begins at axon hillock, and flow orthodromically down the axon to the nerve terminus. During ap, current carried by positive ions: non-myelinated neurons. Diagram on ec-65 shows cathodal electrode (i. e. attracts positive charges) Regions adjacent to original ap become depolarized as the positivity inside the cell spreads in both directions. Causes the action potential to occur in adjacent regions. In vivo, action potential only travels in one direction because of refractory periods. Action potentials stays all-or-none all along the axon: myelinated neurons. Insulated by myelin which is produced by. Myelin increases resistance across membrane by about 5,000 times, so ions won"t move across membrane where there is myelin. Voltage-gated channels located at nodes of ranvier only. conduction velocity increases: with the square root of diameter in a non-myelinated axon, directly with the diameter of a myelinated axon, conserves energy. Disadvantages: neuromuscular junction, susceptibility of myelinated fibres (multiple sclerosis)

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