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HOW MESSAGES ARE SENT A message travelling down a neuron It comes from: Another neuron A sensory receptor Also called an ACTION POTENTIAL Sodium (Na+) Potassium (K+) Since both are positive…. Its all relative Positive = more positive ions Negative = fewer positive ions Not sending an impulse Neuron impermeable to Na+ Na+ collects outside Potassium moves freely (permeable) Outside is positive All Na+ and some K+ Inside is negative Some K+ Polarized Na+ channels (gates) open Neurons now permeable to Na+ Na+ diffuse into cell Polarity reversed Inside positive Outside negative Depolarized K+ moving out of the cell (closes Na+ gates) Depolarization occurs in a small area Affects adjacent gates ▪ Creates “wave” of electricity ▪ Travels length of axon Na+ gates are only open for a fraction of a second Na+ gets trapped inside the cell Recovery period Few thousandths of a second Neuron cannot be stimulated again Neuron must ne returned to “resting potential” Sodium potassium pumps returns membrane to rest Na+ moves out K+ moves in Repolarized Outside now + Inside now - Myelinated neuron Faster transmission (100 m/s) 2m/s (unmyelinated) Jumps from one node of Ranvier to next Uses less energy Minimum strength stimulus required for action potential to occur Different for each neuron Impulses are all alike once threshold reached Strength only changes with number sent