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Absolute refractory period
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The time immediately after an action potential, when the sodium gates close and the membrane cannot produce an action potential in response to stimulation of any intensity
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Action potential
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Rapid depolarization and slight reversal of the usual polarization caused by stimulation beyond the threshold
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Active transport
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Protein-mediated process that expends energy to pump chemicals from the blood into the brain
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Afferent axon
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Neuron that brings information into a structure
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All-or-none law
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Principle stating that the size, amplitude, and velocity of the action potential are independent of the intensity of the stimulus that initiated it
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Astrocyte
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(astroglia) relatively large star-shaped glia cell
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Axon
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Single thin fibers of constant diameter that extend from a neuron
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Axon hillock
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Swelling of the soma, the point where the axon begins
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Blood-brain barrier
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The mechanism that keeps many chemicals out of the brain
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Cell body, or soma
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The structure of a cell that contains the nucleus
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Concentration gradient
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The difference in distribution of ions across a membrane
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Dendrite
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Branching fiber that emanates from a neuron, growing narrower as it extends from the cell body toward the periphery
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Dendrite spine
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Short outgrowth along the dendrites
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Depolarization
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Reduction in the level of polarization across a membrane
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Efferent axon
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Neuron that carries information away from a structure
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