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How do nerves work?
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Are nerves simply the wires in the body
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that conduct electricity, like the wires in the walls of your home
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or in your computer?
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This is an analogy often made,
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but the reality is that nerves have a much more complex job in the body.
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They are not just the wires, but the cells that are the sensors,
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detectors of the external and internal world,
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the transducers that convert information to electrical impulses,
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the wires that transmit these impulses,
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the transistors that gate the information
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and turn up or down the volume-
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and finally, the activators that take that information
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and cause it to have an effect on other organs.
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Consider this. Your mother gently strokes your forearm
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and you react with pleasure.
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Or a spider crawls on your forearm and you startle and slap it off.
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Or you brush your forearm against a hot rack while removing a cake from the oven
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and you immediately recoil.
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Light touch produced pleasure, fear, or pain.
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How can one kind of cell have so many functions?
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Nerves are in fact bundles of cells called neurons
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and each of these neurons is highly specialized to carry nerve impulses,
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their form of electricity,
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in response to only one kind of stimulus, and in only one direction.
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The nerve impulse starts with a receptor,
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a specialized part of each nerve,
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where the electrical impulse begins.
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One nerve's receptor might be a thermal receptor,
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designed only to respond to a rapid increase in temperature.
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Another receptor type is attached to the hairs of the forearm,
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detecting movement of those hairs, such as when a spider crawls on your skin.
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Yet another kind of neuron is low-threshold mechanoreceptor,
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activated by light touch.
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Each of these neurons then carry their specific information:
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pain, warning, pleasure.
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And that information is projected to specific areas of the brain
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and that is the electrical impulse.
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The inside of a nerve is a fluid that is very rich in the ion potassium.
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It is 20 times higher than in the fluid outside the nerve
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while that outside fluid has 10 times more sodium than the inside of a nerve.
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This imbalance between sodium outside and potassium inside the cell
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results in the inside of the nerve having a negative electrical charge
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relative to the outside of the nerve,
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about equal to -70 or -80 millivolts.
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This is called the nerve's resting potential.
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But in response to that stimulus the nerve is designed to detect,
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pores in the cell wall near the receptor of the cell open.
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These pores are specialized protein channels
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that are designed to let sodium rush into the nerve.
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