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Published byNorma Sparks Modified over 8 years ago
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NERVE IMPULSE TRANSMISSION nerve cells are like no other cell in the body because they possess an electrical charge the axon of a neuron has a cell membrane that is semipermeable
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imbedded in the membrane are specialized proteins called ION PUMPS that produce an unequal concentration of charged particles between the cell and its fluid extracellular environment
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RESTING MEMBRANE POTENTIAL (Polarized RESTING MEMBRANE POTENTIAL (Polarized) this refers to the charge of an axon that is waiting for a nerve impulse (resting) Na + and K + ions are found both outside and inside the neuron
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there is a higher concentration of Na + in the extracellular environment than inside K + is more highly concentrated inside than out
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a SODIUM POTASSIUM PUMP, in the membrane, is used to actively transport 3 Na + out of the axon for every 2 K + it moves in; this creates a charge of -70mV
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ACTION POTENTIAL an action potential is the name for the transmission of an electro- chemical stimulus through a nerve in order for an action potential to occur the stimulus has to be strong enough, this is referred to as THRESHOLD LEVEL
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there are two stages to an action potential: Depolarization and Repolarization
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DEPOLARIZATION: when the neuron is stimulated, its membrane becomes more permeable to Na + ions, and impermeable to K +, so Na + ions move into the neuron by diffusion and K + ions are not able to move out.
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this creates a reversal of charge in the neuron called depolarization, now the neuron is more positive than its surroundings (+40mV)
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REPOLARIZATION: is the return of the neuron to its resting state. Na + channels close so Na + can no longer move into the neuron K + rushes out of the axon and into the extracellular fluid by diffusion
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The Sodium Potassium Ion pump then begins functioning; it pumps 3 Na + ions out of the neuron and 2K + ions into the neuron, returning the cell to its polarized condition (-70 mV)
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depolarization and repolarization must be complete before a neuron can transmit another stimulus; this is called the REFRACTORY PERIOD
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a neuron transmits the electrical impulse in wavelike fashion, once a region of the axon becomes depolarized adjacent regions will also become depolarized.
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once a neuron’s threshold level has been reached it will respond totally, if it is not reached the neuron will not respond = ALL OR NONE RESPONSE
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neurons in your body have different threshold levels allowing for different intensities of response. the more neurons that reach threshold levels the more intense the response.
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w The more rapidly impulses are sent, the more intense the response as well
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Graphing an Action Potential ChargemV Restingpotential Depolarization Repolariztion Restingpotential Time(us) + 40 - 70 0
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