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BIO12 - Nervous System - Action Potential

...a first look at how a neuron transmits a nerve impulse

Ashleigh Akehurst

on 1 June 2013

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Transcript of BIO12 - Nervous System - Action Potential

The Nerve Impulse RESTING POTENTIAL - the "normal" state when axon is not conducting an impulse - the inside of the axon (axomembrane) is negative compared to the outside mV the SODIUM-POTASSIUM pump ...this is because of the... - is found imbedded in (and spans) the axomembrane - this "pump" requires energy to carry ions against their concentration gradient - it exchanges 3Na for 2K + + IN 2K + OUT 3Na + axoplasm extracellular fluid ...this results in a difference in POLARITY - the INSIDE of the axon has a smaller concentration of +ve ions (2K ) + - the OUTSIDE of the axon has a larger concentration of +ve ions (3Na ) + - this makes the inside NEGATIVE (with a high [K ]) relative to the outside (with a high [Na ]) + inside axon outside axon ...this is amplified by MEMBRANE PERMEABILITY - the axomembrane is MORE permeable to K (potassium) than it is to Na (sodium) - this allows K to leak OUT of the axon, making the inside of the axon even MORE negative relative to the outside + + ...and now we can talk about the NERVE IMPULSE - this is how one neuron sends its message to the next neuron - it is an electrical signal that relays down the axon via. "Saltatory Conduction" (conduction can only occur at the Nodes of Ranvier) NERVE IMPULSE the - when a neuron "wants" to send a message, it does so through the nerve impulse - this is a wave of that travels down the axon from the cell body to the axon terminal depolarization - it is possible due to the exchange of ions across the axomembrane ACTION POTENTIAL ...the messaging unit of a nerve impulse is the... 1. Na gates OPEN

2. K gates OPEN

3. Na /K pump activates and Na gates CLOSE and K gates CLOSE + + + + + + Na rushes INTO axon K rushes OUT of axon re-establishes Resting Potential RESTING POTENTIAL Na GATES OPEN K GATES OPEN REFRACTION PERIOD ...and this all ends in the REFRACTORY PERIOD - after the firing of an ACTION POTENTIAL, the ions need to be returned to their starting position - this is done by the Na/K Pump - this helps the ACTION POTENTIAL to always flow FORWARD - when the ions are not in their RESTING POTENTIAL position, no AP can happen - the time it takes for the ions to RESET is the REFRACTORY PERIOD NO ACTION POTENTIAL CAN FIRE!
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