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6.5.5 Explain how a nerve impulse passes along a non-myelinated neurone

6.5.5 Explain how a nerve impulse passes along a non-myelinated neurone1) Resting Potential is -70mV on the inside of the axon. This is achieved by movement of Na+ to the outside and K+ to the inside of the axon via active transport using the Sodium-Potassium pump. This pumps Na+ and K+ in the ratio 3Na+:2K+ and requires ATP. This combined with the chloride ions (Cl-) present on the inside of the axon result in a relatively negative charge on the inside of the axon and positive charge on the outside of the axon.2) Depolarization (Action Potential). This stage is when the sodium ion channels open and the Na+ flows along its concentration gradient into the inside of the axon. The inside of the axon therefore becomes relatively positively charged.3) Repolarization. During this stage the Na+ channels are closed, and the K+ channels open. This allows for K+ to flow down its concentration gradient to the outside of the axon making the outside relatively positively charged and the inside relatively negatively charged. This can be seen in the video by there being more chloride ions (Cl-) than Na+ on the inside. The charges are now as they were at resting potential but the ions are not where they were at resting potential. At this point, as a result of the sodium ion channels being closed, an impulse (Action Potential) cannot be sent. This is called the Refractory Period.4) Return to Resting Potential. As per step 1, this is achieved by movement of Na+ to the outside and K+ to the inside of the axon via active transport using the sodium-potassium pump. This pumps Na+ and K+ in the ratio 3Na+:2K+ and requires ATP. The chloride ions present on the inside of the axon result in a relatively negative charge on the inside of the axon and positive charge on the outside of the axon.The action potential propagated along the axon by these voltage-gated ion channels (for Na+ and K+) opening when detecting the reversal in polarity in neighboring regions. This can be seen on the animation. Once the action potential has passed the sodium-potassium pump restores the resting potential state.The graph shows time on the x-axis and membrane potential (on the inside of the axon) on the y-axis. As per steps 1-4 the membrane potential on the inside of the axon changes. For good practice, draw this graph and use the video to review and explain how the changes in membrane potential occur.
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