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Action potentials are responsible for the majority of the distinct features that are witnessed in nerve fibres, such as the uses of temporal and spatial summation and the phenomenon of ‘all or nothing’ from which this spurs. It is therefore of upmost importance that we understand both the process of propagation as well as creation of action potentials.
An action potential is when rapid changes in membrane ion permeability result in a change in membrane potential that spreads rapidly along the nerve fibre membrane. At the resting potential the nerve membrane is polarized, with the inside being –90mV relative to the outside. This is due to several factors: the relative concentrations and permeabilities of both potassium and sodium ions and the contribution of the sodium-potassium pump. ... These potential changes can then be passed down the axon. ... Therefore passive conduction can only occur over short distances, for longer distances the voltage must be regenerated, this occurs in active conduction via the action potential.
The action potential occurs due to the membrane becoming more permeable to sodium ions due to the opening of voltage gated sodium channels. ... Potassium channels also open when the membrane potential rises from zero however their conformational change is much slower and so they are mainly opening when the sodium channels are beginning their inactivation, this causes the membrane potential to return to its resting value. In order for an action potential to propagate the potential difference must reach a threshold value where the Na+ current through the voltage activated Na+ channels exceeds the outwards K+ current. When this occurs a positive feedback loop occurs for the sodium ions since their increased permeability causes a decreased potential difference and the decreased potential difference increases their permeability further, since the probability of the sodium channel being open depends on the potential difference across the membrane (the smaller the pd the higher the probability.
Approximate Word count = 1364
Approximate Pages = 5.5
(250 words per page double spaced)
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