So I am trying to understand the process of neuron firing a little more. When a neuron fires, the soma goes from a negative charge to a less negative, neutral, or positive charge. What is the mechanism that allows the sodium ions to transfer? Is it purely due to an electrical potential difference or is it diffusion due to a partial pressure difference (or both)? Secondly, if it is due to electrical potential difference, does that mean that the electric potential outside the soma is quite high to allow for the sodium ions to create a +ve charge within the soma when the transfer?
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There is an electrogradient that helps the ions transfer across the membrane but the Na+ ions also use facilitated diffusion to cross the membrane because their charge slows down the rate at which the ions move across the membrane; hence, the phospholipid bilayer has a polar head & non-polar tails. The polar head will try repelling the ions while the non-polar tail will try attracting it. Hence, ions are polar.
When the Na+ ions enter the cell membrane then they have a difficult time getting out, they then require the use of active transport proteins aka Na+ / K+ active transport pump because the concentration of Na+ ions is much greater in the extracellular fluids than it is in the intracellular fluids.
The electrogradient itself plays mostly a role when the K+ ions momentarily leave the cell when trying to return the neuron back to it's resting potentional so the Na+ active transport pumps can be turned back on, so Na+ ions can leave the cell & so the next action potentional can occur. While the K+ ions can still use the pump, the eletrogradient is much quicker to get back into the cell
Hope this helps some.
EDIT: As to your second question...In general, the extracellular fluid always has a greater + charge because of all the Na+ ions while the intracellular (inside the soma) has more of a negative charge because of all the proteins...So, the electrogradient potential does help this but also as I mentioned terms of diffusion help out here too...Also, if you don't know this yet or not the soma works off a graded potentional instead of the all-or-none law. In other words, the charge inside the cell only needs to reach threshold for an action potentional to occur unlike in the all-or-none law the neuron most be completely charged (+30mV) to reach an action potentional like in the axons.
When the Na+ ions enter the cell membrane then they have a difficult time getting out, they then require the use of active transport proteins aka Na+ / K+ active transport pump because the concentration of Na+ ions is much greater in the extracellular fluids than it is in the intracellular fluids.
The electrogradient itself plays mostly a role when the K+ ions momentarily leave the cell when trying to return the neuron back to it's resting potentional so the Na+ active transport pumps can be turned back on, so Na+ ions can leave the cell & so the next action potentional can occur. While the K+ ions can still use the pump, the eletrogradient is much quicker to get back into the cell
Hope this helps some.
EDIT: As to your second question...In general, the extracellular fluid always has a greater + charge because of all the Na+ ions while the intracellular (inside the soma) has more of a negative charge because of all the proteins...So, the electrogradient potential does help this but also as I mentioned terms of diffusion help out here too...Also, if you don't know this yet or not the soma works off a graded potentional instead of the all-or-none law. In other words, the charge inside the cell only needs to reach threshold for an action potentional to occur unlike in the all-or-none law the neuron most be completely charged (+30mV) to reach an action potentional like in the axons.