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In this metaphor:
female sailors = anions
male British sailors = potassium ions
male American sailors sodium ions
Week 1
Week 1
They're all hanging out in 2 bars - about the amount of both genders of sailors in both bars, but males are separated - mostly Brits in one bar, mostly Americans in the other.
metaphor: untrue description to helps explain an idea
This metaphor can be a way to remember.
The cell and its surround are 2 bars:
inside bar = intracellular space
outside bar = extracellular space
All cell's actions take place near the cell membrane (both sides).
There are groups of people in both bars as different ions, which move around randomly and bump into each other.
cations, positive ions = male sailors
anions, negative ions = female sailors
The gender balance in both bars starts out close to equal.
It's akin to how ions start as electrically balanced, as intracelullar and extracellular spaces are both electroneutral.
British = potassium (K+) ions
US = sodium (Na+) ions
2 forces driving the resting potential:
diffusion and electrostatic forces.
Diffusion representation
Diffusion representation
Both navy try to balance between the 2 bars to have both equal beer in both bars
If a bar has more Americans then some of them will move to the other one
so do to the Brits of the other bar
This is diffusion
Another force working are the number of genders.
desire to balance gender = how positive and negative ion interact
If there's excess of male in a bar, they try to move to the other bar.
While female often stay
gender balance-seeking force = electrostatic force and any ratio difference generates a voltage across the membrane
The gender balance-seeking is the electrostatic force and any difference in gender ratios generates a voltage across the membrane.
If a bar has excess of a gender, it has a net "charge".
In context of neurons, recall that voltage = difference in electric potential made by ion flow, resulting in net charges near the membrane
voltage = size of gender ratio difference and the electrostatic force describes how much the male sailors want to move to correct it.
Depending on relative magnitude of a bar's gender imbalance, male sailors will try to move to minimize the imbalance so that both bars are close as possible.
Week 2
Week 2
Brits and Americans want to equally cover both bars (diffusions)
Both want to keep the gender ratios balanced (electrostatic force)
There's negative resting potential in the cell because the starting ratios of Brits and American are imbalanced.
and there's British bouncer who lets them go between the 2 bars
By default most Brits are inside, only a few are in the outside bar.
so the Brits want to move to the outside to balance, but it's crowded outside, with many females and male Americans.
If male Brits (K+ ions) fully balanced out their number in both bars, while leaving the females and Americans (Na+ ions) in place, there's significant excess of males - positive charges in outside bar.
The Americans can trade places with the Brits to preserve balance, but the Brit bouncer won't let them into the inside bar and are stuck outside.
Akin to how K+ and Na+ ions have different abilities to across the cell membrane through ion channels, this difference is key to resting potential (balancing points of many ions)
Male brits (K+ ions) try to reach their balance (equilibrium potential), a balancing point between diffusion and electrostatic forces. Here, it's governed by 2 things:
male Brits' desires (K+ ions) to balance out their numbers in inside and outside bars.
desire to main gender balance
Together, these determine the equilibrium potential.
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