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what factors complicate the process of reaching equalibrium?
- 1.presence of the plasma membrane
- 2.diffusion potentials of individual ions
- 3.large # of dissolved substances
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how does the presence of the plasma membrane complicate the processes of reaching equalibrium?
- a)differentically permeable-> potassium ions (K+) are 50-75 times more permeable than sodium ions (Na+)
- b)contains ion pumps-> sodium-potassium pump-> moves 3Na+ out of the cell for ever 2K+ into the cell
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how does diffusion pontentials of individual ions complicate the process of reaching equalibrium?
- it results from size, shape, and charge of particles
- --K+ and chloride ions (Cl-) are 50% more mobile than Na+
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how do large # of dissolved substances complicate the process of reaching equalibrium?
- we are most concerned about Na+,K+, and Cl- ->but every dissolved molecule effects equalibrium:
- a)glucose,amino acids, lipids,calcium,oxygen, carbon diocide, hormones, enzymes, urea, etc.
- b)large organic molecules inside the cell-> such as negatively charged proteins and phosphates-> are too big to move through membrane
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what is equilibrum potential
it is the result of the chemical and physical properties of all dissolved substances
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what is the net result of the equilibrium potential and what is it said to have?
the net result is a polarized cell said to have a "resting membrane potential" =-70mV(millivolts)
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when does a resting membrane potential occur?
it occurs when concentration forces= electrical forces
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does equilibrium mean equal?
no
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why does equalibrium not mean static?
because 2 forces are still at work causeing ion movement--> dynamic equilibrium
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what happens with dynamic equalibrium?
- 1.potassium movement
- 2.sodium movement
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what is potassium movement due to and what do each of them do?
- 1.concentration forces->tend to move K+ out of the cell
- 2.electrical forces->tend to move K+ into the cell
- a)a little more K+ moves out of the cell passively than in-> but the membrane pump quickley pumps lost K+ back into cell
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what is sodium movement due to and what do each of them do?
- 1.concentration forces-> tend to move Na+ into cell
- 2.electrical forces-> tend to move Na+ into the cell
- both forces are working to move Na+ into the cell
- a) plasma membrane of neuron is almost totally impermeable to Na+->if any Na+ does enter the cell it is quickly pumped out
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