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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
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
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+
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
what is equilibrum potential
it is the result of the chemical and physical properties of all dissolved substances
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)
when does a resting membrane potential occur?
it occurs when concentration forces= electrical forces
does equilibrium mean equal?
why does equalibrium not mean static?
because 2 forces are still at work causeing ion movement--> dynamic equilibrium
what happens with dynamic equalibrium?
- 1.potassium movement
- 2.sodium movement
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
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