Term
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Definition
concentration gradient
describes the difference from one side of a membrane to another as it relates solely to the concentration of a molecule
electrical charge is not relevant with discussing chemical gradient |
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Term
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Definition
describes the electrical forces acting across a membrane
significant when the molecules involved are charged
(anions are negative, cations are positive)
(like charges repel, opposite charges attract) |
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Term
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Definition
| combined net effect of the chemical and electrical gradients |
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Term
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Definition
magnitude of the electrical gradient that exactly opposes the diffusion of an ion across a membrane, down its chemical gradient
no net flux |
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Term
| relationship of Na+, K+, and proteins in intracellular and extracellular fluid |
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Definition
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Term
| resting membrane potential |
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Definition
reflects the overall effect of multiple ions on the cell's resting electrical charge (taking into account multiple different ions, varying permeability to specific ions, etc.)
-70 mV for a typical neuron
membrane is most permeable to K+ at rest
if a membrane is made more permeable to a specific ion, the membrane potential will move toward that specific ions equilibrium potential |
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Term
| establisment of resting membrane potential |
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Definition
dependent on
--relative permeability of the cell membrane to Na+ and K+ (relative ease with which these ions can move across the cell membrane. K+ is able to move across the cell membrane much more readily than Na+
***It is the relative permeability of the cell membrane via leak channels that creates the resting membrane potential. There are many more K+ leak channels than any other, thus cell membranes are ~50-100x more permeable to K+ than Na+***
--Concentration gradients of Na+ and K+ (see "Concentration Gradients of Na+ and K+" notecard) |
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Term
| Concentration gradients of Na+ and K+ |
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Definition
Na+/K+ pumps maintain a concentration gradient of Na+ and K+ the final membrane potential is the weighted sum of equilibrium potential of Na+ and K+ (in addition to other ions). Because the membrane is much more permeable to K+ ions, the resulting resting membrane potential of -70 mV is closer to the K+ equilibrium potential (-90 mV) than that of Na+ (+60 mV) The fact that the resting membrane potential of -70 mV is not equal to either the Na+ or the K+ equilibrium potentials, both ions have forces acting on them. At resting membrane potential, the electrochemical force on K+ is directed out of the cell. The electrochemical force for Na+ is directed into the cell. In light of K+ "leak" channels, K+ continuously moves out of the cell, down its electrochemical gradient. Na+ may also move down its electrochemical gradient into the cell. The Na+/K+ pump is incessantly working. The activity of the pump maintains the Na+ and K+ concentrations at a relatively stable concentration.
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