Term
| The different passive and active transport systems are coordinated in a living cell to maintain intracellular ions and other solutes at concentrations compatible with life. The cell does not equilibrate with the extracellular fluid but rather exists in a steady state with the extracellular solution. Maintenance of this steady state is the basis or the difference in electrical potential across the cell membrane, or ??? |
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Definition
| Resting membrane potential. |
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Term
Flow of ions (K+ and Na+) down their electrochemical potential gradient is directly responsible for generating most of the resting membrane potential.
• Changing the concentration of K+ has greater effect than changing the concentration of Na+
• If the membrane was equally permeable to both ions, the resting membrane potential would be directly in the middle.
• Instead, cells are 50X more permeable to K+
• Each permeant ion attempts to drive the membrane potential toward its own equilibrium potential.
The Na+K+ATPase contributes about -4mV to resting membrane potential because of its ??? |
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Definition
electrogenic nature (a net transfer of
positive charge out of the cell). |
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Term
Most cell membranes not only possess a resting
permeability to K+ ions, but also have a degree of permeability to Na+ and Cl- ions. Therefore, the influence of these additional ionic permeabilities on the diffusion potential or membrane potential must be taken into account. The polarity of the electrical charge of each ion, the permeability of the membrane (P) to each ion, and the concentrations (C) of the respective ions on the inside (i) and
outside (o) of the membrane influence the membrane potential. This relationship is given quantitatively by the ??? |
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Definition
| Goldman-Hodgkin-Katz equation |
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Term
The membrane potential approaches the equilibrium potential for any ion whose permeability becomes much greater than the others. Such shifts are of
paramount importance in excitability phenomena such as the action potentials of nerve and muscle. In most resting plasma membranes PK is much greater
than PNa (roughly 50-100 times greater).
[NOTE: It is because Pk is much larger than PNa and [K+]i is much larger than [K+]o
that the resting membrane potential is negative and often approaches Ek.] |
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Definition
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Term
While permeability describes the ease with which an ion can move through the membrane, conductance describes the ability of a given ion species to carry electrical current across the membrane.
Ohm’s Law allows us to predict the amplitude of ion fluxes.
Iion = gion(Em – Eion)
Iion = current carried by an ion
gion = conductance
(Em – Eion) = (Em, membrane potential – Eion, Nernst potential for a specified ion) is the electromotive or driving force for an ion |
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Definition
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Term
Ohm’s Law – Amplitude of Ion Flux
The K+ current (IK) is described by:
IK = gK(Em -EK)
IK = current carried by K+
gK = K+ conductance
Em -EK = electrochemical gradient driving K+ movement |
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Definition
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Term
Excitability
o Changes in Membrane Potential - All cells have membrane potentials. Membrane potential will change when the cell is perturbed. Excitable cells are those that can undergo action potentials. The key to excitability is self-depolarization. The same
techniques for examining resting membrane potentials can be used to study the changes of membrane potential and any elicited action potentials due to an increased excitability.
o The membrane potential will change if an electrical current is passed across the membrane. Current pulses can be depolarizing or hyperpolarizing depending on the direction of current flow. |
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Definition
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Term
| When the membrane potential is less negative than the resting potential the cell is ???, a decrease in potential difference (e.g., a change from -70 mV to -40 mV). |
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Definition
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Term
| When the membrane potential is more negative, the cell is ??? and this occurs when polarization across the membrane is increased (e.g., a change from -70 mV to -100 mV). |
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Definition
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Term
| The depolarization level prior to reaching threshold |
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Definition
| Subthreshold Depolarization |
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Term
| Membrane will have downward deflection during? |
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Definition
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