Life: The Science of Biology
11th Edition
ISBN: 9781319010164
Author: David E. Sadava, David M. Hillis, H. Craig Heller, Sally D. Hacker
Publisher: W. H. Freeman
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Chapter 6.3, Problem 3R
Summary Introduction
To review:
The role of cell membrane in maintaining potassium ion (K+) imbalance in neurons and their elimination by K+ membrane channels.
Introduction:
Cells generally have membranes composed of lipids and proteins. The lipids present in the membranes are selectively permeable and does not allow all the substances to enter the cell. The proteins present on the cell membrane form a channel-like structure known as ion channels. Some of these channels are also known as gates.
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Life: The Science of Biology
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- Conformational changes in channel proteins brought about by voltage changes are responsible for opening and closing Na+ and K+ gates during the generation of an action potential. (True or false?)arrow_forwardThe accelerating flow of _______ ions through gated channels across the membrane triggers an action potential. a. potassium b. sodium c. hydrogen d. a and barrow_forwardOne of the important uses of the Nernst equation is in describing the flow of ions across plasma membranes. Ions move under the influence of two forces: the concentration gradient (given in electrical units by the Nernst equation) and the electrical gradient (given by the membrane voltage). This is summarized by Ohms law: Ix=Gx(VmEx) which describes the movement of ion x across the membrane. I is the current in amperes (A); G is the conductance, a measure of the permeability of x, in Siemens (S), which is I/V;Vm is the membrane voltage; and Ex is the equilibrium potential of ion x. Not only does this equation tell how large the current is, but it also tells what direction the current is flowing. By convention, a negative value of the current represents either a positive ion entering the cell or a negative ion leaving the cell. The opposite is true of a positive value of the current. a. Using the following information, calculate the magnitude of Na [ Na+ ]0=145mM,[ Na+ ]i=15mM,Gna+=1nS,Vm=70mV b. Is Na+ entering or leaving the cell? c. Is Na+ moving with or against the concentration gradient? Is it moving with or against the electrical gradient?arrow_forward
- Which of the following statements about voltage gated channels is true? Voltage-gated sodium channels open at a higher (more positive) membrane potential than do potassium-gated channels Voltage-gated sodium channels open at a lower (more negative) membrane potential than do potassium-gated channels Sodium- and postassium-gated channels open at about the same membrane potential, but they have different effects because there are different numbers of the two kinds of channels in neuron cell membranesarrow_forwardDescribe the contribution of each of the following to the establishment and maintenance of membrane potential: Part A Na+K+ Pump Passive movement of K+ across the membrane Passive movement of Na+ across the membrane Part B Resting membrane potential is approximately -70mV. Explain what resting membrane potential is and what -70mV refers to.arrow_forwardWhat happens to the membrane potential when Na+/K+ pump is active?arrow_forward
- Neurons have a resting membrane potential of ___________________. varying votage as type and composition of channels can differ between neurons. theoretically the same votage because the ionic concentration is the same extracellularly and intracellularly for all neurons. equal to the equillibrium potential for potassium. directly opposing the equillibrium potential for sodium.arrow_forwardCalculate: The equilibrium potential for potassium at room temp The equilibrium potential for sodium at room temp Resting membrane potential of this neuron at room temperaturearrow_forwardSimilarly, what will be the effect on membrane potential if Cl- ions move into a cell?arrow_forward
- There are two types of gated ion channels. Name the 2 types and provide a description of how they workarrow_forwardIf a cell with the following ion concentrations had a resting membrane potential of -40mV which of the following can you conclude? Extracellular: Cl- = 110 mM, Na+ = 145 mM, K+ = 5mM. Intracellular Cl- = 20 mM, Na+ = 10 mM, K+ = 140mM a) At rest it is only permeable to potassium b) At rest it has some permeability to more than one of these ions c) At rest it is only permeable to chloride d) Rest it is not permeable to sodiumarrow_forwardThe concentration of potassium ions inside a nerve cell membrane is higher than the concentration of sodium ions outside the mem-brane, yet the inside of the membrane (where the cation concentra-tion is higher) is negative to the outside. Explain this observation in terms of permeability properties of the membrane.arrow_forward
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