College Physics
1st Edition
ISBN: 9781938168000
Author: Paul Peter Urone, Roger Hinrichs
Publisher: OpenStax College
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Textbook Question
Chapter 20, Problem 31CQ
Define depolarization, repolarization, and the action potential.
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Write a question about the electrical action potential of the human nervous system in terms of physics.
Item 13
Cell Membranes and Dielectrics Many cells in the body have a cell
membrane whose inner and outer surfaces carry opposite charges, just like
the plates of a parallel-plate capacitor. Suppose a typical cell membrane has
a thickness of 8.5x109 m, and its inner and outer surfaces carry charge
densities of -6.4×10-4 C/m² and +6.4×10-4 C/m², respectively. In
addition, assume that the material in the cell membrane has a dielectric
constant of 5.4.
Part A
Find the direction of the electric field within the cell membrane.
into the cell
O out of the cell
Submit
Part B
E =
Find the magnitude of the electric field within the cell membrane.
Express your answer using two significant figures.
—| ΑΣΦ
Submit
Part C
Request Answer
|AV| =
Submit
Request Answer
Calculate the potential difference between the inner and outer walls of the membrane.
Express your answer using two significant figures.
17 ΑΣΦ
# ?
Request Answer
N/C
?
mV
Define Stopping-Potential.
Chapter 20 Solutions
College Physics
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Ch. 20 - If aluminum and copper wires of the same length...Ch. 20 - Explain why R=R0(1 + a?T) for the temperature...Ch. 20 - Why do incandescent lightbulbs grow dim late in...Ch. 20 - The power dissipated in a resistor is given by P =...Ch. 20 - Give an example of a use of AC power other than in...Ch. 20 - Why do voltage, current, and power go through zero...Ch. 20 - You are riding in a train, gazing into the...Ch. 20 - Using an ohmmeter, a student measures the...Ch. 20 - What are the two major hazards of electricity?Ch. 20 - Why isn’t a short circuit a shock hazard?Ch. 20 - What determines the severity of a shock? Can you...Ch. 20 - An electrified needle is used to burn off warts,...Ch. 20 - Some surgery is performed with high-voltage...Ch. 20 - Some devices often used in bathrooms, such as...Ch. 20 - We are often advised to not flick electric...Ch. 20 - Before working on a power transmission line,...Ch. 20 - Why is the resistance of wet skin so much smaller...Ch. 20 - Could a person on intravenous infusion (an IV) be...Ch. 20 - In view of the small currents that cause shock...Ch. 20 - Note that in Figure 20.28, both the concentration...Ch. 20 - Define depolarization, repolarization, and the...Ch. 20 - Explain the properties of myelinated nerves in...Ch. 20 - What is the current in milliamperes produced by...Ch. 20 - A total of 600 C of charge passes through a...Ch. 20 - What is the current when a typical static charge...Ch. 20 - Find the current when 2.00 nC jumps between your...Ch. 20 - A large lightning bolt had a 20,000-A current and...Ch. 20 - The 200-A current through a spark plug moves 0.300...Ch. 20 - (a) A defibrillator sends a 6.00-A current through...Ch. 20 - During open-heart surgery, a defibrillator can be...Ch. 20 - (a) A defibrillator passes 12.0 A of current...Ch. 20 - A clock battery wears out after moving 10,000 C of...Ch. 20 - The batteries of a submerged non-nuclear submarine...Ch. 20 - Electron guns are used in X-ray tubes. 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- In Example 23.14 we estimated the capacitance of the cell membrane to be 89 pF, and in Example 23.15 we found that approximately 10,000 Na+ ions flow through an ion channel when it opens. Based on this information and what you learned about the action potential, estimate the total number of sodium channels in the membrane of a nerve cell.arrow_forwardVoltage across the resting membrane potential…A) Can be described by the Nernst equation.B) Is established by a difference in charges across the cell membrane, with the outside more negative than the inside.C) Defines the driving force for flow of a particular ion across the cell membrane, given its equilibrium potentialD) Is equally dependent on the flow of potassium and sodium ions through leak channels across the cell membrane.E) Stays the same during an action potential.arrow_forwardNerve cells in your body can be electrically stimulated; a large enough change in a membrane potential triggers a nerve impulse. Certain plants work the same way. A touch to mimosa pudica, the “sensitive plant,” causes the leaflets to fold inward and droop. We can trigger this response electrically as well. In one experiment, investigators placed electrodes on the thick tissue at the base of a leaf. The electrodes were 3.5 mm apart. When the electrodes were connected to a 47 μF capacitor charged to 1.5 V, this stimulated a response from the plant.a. Eventually, all the charge on the capacitor was transferred to the plant. How much charge was transferred?b. What was the approximate electric field between the electrodes?arrow_forward
- Assume a length of axon membrane of about 0.10 m is excited by an action potential (length excited = nerve speed pulse duration = 50.0 m/s 2.0 103 s = 0.10 m). In the resting state, the outer surface of the axon wall is charged positively with K+ ions and the inner wall has an equal and opposite charge of negative organic ions, as shown in Figure P18.43. Model the axon as a parallel-plate capacitor and take C = 0A/d and Q = C V to investigate the charge as follows. Use typical values for a cylindrical axon of cell wall thickness d = 1.0 108 m, axon radius r = 1.0 101 m, and cell-wall dielectric constant = 3.0. (a) Calculate the positive charge on the outside of a 0.10-m piece of axon when it is not conducting an electric pulse. How many K+ ions are on the outside of the axon assuming an initial potential difference of 7.0 102 V? Is this a large charge per unit area? Hint: Calculate the charge per unit area in terms of electronic charge e per squared (2). An atom has a cross section of about 1 2 (1 = 1010 m). (b) How much positive charge must flow through the cell membrane to reach the excited state of + 3.0 102 V from the resting state of 7.0 102 V? How many sodium ions (Na+) is this? (c) If it takes 2.0 ms for the Na+ ions to enter the axon, what is the average current in the axon wall in this process? (d) How much energy does it take to raise the potential of the inner axon wall to + 3.0 102 V, starting from the resting potential of 7.0 102 V? Figure P18.43 Problem 43 and 44.arrow_forwardIn a certain region of space, the electric field is zero. From this fact, what can you conclude about the electric potential in this region? (a) It is zero, (b) It does not vary with position. (c) It is positive. (d) It is negative. (e) None of those answers is necessarily true.arrow_forwardA myelinated axon conducts nerve impulses at a speed of 40 m/s. What is the signal speed if the thickness of the myelin sheath is halved but no other changes are made to the axon?arrow_forward
- What is the voltage of the resting potential? Give a real life example of this?arrow_forwardPlease help. The nonpolar core of the membrane of a muscle cell has a thickness d = 4nm and a dielectric constancy k = 20. (a) What is the surface capacity of the membrane? Express your response in microcoulombs per square centimeter. (b) During muscle contraction, the internal potential of the cell increases by about 100 mV. For 1 cm2 of membrane, how many Na+ ions must have entered the cell for this purpose? (c) The medium outside the cell initially contains 0.150 mol / L of Na + ions in solution. Considering that it extends to 1 µm from the cell, what is the decrease in Na+ concentration immediately after the change in potential? (d) Estimate the number of times the process can be repeated before the Na+ ion reserve is exhausted. Please show formulas ans steps for my own understandingarrow_forwardCalculate the capacitance of the myelinated neuron membrane (axon), if its thickness is 0.8 micrometres (um) using a value of area of 10-6 m2. The membrane wall is mainly lipids and you will need to find the value of the permittivity in your notes. Give your answer in picoFarads (10-12 F) NB 1um = 10-6 marrow_forward
- 1. How was the spontaneous potential discovered? why is it an electrical phenomenon?arrow_forwardWhat is the potential difference ( in volts) across C2 when C, = 5.0 µF, C2 = 15 µF, C3 = 30 µF, and Vo = 37.4 V? %3D C, C3 Vo Select one: A. 24.93 B. 12.47 Ос. 34.41 D. 18.70 E. 56.10arrow_forwardAssume a length of axon membrane of about 0.10 m is excited by an action potential (length excited = nerve speed x pulse duration = 50.0 m/s x 0.0020 s = 0.10 m). In the resting state, the outer surface of the axon wall is charged positively with K+ ions and the inner wall has an equal and opposite charge of negative organic ions, as shown in the figure below. Model the axon as a parallel-plate capacitor and take C = KE A/d and Q = CAV to investigate the charge as follows. Use typical values for a cylindrical axon of cell wall thickness d = 1.8 x 10-8 m, axon radius r = 1.4 × 10¹ μm, and cell-wall dielectric constant x = 2.0. Positive charge layer Negative charge layer 1+ External fluid + + + Axon wall membrane + Internal fluid Axon radius = r + + + d + (a) Calculate the positive charge on the outside of a 0.10-m piece of axon when it is not conducting an electric pulse. (Assume an initial potential difference of 7.0 x 10-² V.) How many K+ ions are on the outside of the axon assuming…arrow_forward
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