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Physics

Write a question about the electrical action potential of the human nervous system in terms of physics.

University Physics Volume 2

18th Edition

ISBN:9781938168161

Author:OpenStax

Publisher:OpenStax

Chapter7: Electric Potential

Section: Chapter Questions

Problem 2CQ: Why do we need to be careful about work done on the system versus work done by the system in...

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Nerve 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?
A 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?
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.
Every cell in the body has organelles called mitochondria that can generate a voltage difference between their interior and exterior. If the capacitance of a mitochondrion is 4.0×10−11F and the potential difference between the interior and exterior is 0.18 V, how much electrical energy does it store? If a mitochondrion were to use all of its stored electrical energy to produce ATP molecules, and each ATP molecule requires 9.5×10−20J, how many molecules could it produce? (In reality, ATP molecules are produced by the flow of protons caused by the proton motive force, and not by the direct conversion of electrical energy stored by the capacitance of mitochondria.)
Assume 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…
Assume 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 = K² A/d and Q = CAV to investigate the charge as follows. Use typical values for a cylindrical axon of cell wall thickness d = 2.0 x 10-8 m, axon radius r = 1.6 x 10¹ μm, and cell-wall dielectric constant k = 2.9. Positive charge layer Negative charge layer External fluid Axon wall membrane Internal fluid - Axon radius= d -2 (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.) 9.03E-10 C How many K+ ions are on the outside of the axon assuming an…
Assume 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 = 2.0 × 10-8 m, axon radius r = 1.6 × 10¹ µm, and cell-wall dielectric constant x = 2.9. Positive charge layer Negative charge layer External fluid Axon wall membrane Internal fluid Axon radius = r No + (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.) d Your response differs significantly from the correct answer. Rework your…
Assume 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 = 1.3 x 10-8 m, axon radius r = 1.3 × 10¹ μm, and cell-wall dielectric constant x = 2.1. Positive charge layer Negative charge layer External fluid + Axon wall membrane Internal fluid Axon radius = r + + How many sodium ions (Na+) is this? Na+ ions + (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.) C How many K+ ions are on…
When a battery is connected to a capacitor (device that stores charge) the charge q builds up - t - e according to the equation q = qo(1- ), where %o is the maximum charge and T is a constant. At what time t does the charge reach 10% of its maximum value? (Note: Enter your answer in terms of tau, T, using the Greek letters in MathType.) t10% = S
In a typical mammalian cell, the net transport by the sodiumpotassium exchange pump that maintains the 70 mV membrane potential is 500 singly charged ions per second. How much work does the pump do each second?
What is the energy stored in such a cell membrane if the potential difference across it is 7.05×10−2 VV ? Express your answer using two significant figures.
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 × 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 = ??0A/d and Q = CΔV to investigate the charge as follows. Use typical values for a cylindrical axon of cell wall thickness d = 1.1 ✕ 10−8 m, axon radius r = 2.0 ✕ 101 ?m, and cell-wall dielectric constant ? = 2.7. A diagram shows a collection of positive and negative charges in and around an axon. The diagram is divided into three sections, one on top of the other. The top section is labeled "External fluid". A row of positive charges labeled "Positive charge layer" lies along the bottom side of this section. Above the row of positive charges, there is an even mixture of…