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BIO STIMULATING THE BRAIN. Communication in the nervous system is based on the propagation of electrical signals called action potentials along axons, which are extensions of nerve cells (see the Passage Problems in Chapter 26). Action potentials are generated when the electric potential difference across the membrane of the nerve cell changes: Specifically, the inside of the cell becomes more positive. Researchers in clinical medicine and neurobiology cannot stimulate nerves (even noninvasively) at specific locations in conscious human subjects. Using electrodes to apply current to the skin is painful and requires large currents, which could be dangerous.
Anthony Barker and colleagues at the University of Sheffield in England developed a technique called transcranial magnetic stimulation (TMS). In this widely used procedure, a coil positioned near the skull produces a time-varying magnetic field that induces in the
29.72 Consider the brain tissue at the level of the dashed line to be a series of concentric circles, each behaving independently of the others. Where will the induced emf be the greatest? (a) At the center of the dashed line; (b) at the periphery of the dashed line; (c) nowhere—it will be the same in all concentric circles; (d) at the center while the stimulating current increases, at the periphery while the current decreases.
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Chapter 29 Solutions
University Physics with Modern Physics (14th Edition)
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- The speed of propagation of the action potential (an electrical signal) in a nerve cell depends (inversely) on the diameter of the axon (nerve fiber). If the nerve cell connecting the spinal cord to your feet is 1.1 m long, and the nerve impulse speed is 18 m/s, how long does it take for the nerve signal to travel this distance?arrow_forwardMeasuring Blood Flow. Blood contains positive and negative ions and thus is a conductor. A blood vessel, therefore, can be viewed as an electrical wire. We can even picture the flowing blood as a series of parallel conducting slabs whose thickness is the diameter 5.00 mm of the vessel moving with speed. (See in the following figure.(Figure 1)) Figure X X BX X X X X X X X X d 1 of 1 V potential difference of 1.00 mV ? Express your answer with the appropriate units. B = 1.31 T Submit Part C Correct R= Determine the volume rate of flow (R). (Note: Although the method developed here is useful in measuring the rate of blood flow in a vessel, it is limited to use in surgery because measurement of the potential & must be made directly across the vessel.) Express your answer in terms of some or all of the variables B, d, v, and E. Previous Answers A cylindrical blood vessel in a magnetic field. av 4B Submit ΑΣΦ Provide Feedback Bw Previous Answers Request Answer ? X Incorrect; Try Again; 3…arrow_forwardTo measure signal propagation in a nerve in the arm, the nerve is triggered near the armpit. The peak of the action potential is measured at the elbow and then, 4.0 ms later, 24 cm away from the elbow at the wrist.a. What is the speed of propagation along this nerve?b. A determination of the speed made by measuring the time between the application of a stimulus at the armpit and the peak of an action potential at the elbow or the wrist would be inaccurate. Explain the problem with this approach, and why the noted technique is preferable.arrow_forward
- Measuring Blood Flow. Blood contains positive and negative ions and thus is a conductor. A blood vessel, therefore, can be viewed as an electrical wire. We can even picture the flowing blood as a series of parallel conducting slabs whose thickness is the diameter 5.00 mm of the vessel moving with speed. (See in the following figure.( Figure 1)) Figure X XBX X XX X X X X d 1 of 1 V If you expect that the blood will be flowing at 15.3 cm/s for a vessel 5.00 mm in diameter, what strength of magnetic field will you need to produce a potential difference of 1.00 mV ? Express your answer with the appropriate units. B = Submit Part C 0 R = μA Submit Value X Incorrect; Try Again; 5 attempts remaining T Previous Answers Request Answer = VE ΑΣΦ Determine the volume rate of flow (R). (Note: Although the method developed here is useful in measuring the rate of blood flow in a vessel, it is limited to use in surgery because measurement of the potential & must be made directly across the vessel.)…arrow_forwardEvery 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.)arrow_forwardSignal Propagation in Neurons. Neurons are components of the nervous system of the body that transmit signals as electric impulses travel along their length. These impulses propagate when charge suddenly rushes into and then out of a part of the neuron called an axon. Measurements have shown that, during the inflow part of this cycle, approximately 5.6 * 1011 Na+ (sodium ions) per meter, each with charge +e, enter the axon. How many coulombs of charge enter a 1.5 cm length of the axon during this process?arrow_forward
- 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_forwardOpening of voltage-gated channels is driven by an intramembrane electric field acting on charged voltage-sensor domains. These domains move across the membrane and generate gating (displacement) currents. When these currents are integrated over time, they produce the gating charge generated by a population of channels. What would be the gating charge passing through the external circuit when the flat array of charges moves across the distance a inside the membrane? The hydrophobic thickness of the membrane is d, the dielectric constant ɛ, the density of charges is O and the area of the membrane is A (provide an analytic solution). start end A A a d darrow_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
- Neurons are components of the nervous system of the body that transmit signals as electric impulses travel along their length. These impulses propagate when charge suddenly rushes into and then out of a part of the neuron called an axon. Measurements have shown that, during the inflow part of this cycle, approximately 5.6 x 1011 Na+ (sodium ions) per meter, each with charge +e, enter the axon. How many coulombs of charge enter a 1.5-cm length of the axon during this process?arrow_forwardEMF = Vo = 6 volts. and C = 5 μF Calculate the theoretical value of the charge (q) in the capacitor during charging at t = RC. Use equation 3.arrow_forwardWhat are the values of the voltages across the resistances VR1, VR2, and VR3 when the switches SW1, SW2, and SW3 are OPEN?arrow_forward
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