Ch 12 AP 3 PDF

act as metabolic intermediaries between neurons and their circulatory supply. They also serve immune and scavenging functions in order to protect surrounding neurons. Textbook Reference: The Cellular Organization of Neural Tissue Bloom’s Category: 2. Understanding 4. Compare and contrast current an...

act as metabolic intermediaries between neurons and their circulatory supply. They also serve immune and scavenging functions in order to protect surrounding neurons. Textbook Reference: The Cellular Organization of Neural Tissue Bloom’s Category: 2. Understanding 4. Compare and contrast current and voltage with respect to the cell membrane. Answer: The net movement of charge constitutes an electric current. The separation of positive and negative charges constitutes a voltage. In terms of the cell membrane, the current would be a flow of ions through channels in the membrane, whereas the voltage would be the separation of charges across the membrane. Textbook Reference: The Ionic Basis of Membrane Potentials Bloom’s Category: 2. Understanding 5. Since the bulk solutions that make up the intracellular and extracellular fluids maintain charge neutrality, how does the cell produce membrane potentials? Answer: The charge separation producing the membrane potential is an extraordinarily local phenomenon. According to Figure 12.11, in any given 1 µm3 section around each side of the membrane, only six pairs of ions, from the 110,000 cations and 110,000 anions in each fluid compartment, need to sit on the membrane to charge its capacitance, producing a membrane potential of –90 mV. Textbook Reference: The Ionic Basis of Membrane Potentials Bloom’s Category: 2. Understanding 6. Explain in mechanistic terms how the action potential is an all-or-none phenomenon. Answer: The action potential is initiated only when a threshold depolarization is reached near the axon hillock. That is, a certain critical number of voltage-gated Na+ channels have to open in order to cause a depolarization that is strong enough to initiate the Hodgkin cycle and, by definition, perpetuate the further opening of voltage-gated Na+ channels via their own depolarization. If the threshold is not reached, there will be no Hodgkin cycle or action potential. Textbook Reference: The Action Potential Bloom’s Category: 2. Understanding 7. Compare and contrast the techniques of patch clamping and voltage clamping. Answer: Both patch clamping and voltage clamping provide experimental information about membrane currents, especially during an action potential. The patch-clamp technique uses a micropipette to record single channel currents, whereas the voltage- clamp technique shows whole cell ionic currents. Textbook Reference: The Action Potential Bloom’s Category: 2. Understanding 8. What are the similarities and differences among the channels in the voltage-gated channel superfamily? Answer: All the voltage-gated channels have principal subunits with extensive sequence homology and thus are evolutionarily related. Voltage-gated Na+ and Ca2+ channels have © 2016 Sinauer Associates, Inc. four domains, whereas the voltage-gated K+ channel has one domain that is homologous to one of the domains on the Na+ channel. Textbook Reference: The Action Potential Bloom’s Category: 2. Understanding 9. Explain in mechanistic terms why the action potential can travel a great distance along an axon without degrading. Answer: The same mechanism that is responsible for the rising phase of the action potential also aids in its perpetuation along the axon without degradation. The action potential on one location on the axon can itself initiate an action potential at a neighboring location, and the induced action potential will have the same all-or-none amplitude as the original. Textbook Reference: The Propagation of Action Potentials Bloom’s Category: 2. Understanding 10. Describe the significance of myelination. Answer: Myelination greatly increases conduction velocity of an axon by increasing the membrane resistance while decreasing the membrane capacitance. In other words, conduction velocity is increased by increasing the length constant without increasing the time constant. Action potentials occur only at the nodes of Ranvier, in a process that is called saltatory conduction. Textbook Reference: The Propagation of Action Potentials Bloom’s Category: 2. Understanding ONLINE QUIZ QUESTIONS 1. The neuron converts an electrical signal to a chemical signal in the a. dendrite. b. presynaptic terminal. c. cell body. d. axon hillock. Answer: b Textbook Reference: The Physiology of Control: Neurons and Endocrine Cells Compared Bloom’s Category: 1. Remembering 2. Neurons that relay sensory signals to integrative centers of the CNS are called a. interneurons. b. afferent neurons. c. synaptic neurons. d. efferent neurons. Answer: b Textbook Reference: The Physiology of Control: Neurons and Endocrine Cells Compared © 2016 Sinauer Associates, Inc. Bloom’s Category: 1. Remembering 3. Which glial cells function as metabolic intermediaries between capillaries and neurons? a. Schwann cells b. Oligodendrocites c. Astrocytes d. Microglial cells Answer: c Textbook Reference: The Cellular Organization of Neural Tissue Bloom’s Category: 1. Remembering 4. Which term best describes the movement of ions across a membrane? a. Current b. Voltage c. Resistance d. Capacitance Answer: a Textbook Reference: The Ionic Basis of Membrane Potentials Bloom’s Category: 1. Remembering 5. A decrease in the absolute value of the membrane potential toward zero is called a. depolarization. b. an action potential. c. hyperpolarization. d. a membrane potential. Answer: a Textbook Reference: The Ionic Basis of Membrane Potentials Bloom’s Category: 1. Remembering 6. Which of the following actively contributes to the cell’s membrane potential? a. Permeability to K+ b. Permeability to Na+ c. The overall resistance of the membrane d. Electrogenic ion pumps Answer: d Textbook Reference: The Ionic Basis of Membrane Potentials Bloom’s Category: 5. Evaluating 7. The time constant (τ) depends on the _______ of the membrane. a. resistance b. capacitance c. resistance and voltage d. resistance and capacitance Answer: d Textbook Reference: The Ionic Basis of Membrane Potentials © 2016 Sinauer Associates, Inc. Bloom’s Category: 2. Understanding 8. If a current pulse is generated on the membrane and creates a passive potential, which statement will be true? a. The change in the membrane potential will increase as the distance from the current pulse increases. b. The change in the membrane potential will decrease as the distance from the current pulse increases. c. The change in the membrane potential will remain constant throughout the length of the membrane. d. The change in the membrane potential will fluctuate depending on the strength of the initial current pulse. Answer: b Textbook Reference: The Ionic Basis of Membrane Potentials Bloom’s Category: 3. Applying 9. The plasma membrane of a resting neuron is most permeable to which ion? a. Na+ b. K+ c. Cl– d. Ca2+ Answer: b Textbook Reference: The Ionic Basis of Membrane Potentials Bloom’s Category: 2. Understanding 10. If ouabain was used to block Na+–K+-ATPase pumps, a. Na+ would go to equilibrium across the cell membrane. b. the membrane potential would become more negative. c. the concentration of K+ would be equal on both sides of the membrane. d. the cell would maintain steady state with a different membrane potential. Answer: a Textbook Reference: The Ionic Basis of Membrane Potentials Bloom’s Category: 3. Applying 11. In a typical neuron, which ion is in passive equilibrium across the cell membrane? a. Na+ b. K+ c. Cl– d. Both Na+ and K+ Answer: c Textbook Reference: The Ionic Basis of Membrane Potentials Bloom’s Category: 2. Understanding 12. A stimulating depolarizing current that depolarizes the axon hillock just slightly negative to the threshold will a. not change the overall membrane potential at all. © 2016 Sinauer Associates, Inc. b. produce an action potential. c. produce a very small action potential. d. produce a temporary graded potential. Answer: d Textbook Reference: The Action Potential Bloom’s Category: 2. Understanding 13. _______ channels govern the generation of an action potential. a. Ligand-gated Na+ b. Ligand-gated K+ c. Voltage-gated Na+ d. Voltage-gated K+ Answer: c Textbook Reference: The Action Potential Bloom’s Category: 1. Remembering 14. Considering the cycle of an action potential, when is the permeability to K+ at its greatest? a. During the resting membrane potential b. During the rising phase of the action potential c. At the peak of the action potential d. During the falling phase of the action potential Answer: d Textbook Reference: The Action Potential Bloom’s Category: 2. Understanding 15. Which statement regarding the action potential is false? a. In an extremely long axon, the action potential eventually will degrade. b. During the “falling” phase, K+ permeability increases. c. During the “rising” phase, Na+ moves into the neuron. d. In the recovery phase, Na+ channels are closed. Answer: a Textbook Reference: The Action Potential Bloom’s Category: 5. Evaluating 16. What allows the action potential to return to a repolarized state? a. Voltage-gated Na+ channels become inactivated. b. Voltage-gated K+ channels become inactivated. c. Na+ reaches equilibrium across the neural membrane and stops leaking in. d. Voltage-gated Na+ channels close. Answer: a Textbook Reference: The Action Potential Bloom’s Category: 2. Understanding 17. Which statement regarding cardiac pacemaker cells is false? a. They spontaneously generate action potentials. © 2016 Sinauer Associates, Inc. b. The frequency of action potential generation can be modified by neural input. c. The pacemaker cells are modified neural tissue. d. They are connected to myocardium via gap junctions. Answer: c Textbook Reference: The Action Potential Bloom’s Category: 5. Evaluating 18. _______ are responsible for extending the time of the cardiac action potential relative to a neural action potential. a. Slow Ca2+ channels b. Slow Na+ channels c. Slow K+ channels d. Voltage-gated Na+ channels Answer: a Textbook Reference: The Action Potential Bloom’s Category: 2. Understanding 19. Which character of neurons affects conduction velocity the least? a. Axon diameter b. Myelination c. Axon length d. Temperature Answer: c Textbook Reference: The Propagation of Action Potentials Bloom’s Category: 5. Evaluating 20. In myelinated axons, action potentials occur a. all along the axon. b. only at the internodes. c. only at the initial segment of the axon. d. only at the nodes of Ranvier. Answer: d Textbook Reference: The Propagation of Action Potentials Bloom’s Category: 2. Understanding © 2016 Sinauer Associates, Inc.