Chapter 7 Summary - Nerve Cells and Electrical Signaling PDF

CHAPTER 7 The key to answering these questions lies in the Na +>K+ pumps in the neuron membrane. Earlier in this chapter we discussed the Na +>K+ pump in the context of its importance in developing concentration gradients and sustaining the gradients when the cell is at rest, when sodium and potass...

CHAPTER 7 The key to answering these questions lies in the Na +>K+ pumps in the neuron membrane. Earlier in this chapter we discussed the Na +>K+ pump in the context of its importance in developing concentration gradients and sustaining the gradients when the cell is at rest, when sodium and potassium ions are moving in and out of the cell through leak channels. To compensate for the movement of sodium and potassium ions in an active cell (a cell propagating action potentials), the Na +>K+ pump transports even more sodium and potassium ions to compensate for the greater movement of these ions through opened voltage-gated channels. Although an action potential is a relatively large change in the membrane potential, very few ions need to cross the membrane to produce this change. In fact, even without the Na +>K+ pump, no measurable SYSTEMS INTEGRATION In this chapter, we learned about how the nervous system generates and transmits electrical signals. These electrical signals are important for communication among all the organ systems and play a critical role in maintaining homeostasis. Ahead in the text (Chapter 8), we will learn how action potentials trigger neurotransmitter release for Nerve Cells and Electrical Signaling 223 change in the resting membrane potential would occur until a neuron has produced more than 1000 action potentials. Therefore, the action of the Na + >K+ pump is sufficient to prevent changes in concentration gradients for sodium and potassium in a cell performing at normal levels of activity. Quick Check 7.6 ➊ What is meant by “all-or-none” in reference to action potentials? ➋ ➌ In which types of axons does saltatory conduction occur? Explain the effects of fiber diameter and myelination on the conduction velocity of action potentials. intercellular communication. Then (Chapter 10), we will learn how sensory receptors detect energies in our environment and convert them to electrical signals, ultimately resulting in action potentials, being transmitted to the brain for perception of those external energies. Later in the book we will learn about action potentials in muscle (Chapter 12), including the muscle of the heart (Chapter 13). Go to MasteringA&P for Interactive Physiology tutorials, Interactive Flowcharts, Dynamic Study Modules and more! CHAPTER REVIEW SUMMARY Copyright © 2017. Pearson Education, Limited. All rights reserved. 7.1 Overview of the Nervous System, p. 197 • The nervous system can be divided into • • • • the central nervous system and the peripheral nervous system. The central nervous system consists of the brain and spinal cord. The peripheral nervous system is subdivided into afferent and efferent divisions. The afferent division consists of neurons that transmit information from the periphery to the central nervous system; the efferent division consists of neurons that transmit information from the central nervous system to the periphery. The efferent division is divided into two main branches: (1) the somatic nervous system, which communicates to skeletal muscle, and (2) the autonomic nervous system, which communicates to smooth muscle, cardiac muscle, glands, and adipose tissue. • The autonomic nervous system is divided into the sympathetic and parasympathetic nervous systems. • The axon terminal transmits information • Nervous I and II, Orientation 7.2 Cells of the Nervous System, p. 198 • • The nervous system contains neurons, cells specialized for transmitting electrical impulses, and glial cells, which provide metabolic and structural support to the neurons. • Parts of a neuron include the cell body, dendrites, and the axon. • The dendrites, and to a lesser extent the cell body, receive information from other neurons at synapses. • The axon includes an axon hillock, where electrical impulses (action potentials) are initiated, and an axon terminal. • • via neurotransmitters to other neurons at synapses. Slow axonal transport or fast axonal transport are used to move products from the cell body to the axon terminal (anterograde transport) or from the axon terminal to the cell body (retrograde transport). Neurons are classified functionally into three classes: efferent neurons, afferent neurons, and interneurons. Two types of glial cells function in forming myelin around axons: (1) oligodendrocytes, in the central nervous system, and (2) Schwann cells, in the peripheral nervous system. Myelin enhances the propagation of electrical impulses by providing insulation to the axon. Nervous I and II, Anatomy Review Nervous I and II, Ion Channels Stanfield, Cindy. Principles of Human Physiology, Global Edition, Pearson Education, Limited, 2017. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/mqu/detail.action?docID=5187887. Created from mqu on 2023-08-02 08:46:07. 224 CHAPTER 7 Nerve Cells and Electrical Signaling 7.3 Establishment of the Resting Membrane Potential, p. 204 • At rest, cells have a membrane potential across them such that the inside of the cell is negatively charged relative to the outside of the cell. • The membrane potential exists because electrochemical forces encourage potassium ions to move out of the cell and sodium ions to move into the cell and because the cell membrane is more permeable to potassium ions at rest. • The resting membrane potential is close to the potassium equilibrium potential and is maintained by the Na+>K+ pump. Nervous I, The Membrane Potential • • • • Nervous II, Synaptic Potentials and Cellular Integration Resting Membrane Potential • 7.4 Electrical Signaling Through Changes in Membrane Potential, p. 209 • Changes in the membrane potential can be produced by changing the permeability of the plasma membrane to ions. • Graded potentials are small changes in membrane potential that occur in • • response to a stimulus that opens or closes ion channels. An action potential is produced when graded potentials result in a depolarization of the neuron to threshold. A single graded potential is usually not of sufficient magnitude to depolarize a neuron to threshold, but graded potentials can be temporally and/or spatially additive. Action potentials are rapid depolarizations of the plasma membrane that are propagated along axons from the trigger zone to the axon terminal. The rapid depolarization phase of an action potential is caused by the opening of sodium channels and ensuing sodium ion movement into the cell. The repolarization phase is caused by the closing of sodium channels and the opening of potassium channels, followed by potassium movement out of the cell. After-hyperpolarization occurs because potassium channels are slow in closing, allowing continued movement of potassium out of the cell for a brief time. Voltage-gated sodium channels have activation gates and inactivation gates, an arrangement that allows the channels to exist in three configurations: closed but capable of opening, open, and closed and incapable of opening. • Action potentials are all-or-none phenomena, meaning that their size does not vary with the strength of the stimulus eliciting them. • The strength of a stimulus is coded by the frequency of action potentials, with stronger stimuli producing more action potentials per unit time. • Absolute and relative refractory periods ensure the unidirectional flow of action potentials and limit the frequency of action potentials. Nervous I, The Action Potential 7.5 Maintaining Neural Stability, p. 222 • The Na+>K+ pump establishes the con- centration gradients for sodium and potassium ions, thereby generating the chemical gradients that establish the resting membrane potential. • The Na+>K+ pump also prevents dissipation of the concentration gradients by returning sodium and potassium ions that have crossed the membrane to their original sides of that membrane. EXERCISES Copyright © 2017. Pearson Education, Limited. All rights reserved. Multiple-Choice Questions 1. Depolarization of a neuron to threshold stimulates a) Opening of sodium channels. b) Delayed closing of sodium channels. c) Delayed opening of potassium channels. d) Both a and c. e) All of the above. 2. Which of the following glial cells are present in the peripheral nervous system? a) Astrocytes b) Microglia c) Oligodendrocytes d) Schwann cells 3. If a cation is equally distributed across the cell membrane (that is, its concentration inside the cell equals its concentration outside the cell), then which of the following statements is false? a) At 270 mV, the chemical force on the ion is zero. b) At 270 mV, the electrical force on the ion acts to move it into the cell. c) At 130 mV, the chemical force on the ion is zero. d) The equilibrium potential for the ion is zero. e) At 270 mV, the electrochemical force on the ion acts to move it out of the cell. 4. The depolarization phase of an action potential is caused by the a) Opening of potassium channels. b) Closing of potassium channels. c) Opening of sodium channels. d) Closing of sodium channels. 5. During the relative refractory period, a second action potential a) Cannot be elicited. b) Can be elicited by a threshold stimulus. c) Can be elicited by a subthreshold stimulus. d) Can be elicited by a suprathreshold stimulus. 6. The ganglia in the peripheral nervous system are clusters of a) Cell bodies of neurons. b) Myelin sheaths. c) Nodes of Ranvier. d) Glial cells. 7. If the membrane potential of a neuron becomes more negative than it was at rest, then the neuron is . In this state, the neuron is excitable. a) depolarized; more b) hyperpolarized; more c) depolarized; less d) hyperpolarized; less 8. Oubain is a poison that blocks the Na+>K+ pump. If this pump is blocked, then the concentration of potassium inside the cell would a) Increase. b) Decrease. c) Not change. 9. If potassium concentrations in the extracellular fluid of the brain increased, activity in the brain would a) Increase. b) Decrease. c) Not change. 10. Which of the following neurons are part of the peripheral nervous system? a) Motor neurons innervating skeletal muscles Stanfield, Cindy. Principles of Human Physiology, Global Edition, Pearson Education, Limited, 2017. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/mqu/detail.action?docID=5187887. Created from mqu on 2023-08-02 08:46:07.