Chapter 48 Neurons Synapses and Signaling Guided Reading Answers

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Biology in Focus - Chapter 37

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Biology in Focus - Chapter 37

1. 1. CAMPBELL BIOLOGY IN FOCUS © 2014 Pearson Education, Inc. Urry • Cain • Wasserman • Minorsky • Jackson • Reece Lecture Presentations by Kathleen Fitzpatrick and Nicole Tunbridge 37 Neurons, Synapses, and Signaling
2. 2. © 2014 Pearson Education, Inc. Overview: Lines of Communication  The cone snail kills prey with venom that disables neurons  Neurons are nerve cells that transfer information within the body  Neurons use two types of signals to communicate: electrical signals (long distance) and chemical signals (short distance)
3. 3. © 2014 Pearson Education, Inc. Figure 37.1
4. 4. © 2014 Pearson Education, Inc.  Interpreting signals in the nervous system involves sorting a complex set of paths and connections  Processing of information takes place in simple clusters of neurons called ganglia or a more complex organization of neurons called a brain
5. 5. © 2014 Pearson Education, Inc. Concept 37.1: Neuron structure and organization reflect function in information transfer  The neuron is a cell type that exemplifies the close fit of form and function that often arises over the course of evolution
6. 6. © 2014 Pearson Education, Inc. Neuron Structure and Function  Most of a neuron's organelles are in the cell body  Most neurons have dendrites, highly branched extensions that receive signals from other neurons  The single axon, a much longer extension, transmits signals to other cells  The cone-shaped base of an axon, where signals are generated, is called the axon hillock Video: Dendrites
7. 7. © 2014 Pearson Education, Inc. Figure 37.2 Dendrites Nucleus Stimulus Axon hillock Cell body Axon Signal direction Presynaptic cell Synapse Neurotransmitter Synaptic terminals Postsynaptic cell Synaptic terminals
8. 8. © 2014 Pearson Education, Inc.  The branched ends of axons transmit signals to other cells at a junction called the synapse  At most synapses, chemical messengers called neurotransmitters pass information from the transmitting neuron to the receiving cell
9. 9. © 2014 Pearson Education, Inc.  Neurons of vertebrates and most invertebrates require supporting cells called glial cells  In the mammalian brain, glia outnumber neurons 10- to 50-fold
10. 10. © 2014 Pearson Education, Inc. Figure 37.3 Cell bodies of neurons Glia 80 µm
11. 11. © 2014 Pearson Education, Inc. Introduction to Information Processing  Nervous systems process information in three stages  Sensory input  Integration  Motor output
12. 12. © 2014 Pearson Education, Inc. Figure 37.4 Sensory input Motor output Sensor Effector Processing center Integration
13. 13. © 2014 Pearson Education, Inc.  Sensory neurons transmit information from eyes and other sensors that detect external stimuli or internal conditions  This information is sent to the brain or ganglia, where interneurons integrate the information  Neurons that extend out of the processing centers trigger muscle or gland activity  For example, motor neurons transmit signals to muscle cells, causing them to contract
14. 14. © 2014 Pearson Education, Inc.  In many animals, neurons that carry out integration are organized in a central nervous system (CNS)  The neurons that carry information into and out of the CNS form the peripheral nervous system (PNS)  PNS neurons, bundled together, form nerves
15. 15. © 2014 Pearson Education, Inc. Figure 37.5 Dendrites Axon Cell body Portion of axon InterneuronsSensory neuron Motor neuron
16. 16. © 2014 Pearson Education, Inc. Concept 37.2: Ion pumps and ion channels establish the resting potential of a neuron  The inside of a cell is negatively charged relative to the outside  This difference is a source of potential energy, termed membrane potential  The resting potential is the membrane potential of a neuron not sending signals  Changes in membrane potential act as signals, transmitting and processing information
17. 17. © 2014 Pearson Education, Inc. Formation of the Resting Potential  K+ and Na+ play an essential role in forming the resting potential  In most neurons, the concentration of K+ is highest inside the cell, while the concentration of Na+ is highest outside the cell  Sodium-potassium pumps use the energy of ATP to maintain these K+ and Na+ gradients across the plasma membrane Animation: Resting Potential
18. 18. © 2014 Pearson Education, Inc. Table 37.1
19. 19. © 2014 Pearson Education, Inc. Figure 37.6 OUTSIDE OF CELL INSIDE OF CELL Key Na+ K+ Sodium- potassium pump Potassium channel Sodium channel
20. 20. © 2014 Pearson Education, Inc.  The opening of ion channels in the plasma membrane converts the chemical potential energy of the ion gradients to electrical potential energy  Ion channels are selectively permeable, allowing only certain ions to pass through  A resting neuron has many open potassium channels, allowing K+ to flow out  The resulting buildup of negative charge within the neuron is the major source of membrane potential
21. 21. © 2014 Pearson Education, Inc. Modeling the Resting Potential  Resting potential can be modeled by an artificial membrane that separates two chambers  The concentration of KCl is higher in the inner chamber and lower in the outer chamber  K+ diffuses down its gradient to the outer chamber  Negative charge (Cl− ) builds up in the inner chamber  At equilibrium, both the electrical and chemical gradients are balanced
22. 22. © 2014 Pearson Education, Inc. Figure 37.7 Inner chamber Outer chamber 140 mM KCI 5 mM KCI −90 mV Inner chamber Outer chamber 15 mM NaCI 150 mM NaCI +62 mV Cl− Cl−Potassium channel Artificial membrane K+ Na+ Sodium channel (b) Membrane selectively permeable to Na+ (a) Membrane selectively permeable to K+ EK = 62 mV = −90 mVlog 5 mM 140 mM ENa = 62 mV = +62 mVlog 150 mM 15 mM
23. 23. © 2014 Pearson Education, Inc.  The equilibrium potential (Eion) is the membrane voltage for a particular ion at equilibrium and can be calculated using the Nernst equation  The equilibrium potential for K+ is −90 mV  The resting potential of an actual neuron is about −60 to −80 mV because a small amount of Na+ diffuses into the cell
24. 24. © 2014 Pearson Education, Inc.  In a resting neuron, the currents of K+ and Na+ are equal and opposite, and the resting potential across the membrane remains steady
25. 25. © 2014 Pearson Education, Inc. Concept 37.3: Action potentials are the signals conducted by axons  Researchers can record the changes in membrane potential when a neuron responds to a stimulus  Changes in membrane potential occur because neurons contain gated ion channels that open or close in response to stimuli
26. 26. © 2014 Pearson Education, Inc. Figure 37.8 Voltage recorder Microelectrode Technique Reference electrode
27. 27. © 2014 Pearson Education, Inc. Figure 37.9 Ions Change in membrane potential (voltage) (b) Gate open: Ions flow through channel. a) Gate closed: No ions flow across membrane. Ion channel
28. 28. © 2014 Pearson Education, Inc.  When gated K+ channels open, K+ diffuses out, making the inside of the cell more negative  This is hyperpolarization, an increase in magnitude of the membrane potential Hyperpolarization and Depolarization
29. 29. © 2014 Pearson Education, Inc. Figure 37.10 (a) Graded hyperpolarizations produced by two stimuli that increase membrane permeability to K+ (b) Graded depolarizations produced by two stimuli that increase membrane permeability to Na+ (c) Action potential triggered by a depolarization that reaches the threshold Resting potential Time (msec) 0 1 2 3 4 5 6 Threshold −100 −50 0 +50 Membranepotential(mV) Action potential Strong depolarizing stimulus Resting potential Time (msec) 0 1 2 3 4 5 Threshold −100 −50 0 +50 Membranepotential(mV) Stimulus Depolarizations Resting potential Time (msec) 0 1 2 3 4 5 Threshold −100 −50 0 +50 Membranepotential(mV) Stimulus Hyperpolarizations
30. 30. © 2014 Pearson Education, Inc. Figure 37.10a (a) Graded hyperpolarizations produced by two stimuli that increase membrane permeability to K+ Resting potential Time (msec) 0 1 2 3 4 5 Threshold −100 −50 0 +50 Membranepotential(mV) Stimulus Hyperpolarizations
31. 31. © 2014 Pearson Education, Inc.  Opening other types of ion channels triggers a depolarization, a reduction in the magnitude of the membrane potential  For example, depolarization occurs if gated Na+ channels open and Na+ diffuses into the cell
32. 32. © 2014 Pearson Education, Inc. Figure 37.10b (b) Graded depolarizations produced by two stimuli that increase membrane permeability to Na+ Resting potential Time (msec) 0 1 2 3 4 5 Threshold −100 −50 0 +50 Membranepotential(mV) Stimulus Depolarizations
33. 33. © 2014 Pearson Education, Inc.  Graded potentials are changes in polarization where the magnitude of the change varies with the strength of the stimulus  Graded potentials decay with distance from the source Graded Potentials and Action Potentials
34. 34. © 2014 Pearson Education, Inc.  If a depolarization shifts the membrane potential sufficiently, it results in a massive change in membrane voltage, called an action potential  Action potentials have a constant magnitude and transmit signals over long distances  They arise because some ion channels are voltage gated, opening or closing when the membrane potential passes a certain level
35. 35. © 2014 Pearson Education, Inc.  Action potentials occur whenever a depolarization increases the membrane potential to a particular value, called the threshold  Action potentials are all or none
36. 36. © 2014 Pearson Education, Inc. Figure 37.10c (c) Action potential triggered by a depolarization that reaches the threshold Resting potential Time (msec) 0 1 2 3 4 5 Threshold −100 −50 0 +50 Membranepotential(mV) Strong depolarizing stimulus Action potential
37. 37. © 2014 Pearson Education, Inc. Generation of Action Potentials: A Closer Look  An action potential can be considered as a series of stages  At resting potential 1. Most voltage-gated sodium (Na+ ) channels are closed; most of the voltage-gated potassium (K+ ) channels are also closed Animation: Action Potential Animation: How Neurons Work
38. 38. © 2014 Pearson Education, Inc. 1 Figure 37.11 Key Na+ K+ Action potential Threshold Resting potential Time −100 −50 0 +50 Membranepotential (mV) Rising phase of the action potential Depolarization Falling phase of the action potential Resting state Undershoot Sodium channel Potassium channel Inactivation loop OUTSIDE OF CELL INSIDE OF CELL 1 5 4 3 2 1 5 42 3
39. 39. © 2014 Pearson Education, Inc. Figure 37.11a Key Na+ K+ Resting state Sodium channel Potassium channel Inactivation loop OUTSIDE OF CELL INSIDE OF CELL 1
40. 40. © 2014 Pearson Education, Inc.  When stimulus depolarizes the membrane 2. Some gated Na+ channels open first and Na+ flows into the cell 3. During the rising phase, the threshold is crossed, and the membrane potential increases 4. During the falling phase, voltage-gated Na+ channels become inactivated; voltage-gated K+ channels open, and K+ flows out of the cell
41. 41. © 2014 Pearson Education, Inc. Figure 37.11b Depolarization2 Key Na+ K+
42. 42. © 2014 Pearson Education, Inc. Figure 37.11c 3 Key Na+ K+ Rising phase of the action potential
43. 43. © 2014 Pearson Education, Inc. Figure 37.11d 4 Key Na+ K+ Falling phase of the action potential
44. 44. © 2014 Pearson Education, Inc. 5. During the undershoot, membrane permeability to K+ is at first higher than at rest, and then voltage-gated K+ channels close and resting potential is restored
45. 45. © 2014 Pearson Education, Inc. Figure 37.11e 5 Key Na+ K+ Undershoot
46. 46. © 2014 Pearson Education, Inc. Figure 37.11f 5 Action potential Threshold Resting potential Time −100 Membranepotential (mV) −50 0 +50 11 2 3 4
47. 47. © 2014 Pearson Education, Inc.  During the refractory period after an action potential, a second action potential cannot be initiated  The refractory period is a result of a temporary inactivation of the Na+ channels  For most neurons, the interval between the start of an action potential and the end of the refractory period is only 1–2 msec
48. 48. © 2014 Pearson Education, Inc. Conduction of Action Potentials  At the site where the action potential is initiated (usually the axon hillock), an electrical current depolarizes the neighboring region of the axon membrane  Action potentials travel only toward the synaptic terminals  Inactivated Na+ channels behind the zone of depolarization prevent the action potential from traveling backward
49. 49. © 2014 Pearson Education, Inc. Figure 37.12-1 Axon Plasma membrane Cytosol Action potential Na+ 11
50. 50. © 2014 Pearson Education, Inc. Figure 37.12-2 Axon Plasma membrane Cytosol Action potential Action potential K+ K+ Na+ Na+ 11 2
51. 51. © 2014 Pearson Education, Inc. Figure 37.12-3 Axon Plasma membrane Cytosol Action potential Action potential Action potential K+ K+ K+ K+ Na+ Na+ Na+ 1 2 3
52. 52. © 2014 Pearson Education, Inc. Evolutionary Adaptations of Axon Structure  The speed of an action potential increases with the axon's diameter  In vertebrates, axons are insulated by a myelin sheath, which enables fast conduction of action potentials  Myelin sheaths are produced by glia— oligodendrocytes in the CNS and Schwann cells in the PNS
53. 53. © 2014 Pearson Education, Inc. Figure 37.13 Axon Myelin sheath Schwann cell Nodes of Ranvier Nucleus of Schwann cell Schwann cell Node of Ranvier Layers of myelin Axon 0.1 µm
54. 54. © 2014 Pearson Education, Inc. Figure 37.13a 0.1 µm
55. 55. © 2014 Pearson Education, Inc.  Action potentials are formed only at nodes of Ranvier, gaps in the myelin sheath where voltage- gated Na+ channels are found  Action potentials in myelinated axons jump between the nodes of Ranvier in a process called saltatory conduction  A selective advantage of myelination is space efficiency
56. 56. © 2014 Pearson Education, Inc. Figure 37.14 Cell body Schwann cell Depolarized region (node of Ranvier) Myelin sheath Axon
57. 57. © 2014 Pearson Education, Inc. Concept 37.4: Neurons communicate with other cells at synapses  At electrical synapses, the electrical current flows from one neuron to another  Most synapses are chemical synapses, in which a chemical neurotransmitter carries information from the presynaptic neuron to the postsynaptic cell
58. 58. © 2014 Pearson Education, Inc.  The presynaptic neuron synthesizes and packages the neurotransmitter in synaptic vesicles located in the synaptic terminal  The arrival of the action potential causes the release of the neurotransmitter  The neurotransmitter diffuses across the synaptic cleft and is received by the postsynaptic cell Animation: Synapse Animation: How Synapses Work
59. 59. © 2014 Pearson Education, Inc. Figure 37.15 Presynaptic cell Postsynaptic cell Axon Synaptic vesicle containing neurotransmitter Synaptic cleft Postsynaptic membrane Ca2+ K+ Na+ Ligand-gated ion channels Voltage-gated Ca2+ channel Presynaptic membrane 1 2 3 4
60. 60. © 2014 Pearson Education, Inc. Generation of Postsynaptic Potentials  Direct synaptic transmission involves binding of neurotransmitters to ligand-gated ion channels in the postsynaptic cell  Neurotransmitter binding causes ion channels to open, generating a postsynaptic potential
61. 61. © 2014 Pearson Education, Inc.  Postsynaptic potentials fall into two categories  Excitatory postsynaptic potentials (EPSPs) are depolarizations that bring the membrane potential toward threshold  Inhibitory postsynaptic potentials (IPSPs) are hyperpolarizations that move the membrane potential farther from threshold
62. 62. © 2014 Pearson Education, Inc.  The duration of postsynaptic potential is limited by rapidly clearing neurotransmitter molecules from the synaptic cleft  Some neurotransmitters are recaptured into presynaptic neurons to be repackaged into synaptic vesicles  Some are recaptured into glia to be used as fuel or recycled to neurons  Others are removed by simple diffusion or hydrolysis of the neurotransmitter
63. 63. © 2014 Pearson Education, Inc. Summation of Postsynaptic Potentials  The cell body of one postsynaptic neuron may receive inputs from hundreds or thousands of synaptic terminals  A single EPSP is usually too small to trigger an action potential in a postsynaptic neuron
64. 64. © 2014 Pearson Education, Inc. Figure 37.16 Postsynaptic neuron Synaptic terminals of pre- synaptic neurons 5µm
65. 65. © 2014 Pearson Education, Inc. Figure 37.17 Terminal branch of presynaptic neuron Postsynaptic neuron Axon hillock E1 E2 E2 E1 E1 E2 II I E1 E2 I Threshold of axon of postsynaptic neuron Resting potential Membranepotential(mV) E1 E1 E1 E1 Action potential −70 0 (a) Subthreshold, no summation (b) Temporal summation (c) Spatial summation Action potential E1 + E2 E1 + IE1 I (d) Spatial summation of EPSP and IPSP
66. 66. © 2014 Pearson Education, Inc. Figure 37.17a Terminal branch of presynaptic neuron Postsynaptic neuron Axon hillock E1 E2 E2 E1 II Threshold of axon of postsynaptic neuron Resting potential Membranepotential(mV) E1 E1 E1 E1 Action potential −70 0 (a) Subthreshold, no summation (b) Temporal summation
67. 67. © 2014 Pearson Education, Inc.  If two EPSPs are produced in rapid succession, an effect called temporal summation occurs
68. 68. © 2014 Pearson Education, Inc.  In spatial summation, EPSPs produced nearly simultaneously by different synapses on the same postsynaptic neuron add together  The combination of EPSPs through spatial and temporal summation can trigger an action potential
69. 69. © 2014 Pearson Education, Inc. Figure 37.17b E1 E2 I E1 E2 I (c) Spatial summation Action potential E1 + E2 E1 + IE1 I (d) Spatial summation of EPSP and IPSP Terminal branch of presynaptic neuron Postsynaptic neuron Membranepotential(mV) −70 0
70. 70. © 2014 Pearson Education, Inc.  Through summation, an IPSP can counter the effect of an EPSP  The summed effect of EPSPs and IPSPs determines whether an axon hillock will reach threshold and generate an action potential
71. 71. © 2014 Pearson Education, Inc. Modulated Signaling at Synapses  In some synapses, a neurotransmitter binds to a receptor that is metabotropic  In this case, movement of ions through a channel depends on one or more metabolic steps
72. 72. © 2014 Pearson Education, Inc.  Binding of a neurotransmitter to a metabotropic receptor activates a signal transduction pathway in the postsynaptic cell involving a second messenger  Compared to ligand-gated channels, the effects of second-messenger systems have a slower onset but last longer
73. 73. © 2014 Pearson Education, Inc. Neurotransmitters  Signaling at a synapse brings about a response that depends on both the neurotransmitter from the presynaptic cell and the receptor on the postsynaptic cell  A single neurotransmitter may have more than a dozen different receptors  Acetylcholine is a common neurotransmitter in both invertebrates and vertebrates
74. 74. © 2014 Pearson Education, Inc. Acetylcholine  Acetylcholine is vital for functions involving muscle stimulation, memory formation, and learning  Vertebrates have two major classes of acetylcholine receptor, one that is ligand gated and one that is metabotropic
75. 75. © 2014 Pearson Education, Inc.  The best understood function of the ligand-gated ion channel is in the vertebrate neuromuscular junction  When acetylcholine released by motor neurons binds to this receptor, the ion channel opens and an EPSP is generated  This receptor is also found elsewhere in the PNS and in the CNS
76. 76. © 2014 Pearson Education, Inc.  A number of toxins disrupt neurotransmission by acetylcholine  These include the nerve gas sarin and a bacterial toxin that causes botulism  Acetylcholine is one of more than 100 known neurotransmitters
77. 77. © 2014 Pearson Education, Inc. Table 37.2
78. 78. © 2014 Pearson Education, Inc. Table 37.2a
79. 79. © 2014 Pearson Education, Inc. Table 37.2b
80. 80. © 2014 Pearson Education, Inc. Table 37.2c
81. 81. © 2014 Pearson Education, Inc. Amino Acids  Glutamate (rather than acetylcholine) is used at the neuromuscular junction in invertebrates  Gamma-aminobutyric acid (GABA) is the neurotransmitter at most inhibitory synapses in the brain  Glycine also acts at inhibitory synapses in the CNS that lies outside of the brain
82. 82. © 2014 Pearson Education, Inc. Biogenic Amines  Biogenic amines include  Norepinephrine and the chemically similar ephinephrine  Dopamine  Serotonin  They are active in the CNS and PNS  Biogenic amines have a central role in a number of nervous system disorders and treatments
83. 83. © 2014 Pearson Education, Inc. Neuropeptides  Several neuropeptides, relatively short chains of amino acids, also function as neurotransmitters  Neuropeptides include substance P and endorphins, which both affect our perception of pain  Opiates bind to the same receptors as endorphins and produce the same physiological effects
84. 84. © 2014 Pearson Education, Inc. Gases  Gases such as nitric oxide (NO) and carbon monoxide (CO) are local regulators in the PNS  Unlike most neurotransmitters, these are not stored in vesicles but are instead synthesized as needed
85. 85. © 2014 Pearson Education, Inc. Figure 37.UN01a Radioactive naloxone Drug Proteins are trapped on a filter. Bound naloxone is detected by measuring radioactivity. Radioactive naloxone and a test drug are incubated with a protein mixture. 1 2
86. 86. © 2014 Pearson Education, Inc. Figure 37.UN01b
87. 87. © 2014 Pearson Education, Inc. Figure 37.UN02 Axon hillock Axon Synapse Postsynaptic cell Signal direction Cell body Dendrites Presynaptic cell
88. 88. © 2014 Pearson Education, Inc. Figure 37.UN03 Action potential Falling phase Rising phase Threshold (−55) UndershootDepolarization Time (msec) 0 1 2 3 4 5 6 −100 −70 −50 0 +50 Membranepotential(mV) Resting potential
89. 89. © 2014 Pearson Education, Inc. Figure 37.UN04 Electrode Squid axon

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Biology in Focus - Chapter 37 - Neurons, Synapses. and Signaling

Chapter 48 Neurons Synapses and Signaling Guided Reading Answers

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