1. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Lectures by Chris Romero Chapter 48 Nervous Systems

2. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Overview: Command and Control Center The human brain – Contains an estimated 100 billion nerve cells, or neurons Each neuron – May communicate with thousands of other neurons

3. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Functional magnetic resonance imaging – Is a technology that can reconstruct a three- dimensional map of brain activity Figure 48.1

4. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The results of brain imaging and other research methods – Reveal that groups of neurons function in specialized circuits dedicated to different tasks

5. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 48.1: Nervous systems consist of circuits of neurons and supporting cells All animals except sponges – Have some type of nervous system What distinguishes the nervous systems of different animal groups – Is how the neurons are organized into circuits

6. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Organization of Nervous Systems The simplest animals with nervous systems, the cnidarians – Have neurons arranged in nerve nets Figure 48.2a Nerve net (a) Hydra (cnidarian)

7. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Sea stars have a nerve net in each arm – Connected by radial nerves to a central nerve ring Figure 48.2b Nerve ring Radial nerve (b) Sea star (echinoderm)

8. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings In relatively simple cephalized animals, such as flatworms – A central nervous system (CNS) is evident Figure 48.2c Eyespot Brain Nerve cord Transverse nerve (c) Planarian (flatworm)

9. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Annelids and arthropods – Have segmentally arranged clusters of neurons called ganglia These ganglia connect to the CNS – And make up a peripheral nervous system (PNS) Brain Ventral nerve cord Segmental ganglion Brain Ventral nerve cord Segmental ganglia Figure 48.2d, e (d) Leech (annelid)(e) Insect (arthropod)

10. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Anterior nerve ring Longitudinal nerve cords Ganglia Brain Ganglia Figure 48.2f, g (f) Chiton (mollusc) (g) Squid (mollusc) Nervous systems in molluscs – Correlate with the animals’ lifestyles Sessile molluscs have simple systems – While more complex molluscs have more sophisticated systems

11. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings In vertebrates – The central nervous system consists of a brain and dorsal spinal cord – The PNS connects to the CNS Figure 48.2h Brain Spinal cord (dorsal nerve cord) Sensory ganglion (h) Salamander (chordate)

12. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Information Processing Nervous systems process information in three stages – Sensory input, integration, and motor output Figure 48.3 Sensor Effector Motor output Integration Sensory input Peripheral nervous system (PNS) Central nervous system (CNS)

13. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Sensory neurons transmit information from sensors – That detect external stimuli and internal conditions Sensory information is sent to the CNS – Where interneurons integrate the information Motor output leaves the CNS via motor neurons – Which communicate with effector cells

14. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The three stages of information processing – Are illustrated in the knee-jerk reflex Figure 48.4 Sensory neurons from the quadriceps also communicate with interneurons in the spinal cord. The interneurons inhibit motor neurons that supply the hamstring (flexor) muscle. This inhibition prevents the hamstring from contracting, which would resist the action of the quadriceps. The sensory neurons communicate with motor neurons that supply the quadriceps. The motor neurons convey signals to the quadriceps, causing it to contract and jerking the lower leg forward. 4 5 6 The reflex is initiated by tapping the tendon connected to the quadriceps (extensor) muscle. 1 Sensors detect a sudden stretch in the quadriceps. 2 Sensory neurons convey the information to the spinal cord. 3 Quadriceps muscle Hamstring muscle Spinal cord (cross section) Gray matter White matter Cell body of sensory neuron in dorsal root ganglion Sensory neuron Motor neuron Interneuron

15. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Neuron Structure Most of a neuron’s organelles – Are located in the cell body Figure 48.5 Dendrites Cell body Nucleus Axon hillock Axon Signal direction Synapse Myelin sheath Synaptic terminals Presynaptic cell Postsynaptic cell

16. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Most neurons have dendrites – Highly branched extensions that receive signals from other neurons The axon is typically a much longer extension – That transmits signals to other cells at synapses – That may be covered with a myelin sheath

17. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Neurons have a wide variety of shapes – That reflect their input and output interactions Figure 48.6a–c Axon Cell body Dendrites (a) Sensory neuron (b) Interneurons (c) Motor neuron

18. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Supporting Cells (Glia) Glia are supporting cells – That are essential for the structural integrity of the nervous system and for the normal functioning of neurons

19. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings In the CNS, astrocytes – Provide structural support for neurons and regulate the extracellular concentrations of ions and neurotransmitters Figure 48.7 50 µm

20. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Oligodendrocytes (in the CNS) and Schwann cells (in the PNS) – Are glia that form the myelin sheaths around the axons of many vertebrate neurons Myelin sheath Nodes of Ranvier Schwann cell Schwann cell Nucleus of Schwann cell Axon Layers of myelin Node of Ranvier 0.1 µm Axon Figure 48.8

21. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 48.2: Ion pumps and ion channels maintain the resting potential of a neuron Across its plasma membrane, every cell has a voltage – Called a membrane potential The inside of a cell is negative – Relative to the outside

22. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The membrane potential of a cell can be measured Figure 48.9 APPLICATION Electrophysiologists use intracellular recording to measure the membrane potential of neurons and other cells. TECHNIQUE A microelectrode is made from a glass capillary tube filled with an electrically conductive salt solution. One end of the tube tapers to an extremely fine tip (diameter < 1 µm). While looking through a microscope, the experimenter uses a micropositioner to insert the tip of the microelectrode into a cell. A voltage recorder (usually an oscilloscope or a computer-based system) measures the voltage between the microelectrode tip inside the cell and a reference electrode placed in the solution outside the cell. Microelectrode Reference electrode Voltage recorder –70 mV

23. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Resting Potential The resting potential – Is the membrane potential of a neuron that is not transmitting signals

24. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings In all neurons, the resting potential – Depends on the ionic gradients that exist across the plasma membrane CYTOSOL EXTRACELLULAR FLUID [Na + ] 15 mM [K + ] 150 mM [Cl – ] 10 mM [A – ] 100 mM [Na + ] 150 mM [K + ] 5 mM [Cl – ] 120 mM – – – – – + + + + + Plasma membrane Figure 48.10

25. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The concentration of Na + is higher in the extracellular fluid than in the cytosol – While the opposite is true for K +

26. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings By modeling a mammalian neuron with an artificial membrane – We can gain a better understanding of the resting potential of a neuron Figure 48.11a, b Inner chamber Outer chamber Inner chamber Outer chamber –92 mV+62 mV Artificial membrane Potassium channel K+K+ Cl – 150 mM KCL 150 mM NaCl 15 mM NaCl 5 mM KCL Cl – Na + Sodium channel + – (a) Membrane selectively permeable to K + (b) Membrane selectively permeable to Na +

27. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings A neuron that is not transmitting signals – Contains many open K + channels and fewer open Na + channels in its plasma membrane The diffusion of K + and Na + through these channels – Leads to a separation of charges across the membrane, producing the resting potential

28. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Gated Ion Channels Gated ion channels open or close – In response to membrane stretch or the binding of a specific ligand – In response to a change in the membrane potential

29. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 48.3: Action potentials are the signals conducted by axons If a cell has gated ion channels – Its membrane potential may change in response to stimuli that open or close those channels

30. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Some stimuli trigger a hyperpolarization – An increase in the magnitude of the membrane potential Figure 48.12a +50 0 –50 –100 Time (msec) 0 1 2 3 4 5 Threshold Resting potential Hyperpolarizations Membrane potential (mV) Stimuli (a) Graded hyperpolarizations produced by two stimuli that increase membrane permeability to K +. The larger stimulus produces a larger hyperpolarization.

31. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Other stimuli trigger a depolarization – A reduction in the magnitude of the membrane potential Figure 48.12b +50 0 –50 –100 Time (msec) 0 1 2 3 4 5 Threshold Resting potential Depolarizations Membrane potential (mV) Stimuli (b) Graded depolarizations produced by two stimuli that increase membrane permeability to Na+. The larger stimulus produces a larger depolarization.

32. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Hyperpolarization and depolarization – Are both called graded potentials because the magnitude of the change in membrane potential varies with the strength of the stimulus

33. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Production of Action Potentials In most neurons, depolarizations – Are graded only up to a certain membrane voltage, called the threshold

34. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings A stimulus strong enough to produce a depolarization that reaches the threshold – Triggers a different type of response, called an action potential Figure 48.12c +50 0 –50 –100 Time (msec) 0 1 2 3 4 5 6 Threshold Resting potential Membrane potential (mV) Stronger depolarizing stimulus Action potential (c) Action potential triggered by a depolarization that reaches the threshold.

35. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings An action potential – Is a brief all-or-none depolarization of a neuron’s plasma membrane – Is the type of signal that carries information along axons

36. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Both voltage-gated Na + channels and voltage- gated K + channels – Are involved in the production of an action potential When a stimulus depolarizes the membrane – Na + channels open, allowing Na + to diffuse into the cell

37. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings As the action potential subsides – K + channels open, and K + flows out of the cell A refractory period follows the action potential – During which a second action potential cannot be initiated

38. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The generation of an action potential – – – – + + + + + – + – + – + – + – + – + – + – + – + – + – + – + – + – + – + – + Na + K+K+ K+K+ K+K+ K+K+ K+K+ 5 1 Resting state 2 Depolarization 3 Rising phase of the action potential 4 Falling phase of the action potential Undershoot 1 2 3 4 5 1 Sodium channel Action potential Resting potential Time Plasma membrane Extracellular fluid Activation gates Potassium channel Inactivation gate Threshold Membrane potential (mV) +50 0 –50 –100 Threshold Cytosol Figure 48.13 Depolarization opens the activation gates on most Na + channels, while the K + channels’ activation gates remain closed. Na + influx makes the inside of the membrane positive with respect to the outside. The inactivation gates on most Na + channels close, blocking Na + influx. The activation gates on most K + channels open, permitting K + efflux which again makes the inside of the cell negative. A stimulus opens the activation gates on some Na + channels. Na + influx through those channels depolarizes the membrane. If the depolarization reaches the threshold, it triggers an action potential. The activation gates on the Na + and K + channels are closed, and the membrane’s resting potential is maintained. Both gates of the Na + channels are closed, but the activation gates on some K + channels are still open. As these gates close on most K + channels, and the inactivation gates open on Na + channels, the membrane returns to its resting state.

39. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Conduction of Action Potentials An action potential can travel long distances – By regenerating itself along the axon

40. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 48.14 – + – + + ++ + – + – + + ++ + + – + –+++ + + – + – +++ + + – + – – –– – + – + – – –– – –– – – –– – – –– –– + + ++ + + + + – – – – + + + + – –– – – – – – ++ ++ –– – – ++ ++ Na + Action potential K+K+ K+K+ K+K+ Axon An action potential is generated as Na + flows inward across the membrane at one location. 1 2 The depolarization of the action potential spreads to the neighboring region of the membrane, re-initiating the action potential there. To the left of this region, the membrane is repolarizing as K + flows outward. 3 The depolarization-repolarization process is repeated in the next region of the membrane. In this way, local currents of ions across the plasma membrane cause the action potential to be propagated along the length of the axon. K+K+ At the site where the action potential is generated, usually the axon hillock – An electrical current depolarizes the neighboring region of the axon membrane

41. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Conduction Speed The speed of an action potential – Increases with the diameter of an axon In vertebrates, axons are myelinated – Also causing the speed of an action potential to increase

42. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Action potentials in myelinated axons – Jump between the nodes of Ranvier in a process called saltatory conduction Cell body Schwann cell Myelin sheath Axon Depolarized region (node of Ranvier) + + + + – – – – – – Figure 48.15

43. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 48.4: Neurons communicate with other cells at synapses In an electrical synapse – Electrical current flows directly from one cell to another via a gap junction The vast majority of synapses – Are chemical synapses

44. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings In a chemical synapse, a presynaptic neuron – Releases chemical neurotransmitters, which are stored in the synaptic terminal Figure 48.16 Postsynaptic neuron Synaptic terminal of presynaptic neurons 5 µm

45. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings When an action potential reaches a terminal – The final result is the release of neurotransmitters into the synaptic cleft Figure 48.17 Presynaptic cell Postsynaptic cell Synaptic vesicles containing neurotransmitter Presynaptic membrane Postsynaptic membrane Voltage-gated Ca 2+ channel Synaptic cleft Ligand-gated ion channels Na + K+K+ Ligand- gated ion channel Postsynaptic membrane Neuro- transmitter 1Ca 2+ 2 3 4 5 6

46. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Direct Synaptic Transmission The process of direct synaptic transmission – Involves the binding of neurotransmitters to ligand-gated ion channels

47. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Neurotransmitter binding – Causes the ion channels to open, generating a postsynaptic potential

48. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Postsynaptic potentials fall into two categories – Excitatory postsynaptic potentials (EPSPs) – Inhibitory postsynaptic potentials (IPSPs)

49. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings After its release, the neurotransmitter – Diffuses out of the synaptic cleft – May be taken up by surrounding cells and degraded by enzymes

50. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Summation of Postsynaptic Potentials Unlike action potentials – Postsynaptic potentials are graded and do not regenerate themselves

51. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Since most neurons have many synapses on their dendrites and cell body – A single EPSP is usually too small to trigger an action potential in a postsynaptic neuron Figure 48.18a E1E1 E1E1 Resting potential Threshold of axon of postsynaptic neuron (a) Subthreshold, no summation Terminal branch of presynaptic neuron Postsynaptic neuron E1E1 0 –70 Membrane potential (mV)

52. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings If two EPSPs are produced in rapid succession – An effect called temporal summation occurs Figure 48.18b E1E1 E1E1 Action potential (b) Temporal summation E1E1 Axon hillock

53. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings In spatial summation – EPSPs produced nearly simultaneously by different synapses on the same postsynaptic neuron add together Figure 48.18c E 1 + E 2 Action potential (c) Spatial summation E1E1 E2E2

54. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Through summation – An IPSP can counter the effect of an EPSP Figure 48.18d E1E1 E 1 + I I (d) Spatial summation of EPSP and IPSP E1E1 I

55. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Indirect Synaptic Transmission In indirect synaptic transmission – A neurotransmitter binds to a receptor that is not part of an ion channel This binding activates a signal transduction pathway – Involving a second messenger in the postsynaptic cell, producing a slowly developing but long-lasting effect

56. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Neurotransmitters The same neurotransmitter – Can produce different effects in different types of cells

57. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Major neurotransmitters Table 48.1

58. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Acetylcholine – Is one of the most common neurotransmitters in both vertebrates and invertebrates – Can be inhibitory or excitatory

59. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Biogenic Amines Biogenic amines – Include epinephrine, norepinephrine, dopamine, and serotonin – Are active in the CNS and PNS

60. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Amino Acids and Peptides Various amino acids and peptides – Are active in the brain

61. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Gases Gases such as nitric oxide and carbon monoxide – Are local regulators in the PNS

62. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 48.5: The vertebrate nervous system is regionally specialized In all vertebrates, the nervous system – Shows a high degree of cephalization and distinct CNS and PNS components Figure 48.19 Central nervous system (CNS) Peripheral nervous system (PNS) Brain Spinal cord Cranial nerves Ganglia outside CNS Spinal nerves

63. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The brain provides the integrative power – That underlies the complex behavior of vertebrates The spinal cord integrates simple responses to certain kinds of stimuli – And conveys information to and from the brain

64. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The central canal of the spinal cord and the four ventricles of the brain – Are hollow, since they are derived from the dorsal embryonic nerve cord Gray matter White matter Ventricles Figure 48.20

65. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Peripheral Nervous System The PNS transmits information to and from the CNS – And plays a large role in regulating a vertebrate’s movement and internal environment

66. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The cranial nerves originate in the brain – And terminate mostly in organs of the head and upper body The spinal nerves originate in the spinal cord – And extend to parts of the body below the head

67. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The PNS can be divided into two functional components – The somatic nervous system and the autonomic nervous system Peripheral nervous system Somatic nervous system Autonomic nervous system Sympathetic division Parasympathetic division Enteric division Figure 48.21

68. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The somatic nervous system – Carries signals to skeletal muscles The autonomic nervous system – Regulates the internal environment, in an involuntary manner – Is divided into the sympathetic, parasympathetic, and enteric divisions

69. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The sympathetic and parasympathetic divisions – Have antagonistic effects on target organs Parasympathetic divisionSympathetic division Action on target organs: Location of preganglionic neurons: brainstem and sacral segments of spinal cord Neurotransmitter released by preganglionic neurons: acetylcholine Location of postganglionic neurons: in ganglia close to or within target organs Neurotransmitter released by postganglionic neurons: acetylcholine Constricts pupil of eye Stimulates salivary gland secretion Constricts bronchi in lungs Slows heart Stimulates activity of stomach and intestines Stimulates activity of pancreas Stimulates gallbladder Promotes emptying of bladder Promotes erection of genitalia Cervical Thoracic Lumbar Synapse Sympathetic ganglia Dilates pupil of eye Inhibits salivary gland secretion Relaxes bronchi in lungs Accelerates heart Inhibits activity of stomach and intestines Inhibits activity of pancreas Stimulates glucose release from liver; inhibits gallbladder Stimulates adrenal medulla Inhibits emptying of bladder Promotes ejaculation and vaginal contractions Sacral Location of preganglionic neurons: thoracic and lumbar segments of spinal cord Neurotransmitter released by preganglionic neurons: acetylcholine Location of postganglionic neurons: some in ganglia close to target organs; others in a chain of ganglia near spinal cord Neurotransmitter released by postganglionic neurons: norepinephrine Figure 48.22

70. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The sympathetic division – Correlates with the “fight-or-flight” response The parasympathetic division – Promotes a return to self-maintenance functions The enteric division – Controls the activity of the digestive tract, pancreas, and gallbladder

71. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Embryonic Development of the Brain In all vertebrates – The brain develops from three embryonic regions: the forebrain, the midbrain, and the hindbrain Figure 48.23a Forebrain Midbrain Hindbrain Midbrain Hindbrain Forebrain (a) Embryo at one month Embryonic brain regions

72. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings By the fifth week of human embryonic development – Five brain regions have formed from the three embryonic regions Figure 48.23b Telencephalon Diencephalon Mesencephalon Metencephalon Myelencephalon (b) Embryo at five weeks Mesencephalon Metencephalon Myelencephalon Spinal cord Diencephalon Telencephalon Embryonic brain regions

73. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings As a human brain develops further – The most profound change occurs in the forebrain, which gives rise to the cerebrum Figure 48.23c Brain structures present in adult Cerebrum (cerebral hemispheres; includes cerebral cortex, white matter, basal nuclei) Diencephalon (thalamus, hypothalamus, epithalamus) Midbrain (part of brainstem) Pons (part of brainstem), cerebellum Medulla oblongata (part of brainstem) (c) Adult Cerebral hemisphere Diencephalon: Hypothalamus Thalamus Pineal gland (part of epithalamus) Brainstem: Midbrain Pons Medulla oblongata Cerebellum Central canal Spinal cord Pituitary gland

74. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Brainstem The brainstem consists of three parts – The medulla oblongata, the pons, and the midbrain

75. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The medulla oblongata – Contains centers that control several visceral functions The pons – Also participates in visceral functions The midbrain – Contains centers for the receipt and integration of several types of sensory information

76. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Arousal and Sleep A diffuse network of neurons called the reticular formation – Is present in the core of the brainstem Figure 48.24 Eye Reticular formation Input from touch, pain, and temperature receptors Input from ears

77. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings A part of the reticular formation, the reticular activating system (RAS) – Regulates sleep and arousal

78. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Cerebellum The cerebellum – Is important for coordination and error checking during motor, perceptual, and cognitive functions

79. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The cerebellum – Is also involved in learning and remembering motor skills

80. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Diencephalon The embryonic diencephalon develops into three adult brain regions – The epithalamus, thalamus, and hypothalamus

81. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The epithalamus – Includes the pineal gland and the choroid plexus

82. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The thalamus – Is the main input center for sensory information going to the cerebrum and the main output center for motor information leaving the cerebrum

83. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The hypothalamus regulates – Homeostasis – Basic survival behaviors such as feeding, fighting, fleeing, and reproducing

84. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Circadian Rhythms The hypothalamus also regulates circadian rhythms – Such as the sleep/wake cycle Animals usually have a biological clock – Which is a pair of suprachiasmatic nuclei (SCN) found in the hypothalamus

85. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Biological clocks usually require external cues – To remain synchronized with environmental cycles Figure 48.25 In the northern flying squirrel (Glaucomys sabrinus), activity normally begins with the onset of darkness and ends at dawn, which suggests that light is an important external cue for the squirrel. To test this idea, researchers monitored the activity of captive squirrels for 23 days under two sets of conditions: (a) a regular cycle of 12 hours of light and 12 hours of darkness and (b) constant darkness. The squirrels were given free access to an exercise wheel and a rest cage. A recorder automatically noted when the wheel was rotating and when it was still. EXPERIMENT Light Dark Light 20 15 10 5 1 (a) 12 hr light-12 hr dark cycle (b) Constant darkness 12 16 2024 48 12 16 2024 48 12 Time of day (hr) When the squirrels were exposed to a regular light/dark cycle, their wheel-turning activity (indicated by the dark bars) occurred at roughly the same time every day. However, when they were kept in constant darkness, their activity phase began about 21 minutes later each day. RESULTS The northern flying squirrel’s internal clock can run in constant darkness, but it does so on its own cycle, which lasts about 24 hours and 21 minutes. External (light) cues keep the clock running on a 24-hour cycle. CONCLUSION Dark Days of experiment

86. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Cerebrum The cerebrum – Develops from the embryonic telencephalon

87. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The cerebrum has right and left cerebral hemispheres – That each consist of cerebral cortex overlying white matter and basal nuclei Left cerebral hemisphere Corpus callosum Neocortex Right cerebral hemisphere Basal nuclei Figure 48.26

88. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The basal nuclei – Are important centers for planning and learning movement sequences In mammals – The cerebral cortex has a convoluted surface called the neocortex

89. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings In humans, the largest and most complex part of the brain – Is the cerebral cortex, where sensory information is analyzed, motor commands are issued, and language is generated

90. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings A thick band of axons, the corpus callosum – Provides communication between the right and left cerebral cortices

91. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 48.6: The cerebral cortex controls voluntary movement and cognitive functions Each side of the cerebral cortex has four lobes – Frontal, parietal, temporal, and occipital Frontal lobe Temporal lobeOccipital lobe Parietal lobe Frontal association area Speech Smell Hearing Auditory association area Vision Visual association area Somatosensory association area Reading Speech Taste Somatosensory cortex Motor cortex Figure 48.27

92. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Each of the lobes – Contains primary sensory areas and association areas

93. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Information Processing in the Cerebral Cortex Specific types of sensory input – Enter the primary sensory areas Adjacent association areas – Process particular features in the sensory input and integrate information from different sensory areas

94. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings In the somatosensory cortex and motor cortex – Neurons are distributed according to the part of the body that generates sensory input or receives motor input Figure 48.28 Tongue Jaw Lips Face Eye Brow Neck Thumb Fingers Hand Wrist Forearm Elbow Shoulder Trunk Hip Knee Primary motor cortex Abdominal organs Pharynx Tongue Teeth Gums Jaw Lips Face Nose Eye Fingers Hand Forearm Elbow Upper arm Trunk Hip Leg Thumb Neck Head Genitalia Primary somatosensory cortex Toes Parietal lobeFrontal lobe

95. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Lateralization of Cortical Function During brain development, in a process called lateralization – Competing functions segregate and displace each other in the cortex of the left and right cerebral hemispheres

96. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The left hemisphere – Becomes more adept at language, math, logical operations, and the processing of serial sequences The right hemisphere – Is stronger at pattern recognition, nonverbal thinking, and emotional processing

97. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Language and Speech Studies of brain activity – Have mapped specific areas of the brain responsible for language and speech Figure 48.29 Hearing words Seeing words Speaking words Generating words Max Min

98. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Portions of the frontal lobe, Broca’s area and Wernicke’s area – Are essential for the generation and understanding of language

99. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Emotions The limbic system – Is a ring of structures around the brainstem Figure 48.30 Hypothalamus Thalamus Prefrontal cortex Olfactory bulb Amygdala Hippocampus

100. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings This limbic system includes three parts of the cerebral cortex – The amygdala, hippocampus, and olfactory bulb These structures interact with the neocortex to mediate primary emotions – And attach emotional “feelings” to survival- related functions

101. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Structures of the limbic system form in early development – And provide a foundation for emotional memory, associating emotions with particular events or experiences

102. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Memory and Learning The frontal lobes – Are a site of short-term memory – Interact with the hippocampus and amygdala to consolidate long-term memory

103. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Many sensory and motor association areas of the cerebral cortex – Are involved in storing and retrieving words and images

104. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cellular Mechanisms of Learning Experiments on invertebrates – Have revealed the cellular basis of some types of learning Figure 48.31a, b (a) Touching the siphon triggers a reflex that causes the gill to withdraw. If the tail is shocked just before the siphon is touched, the withdrawal reflex is stronger. This strengthening of the reflex is a simple form of learning called sensitization. (b) Sensitization involves interneurons that make synapses on the synaptic terminals of the siphon sensory neurons. When the tail is shocked, the interneurons release serotonin, which activates a signal transduction pathway that closes K + channels in the synaptic terminals of the siphon sensory neurons. As a result, action potentials in the siphon sensory neurons produce a prolonged depolarization of the terminals. That allows more Ca 2+ to diffuse into the terminals, which causes the terminals to release more of their excitatory neurotransmitter onto the gill motor neurons. In response, the motor neurons generate action potentials at a higher frequency, producing a more forceful gill withdrawal. Siphon Mantle Gill Tail Head Gill withdrawal pathway Touching the siphon Shocking the tail Tail sensory neuron Interneuron Sensitization pathway Siphon sensory neuron Gill motor neuron Gill

105. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings In the vertebrate brain, a form of learning called long-term potentiation (LTP) – Involves an increase in the strength of synaptic transmission Figure 48.32 PRESYNAPTIC NEURON NO Glutamate NMDA receptor Signal transduction pathways NO Ca 2+ AMPA receptor POSTSYNAPTIC NEURON Ca 2+ initiates the phos- phorylation of AMPA receptors, making them more responsive. Ca 2+ also causes more AMPA receptors to appear in the postsynaptic membrane. 5 Ca 2+ stimulates the postsynaptic neuron to produce nitric oxide (NO). 6 The presynaptic neuron releases glutamate. 1 Glutamate binds to AMPA receptors, opening the AMPA- receptor channel and depolarizing the postsynaptic membrane. 2 Glutamate also binds to NMDA receptors. If the postsynaptic membrane is simultaneously depolarized, the NMDA-receptor channel opens. 3 Ca 2+ diffuses into the postsynaptic neuron. 4 NO diffuses into the presynaptic neuron, causing it to release more glutamate. 7 P

106. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Consciousness Modern brain-imaging techniques – Suggest that consciousness may be an emergent property of the brain that is based on activity in many areas of the cortex

107. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 48.7: CNS injuries and diseases are the focus of much research Unlike the PNS, the mammalian CNS – Cannot repair itself when damaged or assaulted by disease Current research on nerve cell development and stem cells – May one day make it possible for physicians to repair or replace damaged neurons

108. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Nerve Cell Development Signal molecules direct an axon’s growth – By binding to receptors on the plasma membrane of the growth cone

109. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings This receptor binding triggers a signal transduction pathway – Which may cause an axon to grow toward or away from the source of the signal Figure 48.33a, b Midline of spinal cord Developing axon of interneuron Growth cone Netrin-1 receptor Netrin-1 Floor plate Cell adhesion molecules Slit receptor Slit Developing axon of motor neuron Netrin-1 receptor Slit receptor Slit Netrin-1 1 Growth toward the floor plate. Cells in the floor plate of the spinal cord release Netrin-1, which diffuses away from the floor plate and binds to receptors on the growth cone of a developing interneuron axon. Binding stimulates axon growth toward the floor plate. 2Growth across the mid-line. Once the axon reaches the floor plate, cell adhesion molecules on the axon bind to complementary molecules on floor plate cells, directing the growth of the axon across the midline. 3 No turning back. Now the axon synthesizes receptors that bind to Slit, a repulsion protein re- leased by floor plate cells. This prevents the axon from growing back across the midline. Netrin-1 and Slit, produced by cells of the floor plate, bind to receptors on the axons of motor neurons. In this case, both proteins act to repel the axon, directing the motor neuron to grow away from the spinal cord. (a) Growth of an interneuron axon toward and across the midline of the spinal cord (diagrammed here in cross section) (b) Growth of a motor neuron axon away from the midline of the spinal cord

110. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The genes and basic events involved in axon guidance – Are similar in invertebrates and vertebrates Knowledge of these events may be applied one day – To stimulate axonal regrowth following CNS damage

111. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Neural Stem Cells The adult human brain – Contains stem cells that can differentiate into mature neurons Figure 48.34 10  m

112. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The induction of stem cell differentiation and the transplantation of cultured stem cells – Are potential methods for replacing neurons lost to trauma or disease

113. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Diseases and Disorders of the Nervous System Mental illnesses and neurological disorders – Take an enormous toll on society, in both the patient’s loss of a productive life and the high cost of long-term health care

114. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Schizophrenia About 1% of the world’s population – Suffers from schizophrenia

115. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Schizophrenia is characterized by – Hallucinations, delusions, blunted emotions, and many other symptoms Available treatments have focused on – Brain pathways that use dopamine as a neurotransmitter

116. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Depression Two broad forms of depressive illness are known – Bipolar disorder and major depression

117. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Bipolar disorder is characterized by – Manic (high-mood) and depressive (low-mood) phases In major depression – Patients have a persistent low mood

118. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Treatments for these types of depression include – A variety of drugs such as Prozac and lithium

119. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Alzheimer’s Disease Alzheimer’s disease (AD) – Is a mental deterioration characterized by confusion, memory loss, and other symptoms

120. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings AD is caused by the formation of – Neurofibrillary tangles and senile plaques in the brain Figure 48.35 Senile plaque Neurofibrillary tangle 20  m

121. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings A successful treatment for AD in humans – May hinge on early detection of senile plaques

122. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Parkinson’s Disease Parkinson’s disease is a motor disorder – Caused by the death of dopamine-secreting neurons in the substantia nigra – Characterized by difficulty in initiating movements, slowness of movement, and rigidity

123. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings There is no cure for Parkinson’s disease – Although various approaches are used to manage the symptoms