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Chapter 28 Nervous System

Chapter 28 Nervous System. Spinal cord. 0. Can an Injured Spinal Cord Be Fixed? Injuries to the spinal cord Disrupt communication between the central nervous system (brain and spinal cord) and the rest of the body. 0. The late actor Christopher Reeve

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Chapter 28 Nervous System

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  1. Chapter 28 Nervous System

  2. Spinalcord 0 • Can an Injured Spinal Cord Be Fixed? • Injuries to the spinal cord • Disrupt communication between the central nervous system (brain and spinal cord) and the rest of the body

  3. 0 • The late actor Christopher Reeve • Suffered a spinal cord injury during an equestrian competition • Was an influential advocate for spinal cord research

  4. NERVOUS SYSTEM STRUCTURE AND FUNCTION 0 • 28.1 Nervous systems receive sensory input, interpret it, and send out appropriate commands • Nervous systems • Are the most intricately organized data-processing systems on Earth

  5. Sensory input Integration Sensory receptor Motor output Brain and spinal cord Central nervous system (CNS) Effector cells Peripheral nervous system (PNS) 0 • The nervous system obtains and processes sensory information • And sends commands to effector cells, such as muscles, that carry out appropriate responses Figure 28.1A

  6. 0 • Sensory neurons • Conduct signals from sensory receptors to the central nervous system (CNS) • The CNS • Consists of the brain and spinal cord

  7. 0 • Interneurons in the CNS • Integrate information and send it to motor neurons • Motor neurons • Convey signals to effector cells

  8. 1 Sensory receptor 2 Sensory neuron Brain Ganglion Motor neuron 3 Spinal cord 4 Quadriceps muscles Interneuron CNS Flexor muscles Nerve PNS 0 • Automatic responses called reflexes • Provide an example of nervous system function Figure 28.1B

  9. 0 • Located outside the CNS, the peripheral nervous system (PNS) • Consists of nerves (bundles of fibers of sensory and motor neurons) and ganglia (clusters of cell bodies of the neurons)

  10. 0 • 28.2 Neurons are the functional units of nervous systems • Neurons • Are cells specialized for carrying signals

  11. Dendrites Signal direction Cell body Cell body SEM 3,600 Node of Ranvier Layers of myelin in sheath Signal pathway Axon Schwann cell Nucleus Nucleus Nodes of Ranvier Schwann cell Myelin sheath Synaptic terminals 0 • A neuron consists of • A cell body • Two types of extensions (fibers) that conduct signals, dendrites and axons Figure 28.2

  12. 0 • Many axons are enclosed by cellular insulation called the myelin sheath • Which speeds up signal transmission

  13. Microelectrode inside cell Plasma membrane Microelectrode outside cell – 70 mV + + + + + + + + – – – – – – – – – – – – – – – – + + + + + + + + Axon Neuron Figure 28.3A NERVE SIGNALS AND THEIR TRANSMISSION 0 • 28.3 A neuron maintains a membrane potential across its membrane • At rest, a neuron’s plasma membrane • Has an electrical voltage called the resting potential Voltmeter

  14. Outside of cell Na+ Na+ K+ Na+ Na+ Na+ K+ Na+ Na+ Na+ Na+ Na+ Na+ channel Na+ Na+ Na+ K+ Na+ - K+ pump Plasma membrane K+ channel Na+ K+ K+ K+ Protein K+ K+ K+ K+ K+ K+ Na+ Inside of cell 0 • The resting potential • Is caused by the membrane’s ability to maintain a positive charge on its outer surface opposing a negative charge on its inner surface Figure 28.3B

  15. 0 • 28.4 A nerve signal begins as a change in the membrane potential • A stimulus alters the permeability of a portion of the membrane • Allowing ions to pass through and changing the membrane’s voltage

  16. Na+ + + + + + + + – – + + – – – – – + + – – – + + + + + + + K+ + + + + + + + – – – – – – – – – – – – – – + + + + + + + Na+ K+ Additional Na+ channels open, K+ channels are closed; interior of cell becomes more positive. 3 Na+ channels close and inactivate. K+ channels open, and K+ rushes out; interior of cell more negative than outside. 4 +50 Na+ Action potential + + + + + + + – – + – – – – – – + – – – – + + + + + + + 3 0 Membrane potential (mV) 4 2 The K+ channels closerelatively slowly, causinga brief undershoot. 5 Na+ Threshold – 50 A stimulus opens some Na+ channels; if threshold is reached, action potential is triggered. 2 1 1 5 Resting potential – 100 Time (msec) + + + + + + + + – – – – – – – – – – – – – – – – + + + + + + + + + + + + + + + + – – – – – – – – – – – – – – – – + + + + + + + + Neuron interior Neuron interior Resting state: voltage-gated Na+ and K+ channels closed; resting potential is maintained. 1 1 Return to resting state. Figure 28.4 0 • A nerve signal, called an action potential • Is a change in the membrane voltage from the resting potential to a maximum level and back to the resting potential

  17. 0 • 28.5 The action potential propagates itself along the neuron • Action potentials • Are self-propagated in a one-way chain reaction along a neuron • Are all-or-none events

  18. Axon + +     Action potential + + + +         + +     Axonsegment Na+             Action potential K+    +         Na+ + +         + + K+ Action potential K+ Na+   + +       + + K+ 0 • Propagation of the action potential along an axon 1 2 3 Figure 28.5

  19. 0 • The frequency of action potentials, but not their strength • Changes with the strength of the stimulus

  20. 0 • 28.6 Neurons communicate at synapses • The transmission of signals between neurons • Or between neurons and effector cells occurs at junctions called synapses

  21. 0 • Electrical signals • Pass between cells at electrical synapses

  22. 0 • At chemical synapses • The sending cell secretes a chemical signal, a neurotransmitter • The neurotransmitter • Crosses the synaptic cleft and binds to a receptor on the surface of the receiving cell

  23. Sending neuron 1 Actionpotentialarrives Vesicles Axon ofsendingneuron Synapticterminal Synapse 2 3 Vesicle fuseswith plasmamembrane Neurotransmitteris released intosynaptic cleft Synapticcleft Receivingneuron 4 Neurotransmitterbinds to receptor Receivingneuron Neurotransmittermolecules Ion channels Neurotransmitter brokendown and released Neurotransmitter Receptor Ions Ion channel opens Ion channel closes 5 6 • Neuron communication Figure 28.6

  24. Synaptic terminals Dendrites Inhibitory Excitatory Myelinsheath Receivingcell body Axon Synapticterminals SEM 5,500 Figure 28.7 0 • 28.7 Chemical synapses make complex information processing possible • A neuron may receive information • From hundreds of other neurons via thousands of synaptic terminals

  25. 0 • Some neurotransmitters • Excite the receiving cell • Other types of neurotransmitters • Inhibit the receiving cell’s activity by decreasing its ability to develop action potentials

  26. 0 • The summation of excitation and inhibition • Determines whether or not a neuron will transmit a nerve signal

  27. 0 • 28.8 A variety of small molecules function as neurotransmitters • Many small, nitrogen-containing molecules • Serve as neurotransmitters

  28. CONNECTION 0 • 28.9 Many drugs act at chemical synapses • Many psychoactive drugs • Act at synapses and affect neurotransmitter action Figure 28.9

  29. Nervenet Neuron A Hydra (cnidarian) AN OVERVIEW OF ANIMAL NERVOUS SYSTEMS 0 • 28.10 Nervous system organization usually correlates with body symmetry • Radially symmetrical animals • Have a nervous system arranged in a weblike system of neurons called a nerve net Figure 28.10A

  30. Eyespot Brain Brain Brain Ventralnervecord Brain Ventralnervecord Nervecord Giantaxon Tranversenerve Segmentalganglion Ganglia D Insect (arthropod) C Leech (annelid) B Flatworm (planarian) E Squid (mollusc) 0 • Most bilaterally symmetrical animals exhibit • Cephalization, the concentration of the nervous system in the head region • Centralization, the presence of a central nervous system Figure 28.10B–E

  31. Central nervoussystem (CNS) Peripheralnervoussystem (PNS) Brain Cranialnerves Spinal cord Gangliaoutside CNS Spinalnerves 0 • 28.11 Vertebrate nervous systems are highly centralized and cephalized Figure 28.11A

  32. Cerebrospinal fluid Brain Meninges Gray matter Dorsal root ganglion (part of PNS) White matter Spinal nerve (part of PNS) Central canal Ventricles Spinal cord (cross section) Central canal of spinal cord Spinal cord 0 • The brain and spinal cord • Contain fluid-filled spaces Figure 28.11B

  33. 0 • Cranial and spinal nerves • Make up the peripheral nervous system

  34. Peripheral nervous system Somatic nervous system Autonomic nervous system Sympathetic division Parasympathetic division Enteric division 0 • 28.12 The peripheral nervous system of vertebrates is a functional hierarchy • The PNS can be divided into two functional components • The somatic nervous system and the autonomic nervous system Figure 28.12

  35. 0 • The somatic nervous system • Carries signals to and from skeletal muscles, mainly in response to external stimuli • The autonomic nervous system • Regulates the internal environment by controlling smooth and cardiac muscles and the organs of various body systems

  36. 0 • 28.13 Opposing actions of sympathetic and parasympathetic neurons regulate the internal environment • The parasympathetic division of the autonomic nervous system • Primes the body for activities that gain and conserve energy for the body • The sympathetic division of the autonomic nervous system • Prepares the body for intense, energy-consuming activities

  37. Parasympathetic division Sympathetic division Brain Eye Constricts pupil Dilates pupil Salivary glands Stimulates saliva production Inhibits saliva production Lung Dilates bronchi Constricts bronchi Accelerates heart Slows heart Adrenal gland Heart Spinal cord Stimulates epinephrine and norepinep- hrine release Liver Stomach Stimulates stomach, pancreas, and intestines Stimulates glucose release Pancreas Inhibits stomach, pancreas, and intestines Intestines Bladder Inhibits urination Stimulates urination Promotes ejaculation and vaginal contractions Promotes erection of genitals Genitalia 0 • The autonomic nervous system Figure 28.13

  38. Embryonic Brain Regions Brain Structures Present in Adult Cerebrum (cerebral hemispheres; includes cerebral cortex, white matter, basal ganglia) Forebrain Diencephalon (thalamus, hypothalamus, posterior pituitary, pineal gland) Midbrain Midbrain (part of brainstem) Pons (part of brainstem), cerebellum Hindbrain Medulla oblongata (part of brainstem) Cerebral hemisphere Diencephalon Midbrain Hindbrain Midbrain Pons Cerebellum Medulla oblongata Spinal cord Forebrain Embryo (one month old) Fetus (three months old) 0 • 28.14 The vertebrate brain develops from three anterior bulges of the neural tube • The vertebrate brain • Develops from the forebrain, midbrain, and hindbrain Figure 28.14

  39. 0 • The size and complexity of the cerebrum in birds and mammals • Correlates with their sophisticated behavior

  40. THE HUMAN BRAIN 0 • 28.15 The structure of a living supercomputer: The human brain • The human brain • Is more powerful than the most sophisticated computer

  41. Cerebral cortex Cerebrum Thalamus Forebrain Hypothalamus Pituitary gland Midbrain Pons Spinal cord Medulla oblongata Hindbrain Cerebellum 0 • The human brain is composed of three main parts • The forebrain, the midbrain, and the hindbrain Figure 28.15A

  42. 0 • Major structures of the human brain Table 28.15

  43. 0 • The midbrain and subdivisions of the hindbrain, together with the thalamus and hypothalamus • Function mainly in conducting information to and from higher brain centers • Regulate homeostatic functions, keep track of body position, and sort sensory information

  44. 0 • The forebrain’s cerebrum • Is the largest and most complex part of the brain

  45. Right cerebral hemisphere Left cerebral hemisphere Basal ganglia Corpus callosum 0 • Most of the cerebrum’s integrative power • Resides in the cerebral cortex of the two cerebral hemispheres Figure 28.15B

  46. Frontal lobe Parietal lobe Somatosensory association area Frontal association area Somatosensory cortex Motor cortex Speech Taste Reading Speech Hearing Smell Visual association area Auditory association area Vision Temporal lobe Occipital lobe 0 • 28.16 The cerebral cortex is a mosaic of specialized, interactive regions • Specialized integrative regions of the cerebral cortex include • The somatosensory cortex and centers for vision, hearing, taste, and smell Figure 28.16

  47. 0 • The motor cortex • Directs responses • Association areas • Concerned with higher mental activities such as reasoning and language, make up most of the cerebrum • The right and left cerebral hemispheres • Tend to specialize in different mental tasks

  48. Figure 28.17A, B CONNECTION 0 • 28.17 Injuries and brain operations provide insight into brain function • Brain injuries and surgeries • Have been used to study brain function

  49. 0 • 28.18 Several parts of the brain regulate sleep and arousal • Sleep and arousal involve • Activity by the hypothalamus, medulla oblongata, pons, and neurons of the reticular formation

  50. Data to cerebral cortex Input from ears Eye Reticular formation Input from touch, pain, and temperature receptors 0 • The reticular formation • Receives data from sensory receptors and sends useful data to the cerebral cortex Figure 28.18A

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