1. HUMAN ANATOMY fourth edition MARIEB | MALLATT | WILHELM Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings PowerPoint ® Lecture Slides prepared by Leslie Hendon, University of Alabama, Birmingham 12 Fundamentals of the Nervous System and Nervous Tissue PART 1

2. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Nervous System Master control and communication system

3. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Nervous System: Functions Three overlapping functions Sensory receptors monitor changes inside and outside the body Change – a stimulus Gathered information – sensory input CNS Processes and interprets sensory input Makes decisions – integration Dictates a response by activating effector organs Response – motor output

4. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Basic Divisions of the Nervous System: CNS Central nervous system (CNS) Brain and spinal cord Integrating and command center

5. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Basic Divisions of the Nervous System: PNS Peripheral nervous system (PNS) Outside the CNS Nerves extending from brain and spinal cord Cranial nerves Spinal nerves Link all regions of the body to the CNS

6. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Sensory Input and Motor Output Sensory signals picked up by sensory receptors Carried by afferent nerve fibers of PNS to the CNS Motor signals are carried away from the CNS Carried by efferent nerve fibers of PNS to effectors Innervate muscles and glands

7. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Sensory Input and Motor Output Divided according to region they serve Somatic body region Visceral body region Results in four main subdivisions Somatic sensory Visceral sensory Somatic motor Visceral motor

8. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Somatic Sensory Somatic sensory General somatic senses – receptors are widely spread Touch, pain, vibration, pressure, and temperature Proprioceptive senses – detect stretch in tendons and muscle Body sense – position and movement of body in space Special somatic senses Hearing, balance, vision, and smell

9. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Visceral Sensory Visceral sensory General visceral senses – stretch, pain, temperature, nausea, and hunger Widely felt in digestive and urinary tracts, reproductive organs Special visceral senses – taste

10. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Somatic Motor Somatic motor General somatic motor – signals contraction of skeletal muscles Under voluntary control Often called “voluntary nervous system”

11. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Visceral Motor Visceral motor Regulates the contraction of smooth and cardiac muscle and gland secretion Makes up autonomic nervous system Controls function of visceral organs Often called “involuntary nervous system”

12. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Peripheral Nervous System Summary Figure 12.3

13. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Types of Sensory and Motor Information Figure 12.3

14. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Types of Sensory and Motor Information Figure 12.3

15. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Nervous Tissue Cells are densely packed and intertwined Two main cell types Neurons – transmit electrical signals Support cells (neuroglial cells) – nonexcitable Surround and wrap neurons

16. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings The Neuron The human body contains billions of neurons Basic structural unit of the nervous system Specialized cells conduct electrical impulses along the plasma membrane Graded potentials Action potentials

17. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings The Neuron: Special Characteristics Longevity – can live and function for a lifetime Do not divide – fetal neurons lose their ability to undergo mitosis; neural stem cells are an exception High metabolic rate – require abundant oxygen and glucose

18. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Neuron Structure

19. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings The Cell Body or Soma (also called Perikaryon) Size varies from 5–140µm Contains nucleus, organelles plus other structures Chromatophilic bodies (Nissl bodies) Clusters of rough ER and free ribosomes Stain darkly and renew membranes of the cell Neurofibrils – bundles of intermediate filaments Form a network between chromatophilic bodies

20. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Nissl Body Staining

21. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings The Cell Body Most neuronal cell bodies Located within the CNS (clustered in nuclei) Protected by bones of the skull and vertebral column Ganglia – clusters of cell bodies in PNS

22. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Cell Body Structure Figure 12.4

23. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Neuron Processes: Dendrites Dendrites Extensively branching from the cell body Transmit electrical signals (graded potentials) toward the cell body Chromatophilic bodies – only extend into the basal part of dendrites Function as receptive sites

24. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Dendritic Spines

25. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Dendritic Spines

26. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Neuron Processes: Axons Axons (nerve fibers) Neuron has only one, but it can branch Impulse generator and conductor Transmits action potentials away from the cell body Chromatophilic bodies absent No protein synthesis in axon

27. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Neuron Processes: Axons Axons Neurofilaments, actin microfilaments, and microtubules Provide strength along length of axon Aid in the transport of substances to and from the cell body Axonal transport

28. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Neuron Processes Neuron Structure Axons Branches along length are infrequent Axon collaterals Multiple branches at end of axon Terminal branches (telodendria) End in knobs called axon terminals (also called end bulbs or boutons)

29. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Neuron Processes: Action Potentials Nerve impulse (action potential) Generated at the initial segment of the axon Conducted along the axon Releases neurotransmitters at axon terminals Neurotransmitters – excite or inhibit neurons Neuron receives and sends signals

30. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Synapses Site at which neurons communicate Signals pass across synapse in one direction Presynaptic neuron Conducts signal toward a synapse Postsynaptic neuron Transmits electrical activity away from a synapse

31. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Two Neurons Communicating at a Synapse Figure 12.6

32. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Types of Synapses Axodendritic Between axon terminals of one neuron and dendrites of another Most common type of synapse Axosomatic Between axons and neuronal cell bodies Axoaxonic, dendrodendritic, and dendrosomatic Less common types of synapses Function not as well understood

33. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Types of Synapses Figure 12.7

34. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Synapses Axodendritic synapses – representative type Synaptic vesicles on presynaptic side Membrane-bound sacs containing neurotransmitters Mitochondria abundant in axon terminals Synaptic cleft separates the plasma membrane of the two neurons

35. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Structure of a Synapses Figure 12.8a, b PLAY Synapse

36. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Synapse

37. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Signals Carried by Neurons: Resting Membrane Potential Plasma membranes of neurons conduct electrical signals Resting neuron – membrane is polarized Inner, cytoplasmic side is negatively charged

38. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Changes in Membrane Potential Signals occur as changes in membrane potential

39. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Directional Signals Stimulation of the neuron  depolarization Inhibition of the neuron  hyperpolarization

40. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Action Potentials Figure 12.9a, b

41. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Action Potentials on Axons Strong depolarizing stimulus applied to the axon hillock triggers Action potential Membrane becomes positive internally Action potential travels the length of the axon Membrane repolarizes itself

42. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Action Potentials on Axons Figure 12.9c–e

43. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Graded Potentials on Dendrites and the Cell Body Natural stimuli applied to dendrites and the cell body Receptive zone of the neuron Membrane stimulation causes local depolarization A graded potential – inner surface becomes less negative Depolarization spreads from receptive zone to the axon hillock Acts as the trigger that initiates an action potential in the axon

44. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Synaptic Potentials Excitatory synapses Neurotransmitters alter the permeability of the postsynaptic membrane Leads to an inflow of positive ions Depolarizes the postsynaptic membrane Drives the postsynaptic neuron toward impulse generation

45. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Synaptic Potentials Inhibitory synapses The external surface of the postsynaptic membrane becomes more positive Reduces the ability of the postsynaptic neuron to generate an action potential

46. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Classification of Neurons Structural Classification Functional Classification

47. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Structural Classification of Neurons Classification based on number of processes Multipolar Bipolar Unipolar (pseudounipolar)

48. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Multipolar Neurons Figure 12.10a–c Possess more than two processes Numerous dendrites and one axon

49. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Bipolar Neurons Figure 12.10a–c Possess two processes Rare neurons – found in some special sensory organs

50. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Unipolar (Pseudounipolar) Neurons Figure 12.10a–c Possess one single process Start as bipolar neurons during development

51. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Functional Classification of Neurons Classification based on direction of action potential propagation Afferents – from CNS to periphery Efferents – from periphery to CNS Interneurons – within CNS

52. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Afferent neurons Afferent (sensory) neurons – transmit impulses toward the CNS Virtually all are pseudounipolar neurons (some true bipolar) Cell bodies in ganglia outside the CNS Short, single process divides into The central process – runs centrally into the CNS The peripheral process – extends peripherally to the receptors

53. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Afferent Neurons Sensory receptors Axon terminals Periphery CNS

54. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Efferent Neurons Efferent (motor) neurons Carry impulses away from the CNS to effector organs Most efferent neurons are multipolar Cell bodies are within the CNS Form junctions with effector cells

55. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Interneurons Interneurons (association neurons) – most are multipolar Lie between afferent and efferent neurons Confined to the CNS

56. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Neurons Classified by Function Figure 12.11

57. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Variety of Interneurons Purkinje cell, stellate cell, granule cell, and basket cell Located in the cerebellum Pyramidal cell – located in the cerebral cortex

58. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Variety of Interneurons

59. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Glial Cells (Supporting Cells) Six types of glial cells Four in the CNS Two in the PNS Provide supportive functions for neurons Cover nonsynaptic regions of the neurons

60. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Supporting Cells (Neuroglial Cells) in the CNS Neuroglia – usually only refers to supporting cells in the CNS, but can be used for PNS Glial cells have branching processes and a central cell body Outnumber neurons 10 to 1 Make up half the mass of the brain Can divide throughout life

61. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Types of Glial Cells in the CNS Astrocytes Microglia Ependymal Cells Oligodendrocytes

62. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Astrocytes Astrocytes – most abundant glial cell type Take up and release ions to control the environment around neurons Recapture and recycle neurotransmitters Involved with synapse formation in developing neural tissue Produce molecules necessary for neural growth (BDTF) Propagate calcium signals that may be involved in memory

63. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Astrocytes Figure 12.12a Necessary for development and maintenance of theblood brain barrier

64. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Microglia – smallest and least abundant Phagocytes – the macrophages of the CNS Engulf invading microorganisms and dead neurons Derived from blood cells called monocytes Microglia Figure 12.12b

65. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Ependymal Cells Ependymal cells Line the central cavity of the spinal cord and brain Bear cilia – help circulate the cerebrospinal fluid

66. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Oligodendrocytes Oligodendrocytes – have few branches Wrap their cell processes around axons in CNS Produce myelin sheaths

67. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12.13 Supporting Cells in the PNS Satellite cells – surround neuron cell bodies within ganglia Schwann cells (neurolemmocytes) – surround axons in the PNS Form myelin sheath around axons of the PNS

68. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Myelin Sheaths Segmented structures composed of the lipoprotein myelin Surround thicker axons Form an insulating layer Prevent leakage of electrical current Increase the speed of impulse conduction

69. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Myelin Sheaths in the PNS Formed by Schwann cells Develop during fetal period and in the first year of postnatal life Schwann cells wrap in concentric layers around the axon Cover the axon in a tightly packed coil of membranes

70. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Myelin Sheaths in the PNS Nodes of Ranvier – gaps along axon Allow current exchange across axon membrane

71. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Myelin Sheaths in the PNS Thick axons are myelinated Fast conduction velocity Thin axons are unmyelinated Slow conduction velocity

72. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Myelin Sheaths in the PNS Figure 12.14a

73. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Myelin Sheaths in the PNS – myelinated axon Figure 12.15b

74. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Myelin Sheaths in the PNS – unmyelinated axons Figure 12.15b

75. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Myelin Sheaths in the CNS Oligodendrocytes form the myelin sheaths in the CNS Have multiple processes Coil around several different axons

76. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Oligodendrocytes

77. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Nerves Nerves – cordlike organs in the PNS Consists of numerous axons wrapped in connective tissue Axon is surrounded by Schwann cells

78. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Nerves Endoneurium – layer of delicate connective tissue surrounding the axon Nerve fascicles – groups of axons bound into bundles Perineurium – connective tissue wrapping surrounding a nerve fascicle Epineurium – whole nerve is surrounded by tough fibrous sheath

79. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Simplified Design of the Nervous System Sensory neurons – located dorsally Cell bodies outside the CNS in sensory ganglia Central processes enter dorsal aspect of the spinal cord Motor neurons – located ventrally Axons exit the ventral aspect of the spinal cord Interneurons – located centrally Provide communication between sensory and motor neurons and between levels of the CNS

80. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Example of Neuronal Organization: Reflexes Reflex arcs – simple neural pathways Responsible for reflexes Rapid, autonomic motor responses Can be visceral or somatic

81. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Five Essential Components to the Reflex Arc Receptor – detects the stimulus Afferent (sensory neuron) – transmits impulses to the CNS Integration center – consists of one or more synapses in the CNS Efferent (motor neuron) – conducts impulses from integration center to an effector Effector – muscle or gland cell Responds to efferent impulses Contraction or secretion

82. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Example of the Five Components to the Reflex Arc Figure 12.17

83. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Reflex Classification Monosynaptic or polysynaptic Spinal or cranial Somatic or autonomic Innate or learned

84. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Types of Reflexes: Number of Classes Monosynaptic reflex – simplest of all reflexes Just one synapse The fastest of all reflexes Example – knee-jerk reflex Polysynaptic reflex – more common type of reflex Most have a single interneuron between the sensory and motor neuron Example – withdrawal reflexes

85. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Monosynaptic Reflex Figure 12.18a, b

86. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Polysynaptic Reflex Figure 12.18a, b

87. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Spinal vs Cranial Reflexes Spinal = spinal cord integration center Ex. Knee-jerk reflex Cranial = brain as integration center Ex. Pupillary light reflex

88. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Somatic vs Autonomic Reflexes Somatic = motor neurons to skeletal muscles Ex. Knee-jerk reflex Autonomic = autonomic neurons to smooth muscle and glands Ex. Pupillary light reflex

89. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Innate vs Learned Reflexes Innate = born-with Knee-jerk reflex, pupillary reflex Learned = develops based on experiences Pavlov’s dogs salivation in response to bell

90. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Neuronal Circuits Diverging circuit Converging circuit Reverberating circuit

91. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Diverging Circuit Diverging circuit – one presynaptic neuron synapses with several other neurons (divergence)

92. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Converging Circuit Converging circuit – many neurons synapse on a single postsynaptic neuron (convergence)

93. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Reverberating Circuit Reverberating circuit – circuit that receives feedback via a collateral axon from a neuron in the circuit

94. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Neural Processing Serial processing Parallel processing

95. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Serial Processing Serial processing – neurons pass a signal to a specific destination along a single pathway from one to another

96. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Parallel Processing Parallel processing – input is delivered along many pathways; a single sensory stimulus results in multiple perceptions

97. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Gray versus White Matter in the Central Nervous System Gray matter Cell bodies Dendrites Synapses White matter Axons (myelin)

98. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Gray Matter in the Spinal Cord Gray matter in the spinal cord H-shaped (butterfly) region – surrounds central cavity Dorsal half contains cell bodies of interneurons Ventral half contains cell bodies of motor neurons Cell bodies are clustered in the gray matter

99. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings White Matter in the Spinal Cord White matter in the spinal cord Located externally to the gray matter Contains no neuronal cell bodies, but millions of axons Myelin sheath – white color Consists of axons running between different parts of the CNS Tracts – bundles of axons traveling to similar destinations

100. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Gray Matter in Brain Cortex and nuclei

101. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings White Matter in Brain Pathways, tracts and commissures

102. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Disorders of the Nervous System Multiple sclerosis – common cause of neural disability Varies widely in intensity among those affected Cause is incompletely understood An autoimmune disease Immune system attacks the myelin around axons in the CNS

103. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Multiple Sclerosis Videos Symptoms of multiple sclerosis