1. Copyright (c) Allyn & Bacon 20041 Chapter 2 Structure and Functions of Cells of the Nervous System

2. Copyright (c) Allyn & Bacon 20042  The Nervous System  Central Nervous System (CNS) Comprised of the brain and spinal cord Encased within the skull and spinal column  Peripheral Nervous System (PNS) Comprised of nerve tissue located outside of the brain and spinal cord.

3. Copyright (c) Allyn & Bacon 20043  Cells of the Nervous System Neuron Basic Structure  Soma or “cell body”: The cell body of a neuron, which contains the nucleus.  Dendrite: A branched treelike structure attached to the soma of a neuron; receives information from the terminal button of other neurons.

4. Copyright (c) Allyn & Bacon 20044  Cells of the Nervous System Neuron Basic Structure  Terminal button: The bud at the end of a branch of an axon; forms synapses with another neuron; sends information to that neuron.  Neurotransmitter: A chemical that is released by a terminal button; has an excitatory or inhibitory effect on another neuron.

5. Copyright (c) Allyn & Bacon 20045  Neuron

6. Copyright (c) Allyn & Bacon 20046  Cells of the Nervous System Neuron Basic Structure  Synapse: A junction between the terminal button of an axon and the membrane of another neuron.  Axon: The long, thin cylindrical structure that conveys information from the soma of a neuron to its terminal button.

7. Copyright (c) Allyn & Bacon 20047  Cells of the Nervous System  There are three general types of neurons:  Sensory neuron: A neuron that detects changes in the external or internal environment and sends information about these changes to the central nervous system.

8. Copyright (c) Allyn & Bacon 20048  Cells of the Nervous System  There are three general types of neurons:  Motor neuron: A neuron located within the central nervous system that controls the contraction of a muscle or the secretion of a gland.

9. Copyright (c) Allyn & Bacon 20049  Cells of the Nervous System  There are three general types of neurons:  Interneuron: A neuron located entirely within the central nervous system.

10. Copyright (c) Allyn & Bacon 200410  Cells of the Nervous System Neuron Basic Structure  Multipolar neurons: A neuron with one axon and many dendrites.

11. Copyright (c) Allyn & Bacon 200411  Cells of the Nervous System Neuron Basic Structure  Bipolar neurons: A neuron with one axon and one dendrite attached to its soma.

12. Copyright (c) Allyn & Bacon 200412  Basic Structures of Neurons  Three classifications of neurons  Unipolar neurons: A neuron with one axon attached to its soma; the axon divides, with one branch receiving sensory information and the other sending the information into the central nervous system.

13. Copyright (c) Allyn & Bacon 200413  Cells of the Nervous System Internal structure  Membrane: A structure consisting principally of lipid molecules that defines the outer boundaries of a cell and also constitutes many of the cell organelles, such as the Golgi apparatus.  Nucleus: A structure in the central region of a cell, containing the nucleolus and chromosomes.

14. Copyright (c) Allyn & Bacon 200414 Copyright © Allyn & Bacon 2004

15. Copyright (c) Allyn & Bacon 200415  Cells of the Nervous System Internal structure  Nucleolus: A structure within the nucleus of a cell that produces the ribosomes.  Ribosomes: A cytoplasmic structure, made of protein, that serves as the site of production of proteins translated from mRNA.

16. Copyright (c) Allyn & Bacon 200416  Nucleus

17. Copyright (c) Allyn & Bacon 200417  Cells of the Nervous System Internal structure  Chromosome: A strand of DNA, with associated proteins, found in the nucleus; carries genetic information.  Deoxyribonucleic acid (DNA): A long complex macromolecule consisting of two interconnected helical strands; along with associated proteins, strands of DNA constitute the chromosomes.

18. Copyright (c) Allyn & Bacon 200418  Cells of the Nervous System Internal structure  Gene: The functional unit of the chromosome, which directs synthesis of one or more proteins.  Messenger ribonucleic acid (mRNA): A macromolecule that delivers genetic information concerning the synthesis of protein from a portion of a chromosome.

19. Copyright (c) Allyn & Bacon 200419 Copyright © Allyn & Bacon 2004

20. Copyright (c) Allyn & Bacon 200420  Cells of the Nervous System Internal structure  Enzyme: A molecule that controls a chemical reaction, combining two substances or breaking a substance into two parts.  Cytoplasm: The viscous, semi-liquid substance contained in the interior of a cell.

21. Copyright (c) Allyn & Bacon 200421  Cells of the Nervous System Internal structure  Mitochondria: An organelle that is responsible for extracting energy from nutrients.  Adenosine triphosphate (ATP): A molecule of prime importance to cellular energy metabolism; its breakdown liberates energy.

22. Copyright (c) Allyn & Bacon 200422  Cells of the Nervous System Internal structure  Endoplasmic reticulum: Parallel layers of membrane found within the cytoplasm of a cell. Rough endoplasmic reticulum contains ribosomes and is involved in production of proteins that are secreted from the cell. Smooth endoplasmic reticulum is the site of synthesis of lipids and provides channels for the segregation of molecules involved in various cellular processes.

23. Copyright (c) Allyn & Bacon 200423  Cells of the Nervous System Internal structure  Golgi apparatus: A complex of parallel membranes in the cytoplasm that wraps the products of a secretory cell.  Exocytosis: The secretion of a substance by a cell through means of vesicles; the process by which neurotransmitters are secreted.

24. Copyright (c) Allyn & Bacon 200424  Cells of the Nervous System Internal structure  Lysosome: An organelle surrounded by membrane; contains enzymes that break down waste products.  Cytoskeleton: Formed of microtubules and other protein fibers, lined to each other and forming cohesive mass that gives a cell its shape.

25. Copyright (c) Allyn & Bacon 200425 Copyright © Allyn & Bacon 2004

26. Copyright (c) Allyn & Bacon 200426  Cells of the Nervous System Internal structure  Microtubule: A long strand of bundles of protein filaments arranged around a hollow core; part of the cytoskeleton and involved in transporting substances from place to place within the cell.  Axoplasmic transport: An active process by which substances are propelled along microtubules that run the length of the axon.

27. Copyright (c) Allyn & Bacon 200427 Copyright © Allyn & Bacon 2004

28. Copyright (c) Allyn & Bacon 200428  Cells of the Nervous System Internal structure  Anterograde: In a direction along an axon from the cell body to the terminal buttons.

29. Copyright (c) Allyn & Bacon 200429  Cells of the Nervous System Internal structure  Retrograde: In a direction along an axon from the terminal buttons toward the cell body.

30. Copyright (c) Allyn & Bacon 200430  Cells of the Nervous System  Glia  Glial cell: The supporting cells of the central nervous system.

31. Copyright (c) Allyn & Bacon 200431  Cells of the Nervous System  Glia  Astrocyte: A glial cell that provides support for neurons of the central nervous system, provides nutrients and other substances, and regulates the chemical composition of the extracellular fluid.

32. Copyright (c) Allyn & Bacon 200432  Cells of the Nervous System  Phagocytosis: The process by which cells engulf and digest other cells or debris caused by cellular degeneration.

33. Copyright (c) Allyn & Bacon 200433  Cells of the Nervous System  Oligodendrocyte: A type of glial cell in the central nervous system that forms myelin sheaths.

34. Copyright (c) Allyn & Bacon 200434  Cells of the Nervous System  Myelin sheath: A sheath that surrounds axons and insulates them, preventing messages from spreading between adjacent axons.

35. Copyright (c) Allyn & Bacon 200435  Cells of the Nervous System  Node of Ranvier: A naked portion of a myelinated axon, between adjacent oligodendroglia or Schwann cells.

36. Copyright (c) Allyn & Bacon 200436  Cells of the Nervous System  Microglia: The smallest glial cells; act as phagocytes and protect the brain from invading microorganisms.  Schwann cell: A cell in the peripheral nervous system that is wrapped around a myelinated axon, providing one segment of its myelin sheath..

37. Copyright (c) Allyn & Bacon 200437  The Blood-Brain Barrier (BBB)  Features of the Blood-Brain Barrier Regulates the chemicals that can enter the CNS from the blood. Helps the CNS maintain the proper composition of fluids inside and outside the neurons.

38. Copyright (c) Allyn & Bacon 200438  The Blood-Brain Barrier (BBB)  Features of the Blood-Brain Barrier  Blood-brain barrier: A semipermeable barrier between the blood and the brain produced by cells in the walls of the brain’s capillaries.

39. Copyright (c) Allyn & Bacon 200439  The Blood-Brain Barrier (BBB)  Features of the Blood-Brain Barrier  Area postrema: A region of the medulla where the blood-brain barrier is weak; poisons can be detected there and can initiate vomiting.

40. Copyright (c) Allyn & Bacon 200440  Communication Within a Neuron  Measuring Electrical Potentials of Axons  Axons have two basic electrical potentials: Resting Membrane Potential Action Potential  The membrane potential can change: Depolarization Hyperpolarization Threshold of excitation

41. Copyright (c) Allyn & Bacon 200441  Communication Within a Neuron  Measuring Electrical Potentials of Axons  Membrane potential: The electrical charge across a cell membrane; the difference in electrical potential inside and outside the cell.

42. Copyright (c) Allyn & Bacon 200442 Copyright © Allyn & Bacon 2004

43. Copyright (c) Allyn & Bacon 200443  Communication Within a Neuron  Measuring Electrical Potentials of Axons  Resting membrane potential: The membrane potential of a neuron when it is not being altered by excitatory or inhibitory postsynaptic potentials; approximately -70 mV in the giant squid axon.

44. Copyright (c) Allyn & Bacon 200444  Communication Within a Neuron  Measuring Electrical Potentials of Axons  Depolarization: Reduction (toward zero) of the membrane potential of a cell from its normal resting potential.  Hyperpolarization: An increase in the membrane potential of a cell, relative to the normal resting potential.

45. Copyright (c) Allyn & Bacon 200445  Communication Within a Neuron  Measuring Electrical Potentials of Axons  Action potential: The brief electrical impulse that provides the basis for conduction of information along an axon.  Threshold of excitation: The value of the membrane potential that must be reached to produce an action potential.

46. Copyright (c) Allyn & Bacon 200446  Communication Within a Neuron  The Membrane Potential is the result of a balance between two forces.  Diffusion: Movement of molecules from a region of high concentration to regions of low concentration.  Electrostatic pressure : The force exerted by the attraction or repulsion of ions, Particles the same charge repel each other. Particles with different charges attract each other.

47. Copyright (c) Allyn & Bacon 200447  Communication Within a Neuron  The Membrane Potential is the result of a balance between two forces.  Diffusion: Movement of molecules from a region of high concentration to regions of low concentration, i.e. when you put sugar in your coffee the sugar goes to the bottom and over time would diffuse throughout the coffee.

48. Copyright (c) Allyn & Bacon 200448  Communication Within a Neuron  The Membrane Potential is the result of a balance between two forces.  Electrostatic Pressure The force exerted by the attraction or repulsion of ions. Particles with the same charge repel each other. Particles with opposite charges attract each other.

49. Copyright (c) Allyn & Bacon 200449  Communication Within a Neuron  The Membrane Potential  Ion: A charged molecule. Cations are positively charged, and anions are negatively charged.

50. Copyright (c) Allyn & Bacon 200450  Communication Within a Neuron  The Membrane Potential  Intracellular fluid: The fluid contained within cells.  Extracellular fluid: Body fluids located outside cells.  Sodium-potassium transporter: A protein found in the membrane of all cells that extrudes sodium ions.

51. Copyright (c) Allyn & Bacon 200451  Communication Within a Neuron  The Membrane Potential  Extracellular fluid: Body fluids located outside cells.

52. Copyright (c) Allyn & Bacon 200452  Communication Within a Neuron  The Membrane Potential  Intracellular fluid: The fluid contained within cells.

53. Copyright (c) Allyn & Bacon 200453  Communication Within a Neuron  The Membrane Potential  Sodium-potassium transporter: A protein found in the membrane of all cells that extrudes sodium ions.

54. Copyright (c) Allyn & Bacon 200454 Copyright © Allyn & Bacon 2004

55. Copyright (c) Allyn & Bacon 200455  Communication Within a Neuron  The Action Potential  Ion channel: A specialized protein molecule that permits specific ions to enter or leave the cell.

56. Copyright (c) Allyn & Bacon 200456  Communication Within a Neuron  The Action Potential  Voltage-dependent ion channel: An ion channel that opens or closes according to the value of the membrane potential.

57. Copyright (c) Allyn & Bacon 200457  Communication Within A Neuron  Conduction of the Action Potential:  All-or-none law: The principle that once an action potential is triggered in an axon, it is propagated without decrement to the end of the fiber.

58. Copyright (c) Allyn & Bacon 200458 Copyright © Allyn & Bacon 2004

59. Copyright (c) Allyn & Bacon 200459  Communication Within A Neuron  Conduction of the Action Potential:  Cable properties: The passive conduction of electrical current, in a decremental fashion, down the length of an axon.  Saltatory conduction: Conduction of action potentials by myelinated axons. The action potential appears to jump from one node of Ranvier to the next..

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61. Copyright (c) Allyn & Bacon 200461 Copyright © Allyn & Bacon 2004

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63. Copyright (c) Allyn & Bacon 200463  Communication Between Neurons  The Concept of Chemical Transmission  Postsynaptic potential: Alterations in the membrane potential of a postsynaptic neuron, produced by the liberation of neurotransmitter at the synapse.

64. Copyright (c) Allyn & Bacon 200464  Communication Between Neurons  The Concept of Chemical Transmission  Neuromodulator: A naturally secreted substance that acts like a neurotransmitter except that it is not restricted to the synaptic cleft but diffuses through the extracellular fluid.

65. Copyright (c) Allyn & Bacon 200465  Communication Between Neurons  Structures of Synapses  Presynaptic membrane: The membrane of a terminal button that lies adjacent to the postsynaptic membrane and through which the neurotransmitter is released.

66. Copyright (c) Allyn & Bacon 200466  Communication Between Neurons  Structures of Synapses  Synaptic cleft: The space between the presynaptic membrane and the postsynaptic membrane.  Synaptic vesicle: A small, hollow, beadlike structure found in the terminal buttons; contains molecules of a neurotransmitter.

67. Copyright (c) Allyn & Bacon 200467  Communication Between Neurons  Structures of Synapses  Release zone: A region of the interior of the presynaptic membrane of a synapse to which synaptic vesicles attach and release their neurotransmitter into the synaptic cleft.

68. Copyright (c) Allyn & Bacon 200468 Copyright © Allyn & Bacon 2004

69. Copyright (c) Allyn & Bacon 200469 Copyright © Allyn & Bacon 2004

70. Copyright (c) Allyn & Bacon 200470  Communication Between Neurons  Activation of Receptors  Postsynaptic receptor: A receptor molecule in the postsynaptic membrane of a synapse that contains a binding site for a neurotransmitter.  Neurotransmitter-dependent ion channel: An ion channel that opens when a molecule of a neurotransmitter binds with a postsynaptic receptor.

71. Copyright (c) Allyn & Bacon 200471  Communication Between Neurons  Activation of Receptors  Ionotropic receptor: A receptor that contains a binding site for a neurotransmitter and an ion channel that opens when a molecule of the neurotransmitter attaches to the binding site.

72. Copyright (c) Allyn & Bacon 200472  Communication Between Neurons  Activation of Receptors  Metabotropic receptor: A receptor that contains a binding site for a neurotransmitter; activates an enzyme that begins a series of events that opens an ion channel elsewhere in the membrane of the cell when a molecule of the neurotransmitter attaches to the binding site.

73. Copyright (c) Allyn & Bacon 200473  Communication Between Neurons  Activation of Receptors  G protein: A protein coupled to a metabotropic receptor; conveys messages to other molecules when a ligand binds with and activates the receptor.  Second messenger: A chemical produced when a g protein activates an enzyme; carries a signal that results in the opening of the ion channel or causes other events to occur in the cell.

74. Copyright (c) Allyn & Bacon 200474  Communication Between Neurons  Postsynaptic Potentials  Excitatory postsynaptic potential (EPSP): An excitatory depolarization of the postsynaptic membrane of a synapse caused by the liberation of a neurotransmitter by the terminal button.

75. Copyright (c) Allyn & Bacon 200475  Communication Between Neurons  Postsynaptic Potentials  Inhibitory postsynaptic potential (IPSP): An inhibitory hyperpolarization of the postsynaptic membrane of a synapse caused by the liberation of a neurotransmitter by the terminal button.

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78. Copyright (c) Allyn & Bacon 200478  Communication Between Neurons  Termination of Postsynaptic Potentials  Reuptake: The reentry of a neurotransmitter just liberated by a terminal button back through its membrane, thus terminating the postsynaptic potential.  Enzymatic deactivation: The destruction of a neurotransmitter by an enzyme after its release, for example, the destruction of acetylcholine by acetylcholinesterase.

79. Copyright (c) Allyn & Bacon 200479  Communication Between Neurons  Effects of Postsynaptic Potentials: Neural Integration  Neural integration: The process by which inhibitory and excitatory postsynaptic potentials summate and control the rate of firing of a neuron.

80. Copyright (c) Allyn & Bacon 200480  Communication Between Neurons  Autoreceptors  Autoreceptor: A receptor molecule located on a neuron that responds to the neurotransmitter released by that neuron.

81. Copyright (c) Allyn & Bacon 200481  Communication Between Neurons  Autoreceptors have a variety of functions: A receptor molecule located on the presynaptic neuron that responds to the neurotransmitter released by the presynaptic neuron. Regulate internal processes of the cell Regulate synthesis of the neurotransmitter Regulate the release of a neurotransmitter Generally serve to inhibit the activity of a transmitter