Diese Präsentation wurde erfolgreich gemeldet.
Wir verwenden Ihre LinkedIn Profilangaben und Informationen zu Ihren Aktivitäten, um Anzeigen zu personalisieren und Ihnen relevantere Inhalte anzuzeigen. Sie können Ihre Anzeigeneinstellungen jederzeit ändern.

Central Nervous System 1

46.814 Aufrufe

Veröffentlicht am

  • DOWNLOAD FULL BOOKS, INTO AVAILABLE FORMAT ......................................................................................................................... ......................................................................................................................... 1.DOWNLOAD FULL. PDF EBOOK here { https://tinyurl.com/y6a5rkg5 } ......................................................................................................................... 1.DOWNLOAD FULL. EPUB Ebook here { https://tinyurl.com/y6a5rkg5 } ......................................................................................................................... 1.DOWNLOAD FULL. doc Ebook here { https://tinyurl.com/y6a5rkg5 } ......................................................................................................................... 1.DOWNLOAD FULL. PDF EBOOK here { https://tinyurl.com/y6a5rkg5 } ......................................................................................................................... 1.DOWNLOAD FULL. EPUB Ebook here { https://tinyurl.com/y6a5rkg5 } ......................................................................................................................... 1.DOWNLOAD FULL. doc Ebook here { https://tinyurl.com/y6a5rkg5 } ......................................................................................................................... ......................................................................................................................... ......................................................................................................................... .............. Browse by Genre Available eBooks ......................................................................................................................... Art, Biography, Business, Chick Lit, Children's, Christian, Classics, Comics, Contemporary, Cookbooks, Crime, Ebooks, Fantasy, Fiction, Graphic Novels, Historical Fiction, History, Horror, Humor And Comedy, Manga, Memoir, Music, Mystery, Non Fiction, Paranormal, Philosophy, Poetry, Psychology, Religion, Romance, Science, Science Fiction, Self Help, Suspense, Spirituality, Sports, Thriller, Travel, Young Adult,
       Antworten 
    Sind Sie sicher, dass Sie …  Ja  Nein
    Ihre Nachricht erscheint hier
  • Nice !! Download 100 % Free Ebooks, PPts, Study Notes, Novels, etc @ https://www.ThesisScientist.com
       Antworten 
    Sind Sie sicher, dass Sie …  Ja  Nein
    Ihre Nachricht erscheint hier
  • how can i download this presentation?
       Antworten 
    Sind Sie sicher, dass Sie …  Ja  Nein
    Ihre Nachricht erscheint hier
  • My dear, How are you today? i will like to be your friend My name is Sheikha Ghunaim , am a 43 years old divorcee. Please write to me in my email ( sheikhaghunaim2@hotmail.com ). im honest and open mind single woman. im going to tell more when i see your response. Regards Sheikha.
       Antworten 
    Sind Sie sicher, dass Sie …  Ja  Nein
    Ihre Nachricht erscheint hier
  • how can downlowad this
       Antworten 
    Sind Sie sicher, dass Sie …  Ja  Nein
    Ihre Nachricht erscheint hier

Central Nervous System 1

  1. 1. NERVOUS SYSTEM
  2. 2. NERVOUS FUNCTIONS <ul><li>Body’s master controlling and communicating system </li></ul><ul><li>Three functions </li></ul><ul><ul><li>Sensory input </li></ul></ul><ul><ul><ul><li>Gathers information from sensory receptors </li></ul></ul></ul><ul><ul><li>Integration </li></ul></ul><ul><ul><ul><li>Processes and interprets sensory input </li></ul></ul></ul><ul><ul><li>Motor output </li></ul></ul><ul><ul><ul><li>Activates effector organs to cause a response </li></ul></ul></ul>
  3. 3. Nervous System Organization
  4. 4. ORGANIZATION <ul><li>Two Principal Parts of the System </li></ul><ul><li>Central nervous system (CNS) </li></ul><ul><ul><li>Brain and spinal cord </li></ul></ul><ul><ul><li>Integrating and command center </li></ul></ul><ul><ul><ul><li>Interprets sensory input </li></ul></ul></ul><ul><ul><ul><li>Dictates motor responses </li></ul></ul></ul><ul><li>Peripheral nervous system (PNS) </li></ul><ul><ul><li>Nerves extending from brain and spinal cord </li></ul></ul><ul><ul><li>Carry impulses to and from the CNS </li></ul></ul>
  5. 5. PERIPHERAL DIVISIONS <ul><li>Two Functional Subdivisions of the PNS </li></ul><ul><li>Sensory division </li></ul><ul><ul><li>“ afferent division” </li></ul></ul><ul><ul><li>Nerve fibers conveying impulses to the CNS </li></ul></ul><ul><ul><ul><li>Somatic afferent fibers convey impulses from the skin, muscles, and joints </li></ul></ul></ul><ul><ul><ul><li>Visceral afferent fibers convey impulses from visceral organs </li></ul></ul></ul><ul><li>Motor division </li></ul><ul><ul><li>, “efferent division” </li></ul></ul><ul><ul><li>Nerve fibers conveying impulses from the CNS </li></ul></ul>
  6. 6. ORGANIZATION
  7. 7. HISTOLOGY <ul><li>Nervous system consists mainly of nervous tissue </li></ul><ul><li>Highly cellular </li></ul><ul><ul><li>e.g., <20% extracellular space in CNS </li></ul></ul><ul><li>Two principal cell types </li></ul><ul><ul><li>Neurons </li></ul></ul><ul><ul><ul><li>Excitable nerve cells that transmit electrical signals </li></ul></ul></ul><ul><ul><li>Supporting cells </li></ul></ul><ul><ul><ul><li>Smaller cells surrounding and wrapping neurons </li></ul></ul></ul><ul><ul><ul><li>“ Neuroglia” </li></ul></ul></ul>
  8. 8. NEUROGLIA <ul><li>“ Nerve glue” </li></ul><ul><li>Six types of small cells associated with neurons </li></ul><ul><ul><li>4 in CNS </li></ul></ul><ul><ul><li>2 in PNS </li></ul></ul><ul><li>Most have central cell body and branching processes </li></ul><ul><li>Several functions </li></ul><ul><ul><li>e.g., Supportive scaffolding for neurons </li></ul></ul><ul><ul><li>e.g., Electrical isolation of neurons </li></ul></ul><ul><ul><li>e.g., Neuron health and growth </li></ul></ul>
  9. 9. CNS NEUROGLIA <ul><li>Astrocytes </li></ul><ul><li>Microglia </li></ul><ul><li>Ependymal cells </li></ul><ul><li>Oligodendrocytes </li></ul>
  10. 10. CNS NEUROGLIA <ul><li>Astrocytes </li></ul><ul><li>Most abundant and versatile glial cells </li></ul><ul><li>Numerous processes support branching neurons </li></ul><ul><ul><li>Anchor neurons to capillary blood supply </li></ul></ul><ul><li>Guide migration of young neurons </li></ul><ul><li>Facilitate nutrient delivery to neurons </li></ul><ul><ul><li>(blood  glial cell  neuron) </li></ul></ul><ul><li>Control chemical environment around neurons </li></ul><ul><ul><li>Uptake of K + , neurotransmitters </li></ul></ul><ul><li>Communicate with astrocytes & neurons </li></ul><ul><ul><li>Gap junctions </li></ul></ul>
  11. 11. CNS NEUROGLIA <ul><li>Microglia </li></ul><ul><li>Small ovoid cells </li></ul><ul><li>Relatively long “thorny” processes </li></ul><ul><ul><li>Processes touch nearby neurons </li></ul></ul><ul><li>Migrate toward injured neurons </li></ul><ul><li>Transform into macrophage </li></ul><ul><ul><li>Phagocytize microorganisms, debris </li></ul></ul><ul><ul><li>(Cells of immune system cannot enter the CNS) </li></ul></ul>
  12. 12. CNS NEUROGLIA <ul><li>Ependymal Cells </li></ul><ul><li>Line central cavities of brain and spinal cord </li></ul><ul><ul><li>Form permeable barrier between cerebrospinal fluid inside these cavities and tissue fluid of CNS tissue </li></ul></ul><ul><li>Shapes range from squamous to columnar </li></ul><ul><li>Many are ciliated </li></ul><ul><ul><li>Beating helps circulate cerebrospinal fluid cushioning brain and spinal cord </li></ul></ul>
  13. 13. CNS NEUROGLIA <ul><li>Oligodendrocytes </li></ul><ul><li>Fewer processes than astrocytes </li></ul><ul><li>Wrap processes tightly around thicker neuron fibers in CNS </li></ul><ul><ul><li>“ Myelin sheath” </li></ul></ul><ul><ul><li>Insulating covering </li></ul></ul>
  14. 14. PNS NEUROGLIA <ul><li>Satellite cells </li></ul><ul><li>Schwann cells </li></ul>
  15. 15. PNS NEUROGLIA <ul><li>Satellite cells </li></ul><ul><li>Surround neuron cell bodies within ganglia </li></ul><ul><ul><li>(A ganglion is a collection of nerve cell bodies outside of the CNS) </li></ul></ul><ul><li>Function poorly understood </li></ul>
  16. 16. PNS NEUROGLIA <ul><li>Schwann cells </li></ul><ul><li>“ Neurolemmocytes” </li></ul><ul><li>Surround and form myelin sheaths around larger nerve fibers of PNS </li></ul><ul><ul><li>Functionally similar to oligodendrocytes </li></ul></ul><ul><li>Vital to regeneration of peripheral nerve fibers </li></ul>
  17. 17. NEURONS <ul><li>Nerve cells </li></ul><ul><li>Structural units of nervous system </li></ul><ul><ul><li>Billions are present in nervous system </li></ul></ul><ul><li>Conduct messages throughout body </li></ul><ul><ul><li>Nerve impulses </li></ul></ul><ul><li>Extreme longevity </li></ul><ul><ul><li>Can function optimally for entire lifetime </li></ul></ul><ul><li>Amitotic </li></ul><ul><ul><li>Ability to divide is lost in mature cells </li></ul></ul><ul><ul><li>Cannot be replaced if destroyed </li></ul></ul><ul><ul><ul><li>Some (very few) exceptions </li></ul></ul></ul><ul><ul><ul><li>e.g., stem cells present in olfactory epithelium can produce new neurons </li></ul></ul></ul><ul><ul><li>Stem cell research shows great promise in repairing damaged neurons </li></ul></ul><ul><li>High metabolic rate </li></ul><ul><ul><li>Require large amounts of oxygen and glucose </li></ul></ul>
  18. 18. Neurotrophins <ul><li>Promote neuron growth. </li></ul><ul><li>Nerve growth factors include: </li></ul><ul><ul><li>Nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), glial-derived neurotrophic factor (GDNF), neurotrophin-3, and neurotrophin-4/5. </li></ul></ul><ul><li>Fetus: </li></ul><ul><ul><li>Embryonic development of sensory neurons and sympathetic ganglia (NGF and neurotrophin-3). </li></ul></ul><ul><li>Adult: </li></ul><ul><ul><li>Maintenance of sympathetic ganglia (NGF). </li></ul></ul><ul><ul><li>Mature sensory neurons need for regeneration. </li></ul></ul><ul><ul><li>Required to maintain spinal neurons (GDNF). </li></ul></ul><ul><ul><li>Sustain neurons that use dopamine (GDNF). </li></ul></ul><ul><li>Myelin-associated inhibitory proteins: </li></ul><ul><ul><li>Inhibit axon regeneration. </li></ul></ul>
  19. 19. Neurons Axon of another neuron Dendrites of another neuron Cell Body Dendrites Axon Myelin Sheath
  20. 20. NEURONS <ul><li>Generally large, complex cells </li></ul><ul><li>Structures vary, but all neurons have the same basic structure </li></ul><ul><ul><li>Cell body </li></ul></ul><ul><ul><li>Slender processes extending from cell body </li></ul></ul><ul><ul><li>Plasma membrane is site of signaling </li></ul></ul>
  21. 21. NEURON CELL BODY <ul><li>Most neuron cell bodies are located in the CNS </li></ul><ul><ul><li>Protected by bones of skull or vertebral column </li></ul></ul><ul><li>Clusters of cell bodies in the CNS are termed “nuclei” </li></ul><ul><li>Clusters of cell bodies in the PNS are termed “ganglia” </li></ul>
  22. 22. NEURON CELL BODY <ul><li>a.k.a., “perikaryon” or “soma” </li></ul><ul><li>5 – 140  m in diameter </li></ul><ul><li>Transparent spherical nucleus </li></ul><ul><ul><li>Contains conspicuous nucleolus </li></ul></ul>
  23. 23. NEURON CELL BODY <ul><li>Major biosynthetic center of neuron </li></ul><ul><li>Other usual organelles present </li></ul><ul><ul><li>ER & ribosomes most active and best developed in body </li></ul></ul><ul><ul><ul><li>What do they do? </li></ul></ul></ul><ul><ul><li>Centrioles absent </li></ul></ul><ul><ul><ul><li>What do centrioles do? </li></ul></ul></ul><ul><ul><li>Sometimes contains pigment inclusions </li></ul></ul>
  24. 24. NEURON CELL BODY <ul><li>Focal point for the outgrowth of neuron processes during embryonic development </li></ul><ul><ul><li>Some processes receive signals </li></ul></ul><ul><ul><li>Plasma membrane generally also acts as part of the receptive surface </li></ul></ul>
  25. 25. NEURON PROCESSES <ul><li>Extend from the neuron’s cell body </li></ul><ul><li>CNS contains both neuron cell bodies and their processes </li></ul><ul><ul><li>Bundles of CNS processes are termed “tracts” </li></ul></ul><ul><li>PNS consists mainly of neuronal processes </li></ul><ul><ul><li>Bundles of PNS processes are termed “nerves” </li></ul></ul><ul><li>Two types of neuron processes </li></ul><ul><ul><li>Dendrites </li></ul></ul><ul><ul><li>Axons </li></ul></ul>
  26. 26. NEURON PROCESSES <ul><li>Typical Dendrite </li></ul><ul><li>Short, tapering, diffusely branching extensions </li></ul><ul><ul><li>Generally hundreds clustering close to cell body </li></ul></ul><ul><ul><li>Most cell body organelles also present in dendrites </li></ul></ul><ul><li>Main receptive / input regions </li></ul><ul><ul><li>Large surface area for receiving signals from other neurons </li></ul></ul><ul><ul><li>Convey incoming messages toward cell body </li></ul></ul><ul><ul><li>Short-distance signals are “graded potentials” </li></ul></ul><ul><ul><ul><li>Not action potentials </li></ul></ul></ul>
  27. 27. NEURON PROCESSES <ul><li>Typical Axon </li></ul><ul><li>Single axon per neuron </li></ul><ul><li>“ Axon hillock” of cell body narrows to form a slender process of uniform diameter </li></ul><ul><li>Sometimes very short </li></ul><ul><li>Sometimes very long </li></ul><ul><ul><li>e.g., axons controlling big toe are 3 – 4 feet long </li></ul></ul>
  28. 28. NEURON PROCESSES <ul><li>Typical Axon </li></ul><ul><li>Single axon may branch along length </li></ul><ul><li>“ Axon collaterals” extend from neurons at ~ 90 o angles </li></ul><ul><li>Usually branches profusely at end </li></ul><ul><ul><li>10,000 or more terminal branches is common </li></ul></ul><ul><ul><li>Distal endings termed “axonal terminals” </li></ul></ul>
  29. 29. NEURON PROCESSES <ul><li>Typical Axon </li></ul><ul><li>Conducting component of neuron </li></ul><ul><li>Generates nerve impulses </li></ul><ul><ul><li>Generated at axon hillock / axon junction in motor neurons </li></ul></ul><ul><ul><li>“ Trigger zone” </li></ul></ul><ul><li>Transmits nerve impulses away from cell body </li></ul><ul><ul><li>To axonal terminals </li></ul></ul>
  30. 30. NEURON PROCESSES <ul><li>Typical Axon </li></ul><ul><li>Axonal terminals are secretory component of neuron </li></ul><ul><li>Sequence of events </li></ul><ul><ul><li>Signal reaches terminals </li></ul></ul><ul><ul><li>Membranes of vesicles fuse with plasma membrane </li></ul></ul><ul><ul><ul><li>“ Axolemma” </li></ul></ul></ul><ul><ul><li>Neurotransmitters released </li></ul></ul><ul><ul><li>Neurotransmitters interact with either other neurons or effector cells </li></ul></ul><ul><ul><ul><li>Excite or inhibit </li></ul></ul></ul>
  31. 31. NEURON PROCESSES <ul><li>Typical Axon </li></ul><ul><li>Contains most of the same organelles found in dendrites and cell body </li></ul><ul><ul><li>Lacks ER and Golgi apparatus </li></ul></ul>
  32. 32. NEURON PROCESSES <ul><li>Typical Axon </li></ul><ul><li>Rely on cell body for some molecules </li></ul><ul><li>Rely on efficient transport mechanisms for delivery </li></ul><ul><ul><li>Anterograde movement toward axonal terminals </li></ul></ul><ul><ul><ul><li>e.g., Mitochondria, membrane components, neurotransmitters or enzymes required for neurotransmitter synthesis, etc. </li></ul></ul></ul><ul><ul><li>Retrograde movement toward cell body </li></ul></ul><ul><ul><ul><li>e.g., Organelles being returned for recycling </li></ul></ul></ul>
  33. 33. NEURON PROCESSES <ul><li>Typical Axon </li></ul><ul><li>Some viruses and bacterial toxins use retrograde transport to reach the cell body </li></ul><ul><ul><li>e.g., poliovirus, rabies virus, herpes simplex viruses, tetanus toxin, etc. </li></ul></ul><ul><li>Such viruses can be used as vehicles for the therapeutic delivery of engineered DNA </li></ul><ul><ul><li>“ Gene therapy” </li></ul></ul>
  34. 34. MYELIN SHEATH <ul><li>Whitish, fatty covering of many nerve fibers </li></ul><ul><ul><li>Particularly those long are large in diameter </li></ul></ul><ul><li>Protects and electrically insulates fibers </li></ul><ul><li>Increases speed of nerve impulse transmission </li></ul><ul><ul><li>Some axons and all dendrites are unmyelinated </li></ul></ul>
  35. 35. MYELIN SHEATH <ul><li>In PNS, myelin sheaths formed by Schwann cells </li></ul><ul><ul><li>Continually wrap around nerve </li></ul></ul><ul><ul><li>Cytoplasm gradually squeezed from intracellular space </li></ul></ul><ul><ul><li>Result is many concentric layers of plasma membrane surrounding the axon </li></ul></ul><ul><ul><ul><li>These plasma membranes contain little protein </li></ul></ul></ul><ul><ul><ul><ul><li>Some proteins present interlock adjacent membranes </li></ul></ul></ul></ul><ul><ul><li>Thickness depends on number of wrappings </li></ul></ul><ul><li>Nucleus and most of cytoplasm exist as a bulge external to the myelin sheath </li></ul><ul><ul><li>“ Neurilemma” </li></ul></ul>
  36. 36. MYELIN SHEATH <ul><li>Adjacent Schwann cells on axon do not touch each other </li></ul><ul><ul><li>Gaps in sheath occur at regular intervals </li></ul></ul><ul><ul><ul><li>“ Nodes of Ranvier” </li></ul></ul></ul><ul><ul><ul><li>a.k.a., “Neurofibril nodes” </li></ul></ul></ul><ul><ul><li>Axon collaterals can emerge at these nodes </li></ul></ul>
  37. 37. MYELIN SHEATH <ul><li>CNS contains both myelinated and unmyelinated axons </li></ul><ul><ul><li>Those long are large in diameter are typically myelinated </li></ul></ul><ul><li>Oligodendrocytes, not Schwann cells, form CNS myelin sheaths </li></ul><ul><ul><li>Oligodendrocytes possess numerous processes that can coil around numerous (up to 60) axons at once </li></ul></ul><ul><ul><ul><li>CNS myelin sheaths lack a neurilemma </li></ul></ul></ul>
  38. 38. MYELIN SHEATH <ul><li>White matter </li></ul><ul><ul><li>Regions of the brain and spinal cord containing dense collections of myelinated fibers </li></ul></ul><ul><li>Gray matter </li></ul><ul><ul><li>Regions of the brain and spinal cord containing mostly nerve cell bodies and unmyelinated fibers </li></ul></ul>
  39. 39. NEURON CLASSIFICATION <ul><li>Structural classification based upon number of processes </li></ul><ul><ul><li>Multipolar neurons </li></ul></ul><ul><ul><li>Bipolar neurons </li></ul></ul><ul><ul><li>Unipolar neurons </li></ul></ul><ul><li>Functional classification based upon direction nerve impulse travels </li></ul><ul><ul><li>Sensory (afferent) neurons </li></ul></ul><ul><ul><li>Motor (efferent) neurons </li></ul></ul><ul><ul><li>Interneurons (association neurons) </li></ul></ul>
  40. 40. NEURON CLASSIFICATION <ul><li>Structural Classification </li></ul><ul><li>Multipolar neurons </li></ul><ul><ul><li>Three or more processes </li></ul></ul><ul><ul><li>Most common neuron type in humans </li></ul></ul><ul><ul><ul><li>(> 99% of neurons) </li></ul></ul></ul><ul><li>Bipolar neurons </li></ul><ul><ul><li>Two processes – axon and dendrite </li></ul></ul><ul><ul><li>Found only in some special sense organs </li></ul></ul><ul><ul><ul><li>e.g., retina of eye </li></ul></ul></ul><ul><ul><li>Act as receptor cells </li></ul></ul><ul><li>Unipolar neurons </li></ul><ul><ul><li>Single short process </li></ul></ul><ul><ul><li>“ Pseudounipolar neurons” </li></ul></ul><ul><ul><ul><li>Originate as bipolar neurons </li></ul></ul></ul><ul><ul><ul><li>Two processes converge and fuse </li></ul></ul></ul><ul><ul><li>Process divides into proximal and distal branches </li></ul></ul><ul><ul><ul><li>Distal process often associated with a sensory receptor </li></ul></ul></ul><ul><ul><ul><ul><li>“ Peripheral process” </li></ul></ul></ul></ul><ul><ul><ul><li>Central process enters CNS </li></ul></ul></ul><ul><ul><li>Most are sensory neurons in PNS </li></ul></ul>
  41. 41. Classification of neurons by shape
  42. 42. NEURON CLASSIFICATION <ul><li>Functional Classification </li></ul><ul><li>Sensory (afferent) neurons </li></ul><ul><ul><li>Transmit impulses toward CNS </li></ul></ul><ul><ul><ul><li>From sensory receptors or internal organs </li></ul></ul></ul><ul><ul><li>Most are unipolar </li></ul></ul><ul><ul><li>Cell bodies are located outside CNS </li></ul></ul><ul><li>Motor (efferent) neurons </li></ul><ul><ul><li>Carry impulses away from CNS </li></ul></ul><ul><ul><ul><li>Toward effector organs </li></ul></ul></ul><ul><ul><li>Multipolar </li></ul></ul><ul><ul><li>Cell bodies generally located in the CNS </li></ul></ul><ul><li>Interneurons </li></ul><ul><ul><li>a.k.a., association neurons </li></ul></ul><ul><ul><li>Lie between motor and sensory neurons in neural pathways </li></ul></ul><ul><ul><li>Shuttle signals through CNS pathways where integration occurs </li></ul></ul><ul><ul><li>> 99% of neurons in body </li></ul></ul><ul><ul><li>Most are multipolar </li></ul></ul><ul><ul><li>Most are confined within the CNS </li></ul></ul>
  43. 43. NEUROPHYSIOLOGY <ul><li>Neurons are highly irritable </li></ul><ul><ul><li>Responsive to stimuli </li></ul></ul><ul><li>Response to stimulus is action potential </li></ul><ul><ul><li>Electrical impulse carried along length of axon </li></ul></ul><ul><ul><li>Always the same regardless of stimulus </li></ul></ul><ul><ul><li>The underlying functional feature of the nervous system </li></ul></ul>
  44. 44. ION CHANNELS <ul><li>Plasma membranes contain various ion channels </li></ul><ul><li>Passive channels (leakage channels) </li></ul><ul><ul><li>Always open </li></ul></ul><ul><li>Active channels (gated channels) </li></ul><ul><ul><li>Ligand-gated channels </li></ul></ul><ul><ul><ul><li>Open when specific chemical binds </li></ul></ul></ul><ul><ul><li>Voltage-gated channels </li></ul></ul><ul><ul><ul><li>Open and close in response to membrane potential </li></ul></ul></ul><ul><ul><li>Mechanically-gated channels </li></ul></ul><ul><ul><ul><li>Open in response to physical deformation of receptor </li></ul></ul></ul><ul><ul><ul><ul><li>e.g., touch and pressure receptors </li></ul></ul></ul></ul>
  45. 45. MEMBRANE POTENTIALS <ul><li>A voltage exists across the plasma membrane </li></ul><ul><ul><li>Due to separation of oppositely charged ions </li></ul></ul><ul><li>Potential difference in a resting membrane is termed its “resting membrane potential” </li></ul><ul><ul><li>~ -70 mV in a resting neuron </li></ul></ul><ul><ul><li>Membrane is “polarized” </li></ul></ul>
  46. 46. MEMBRANE POTENTIALS <ul><li>Neurons use changes in membrane potentials as signals </li></ul><ul><ul><li>Used to receive, integrate, and send signals </li></ul></ul><ul><li>Changes in membrane potentials produced by </li></ul><ul><ul><li>Anything changing membrane permeability to ions </li></ul></ul><ul><ul><li>Anything altering ion concentrations </li></ul></ul><ul><li>Two types of signals </li></ul><ul><ul><li>Graded potentials </li></ul></ul><ul><ul><ul><li>Short-distance signals </li></ul></ul></ul><ul><ul><li>Action potentials </li></ul></ul><ul><ul><ul><li>Long-distance signals </li></ul></ul></ul>
  47. 47. MEMBRANE POTENTIALS <ul><li>Graded Potentials </li></ul><ul><li>Short-lived local changes in membrane potential </li></ul><ul><ul><li>Either depolarizations or hyperpolarizations </li></ul></ul><ul><li>Cause current flows that decrease in magnitude with distance </li></ul><ul><li>Magnitude of potential dependent upon stimulus strength </li></ul><ul><ul><li>Stronger stimulus  larger voltage change </li></ul></ul><ul><ul><li>Larger voltage change  farther current flows </li></ul></ul>
  48. 48. MEMBRANE POTENTIALS <ul><li>Graded Potentials </li></ul><ul><li>Triggered by change in neuron’s environment </li></ul><ul><ul><li>Change causes gated ion channels to open </li></ul></ul><ul><li>Small area of neuron’s plasma membrane becomes depolarized (by this stimulus) </li></ul><ul><li>Current flows on both sides of the membrane </li></ul><ul><ul><li>+ moves toward – and vise versa </li></ul></ul>
  49. 49. MEMBRANE POTENTIALS <ul><li>Graded Potentials </li></ul><ul><li>Inside cell: + ions move away from depolarized area </li></ul><ul><li>Outside cell: + ions move toward depolarized area </li></ul><ul><ul><li>(+ and – ions switch places) </li></ul></ul><ul><li>Membrane is leaky </li></ul><ul><ul><li>Most of the charge is quickly lost through membrane </li></ul></ul><ul><ul><li>Current dies out after traveling a short distance </li></ul></ul>
  50. 50. MEMBRANE POTENTIALS <ul><li>Graded Potentials </li></ul><ul><li>Act as signals over very short distances </li></ul><ul><li>Important in initiating action potentials </li></ul>
  51. 51. MEMBRANE POTENTIALS <ul><li>Action Potentials </li></ul><ul><li>Principal means by which neurons communicate </li></ul><ul><ul><li>Brief reversal of membrane potential </li></ul></ul><ul><ul><ul><li>Total amplitude of ~ 100 mV (-70  +30) </li></ul></ul></ul><ul><ul><li>Depolarization followed by repolarization, then brief period of hyperpolarization </li></ul></ul><ul><ul><li>Time for entire event is only a few milliseconds </li></ul></ul><ul><li>Events in generation and transmission of an action potential identical between neurons and skeletal muscle cells </li></ul>
  52. 52. ACTION POTENTIALS
  53. 53. ACTION POTENTIALS <ul><li>Not all local depolarizations produce action potentials </li></ul><ul><li>Depolarization must reach threshold values </li></ul><ul><ul><li>Brief, weak stimuli produce subthreshold depolarizations that are not translated into nerve impulses </li></ul></ul><ul><ul><li>Stronger threshold stimuli produce depolarizing events </li></ul></ul>
  54. 54. ACTION POTENTIALS <ul><li>Action potential is all-or-nothing phenomenon </li></ul><ul><ul><li>Happens completely or doesn’t happen </li></ul></ul><ul><li>Independent of stimulus strength once generated </li></ul><ul><ul><li>Strong stimuli generate more impulses of the same strength per unit time </li></ul></ul><ul><ul><li>Intensity is determined by number of impulses per unit time </li></ul></ul>
  55. 55. ACTION POTENTIALS <ul><li>Refractory Periods </li></ul><ul><li>Neuron cannot respond to a second stimulus while the Na + channels are still open from previous stimulus </li></ul><ul><ul><li>This period of time is termed the “absolute refractory period” </li></ul></ul><ul><li>“ Relative refractory period” follows the absolute refractory period </li></ul><ul><ul><li>Repolarization is occurring </li></ul></ul><ul><ul><li>Threshold for impulse generation is elevated </li></ul></ul><ul><ul><ul><li>Only strong stimuli can generate impulses </li></ul></ul></ul>
  56. 56. ACTION POTENTIALS <ul><li>Conduction Velocities </li></ul><ul><li>Conduction velocities of neurons vary widely </li></ul><ul><li>Rate of impulse propagation dependent upon </li></ul><ul><ul><li>Axon diameter </li></ul></ul><ul><ul><ul><li>Larger axons conduct impulses faster </li></ul></ul></ul><ul><ul><li>Degree of myelination </li></ul></ul><ul><ul><ul><li>Myelin sheath dramatically increases rate of propagation </li></ul></ul></ul><ul><ul><ul><ul><li>Myelin acts as an insulator to prevent almost all leakage from axon </li></ul></ul></ul></ul>
  57. 57. ACTION POTENTIALS <ul><li>Multiple Sclerosis (MS) </li></ul><ul><li>Autoimmune disease mainly affecting young adults </li></ul><ul><li>Myelin sheaths in CNS are gradually destroyed </li></ul><ul><li>Interferes with impulse conduction </li></ul><ul><ul><li>Visual disturbances, muscle control problems, speech disturbances, etc. </li></ul></ul><ul><li>Some modern treatments showing some promise in delaying problems </li></ul>
  58. 58. NERVE FIBERS <ul><li>Classified based on </li></ul><ul><ul><li>Diameter </li></ul></ul><ul><ul><li>Degree of myelination </li></ul></ul><ul><ul><li>Conduction speed </li></ul></ul>
  59. 59. NERVE FIBER CLASSIFICATION <ul><li>Group A fibers </li></ul><ul><ul><li>Largest diameter </li></ul></ul><ul><ul><li>Thick myelin sheaths </li></ul></ul><ul><ul><li>Conduct impulses at high speeds (> 300 mph) </li></ul></ul><ul><ul><li>Mostly somatic sensory ad motor fibers serving skin, skeletal muscles, and joints </li></ul></ul><ul><li>Group B fibers </li></ul><ul><ul><li>Intermediate diameter </li></ul></ul><ul><ul><li>Lightly myelinated </li></ul></ul><ul><ul><li>Transmit impulses at moderate speeds (40 mph) </li></ul></ul><ul><li>Group C fibers </li></ul><ul><ul><li>Smallest diameter </li></ul></ul><ul><ul><li>Unmyelinated </li></ul></ul><ul><ul><li>Transmit impulses comparatively slowly (2 mph or less) </li></ul></ul>
  60. 60. Nerve Fiber Classification <ul><li>General classification scheme (Erlanger-Gasser): </li></ul><ul><ul><li>A fibers: Myelinated </li></ul></ul><ul><ul><ul><li>Subtypes:  some overlap in ranges  </li></ul></ul></ul><ul><ul><ul><li>Fastest conducting and largest diameter –  m/sec,  </li></ul></ul></ul><ul><ul><ul><li>“ A” often dropped: alpha motor neuron </li></ul></ul></ul><ul><ul><li>B fibers: Slower myelinated (seldom used) </li></ul></ul><ul><ul><li>C fibers: Unmyelinated </li></ul></ul><ul><ul><ul><li>Slower conducting than As and smallest diameter (0.5 m/sec, 0.5  ) </li></ul></ul></ul>
  61. 61. Nerve Fiber Classification <ul><li>Sensory nerve classification (Lloyd-Hunt): </li></ul><ul><ul><li>I, II, III fibers: Myelinated </li></ul></ul><ul><ul><ul><li>Subtypes: Ia, Ib  </li></ul></ul></ul><ul><ul><ul><li>Fastest conducting and largest diameter – Ia </li></ul></ul></ul><ul><ul><li>IV fibers: Unmyelinated </li></ul></ul><ul><ul><ul><li>Slower conducting than IIIs and smallest diameter </li></ul></ul></ul>
  62. 62. SYNAPSE <ul><li>Junction mediating information transfer from one neuron to another neuron or an effector cell </li></ul><ul><li>Axodendritic synapses </li></ul><ul><ul><li>Axonal endings  dendrites of second neuron </li></ul></ul><ul><li>Axosomatic synapses </li></ul><ul><ul><li>Axonal endings  cell body of neuron </li></ul></ul><ul><li>Presynaptic neuron </li></ul><ul><ul><li>Conducts impulses toward the synapse </li></ul></ul><ul><li>Postsynaptic neuron </li></ul><ul><ul><li>Transmits impulse away from the synapse </li></ul></ul>
  63. 63. SYNAPSE TYPES <ul><li>Electrical Synapses </li></ul><ul><li>Less common than chemical synapses </li></ul><ul><li>Correspond to gap junctions found elsewhere </li></ul><ul><ul><li>Cytoplasm of adjacent neurons connected through protein channels </li></ul></ul><ul><ul><li>Ions flow directly between neurons </li></ul></ul><ul><ul><li>Neurons are “electrically coupled” </li></ul></ul><ul><li>Transmission across synapse is very rapid </li></ul>
  64. 64. SYNAPSE TYPES <ul><li>Chemical Synapses </li></ul><ul><li>Specialized for release & reception of neurotransmitters </li></ul><ul><li>Two parts </li></ul><ul><ul><li>Axonal terminal of presynaptic neuron </li></ul></ul><ul><ul><ul><li>Contains numerous synaptic vesicles filled with neurotransmitter molecules </li></ul></ul></ul><ul><ul><li>Neurotransmitter receptor region </li></ul></ul><ul><ul><ul><li>Present on dendrite or cell body of postsynaptic neuron </li></ul></ul></ul><ul><li>Separated by synaptic cleft </li></ul><ul><ul><li>Remember this stuff in muscles? </li></ul></ul>
  65. 65. SYNAPSE <ul><li>Nerve impulse reaches axonal terminal </li></ul><ul><li>Voltage-gated Ca 2+ channels open in axon </li></ul><ul><ul><li>Ca 2+ enters presynaptic neuron </li></ul></ul><ul><li>Neurotransmitter is released via exocytosis </li></ul><ul><ul><li>Vesicles fuse with axonal membrane </li></ul></ul><ul><li>Neurotransmitter binds to postsynaptic receptors </li></ul><ul><li>Ion channels open in postsynaptic membrane </li></ul><ul><ul><li>Result is excitation or inhibition </li></ul></ul>
  66. 66. SYNAPSE <ul><li>Binding of neurotransmitter to its receptor is reversible </li></ul><ul><li>Permeability affected as long as neurotransmitter is bound to its receptor </li></ul><ul><li>Neurotransmitters do not persist in the synaptic cleft </li></ul><ul><ul><li>Degraded by enzymes associated with postsynaptic membrane </li></ul></ul><ul><ul><li>Reuptake by astrocytes or presynaptic terminal </li></ul></ul><ul><ul><li>Diffusion of neurotransmitters away from synapse </li></ul></ul>
  67. 67. SYNAPSE <ul><li>Transmission of impulses along axon can be very fast </li></ul><ul><ul><li>Up to 300 mph (150 m/s) </li></ul></ul><ul><li>Transmission of a signal across a synapse is slow in comparison </li></ul><ul><ul><li>Leads to “synaptic delay” </li></ul></ul><ul><ul><li>~0.3 0 5.0 milliseconds </li></ul></ul><ul><ul><li>Rate-limiting step of neural transmission </li></ul></ul><ul><ul><li>Transmission along multisynaptic pathways is slower than along pathways with fewer synapses </li></ul></ul>
  68. 68. SYNAPSE <ul><li>Postsynaptic Potentials </li></ul><ul><li>Many receptors present on postsynaptic membranes open ion channels </li></ul><ul><ul><li>Ligand-gated channels </li></ul></ul><ul><ul><li>Electrical signal converted to chemical signal converted to electrical signal </li></ul></ul><ul><ul><li>Graded potential is produced </li></ul></ul><ul><ul><ul><li>Magnitude is dependent upon amount of neurotransmitter released </li></ul></ul></ul><ul><ul><ul><li>Action potential may be produced </li></ul></ul></ul><ul><ul><li>Either excitatory or inhibitory </li></ul></ul>
  69. 69. SYNAPSE <ul><li>Excitatory Synapses </li></ul><ul><li>Neurotransmitter binding causes depolarization </li></ul><ul><ul><li>Single type of channel opens in membrane </li></ul></ul><ul><ul><li>Na + and K + simultaneously diffuse through the membrane in opposite directions </li></ul></ul><ul><ul><li>Na + influx exceeds K + efflux </li></ul></ul><ul><ul><li>Net depolarization occurs </li></ul></ul><ul><ul><li>Local graded depolarization events formed </li></ul></ul><ul><ul><ul><li>“ Excitatory postsynaptic potential (EPSP)” </li></ul></ul></ul><ul><ul><ul><li>May trigger an action potential at axon hillock </li></ul></ul></ul><ul><ul><ul><ul><li>Voltage-gated channels at hillock open, etc. </li></ul></ul></ul></ul>
  70. 70. SYNAPSE <ul><li>Inhibitory Synapses </li></ul><ul><li>Neurotransmitter binding reduces a postsynaptic neuron’s ability to generate an action potential </li></ul><ul><ul><li>Increased permeability to K + and Cl - , not Na + </li></ul></ul><ul><ul><li>Postsynaptic neuron becomes less likely to fire </li></ul></ul><ul><ul><li>“ Inhibitory postsynaptic potential (IPSP)” </li></ul></ul>
  71. 71. SYNAPSE <ul><li>Summation </li></ul><ul><li>A single ESPS cannot induce an action potential </li></ul><ul><ul><li>Requires multiple axonal termini firing in concert </li></ul></ul><ul><ul><ul><li>Hundreds or thousands of EPSPs act together </li></ul></ul></ul><ul><ul><ul><ul><li>“ Summation” </li></ul></ul></ul></ul><ul><li>Two types of summation </li></ul><ul><ul><li>Temporal summation </li></ul></ul><ul><ul><ul><li>One or more neurons transmit in rapid succession </li></ul></ul></ul><ul><ul><li>Spatial summation </li></ul></ul><ul><ul><ul><li>Simultaneous stimulation by numerous termini from one or more neurons </li></ul></ul></ul><ul><ul><li>(Both EPSPs and IPSPs summate) </li></ul></ul>
  72. 72. SYNAPSE <ul><li>Synaptic Potentiation </li></ul><ul><li>Repeated or continuous use of a synapse enhances presynaptic neuron’s ability to excite </li></ul><ul><ul><li>Larger postsynaptic potentials produced </li></ul></ul><ul><ul><li>“ Synaptic potentiation” </li></ul></ul><ul><ul><ul><li>Greater [Ca++] inside presynaptic terminals </li></ul></ul></ul><ul><ul><ul><li>More neurotransmitter released </li></ul></ul></ul><ul><ul><ul><li>Larger EPSPs produced </li></ul></ul></ul>
  73. 73. SYNAPSE <ul><li>Presynaptic Inhibition </li></ul><ul><li>Release of excitatory neurotransmitter can be inhibited by activity of another neuron </li></ul><ul><ul><li>Less neurotransmitter released and bound </li></ul></ul>
  74. 74. NEUROTRANSMITTERS <ul><li>More than fifty neurotransmitters identified </li></ul><ul><li>Most neurons make two or more </li></ul><ul><ul><li>Can be released singly or together </li></ul></ul><ul><li>Classification by Structure </li></ul><ul><li>Acetylcholine (ACh) </li></ul><ul><li>Biogenic amines </li></ul><ul><li>Amino acids </li></ul><ul><li>Peptides </li></ul><ul><li>ATP </li></ul><ul><li>Dissolved gases </li></ul><ul><li>Classification by Function </li></ul><ul><li>Excitatory/Inhibitory </li></ul><ul><li>Direct/Indirect </li></ul>
  75. 75. NEURAL INTEGRATION <ul><li>Neurons function in groups, not singly </li></ul><ul><li>These various components must interact </li></ul><ul><li>Multiple levels of neural integration </li></ul>
  76. 76. NEURONAL POOLS <ul><li>Neurons in CNS are organized into pools </li></ul><ul><ul><li>Functional groups </li></ul></ul><ul><ul><li>Integrate incoming information </li></ul></ul><ul><ul><li>Forward processed information </li></ul></ul>
  77. 77. NEURONAL POOLS <ul><li>Simple Neuronal Pool </li></ul><ul><li>Incoming fiber branches profusely upon entering pool </li></ul><ul><li>EPSPs induced in multiple postsynaptic neurons </li></ul><ul><li>EPSPs exceed threshold in some neurons </li></ul><ul><ul><li>Mainly those with multiple synaptic contacts </li></ul></ul><ul><li>EPSPs do not exceed threshold in some neurons </li></ul><ul><ul><li>Mainly those with fewer synaptic contacts </li></ul></ul><ul><ul><li>Some close to threshold </li></ul></ul><ul><ul><ul><li>“ Facilitated zone” </li></ul></ul></ul>
  78. 78. TYPES OF CIRCUITS <ul><li>Patterns of synaptic connections in neuronal pools are called circuits </li></ul><ul><ul><li>Determine neuronal pool’s functional capabilities </li></ul></ul><ul><li>Four basic circuit patterns </li></ul><ul><ul><li>Diverging circuits </li></ul></ul><ul><ul><li>Converging circuits </li></ul></ul><ul><ul><li>Reverberating (oscillating) circuits </li></ul></ul><ul><ul><li>Parallel after-discharge circuits </li></ul></ul>
  79. 79. TYPES OF CIRCUITS <ul><li>Diverging (Amplifying) Circuit </li></ul><ul><li>One incoming fiber triggers responses in ever-increasing numbers of neurons </li></ul><ul><li>Common in both sensory and motor systems </li></ul>
  80. 80. TYPES OF CIRCUITS <ul><li>Converging Circuits </li></ul><ul><li>Pool receives inputs from several neurons </li></ul><ul><li>Circuit has “funneling” effect </li></ul><ul><li>Common in sensory and motor systems </li></ul>
  81. 81. TYPES OF CIRCUITS <ul><li>Reverberating (Oscillating) Circuits </li></ul><ul><li>Incoming signal travels through chain of neurons </li></ul><ul><li>Each neuron makes synapses with neurons upstream in the pathway </li></ul><ul><li>Involved in rhythmic activities (e.g., breathing) </li></ul>
  82. 82. TYPES OF CIRCUITS <ul><li>Parallel After-Discharge Circuits </li></ul><ul><li>Incoming fiber stimulated parallel neuron arrays </li></ul><ul><li>Parallel arrays ultimately stimulate a common output cell </li></ul><ul><ul><li>Create prolonged burst of impulses </li></ul></ul><ul><li>Involved in complex mental processing </li></ul>
  83. 83. PROCESSING PATTERNS <ul><li>Serial input processing </li></ul><ul><ul><li>Input travels along one pathway to a specific destination </li></ul></ul><ul><ul><li>All-or-nothing function of system </li></ul></ul><ul><ul><ul><li>e.g., reflexes </li></ul></ul></ul><ul><li>Parallel input processing </li></ul><ul><ul><li>Inputs are segregated into multiple pathways </li></ul></ul><ul><ul><ul><li>Integrated in different CNS regions </li></ul></ul></ul><ul><ul><ul><li>Different circuits do different things with input </li></ul></ul></ul><ul><ul><ul><ul><li>Not repetitious </li></ul></ul></ul></ul>

×