Chapter 12

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dw0975
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20337
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Chapter 12
Updated:
2010-05-27 18:24:31
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Bio
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Nervous System
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  1. Neurons
    functional units
  2. Neuroglia
    nourish and protect neurons
  3. Central Nervous System (CNS)
    • Spinal cord + brain
    • intergrates and coordinates sensory and motor information
  4. Peripheral Nervous System (PNS)
    All neural tissue outside CNS
  5. Afferent Division
    carries sensory info from receptors toward CNS
  6. Efferent Division
    Carries motor commands from CNS to effectors
  7. Somatic Nervous System (SNS)
    controls skeletal muscle contractions
  8. Autonomic Nervous System (ANS)
    Controls smooth/cardiac muscle contractions
  9. Sympathetic Division
    activiated during times of danger
  10. Parasympathetic Division
    Activated during times of NO danger
  11. Cell Body (soma)
    Contains large nucleus, cytoplasm (perokaryon) and Nissl Bodies (RER [rough endoplasmic reticulum] + ribosomes)
  12. Dendrites
    • Branched processes from the soma
    • carry impulses toward soma
  13. Axon
    • Long cytoplasmic processes with smaller branches (telodendria) ending in synaptic terminals
    • May branch into collaterals
    • Cytoplasm (axoplasm) and membrane (axolemma)
    • Base is axon hillock
    • Carry information away from soma
  14. Synapse Overview
    • synapse is where pre and post synaptic cells communicate thru release of chemicals across spaces called synaptic clefts
    • Neuron - Neuron (typical synapse)
    • Neuron - Gland (neuroglandular synapse)
    • Neuron - Muscle (neuromuscular synapse)
  15. Anaxonic Structure
    • small, no defined axon/dendrites
    • unknown function
  16. Bipolar Structure
    • small, cell body in middle, two distinct processes
    • found in eyes, ears
  17. Unipolar Structure
    • cell body to side, axon/dendrites are continuous
    • very long (~1m)
    • found in PNS
  18. Multipolar Structure
    • cell with axon, two or more dendrites
    • very long (~1m)
    • found in CNS
  19. Sensory (afferent neuron)
    (functional classification)
    • Unipolar
    • Axons (afferent fibers) that extend between the receptor and CNS
  20. Motor (efferent) Neuron
    (functional classification)
    • Multipolar
    • Axons (efferent fibers) extend between CNS and effectors
  21. Interneuron (Association Neuron)
    (functional classifcation)
    • Multipolar
    • Distribute information between the sensory neruon and motor neuron
  22. Ependymal Cells (neuroglia of CNS)
    • line central canal and vetricles of the brain
    • secretes and moves CSF
  23. Astrocytes (neuroglia of CNS)
    • large and numerous
    • cell extensions surround capillaries
    • maintain blood/brain barrier
  24. Microglia (neuroglia of CNS)
    remove cell debris and pathogens
  25. Oligodendrocytes (Neuroglia of CNS)
    • lipid-rich pads wrap axons to form a myelin sheath
    • sheath insulates and speeds up action potential
  26. Satellite Cells (neuroglia of PNS)
    surround cell bodies of PNS neurons
  27. Schwann Cells (neuroglia of PNS)
    • lipid-rich pads wrap axons to form a myelin sheath
    • lightly wrap unmyelinated axon
  28. Repair in PNS
    Wallerian Degeneration
    • Step 1: fragmentation of axon myelin occurs in distal stump
    • Step 2: schwann cells form cord, grow in cut, and unite stumps, macrophages engulf disintergrating axon and myelin
    • Step 3: Axon sends buds into network of Schwann cells and then starts growing along cord of schwann cells
    • Step 4: Axon continues to grow into distal stump and is enclosed in schwann cells
  29. Repair in CNS
    • limited due to numerous neurons and scarring
    • some released chemicals (of the inflammatory response) block axon regrowth
  30. Potential Difference
    when positive and negative charges are held apart
  31. Transmembrane Potential
    transmembrane potential is a potential difference across the membrane
  32. Current
    movement of charges to eliminate potential difference
  33. Resistance
    • membrane restricts ion movement
    • creates resistance to current
  34. Resting Potential
    • potential difference at rest is -70mV
    • inside has more K+ and negative proteins
    • outside has more Na+ and Cl-
    • K+ move through leak channels faster than Na+ moves in (negative proteins stay in cell) so inside is negative and outside is positive
  35. Chemical Gradient
    • high concentration of K+ inside and high concentration of Na+ outside
    • drives Na+ in and K+ out
  36. Electrical Gradient
    • high negative charge inside and high positive charge on the outside
    • drives sodium ions in and potassium ions in
  37. Electrochemical Gradient for Potassium Ions
    • drives potassium ions out of cell
    • less than chemical gradient alone due to opposing electrical gradient
  38. Electrochemical Gradient of Sodium Ions
    • drives sodium ions into the cell
    • greater than chemical gradient alone due to the aid of the electrical gradient
  39. Sodium/Potassium Pump
    • uses ATP to pump 3 sodiums out and 2 potassiums in
    • along with leak channels, the pump maintains resting potential of a cell
  40. Leak Channels
    Always open
  41. Gated (active) Channels
    open and close
  42. Chemically Regulated Channel
    open/close in response to chemicals
  43. Voltage Regulated Channel
    open/close in response to changes in the transmembrane potential
  44. Mechanically Regulated Channel
    open/close in response to physical stimulation
  45. Graded Potentials
    • changes in transmembrane potential that do not spread far from the point of stimulus
    • occur at axon hillock, can lead to action potential
  46. Depolarization
    shift in resting potential toward a more positive potential
  47. Repolarization
    the process of restoring resting potential
  48. Hyperpolarization
    increase in negative aspect of the resting potential
  49. Action Potential
    • changes in the transmembrane potential that affects the entire excitable membrane
    • occur at the axon
  50. All or None Principal
    • need stimulus large enough to reach threshold (+10mV) which opens voltage regulated sodium ion channels
    • actional potential properties are independent of the stimulus strength
  51. Generation of an Action Potential
    • stimulus causes depolarization to threshold
    • sodium ion channels open and sodium ions move in (depolarization)
    • sodium ion channels inactivated
    • potassium channels open and potassium ions move out (repolarization)
    • more potassium ions move out (hyperpolarization)
    • potassium ion channels close
    • sodium/potassium ion pump and leak channels restore resting potential
  52. Refractory Period
    time from beginning of action potential until the resting potential is stabilized
  53. Absolute Refractory Period
    • from the time when sodium ion channels open until sodium ion channel inactivation ends
    • membrane does not respond to second stimulus
  54. Relative Refractory Period
    • from when sodium ion channels regain their resting condition until transmembrane potential stabilizes
    • membrane responds to greater than normal second stimulus
  55. Propagation
    repeated action potential along entire membrane (axon)
  56. Continuous Propagation
    • action potential spreads along unmyelinated axon
    • Step 1 - an action potential develops in the initial segment, transmembrane potential depolarizes
    • Step 2 - local current depolarizes the adjacent portion
    • Step 3 - an action potential develops at this location and the initial segment enters refractory period
    • Step 4 - a local current depolarizes the adjacent portion of the membrane and the cycle is repeated
  57. Saltatory Propagation
    • action potential spreads along myelinated axon (faster)
    • the same steps happen but it happens node to node (skips over internode) causing it to be faster
  58. Axon Diameter
    increased diameter decreased resistance
  59. Type A Fibers
    • largest, myelinated, action potential = 140m/sec
    • deliver very important information
  60. Type B Fibers
    • smaller, myelinated, action potential = 18m/sec
    • delivers less urgent info
  61. Type C Fibers
    • smallest, unmyelinated, action potential = 1m/sec
    • delivers least urgent info
  62. Nerve Impulse
    • movement of the action potential along an axon
    • moves from presynaptic cell to a postsynaptic cell
  63. Electrical Synapse
    pre and postsynaptic cell have direct contact via gap junction
  64. Chemical Synapse
    • pre and postsynaptic cell do not have direct contact (synaptic cleft inbetween)
    • neurotransmitter released at synapse
  65. Excitatory Neurotransmitter
    causes depolarization and action potential
  66. Inhibitory Neurotransmitter
    causes hyperpolarization and prevents action potential
  67. Cholenergic Synapse
    • acetylcholine released
    • neuron-neuron synapses in CNS and PNS and neuromuscular junctions
    • action potential arrives, synpatic knob depolarizes, calcium ion channels open, calcium enters
    • entry of calcium ions causes acetylcholine release into synapse which binds receptors of postsynaptic membrane
    • postsynaptic membrane depolarizes
    • acetylcholinesterase digests acetylcholine
  68. Neurotransmitters
    result in changes in postsynaptic cell membrane permeability
  69. Norepinephrine (Noradrenaline)
    released at adrenergic synapses in CNS and ANS with excitatory effects
  70. Dopamine
    released in CNS with inhibatory role that helps control precise movements
  71. Serotonin
    released in CNS with effects on emotions and attention states
  72. Gamma-aminobutyric Acid (GABA)
    released at CNS with effect of reducing anxiety
  73. Neuromodulators
    • affect neurotransmitter release or postsynaptic cell response
    • peptide opioids for pain control
  74. Information Processing by Neurons
    integration process at axon hillock which determines action potential generation
  75. Postsynaptic Potentials
    graded potential at postsynaptic membrane in response to neurotransmitters
  76. Excitatory Postsynaptic Potential (EPSP)
    graded depolarization at postsynaptic membrane
  77. Inhibitory Postsynaptic Potential (IPSP)
    graded hyperpolarization at postsynaptic membrane
  78. Summation
    integrated effect of all graded potentials at membrane
  79. Temporal Summation
    add stimuli in quick succession
  80. Spacial Summation
    simultaneous stimuli having cumulative effects
  81. Facilitation
    • bring neuron transmembrane potential closer to threshold
    • dur to summation of EPSPs or drugs

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