Neuro Exam 1.7

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Neuro Exam 1.7
2013-02-01 16:15:15
neurology neuroscience antomoy

review of neuro lecture 7 for exam 1
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  1. What are two types of excitable neurons?
    • action
    • graded
  2. Excitable neuron
    • if a neuron is charged, it is excitable
    • it can communicate b/w 2 points
    • -electrochemical signal is needed for communication
    • action potentials
    • graded potentials
    • -receptor potentials
    • generator potentials
    • synaptic potentials
  3. Action potential:
    an electrical signal based on depolarization of a neuron, which travels its full length (big difference b/w action and graded), based on the flow of ions into and out of the cell
  4. Where does an action potential begin?
    depends on location in NS
  5. Where does AP begin for a sensory neuron?
    at 1st node of ranvier on the distal process of the sensory neuron
  6. Where does the lower motor neuron AP begin?
    axon hillock
  7. What is the axon hillock?
    where the cell body tapers off
  8. Where does AP begin for projection neurons?
    axon hillock
  9. What is a projection neuron?
    projects from one point to another in brain
  10. Where does AP for commissural neuron begin?
    axon hillock
  11. Where does AP for association neuron begin?
    axon hillock
  12. What does threshold of activation mean?
    What does it take for a neuron to fire?
  13. Threshold of activation:
    critical level of depolarization of neuron's membrane at which the cell can actively generate an AP
  14. What is the threshold of activation in humans?
  15. What does the "all or none law" have to do with threshold of activation?
    • once an action potential starts, it will not stop
    • no matter how fast or slow it takes to reach the threshold, the AP will fire at the same velocity
    • you either activate it, or you don't
  16. What is required to activate threshold?
  17. What makes cell membrane permeable?
    • Energy that could be:
    • -mechanical-voltage gated channels
    • -chemical-ligand gated channels
    • -heat
    • -nociceptive (pain)
    • -electromagnetic
  18. Depolarization:
    after membrane potential is reached there is an influx of NA ions through voltage-gated channels causing depolarization of cell membrane.  When Na comes in, there is a reversal of polarity.  More positive ions inside, tendency to change polarity in inside to be positive and outside to be negative
  19. Stimulation of various kinds will cause a change in cell membrane to make it 600x more:
    permeable to Na
  20. What is the key to action potentials?
    based on the function of Na permeability--influx of Na due to stimulation (mechanical, chemical, heat, general sensation)
  21. What is depolarizaiton due to?
    influx of Na using voltage-gated channels
  22. Does Na conduct to a high or low concentration when passing through a voltage-gated channel?
    high concentration
  23. Na conducts to high concentration and passes through voltage gated channel changing the shape of the membrane and also changing:
    the voltage
  24. W/in milliseconds (of depolarization), Na equilibrium is reached and Na channels:
  25. During depolarization, K gated channels:
    open and let K out of cell
  26. When is K let out of the cell?
    at the same time Na is coming in
  27. Repolarization:
    occurs as a result of efflux of K, reestablishing RMP
  28. An action potential only takes a few ___ ions to cause depolarization.
  29. An action potential only takes a few ___ ions to cause repolarization.
  30. Repeated AP over time results in:
    excess of Na and K, causing an imbalance
  31. How is excess Na and K taken up to maintain the concentration gradient?
    Na/K pump
  32. How many AP would be needed to deplete the concentration gradient to where no more AP will take place?
  33. Local Currents/circuits
    • occur during depolarization; flow from region of positive potential to negative potential
    • decrease in membrane potential ahead of depolarized region occurs, bringing it to threshold
    • -same currents responsible for repolarizing the membrane behind the impulse
    • -consequence of difference in potentials, doesn't create those differences
  34. What are the types of conduction?
    • saltatory
    • continuous
  35. Saltatory conduction involves what kind of neurons?
  36. Are saltatory conduction more rapid or less than non-myelinated?
  37. How fast is saltatory conduction?
  38. How does saltatory conduction work?
    leaps from one node of raniver to another (entire axon does not have to be depolarized
  39. What are examples of saltatory conduction?
    lower motor neurons, proprioceptors (Type 1)
  40. What type of neurons are involved in continuous conduction?
  41. Is continuous conduction faster or slower than myelinated neurons?
  42. How fast is a continuous conduction?
  43. What are examples of continuous conduction?
    Type III (A-delta) and Type IV (C-fibers) (pain receptors)
  44. What determines AP velocity?
    • where or not the axon is myelinated
    • axon diameter
  45. How does the diameter of the axon help to determine AP?
    • the greater the diameter the faster the AP
    • b/c there is less resistance w/ a large diameter than w/ a small diameter (fire hose v. water hose)
  46. Are faster neurons myelinated or non-myelinated?
  47. Hyperpolarization:
    increases the negativity
  48. Following an AP there is a transient:
    hyperpolarization (excessive intracellular negativity)
  49. What happens during hyperpolarization?
    K channels that open during the latter phase of the AP close milliseconds after the RMP has been reached
  50. When does hyperpolarization occur?
    during repolarization, ending w/ excessive negative charge intracellulary
  51. Hyperpolarization is a brief increase in membrane potential that occurs because K channel that opened during the latter pahse of AP:
    closed milliseconds after RMP has been reached
  52. During hyperpolarization, the membrane potential becomes further from:
    threshold of activation
  53. During hyperpolarization, the concentration gradient becomes:
  54. Hyperpolarization is what kind of process?
  55. What are the different types of refractory periods?
    • absolute
    • relative
  56. When does the absolute refractory period occur?
    immediately following an AP
  57. What is an absolute refractory period?
    no matter what the stimulation, the cell cannot create an AP
  58. What is a relative refractory period mean?
    it is possible to trigger an AP, but stimulation must be stronger than normal
  59. When does the relative refractory period occur?
    follows the absolute refractory period
  60. Refractory periods are due to:
    the residual inactivation of Na channels and the opening of K channels
  61. Graded potentials are also called:
    local potentials
  62. Graded potentials:
    • transitions b/w RMP and AP
    • doesn't travel distance of neuron and fades away
  63. Are graded potentials propagating?
  64. Do graded potentials have a threshold?
  65. Do graded potentials have a refractory period?
  66. Are graded potentials faster or slower than AP?
  67. 1000s of localized depolarization might be enough to generate an:
  68. What do graded potentials need to reach threshold?
    additive effect
  69. What are the different forms of graded potentials?
    • receptor potential
    • generator potential
    • synaptic potential
  70. Receptor potential:
    cells are small modified neurons located on the distal end of a sensory neuron (CN VIII vestibular cochlear)
  71. What do receptor potentials release?
    NTM onto receptor organs
  72. What must receptor potential cells do to release NTM?
    cell needs to partially depolarize (making it a graded potential)
  73. Where are receptor potentials found?
    only in hair cells of the inner ear
  74. Are receptor potentials common?
  75. Generator potentials involve:
    receptor organ of sensory neuron (always on distal end of sensory neuron)
  76. Where are generator potentials only found?
  77. What do generator potentials respond to?
    all types of sensation (energy of some sort)
  78. What mediates generator potentials?
    • heat - voltage-gated (mechanical)
    • voltage-gated channels
    • ligand-gated channels
  79. What do voltage-gated channels respond to?
    mechanical stimulation
  80. What do voltage-gated channels open to?
  81. What happens during a generator potential when a voltage-gated channel opens to Na?
    Na moves in causing depolarization of receptor organ but it doesn't get it to -60mV. Therefore, it is just a grade potential
  82. Ligand-gated channels respond to:
    chemical stimulation
  83. Ligand-gated channels open up to?
  84. What happens during generator potential when ligand-gated channels open up to Na?
    chemicals bind to channels and they open up allowing Na in
  85. With mechanical energy, deformation of the cell membrane causes:
    localized (partial) depolarization to occur by opening Na voltage-gated channels, allowing an influx of Na, however, it is not enough to generate an AP
  86. Ligand-gated - chemical stimulation provides:
    localized depolarization
  87. Do generator potentials abide by all-or-none law?
    no, their amplitude and duration vary and threshold may or may not be reached
  88. Can generator potentials instigate an AP?
    never, localized is less than threshold
  89. Where does an AP start?
    at first Node of Ranvier by additive effects of many generator potentials
  90. Enough generator potentials can add up to reach threshold and cause:
    AP (additive)
  91. Whe does a synaptic potential occur?
    when one neuron approximates another neuron via synapse
  92. Where does synaptic potential occur?
    only in CNS
  93. What is the most common type of generator potential?
    synaptic potential
  94. What are the two components of a synapse?
    • presynaptic membrane
    • postsynaptic membrane
  95. The presynaptic membrane belongs to:
    neuron that generates the AP
  96. What are the steps involving the presynaptic membrane of the synaptic potential?
    • 1. AP descends the axon triggering Ca voltage-gated channels to open and allow an influx of Ca which changes voltage of presynaptic membrane
    • 2. Fusion pore complex (vesicles) is formed and NTM is released via exocytosis into synaptic cleft
    • 3. NTM diffuses across synaptic cleft and binds to ligand-gated channels of postsynaptic membrane
  97. The postsynaptic membrane belongs to:
    the neuron that receives the AP
  98. What occurs in the postsynaptic membrane if it is an excitatory NTM?
    • open ligand-gated Na channels
    • generates excitatory postsynaptic potential (EPSP)
    • results in partial depolarization (graded potential)
  99. What occurs in the postsynaptic membrane if it is an inhibitory NTM?
    • open ligand-gated Cl channels
    • generates inhibitory postsynaptic potential (IPSP)
    • results in small amount of hyperpolarization b/c inhibitory
  100. Postsynaptic membrane can have both:
    excitatory and inhibitory ligand-gated channels (receptors)
  101. Both IPSP and EPSP can be going on at:
    the same time
  102. How do you determine if a neuron will be excited or inhibited?
    • function of algebraic addition of input at any point in time on the postsynaptic membrane.
    • The receptors determine a response to any NT is either excitatory or inhibitory
    • A NT that is excitatory for one tissue may be inhibitory in another, dependent on the receptor
  103. If excitatory input exceeds inhibitory=
    AP fire
  104. If inhibitory input exceeds excitatory=
    AP does not fire
  105. How do neurons know when to fire?
    • spatial summation
    • temporal summation
  106. Spatial summation:
    the adding together of the effects of many presynaptic neurons acting at different sites on the postsynaptic cell (dumping a bucket of water)
  107. Temporal summation:
    the process by which consecutive synapses at the same site are added together in the postsynaptic cell (shooting a water gun)
  108. In reality, both types of summation are occurring: