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2010-09-22 09:20:15
signal transduction synaptic transmission neuroscience

Signal Transduction
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  1. four types of glial cells
    oligodendrocytes; Schwann cells; astrocytes; microglial cells
  2. function of oligodendrocytes
    production of myelin in the CNS
  3. function of Schwann cells
    production of myelin in the PNS
  4. function of astrocytes
    nutritive and supportive connections between neurons and capillaries in the CNS
  5. function of microglial cells
    phagocytosis of damaged cells; the macrophages of the CNS
  6. differences between oligodendrocytes and Schwann cells
    oligodendrocytes in CNS and Schwann cells in PNS; oligodendrocytes myelinate many cells while Schwann cells myelinate only one cell
  7. white matter
    one of two components of the CNS; consists mainly of myelinated cells; appears white because myelin is made up mainly of lipids
  8. blood-brain barrier
    separates circulating blood from cerebrospinal fluid; composed mainly of tight junctions in capillary endothelial cells; filters blood plasma; permits entry of ions but not proteins into CSF
  9. functions of blood-brain barrier
    prevention of entry of pathogens into CNS; maintenance of homeostasis in CSF
  10. choroid plexus
    specialized tissue that secretes cerebrospinal fluid into the ventricles; found in multiple locations in the ventricles of the brain; filters blood and actively transports ions to produce CSF
  11. arachnoid villi
    small protrusions of arachnoid mater in the brain that uptake circulating cerebrospinal fluid and allow it to re-enter the bloodstream
  12. Wallerian degeneration
    "the process of axonal degeneration following nerve damage to the axon & separation of the axonal process from the cell body; occurs in both the CNS and the PNS; ""clean-up"" assisted by microglia"
  13. chromatolysis
    lysis of neuronal chromatin; occurs in response to cellular damage; involves swelling of the cell and dispersal of the rER
  14. steps in electrical signaling
    input; summation; conduction; output
  15. axon hillock
    the most electrically sensitive part of the axon; has the lowest threshold for an action potential; initiation site for action potential; involved in summation
  16. resting membrane potential
    the difference in voltage between the interior and exterior of a quiescent cell; primarily determined by potassium in neurons
  17. Nernst equation
    used to calculate the membrane potential based on the internal and external concentrations of a single ion; assumes that only that ion is permeable
  18. relative ion concentrations
    sodium low inside & high outside; potassium high inside & low outside; chlorine low inside & high outside; calcium very low inside & low outside
  19. Goldman-Hodgkin-Katz equation
    used to calculate the membrane potential based on the internal and external concentrations of several monovalent ions
  20. mechanism of unidirectional action potential propagation
    sodium influx provokes depolarization of membrane; depolarization provokes opening of neighboring sodium channels; opening of sodium channels leads to further sodium influx; channels are temporarily inactivated after opening to prevent reversal of direction
  21. voltage clamp
    used by electrophysiologists to measure ion flow while holding membrane potential steady; used by Hodgkin and Huxley to elucidate ionic causes of action potentials
  22. command potential
    the electric potential at which a cell membrane is held in experiments involving voltage clamps
  23. space constant
    represented by lambda; describes the distance that passive voltage will spread along an axon or dendrite; depends on the resistance across and inside the membrane; depends on the number of open ion channels and the diameter of the cell process
  24. time constant
    describes the speed at which a cell membrane potential changes; represented by tau
  25. sodium-potassium pump
    ATP-driven enzyme that pumps 3 sodium ions out of the cell for every 2 potassium ions it pumps into the cell
  26. evidence for existance of a sodium-potassium pump in neurons
    removal of external K+ decreases rate of Na+ transfer; blockage of ATP synthesis decreases rate of Na+ transfer
  27. mechanism of sodium-potassium pump action
    sodium binding on inner cell membrane; phosphorylation of membrane receptor; conformational change of membrane receptor; sodium release; potassium binding; dephosphorylation of receptor; potassium release
  28. synapse
    a junction for communication between two cells
  29. areas in which synaptic transmission occurs
    between two neurons; between a pre-synaptic neuron and a post-synaptic non-neuronal target; between a pre-synaptic sensory cell and a post-synaptic neuron
  30. types of synapses
    electrical and chemical
  31. differences between electrical and chemical synapses
    electrical synapses are much smaller; electrical synapses have cytoplasmic continuity while chemical synapses do not; electrical synapses have no synaptic delay while chemical synapses have variable-length synaptic delays; electrical synapses are theoretically bidirectional while chemical synapses are unidirectional
  32. gap junction plaque
    occurs at electrical synapses; made up of connexon units that form channels; allow passage of small molecules such as cyclic AMP
  33. synaptic densities
    visible as thick black lines on EM of a synapse; composed of exocytotic machinery on the presynaptic side and neurotransmitter-binding receptors on the postsynaptic side
  34. active zone
    the region of the presynaptic plasma membrane at which synaptic vesicles dock
  35. synaptic folds
    found in neuromuscular junctions; postsynaptic membrane displays folding
  36. steps in chemical signaling at the neuromuscular junction
    depolarization of nerve terminal; opening of voltage-gated calcium channels; calcium influx; exocytosis of ACh; activation of nAChRs; opening of sodium and potassium channels; depolarization of post-synaptic cell membrane; conformational change of calcium channels on sarcoplasmic reticulum; calcium release; muscle contraction
  37. neurotransmitter families
    small molecues; peptides and polypeptides
  38. examples of NTs: small molecules
    amines - dopamine and norepinephrine; amino acids - glutamate and GABA and glycine; nucleosides and nucleotides; lipids
  39. examples of NTs: peptides and polypeptides
    hypothalamic peptides - oxytocin and vasopressin; gut peptides - somatostatin and vip; endorphins
  40. differences between small molecule and peptide/polypeptide neurotransmitters
    small molecules are synthesized locally while peptides are synthesized at the cell body and transported; small molecules are packaged in small clear vesicles while peptides are packaged in large dense core vesicles; small molecule vesicles are recycled while peptide vesicles are not; small molecules require low Ca2+ concentration for release while peptides require high Ca2+ concentration for release
  41. acetylcholine
    a small molecule neurotransmitter syntheized in the cytosol from acetate and choline; occurs in neuromuscular junctions
  42. two processes by which neurotransmitter is exocytosed
    """kiss and run"" or complete fusion/conventional vesicle exocytosis"
  43. """kiss and run"" neurotransmitter release"
    a process by which vesicles release neurotransmitter into the synaptic cleft; involves incomplete fusion with the cell membrane and formation of a fusion pore; involves vesicle recycling; occurs when large amounts of neurotransmitter are being released
  44. conventional vesicle exocytosis
    a process by which vesicles release neurotransmitter into the synaptic cleft; involves complete fusion with the cell membrane; involves recovery of the vesicle membrane via clathrin-mediated endocytosis
  45. SNARE hypothesis
    describes the mechanism by which vesicle fusion occurs; involves recognition of vesicle SNARES by target SNARES on the cell membrane
  46. t-SNARES
    target SNARES; protein complexes on the cell membrane that interact with v-SNARES to promote vesicle docking
  47. v-SNARES
    vesicle SNARES; protein complexes on the vesicle that interact with t-SNARES to promote vesicle docking
  48. role of coiled-coil interactions in exocytosis
    the coiled-coil protein domains of v-SNARES and t-SNARES interact to pull the vesicle into a docked position on the membrane for exocytosis
  49. synaptotagmin
    a protein involved in exocytosis; two C2 domains bind calcium; acts as a calcium sensor
  50. tetanus toxin
    a toxin that blocks inhibitory neuronal transmission via proteolysis of the SNARE family VAMP-2; causes rigidity and spasms
  51. botulism toxin
    a toxin that blocks excitatory neuronal transmission via proteolysis of the SNARE family VAMP-1 at the NMJ; causes flaccid paralysis
  52. local synaptic potentials
    small graded electric responses provoked at the postsynaptic membrane; can be excitatory or inhibitory
  53. factors upon which EPSP amplitude depends
    quantity of neurotransmitter released; quantity of neurotransmitter that reaches receptors; number of receptors activated
  54. miniature EPSPs
    spontaneous EPSPs that result in the absence of presynaptic stimulation; result from the release of one vesicle's contents
  55. quantal gradation of EPSPs
    EPSP amplitude is quantal because it depends on the number of presynaptic vesicles released
  56. post-synaptic excitation
    excitatory post-synaptic potentials increase the probability that an action potential will occur post-synaptically; usually involve depolarization
  57. post-synaptic inhibition
    inhibitory post-synaptic potentials decrease the probability that an action potential will occur post-synaptically; usually involve hyperpolarization
  58. ionotropic receptors
    are linked directly to post-synaptic ion channels; mediate fast synaptic transmission; decay is due to diffusion or hydrolysis of neurotransmitter
  59. metabotropic receptors
    movement of ions through post-synaptic channels depends on intermediary molecules; mediate slow synaptic transmission; decay depends on lifetime of second messengers
  60. examples of ionotropic receptors
    nAChRs; GABAARs; NMDA-Rs
  61. examples of metabotropic receptors
    G-protein couple receptors such as beta-adrenergic receptors
  62. beta-adrenergic receptors
    a family of G-protein coupled receptors; stimulate heart contraction; stimulation leads to a cascade that eventually results in phosphorylation of an ion channel; compete with mAChRs (inhibitory)
  63. neurotransmitter inactivation
    NTs can be inactivated by diffusion or reuptake or enzymatic degradation
  64. steps in chemical synapse transmission
    presynaptic events; neurotransmitter diffusion across cleft; binding of NT to post-synaptic receptors; activation of ionotropic or metabotropic receptors; postsynaptic potentials; transmitter inactivation
  65. myasthenia gravis
    an autoimmune disease that affects nAChRs; antibodies decrease nAChRs at the NMJ by causing them to cluster and be internalized and degraded; causes muscle fatigue
  66. treatment for myasthenia gravis
    anti-immune drugs; acetylcholinesterase inhibitors
  67. EMG
    electromyogram; records summation of action potentials in muscle fibers
  68. bungarotoxin
    a toxin that blocks nicotinic acetylcholine receptors
  69. factors that affect the strength of synaptic transmission
    quantity of neurotransmitter per vesicle; number of vesicles available; number of vesicles released; number of post-synaptic receptors; sensitivity of receptors to transmitter; transmitter inactivation