Meeting 17 & 18

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mse263
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148733
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Meeting 17 & 18
Updated:
2012-04-20 13:03:18
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MCBII Exam
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Synapse,
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  1. action potential conduction
    -propagation of action potential by passive spread of current

    -initiates autocatalytic action potential cycle

    -action potential can't move backwards because there's an inactivation of channels located behind
  2. schwann cells
    • -form myelin sheaths around peripheral nerves
    • -each dedicate themselves to one axon (incontrast to oligodendroctes); found in PNS

    -70% lipid (rich in cholesterol) & 30% protein
  3. astrocyte
    • make long thin processes that envelop all the brain's blood vessels; are 2 types
    • 1) protoplasmic astrocytes: in gray matter (cell bodies)
    • 2) fibrous: in white matter (area of axons)
  4. oligodendrocyte
    -form the spiral myelin sheath around axons of the central nervous sytem (CNS)

    -each provides myelin sheaths to MULTIPLE neurons
  5. influx of Na+ ions associated with an action potential can occur only at:
    nodes of Ranvier
  6. saltatory conduction
    • - the fact that an action potential jumps from node to node; an excess of cytosolic ions is generated during depolarization (that comes from action potential)
    • - the ions can't cross the mylenated axon membrane so they spread to the NEXT node, spreading the depolarization/AP

    • - more rapid than continuous conduction; the greater the diameter of the axon, the fast the signal travels
    • - saltatory is more energy efficient

    - myelinated fibers conduct faster than unmyelinated: 5-120 m/s versus less than 2 m/s
  7. types of communication between neurons
    1) electric synapse (gap junctions)

    2) chemical synapses (NTs)
  8. electric synapse
    • -communication through gap junctions; purpose is to coordinate the activity of connected cells; is FASTER than chemical signaling
    • -let's in things as large as ~600Da (all ions can move thru easily)
    • -stay open for a long time
    • -are NEGATIVELY regulated by high concentrations of Ca2+ and H+

    ex. how heart muscle cells tell e/a other to contract: have action potentials that travel from one cell to another through gap junctions (not very specific) from the bottom of the heart to the top
  9. chemical synapses
    employ NTs tp allow one-way communication at a reasonably high speed
  10. glutamate
    abundant amino acid/NT; overdose when you have too much MSG
  11. There are ____ synapses in the brain
    1015 synapses in the brain!
  12. Types of NT Receptors (2)
    1) Ionotropic: receptor itself is a ligand gated channel (meaning that the receptor for the NT is itself a channel for the NT)

    2) Metabotropic: receptor activates signal transduction that opens/closes a channel; receptor acts only as a receptor; binds to NT and simply communicates that information to the inside of the cell; is more indirect/slower than ionotropic, but better when a sustained signal is needed
  13. Acetylcholine Receptor
    • -example of an ionotropic receptor, or ligand-gated CATion channel
    • - is a cation channel found on muslce fibers: let's every +ion go through, but b/c there’s 6x more energy carried by the transport of Na (as opposed to K), sodium gets in much more than K gets
    • out; Na's gradient has more energy

    -IONOTROPIC RECEPTOR: channel directly binds to the ligand (AcTych)
  14. Understand how the movement of ions causes either hyper or depolarization:
    Ca2+: more concentrated outside, + charged

    Cl: more concentrated outside, - charged

    • - to go down their concentration gradients, they'll both move inside the membrane, but Cl- moving into the cell will hyperpolarize it while Ca+ will depolarize it (make it positive)
    • -this is due to their charges; their prefered way to move is due to the MEMBRANE potential (usually more neg. inside and pos. outside)

    • depolarize: let Ca++ or Na+ IN CELL
    • hyperpolarize let K+ OUT of cell, let Cl- IN cell
  15. NT Receptors can be Excitatory or Inhibitory
  16. tissues
    an aggregation of morphologically similar cells and associated intercellular matter

    -liver is a very (most) homogenous tissue; made up of almost all the same cells

    -types of tissues: Epithelial, Connective, Muscular, Nervous, Blood
  17. Organ
    an ensemble of tissues actingtogether to perform specific functions
  18. what holds tissue together?
    - Cell-cell Adhesion Molecules (CAMs): specialized membrane proteins that cause direct adherence between tissue cells

    - Adhesion Receptors: responsible for cell-matrix adhesion; specialized proteins found in the plasma membrane that indirectly bind to parts of the ECM (extracellular matrix) and facilitate communication between tissue cells
  19. Extracellular Matrix Proteins (ECM)
    1) proteoglycans: type of glycoprotein; proteins heavily modified by sugar (so that branching structure can happen, also resist protein breakdown b/c of sugars)

    2) collagens; provides rigidity to epithilium; different collagens have different properties in rigidity

    3) multiadhesive matrix proteins (laminin, fibronectin, nidogen/entactin)

    -elastin: provides elasticity for ECM
  20. Collagen
    • • are Glycine, Proline, and Hydroxy-Proline-rich
    • -proline in a protein makes it BEND (as does glycine)

    • G-X-Y (X&Y are Pro or OH-Pro)

    • Over 20 different types

    –Covalent modifications: Sugars (N-linked), Oxidation of Ly, Hydroxylation of Pro, Cross-linking of oxidized Lys to other Lysine, hydroxy-Lysine, and Histidine

    • –Number and length of triple-helical segments
    • –Flanking or interrupting segments

    -made by the ribosome and modified in the ER/golgi...
  21. Elastin
    • •made up of Glycine, Proline & Hydrophobic amino acids
    • •Large numbers of bends due to Proline
    • •The bent regions can stretch
    • •α-helices between the bent regions are sites of elastin-elastin cross-links
    • -can stretch and relax
  22. Specialized Proteins:
    1) Fibronectin: dimers linked at C-termini via S-S bonds (only found outside b/c redox potential is not sufficient for them to be found inside the cell)

    • 2) Laminin: are heterotrimeric, have many isoforms
    • -bind to many different molecules, including cellular integral membrane proteins

    • BOTH:
    • •help cross link collagens and elastins
    • •also cross link cells to the ECM
  23. 1 protein weights about
    100 KDa
  24. proteoglycans
    • • made in ER
    • •Contain glycosaminoglycans (GAGs) added in the Golgi
    • –Linear polymers
    • –Repeating disaccharide units
    • •GAGs are:
    • -Three-sugar linker to Ser or Asn
    • - Alternate addition of sugar monomers
    • - Covalent linkage of small molecules like sulfate
  25. small intestine
    • - lined with simple columnar epithelium
    • - apical side is lined with microvilli exposed into the intestinal lumen; produce peptidases and glycosidase are present here

    ‚óŹ the apical and basolateral surfaces are NOT symmetric
  26. types of junctions
    •Tight Junctions

    • •Anchoring Junctions:
    • –Adherens Junction (Belt Desmosome)
    • –Desmosome (Spot Desmosome)
    • –Hemidesmosome

    •Gap Junctions: communication between cells that allow ions/ATP (SMALL molecules) to go through; NO proteins
  27. Tight Junctions
    • - two membranes are opposed
    • - tight Junctions don’t have much material in the cytoplasm, just w membranes opposed to one another
    • - mostly involved in preventing anything from going in between the 2 membranes

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