Membrane Physiology


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Membrane Structure and Functions, Overview of Membrane Transport, Membrane Potential

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  • An action potential (AP) or impulse is a sequence of rapidly occurringevents that decrease and reverse the membrane potentialand then eventually restore it to the resting state.
  • In continuous conduction along an unmyelinated axon, ionic currentsflow across each adjacent segment of the membrane. In saltatory conduction along a myelinated axon, the action potential(nerve impulse) at the first node generates ionic currents in the cytosol and interstitial fluid that open voltage-gated Nachannels at the second node, and so on at each subsequent node.
  • Membrane Physiology

    2. 2. The plasma membrane is a fluid lipid bilayer embedded with proteins.
    3. 3. Three views of a Cell Membrane An electron micrograph of a plasma membrane seen in cross-section. These drawings show two-dimensional and three-dimensional views of a cell membrane and the general disposition of its lipid and protein constituents.
    4. 4. Overview of Membrane Transport Transport pathways through the cell membrane, and the basic mechanisms of transport.
    5. 5. Diffusion is the spontaneous movement of a substance down its concentration or electrochemical gradient, from a region where it is more concentrated to a region where it is less concentrated. Simple diffusion, channel-mediated facilitated diffusion, & carrier-mediated facilitated diffusion
    6. 6. Facilitated Diffusion is the passage of molecules/ions down their electrochemical gradient across a biological membrane with the help of specific transmembrane transport proteins, requiring no energy expenditure.
    7. 7. Active transport is carrier-mediated transport that uses energy and moves a substance against its concentration gradient.
    8. 8. Primary Active Transport EXTRACELLULAR [Na] high FLUID [K] low Na Na Na Na Na Na Na Na CYTOPLASM Na 1 [Na] low [K] high P ADP 2 ATP P 3 Na+-K+ Pump K K K 6 K K K 5 4 P Pi
    9. 9. In secondary active transport, the energy stored in a Na+ or H+ concentration gradient is used to drive other substances across the membrane against their own concentration gradients.
    10. 10. Bulk transport across the plasma membrane occurs by Exocytosis and Endocytosis. Endocytosis Movement of substances into a cell in vesicles. Exocytosis Movement of materials out of a cell via membranous vesicles. Transcytosis Movement of a substance through a cell as a result of endocytosis on one side and exocytosis on opposite side.
    11. 11. Ion channels in the Plasma Membrane 1) Leakage channels randomly open and close. 2) A chemical stimulus opens a ligand-gated channel.
    12. 12. Ion channels in the Plasma Membrane 3) A mechanical stimulus opens a mechanically gated channel. 4) A change in membrane potential opens voltage-gated channels.
    13. 13. Chemical compositions of Extracellular & Intracellular fluids A comparison of ion concentrations inside & outside a typical mammalian cell.
    14. 14. Resting Potential
    15. 15. Action Potential
    16. 16. Key Na K Membrane potential (mV) Action potential OUTSIDE OF CELL 100 Sodium channel 3 0 50 2 Depolarization 4 Falling phase of the action potential 50 3 Rising phase of the action potential Threshold 2 1 4 5 Resting potential Time Potassium channel INSIDE OF CELL Inactivation loop 1 Resting state 5 Undershoot 1
    17. 17. Propagation of Action Potentials