EXAM 1: BIO&252 (Chapter 12: Part 1)

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  1. Cell Body
  2. Cell Membrane
    • Perikaryon: Cytoplasm surrounding the nucleus.
    • Cytoskeleton: Neurofilaments and Neurotubules.
    • Nissl Bodies: RER and free ribosomes = gray matter.
  3. Dendrites
    • Recieves information from other neurons.
    • Carries information towards the cell body.
    • Transmit graded potentials, NOT action potentials (usually).
  4. Axon
    • Axolemma, axoplasm
    • Connects to soma at axon hillock.
    • First part = initial segment, which generates actions potentials
  5. Axon Collaterals
    Major branches of an axon.
  6. Telodendria
    Small branches at the end of an axon.
  7. Synaptic Terminals
    • Ends of the telodendria.
    • a.k.a buotons, synaptic end bulbs, synaptic knobs.
    • Stores neurotransmitters in synaptic vesicles.
    • Release neurotransmitter in response to electrical activity.
  8. Transmembrane Potential (basic definition)
    • Electrochemical gradient.
    • "Potential" = voltage difference across a membrane.
    • Arises from the sum of all chemical and electrical forces acting across the cell membrane.
    • Usually reported in millivolts (mV).
    • Inside is negative, outside is positive.
  9. Transmembrane Potential (determining factors?)

    • 1. Ion Concentration Differences (ΔC)
    • 2. Sodium-Potassium pump (maintains ΔC)
    • 3. Membrane permeability diffrerences for ions
    •    Membrane Channel Types:
    •       A. Leak Channels
    •       B. Gated Channels
    • 4. Fixed anions (non-diffusible ions; P≠0)
    •       Mostly negatively-charged proteins and phosphate.
  10. Resting (Membrane) Potential
    Voltage difference across the cell membrane for an unstimulated ("resting") cell.

    (Review Slides 15-19 and Figure 12-9)
  11. Graded Potentials
    • Local changes in membrane potential due to chemical or physical changes in the membrane.
    • DO NOT self-regenerate or spread over long distances.
  12. Actions Potentials
    • Self-regenerating changes in membrane potential due to chemical or physical changes in the membrane.
    • Spread over long distances.
  13. Equilibrium Potential (for a particular ion)
    • The equilibrium potential is the membrane voltage at which electrical forces and the concentration difference forces acting on an ion are equal.
    • No net diffusion of the ion occurs at this membrane potential.

    • K+=-90 mV
    • Na+=+66 mV
    • This results in NO NET movement across the membrane.

    Understanding this concept is REALLY REALLT important!!!!!
  14. Equilibrium Potential for K+
    • At rest, the membrane is at -70 mV
    • Due to the fact that there is a higher chemical concentration of potassium INSIDE than there is out, K+ will want to flow outside. 
    • However, since there is a slight negative charge inside of the membrane, the electrical gradient will want to somewhat pull it back in. ⇣
    • Forces will move K+ out until it reaches its concentration gradient of -90 mV.
  15. Equilibrium Potential for Na+
    • At rest, the membrane is at -70 mV.
    • Due to the fact that there is a higher chemical concentration of sodium OUTSIDE than there is in, Na+ will want to flow in. The electrical gradient will also want to pull in Na+ due to the negative charge. ⇊
    • Forces will move Na+ into the cell until it reaches equilibrium at +66 mV.
  16. Changes in Transmembrane Potential
    • Membrane at rest is "polarized".
    • Ion flow can cause changes in potential.
    • "Depolarized": Inside of the membrane becomes more positive.
    • "Hyperpolarized": Inside of membrane becomes more negative.
  17. Membrane Channel Types
    • Ions cross the membrane through:
    • 1. Leak Channels: Always open.
    • 2. Gated Channels: Open or close.
    •    a. Voltage-gated channels.
    •    b. Chemically-gates (ligand-gated) channels.
    •    c. Mechanically-gated channels.
  18. Leak (Passive) Channels

    • Important for establishing resting potential.
    • Ions "leak" down their electrochemical gradients (eg. K+ leak channels, Na+ leak channels)
    • Size, charge, etc. determine which ions(s) can pass through a channel.
    • Determine resting permeabilities for membrane (PK+ at rest, 50-100X greater than PNa+)
  19. Gated Channels
    • A.K.A Active Channels (does not refer to ATP use)
    • Can exist in 3 states:
    • 1. Open (activated)
    • 2. Closed and cannot be opened (inactivated)
    • 3. Closed, but can be opened
  20. Chemically-gated (Ligand-gated) Channels
    • Image Upload 1
    • Open after binding a specific chemical (ligand)
    • Most abundant on cell body, dendrites and motor end plate

    • Binding of ACh changes shape of receptor.
    • Channel becomes permeable to small ions like Na+ and K+.
  21. Voltage-gated Channels
    • Channels open in response to  changes in membrane potential - Threshold.
    • Important in action potential conduction, neurotransmitter release from end bulbs.

    • Examples: Voltage-gated K+, Na+, and Ca2+ Channels.
    • Resting membrane is closed, but can open (-70 mV).
    • Opens at -60 mV.
    • Closed and inactivated; cannot be opened (-30 mV).
  22. Mechanically-gated Channels
    • Open or close in response to physical distortion.
    • Examples: touch, pressure receptors.
    • Image Upload 2
  23. Graded Potentials
    • A change in membrane potential that decreases with distance.
    • Caused by ions entering cell through channels.
    •    Local depolarization or hyperpolarization.
    •    Does not spread very far from site of stimulus (unlike action potential).
    •    Does not involved voltage-gated channels.
    • Why don't graded potentials travel very far?
    •    Cytoplasm resists ion flow.
    •    The cell membrane is LEAKY TO IONS.
  24. Graded Potentials (present channels).
    Leak channels present, Chemically-gated Na+ channels are present, BUT NOT VOLTAGE-GATED CHANNELS.
  25. Depolarization and Hyperpolarization
    • Depolarization: Inside is more positive than at rest. (Example=NA+ enters the cell)
    • Hyperpolarization: Inside more negative than at rest. (Example=K+ leaves the cell, Cl- enters the cell)
  26. Actions Potentials (Introduction)
    A sudden major change in membrane potential.

    • An all-or-none phenomenon (EITHER IT HAPPENS, OR IT DOESN'T)
    • Occurs when membrane reaches a specific membrane voltage called threshold.
    • Does not degrade over long distance (unlike graded potentials).
    • Depends upon the presence of voltage-gated Na+ and K+ channels.
    • At threshold, voltage-gated Na+ channels open.
  27. Action Potential Recording
    Image Upload 3
  28. Action Potentials and Muscle Cells
    Motor End Plate: Muscle cell membrane at neuromuscular junction.

    • Contains few voltage-gated Na+ channels.
    • Does not generate action potentials (graded potentials ONLY)
    • Local current flow spreads to adjacent sarcolemma where action potentials are produced.
    • About 100 vesicles, each containing 100,000 ACh molecules, are released into synapse to produce muscle action potential.
  29. Action Potential - Continuous Propagation
    Image Upload 4
  30. Action Potential - Saltatory Conduction
    Image Upload 5
  31. Cholinergic Synaptic Activity
    Image Upload 6
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EXAM 1: BIO&252 (Chapter 12: Part 1)
2016-01-19 01:29:29
Chapter 12: Part 1
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