1. Membranes & Nerves

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1. Membranes & Nerves
2010-11-03 17:38:03

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  1. What is Resting Membrane Potential (RMP)?
    A difference in electrical potential across the plasma membrane at rest.
  2. What is Action Potential?
    • Stimulation of i.e. a spinal reflex --> action potential in a spial motor neuron.
    • Allows the neurons (bad at conducting electrical signals long way) to signal across long distances.
  3. What are the intra-/extracellular consentrations for:
    K+, Na+, Cl-, Ca2+
    • K+: High concentration intracellular
    • Na+, Cl-, Ca2+: High concentration extracellular
  4. What are active/passive transporters?
    • Active (ion transporters):
    • Activly move ions into or out of cells, against their concentration gradient.

    • Passive (ion channels):
    • Proteins allow certain kinds of ions to cross the membrane in the direction of their concentration gradient.
  5. Describe the K+/Na+ pump
    • Uses 1 ATP
    • Moves 3 Na+ & 2 K+ against their concentration gradient
    • Active transporter
  6. Describe the passive transport of K+ across the membrane
    • K+ moves outside the cell, taking its positive charge with it
    • Since the charge will be positive outside the cell, it repells the K+ back against it concentration gradient.
    • The equlibrium is an "electrochemical" balance
  7. What is the difference between Nernst and Goldmans equations?
    • Nernst only considers the concentration of a given ion (eg. K+)
    • Goldman considers K+, Na+ and Cl-
  8. Describe the ionic basis of the A.P.
    (the steps of AP)
    • AP are conducted along the axon, which contains voltage gated Na+ and K+ channels.
    • Phases: Rising (depolarization), Overshoot, Falling (repolarization), Undershoot
    • 1. The neuronal membrane becomes temporarily permeable to Na+ during the rising phase and overshoot phase due to opening of more and more Na+ channel that are closed at rest.
    • 2. The membrane potential deoplarizes and approaches ENa.
    • 3. Decrease in Na+ pemebeality (inactivation of Na+ channels) and delayed increase in K+ permeability cause repolarization of the membrane toward the EK and resting levels.
    • 4. During the undershoot phase (afterhyperpolarization) the K+ permability is greater that it is at rest.
    • 5. The membrane potential returns to resting levels

  9. Name the 3 general classes of ion channels found in neurons.
    • Leaked/Non-gated ion channels
    • Voltage gated ion channels
    • Ligand gated ion channels
  10. How does a Leaked/Non-gated ion channel work?
    • Always open and specific for an ion (i.e K+).
    • The ions flow aross the plasma membrane down their concentration gradients, taking their charge with them. This in turn causes the potential!
  11. How does a Voltage-gated ion channel work?
    • These channels have a charged voltage sensor that detects a change in the membrane potential and permits voltage dependent gating of ion channels.
    • Closed at rest, opens when membrane potential changes.
    • Example of Voltage gated ion channels: Na+/Ca2+ channel, K+/Cl- channel
  12. How does a Ligand-gated ion channel work?
    • Open when a ligand (e.g a neurotransmitter) binds to it.
    • Example of neurotransmiters: acetylcholine, glutamate, GABA, glycine.
    • Example of ionotropic receptor: the acetylcholine nicotinic receptor
  13. What are ionotropic, ligand gated channels?
    • Not selective
    • Allow influx of Ca2+ that leads to hyperpolarization
  14. What are the differances between the K+ and Na+ voltage gated channels?
    • The Na+ has 2 gates; Close/Active --> Open --> Close/Inactive --> Close/Active
    • The K+ has only 1 gate; Close --> Open --> Close
    • The Na+ opens faster, causes shooting phase.
    • The K+ is slower and cuases the falling phase.
  15. There are 3 groups of neurotransmittors, which are they?
    • 1. Small molecules:
    • - Biogenic amines (monoamines)
    • ---> Catecholamines: Dopamine, Noradrenaline, Adrenaline
    • ---> Indoleamines: Serotonin
    • - Acetylcholine
    • - Aminoacids
    • --- GABA and Glycine (-)
    • --- Glut and Asp (+)

    • 2. Neuropeptides: Opiopds (endorphin), Somatostatin, Substance P
    • 3. Others (non-vesicular release): Neuroactive gases (NO, CO, arachidonic acid etc)
  16. Name the events from neurotransmittor release to postsynaptic excitatinon or inhibition
    • 1. Neurotransmittor release
    • 2. Receptor binding
    • 3. Ion channels, open or close
    • 4. Conductor change causes current-flow
    • 5. Postsynaptic potential changes
    • 6. Postsynaptic cells, excited or inhibited
    • 7. Summation determines whether or not an AP occurs

  17. Name one inhibitatory and one excitatory neurotransmittor molecule
    • Inhibit: GABA and Glycine
    • Excite: Glutamate and Aspartate