5.3 & 5.4

    Cards (16)

    • Action Potentials:
      -move by continuous regeneration (re-triggering)
      -move in 1 direction (due to refractory periods)
    • Once initiated, an action potential moves along the membrane of a (1.) until it reaches the (2.)
      1. Neuron's axon
      2. Synaptic end bulbs
    • Three Phases of an Action Potential
      • Depolarizing phase
      • Repolarizing phase
      • After-hyperpolarizing phase
    • Propagation of an Action Potential
      1. Entry of Na+ produces a local current → spreads laterally to depolarize adjacent areas of membrane
      2. Adjacent membrane area is depolarized to threshold
      3. Na+ channels open in 'new' region of membrane
      4. Entry of Na+ in 'new' region of membrane produces another local current → spreads to adjacent areas of membrane
      5. The 'new' adjacent membrane area is depolarized to 'threshold' → Depolarization Phase of action potential in this 'new new' region of membrane
    • 1st Factor for Velocity of Propagation of an Action Potential
      1. Size (axon diameter): bigger = faster as diameter increases resistance to current flow In axoplasm decreases
    • 2nd Factor for Velocity of Propagation of an Action Potential
      2. Myelination (insulation): insulation increases speed of action potential propagation
      -glial cells form an insulating sheath around axons
      *oligodendrocytes (CNS)
      *Schwann cells (PNS)
      -sheath is not continuous (has gaps) saltatory conduction
    • Saltatory vs. continuous conduction
      Saltatory: in myelinated axons (faster)
      Continuous: in unmyelinated axons
    • Importance of refractory periods
      • Establishes maximum rate (frequency) of action potentials
      • Ensures forward propagation (axon hillock axon terminal)
    • Saltatory Conduction
      -Action potentials only occur at nodes of Ranvier
      -Ions can only be exchanged at the nodes of Ranvier
    • Demyelination:
      absence of myelin 'insulation' action potential fails
    • Demyelination
      Disruption of myelin sheath
      1. Multiple Sclerosis (central)
      2. Guillan-Barre (peripheral)
    • Fugu (pufferfish) contains tetrodotoxin
    • How is an electrical signal (action potential) transmitted from one excitable cell to another?
      Synaptic transmission
    • Spatial summation
      Signals from MANY pre-synaptic neurons add up at the trigger zone (axon hillock)
    • Temporal summation
      Increased FREQUENCY of action potentials from pre-synaptic neurons add up at the trigger zone
    • Graded potentials (post-synaptic electrical events) are either...
      1. Depolarizing (if Na+ enters): Excitatory Post-Synaptic Potential - EPSP 2. Hyperpolarizing (if K+ leaves or Cl- enters): Inhibitory Post-Synaptic Potential - IPSP
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