Electrical properties of neurons

Cards (14)

  • Neural membranes are selectively permeable and distinguish between ions by pore size, electrical charge, and hydration shell.
  • Hydration shell is a shell of water molecules that surrounds each charged ion in a solution. Water molecules must be separated from the ion for it to pass through the pores on the cell membrane. Passage is more energetically favourable to ions that have diffuse hydration shells(easier to separate water from the ion).
  • 4 major classes of ion channels:
    • leak channels
    • voltage-gated ion channels
    • ligand-gated ion channels (aka. ionotropic )
    • category of all ion channels that are mostly used by sensory systems(open and close depending on response to unique stimuli including distortion, light, etc...)
  • Graded potentials: sub-threshold change in Vm(changes in the charge of the membrane that is below the action potential for the cell to fire)
  • Depolarization: Charge on the cell membrane goes from a more negative charge to a more positive charge
    Hyperpolarization: Charge on the cell membrane goes from a more positive charge to a more negative charge
  • There are 5 steps of an action potential:
    1. Depolarization from incoming neurons
    2. Opening of voltage-gated Na+ channels
    3. Opening of voltage-gated K+ channels
    4. Inactivation of voltage-gated Na+ channels
    5. Deactivation of voltage-gated K+ channels
  • Depolarization from incoming neurons occurs when presynaptic neurons release neurotransmitters onto dendrites of another neuron which will cause a small amount of ion movement. Either excitatory post synaptic potentials are released(causes small depolarization) or inhibitory post synaptic potentials are released(causes small hyperpolarization).
  • Many EPSPs may be required to bring the Vm above the action potential threshold. Inputs can be added by spatial summation or temporal summation.
  • Spatial summation: multiple inputs(presynpatic neurons) fire signals at one postynaptic neuron.
    Temporal summation: one single presynaptic neuron fires rapidly multiple times at one postsynaptic neuron.
  • The opening of voltage-gated Na+ channels begins to occur as the Vm depolarizes. Na+ ions are more likely to flow from high concentration areas(outside of the cell) to low concentration areas(inside of the cell), causing further depolarization. This process can reach a peak positive action potential of +40 mV.
  • The opening of K+ voltage-gated channels occurs when the relatively high K+ ion concentration inside of the cell compared to outside of the cell pushes the K+ ions out of the cell, making the interior of the cell more negative. This process occurs when the peak positive action potential of +40 mV has been reached.
  • Inactivation of voltage-gated Na+ channels occurs when the inactivation gate on the membrane blocks the flow of sodium ions when the cell membrane reaches its positive potential, preventing the further movement of Na+ ions in and out of the cell.
  • Deactivation of voltage-gated K+ channels occurs at a much slower pace than do the Na+ channels. These channels block the flow of K+ ions, stopping hyperpolarization and allowing for the membrane potential to return to equilibrium.
  • Nociception is a complex sesnation that the nervous system detects rapidly in response to noxious stimuli such as extreme temperatures or tissue damage. Allodynia is a condition that causes the individual to experience pain even in the absence of a painful stimuli. Allodynia may be caused by some change in the voltage-gated sodium channel properties, which can cause an increased excitability of pain-sensing neurons.