Neurons & Nervous System part 2

  1. Resting potentials are typically in the __ range
    -50 to -70 mV

    (page 56 on slide)
  2. __ are open at the resting potential
    Leak channels and Na+ inactivation gate

    (No voltage-gated channels are open.)
  3. At resting potential, the membrane is __. As the membrane becomes less negative, the membrane becomes __.
    polarized; depolarized

    (page 56 in slide)
  4. __ occurs as the resting membrane potential increases to the threshold value (before action potential is fired)
    EPSP (spacial and temporal summation)
  5. __ pushes the neuron farther from threshold
    IPSP (inhibitory postsynaptic potential)

    • occurs at dendrites & the soma
    • happens when Cl- flows in
  6. As a depolarizing stimulus raises the membrane potential to __ (typically 10 to 20 mV more positive than the resting potential), the __ gates open causing __
    • threshold;
    • Na+ activation;
    • a burst of Na+ ions to flow into the axon along their concentration gradient

    (page 57 on slide)
  7. The Na+ inactivation gate is open at __ & closes at __ but responds more slowly than the Na+ activation gate opening.
    rest; threshold

    Think of the Na+ activation gate as a door that quickly opens (letting Na+ through) & the Na+ inactivation gate as the door that slowly closes that same channel. (both at the threshold level)
  8. If the Na+ inactivation gate closes more quickly (but still slower than the activation gate), what will happen to the flow of Na+?
    Opening of the Na+ inactivation gate stops more Na+ from going through. Thus, there will be less Na+ going into the cell - less depolarization and a smaller peak in action potential.
  9. Once the __ is reached, the action potential fires as more __ flows in & the membrane potential suddenly increases until it reaches the __.
    • threshold;
    • Na+;
    • peak of the action potential

    (page 57 on slide)
  10. Once the peak of the action potential is reached, the Na+ activation gate __ and the K+ activation gate __.
    closes; opens

    (page 59 on slide)
  11. After the action potential has reached its peak, __ occurs as __ leaves the cell.
    repolarization; K+

    (page 59 on slide)
  12. __ occurs as the membrane potential drops to about -80 mV as K+ tries to reach the __. The __ activation gate then closes. __ will bring the cell back to homeostasis at resting level.
    • Hyperpolarization;
    • K+ membrane potential (-90 mV);
    • K+
    • Leak channels

    (page 60 on slide)
  13. The steps from repolarization to the end of hyperpolarization is called the __. During this time __ cannot occur.
    • refractory period;
    • action potentials

    (Voltage-gated Na+ channels cannot open)

    (The refractory period lasts until the membrane has stabilized at the resting potential.)
  14. Closure of the __ gate & flow of ions from __ stabilizes the membrane potential at the resting value. The __ gate re-opens. The refractory period has now ended & is ready for another action potential
    • K+ activation;
    • leak channels;
    • Na+ inactivation
  15. An action potential is produced only if a stimulus that causes __ charges from outside the neurons to flow inward is strong enough to cause __ that reaches __.
    • positive;
    • depolarization;
    • threshold

    (If threshold is not reached, an action potential will not occur.)

    all-or-nothing principle
  16. If the __ gate stays closed, an action potential can't occur since that means the __ gates are __. The membrane potential will then stay in the __
    • Na+ inactivation;
    • K+ activation;
    • open;
    • refractory period

    (K+ activation gates must close in order to allow membrane potential to go more positive go back to resting value - where Na+ inactivation gates are open)
  17. steps in membrane potential (summary)
    • 1. Leak channels & Na+ inactivation gate are open at resting
    • 2. EPSP (spacial & temporal summation)
    • 3. Threshold is reached & fires an action potential. Na+ activation gate opens quicklyNa+ inactivation gate closes to stop more flow of Na+
    • 4. Depolarization occurs as Na+ flows in until peak of action potential
    • 5. Na+ activation gate closes and K+ activation gate opens: beginning of refractory period
    • 6. K+ flows out during repolarization
    • 7. K+ continues to flow and tries to reach Ek and surpasses the resting value - hyperpolarization
    • 8. K+ activation gate closes. Leak channels brings membrane potential back to resting (end of refractory period)
    • 9. Na+ inactivation re-opens & is ready for another action potential.
Card Set
Neurons & Nervous System part 2
Week 3, Ch. 39