-
Resting potentials are typically in the __ range
-50 to -70 mV
(page 56 on slide)
-
__ are open at the resting potential
Leak channels and Na+ inactivation gate
(No voltage-gated channels are open.)
-
At resting potential, the membrane is __. As the membrane becomes less negative, the membrane becomes __.
polarized; depolarized
(page 56 in slide)
-
__ occurs as the resting membrane potential increases to the threshold value (before action potential is fired)
EPSP (spacial and temporal summation)
-
__ pushes the neuron farther from threshold
IPSP (inhibitory postsynaptic potential)
- occurs at dendrites & the soma
- happens when Cl- flows in
-
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)
-
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)
-
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.
-
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)
-
Once the peak of the action potential is reached, the Na+ activation gate __ and the K+ activation gate __.
closes; opens
(page 59 on slide)
-
After the action potential has reached its peak, __ occurs as __ leaves the cell.
repolarization; K+
(page 59 on slide)
-
__ 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)
-
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.)
-
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
-
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
-
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)
-
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 quickly. Na+ 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.
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