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17 Cards in this Set

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What happens to the membrane potential during the depolarization stage?
it goes from -50mV to +30mV

(membrane rapidly depolarizes but has a +30mV overshoot due to the extremely fast ejection)
What are the phases of an action potential?
1. resting phase
2. depolarization phase
3. repolarization phase
4. Absolute Refractory Period is the time when the inactivation gate is closed (overlaps with repolarization and relative refractory period)
5. Relative Refractory Period - afterpolarization (further polarization past resting membrane level i.e. more negative than -70)
What is the absolute refractory period?
1) no additional action potential can be generated.

2) Determined by the inactivation gate closing (the peak of the action potential)

3) prevents reverberation along the axon

4) Determines maximal discharge frequency for a neuron
What are the components of voltage-gated sodium channels?
1. activation gate
2. inactivation gate
3. conductance pore
4. selectivity filter
5. voltage sensor
What does the Selectivity Filter do?
Selectivity Filter will selectively allow sodium to enter the channel. This is done by the specific placement of negative charges in the protein which can stabilize the sodium atom when it sheds most of its hydration sphere to enter the pore.
What does Tetrodotoxin (TTX) do?
TTX from puffer fish can bind to the selectivity filter in voltage gated ion chanels for sodium blocking the chanel
What causes the sodium activation gate to open?
reaching threshold
What is permeability like at rest?

_________
Rest

Activation closed
Inactivation open
K closed
Pk>Pcl>>Pna
What is permeability like when threshold is reached?

_____/
Threshold

Activation open
Inactivation open
K open
Pna>Pk>Pcl

note:K gates open slower than Na gates
What is permeability like when K gates are fully open? (beginning of repolarization)

_____/\
Repolarization

Activation open
Inactivation closed
K open
Pk>>Pcl>>Pna
What is permeability like during repolarization to threshold? (ACTIVATION GATE CLOSES DURIN REPOLARIZATION)

_________/\
During Repolarization to Threshold

Activation closed
Inactivation closed
K open
Pk>>Pcl>>Pna
What is permeability like when the membrane potential passes back below threshold? (AFTERHYPERPOLARIZATION)

______/\\/
Afterhyperpolarization

Activation closed
Inactivation open
K open
Pk>>Pcl>>Pna
What is permeability like when the membrane returns to its resting membrane potential? (K gate gradually closes resulting in RMP)

_______/\\/------
Rest

Activation closed
Inactivation open
K closed
Pk>Pcl>>Pna
What is the resting membrane potential and what ion does it most represent?
RMP = -70mV

K = -90
How much "overshoot" do we typically get in an action potential?
+30mV
What stage is the neuron in when the inside of the neuron is even more negative than at rest?
Relative Refractory Period
What are the two vector forces that cause an ion to move across a membrane?
Electrical forces
Concentration forces