Action Potential I: Generation Flashcards
Threshold is the point at which _____ and ______ currents are exactly equal and opposite.
sodium; potassium
At rest, the activation gate (m) is shut and the _____ is open.
inactivation gate (h)
The K+ channel gates are _____ at rest.
closed
At rest, the _______ is shut and the inactivation gate (h) is open.
activation gate (m)
Without the _____, the membrane would repolarize very slowly.
voltage-gated K+ channels
Repolarization occurs for two reasons: 1) _____, and 2) _____.
P(Na) declines back to its resting level; P(K) undergoes a transient increase
When the membrane is depolarized, the activation gate _____ and the inactivation gate closes.
opens
The ____ channel behavior is an example of negative feedback.
K+
What is the refractory period?
after generating an AP, the axon cannot produce another one for a few milliseconds
The membrane potential must be _____ to the same level before each action potential occurs.
depolarized
When the membrane is _____, the activation gate opens and the inactivation gate closes.
depolarized
The action potential is always the same size and shape in that neuron, regardless of _______.
how big the stimulus is
What is the absolute refractory period?
during this time, no stimulus, no matter how strong, can evoke another AP
What is an action potential?
when the membrane undergoes a large, rapid, transient depolarization
The threshold is not the point at which all of the ____ open.
Na+ channels
Within each square micrometer of typical axonal membrane are about 100 ____ channels which, at rest, do not permit any ____ to cross the membrane.
sodium; Na+
The K+ channel gates open in response to ______.
depolarization
The action potential depends on the ______.
voltage-gated sodium channels
The _______ depends on the voltage-gated sodium channels.
action potential
The ‘passive’ electrical properties of axons are not sufficient to conduct an action potential ______.
over long distances
What is the relative refractory period?
time during which a stronger-than-normal stimulus is required to evoke another AP
The _____ open in response to depolarization.
K+ channel gates
K+ channels close with _____.
a delay
What controls the behavior of the K+ channel gate?
membrane potential
Why is there a refractory period?
the sodium channel inactivation (h) gates require time to reopen after repolarization
The ______ gate swings faster.
activation
After _____, an axon cannot generate another one for a few milliseconds.
producing an action potential
______ occurs for two reasons: 1) P(Na) declines back to its resting level and 2) P(K) undergoes a transient increase.
Repolarization
Without the sodium channels, electrical signals can’t spread more than _____ from the site of the stimulus.
a few millimeters
____ channels close with a delay.
K+
The action potential is always the same _____ in that neuron, regardless of how big the stimulus is.
size and shape
The K+ channel behavior is an example of ____ feedback.
negative
At the beginning of depolarization, the membrane permeability is drastically altered from one that is largely permeable to _____ to one that is much, much more permeable to ____.
potassium; sodium
The K+ channel gates ____ in response to depolarization.
open
Without the _____, electrical signals can’t spread more than a few millimeters from the site of the stimulus.
sodium channels
The ____ channels start conducting when the cell is depolarized a little bit.
Na+
What does it mean that action potentials are all or none events?
the AP is always the same size and shape regardless of the stimulus
The _____ open as the Na+ channel inactivation gates are closing.
K+ channels
_______ is the point at which sodium and potassium currents are exactly equal and opposite.
Threshold
The _____ is not the point at which all of the Na+ channels open.
threshold
As ______ ions rush into the cell, the inside becomes more positive.
sodium
What does threshold mean?
a certain amount of depolarization is required to initiate an AP
As sodium ions rush into the cell, the inside becomes more _____.
positive
The ____ channel gates are closed at rest.
K+
When the membrane is depolarized, the activation gate opens and the ____.
inactivation gate closes
After producing an action potential, an axon cannot generate another one _____.
for a few milliseconds
The _______ is always the same size and shape in that neuron, regardless of how big the stimulus is.
action potential
_____, the activation gate (m) is shut and the inactivation gate (h) is open.
At rest
What does it mean that there is a threshold for excitation?
the membrane potential must be depolarized to the same level before each action potential occurs
The Na+ opening is an example of ____ feedback.
positive
Without the voltage-gated K+ channels, the membrane would _____.
repolarize very slowly
The membrane potential must be depolarized to the same level before each _____ occurs.
action potential
Why do K+ channels close with a delay?
to allow both maximum height of the AP and rapid repolarization
