AP II Flashcards
Describe the positions of the activation and inactivation gates in sodium channels during an action potential: at rest
activation gate (m) is shut and inactivation gate (h) is open
Describe the positions of the activation and inactivation gates in sodium channels during an action potential: as the membrane depolarizes
activation gate (m) opens as inactivation gate (h) closes • activation gate swings faster thanthe inactivation gate
Describe the positions of the activation and inactivation gates in sodium channels during an action potential: at peak of action potential
activation gate (m) and inactivation gate (h) are open
Describe the positions of the activation and inactivation gates in sodium channels during an action potential: as membrane repolarizes
activation gate (m) is closing and inactivation gate (h) is closed
Describe the positions of the activation and inactivation gates in sodium channels during an action potential: refractory period
activation gate (m) and inactivation gate (h) are closed
In most cells, the influx and efflux of potassium and sodium _______. Therefore,_______
- do not significantly
- many action potentials can be generated before the Na+/K+ pump is required to restore proper ion balances.
The Na+/K+ pump
does not play a direct role in the generation of an action potential. Instead, the Na+/K+ pump functions to restore ion balances after many action potentials have been fired
The number of action potentials that can be fired before Na+/K+ pump activity is required depends on
an axon’s surface area relative to its volume.
An axon with a relatively small surface area compared to volume can fire _______ action potentials before pump activity is needed than an axon with a large surface area to volume ratio
more
A smaller surface area to volume ratio means _______ influx or efflux per unit volume, resulting in a _______ percent change in ion concentrations.
- less
- smaller
The refractory period is
the time after an action potential is fired during which an axon cannot fire another action potential (absolute refractory period) or requires a more extreme stimulus to fire another action potential (relative refractory period)
Mechanism underlying the refractory period: After the axon repolarizes, which gate(s) are closed?
both the activation gate and the inactivation gate of the sodium channel are closed. The inactivation gate requires time to reopen before another activation potential can fire.
Mechanism underlying the refractory period: After the axon repolarizes, what happens to the K+ channels?
The K+ channels are still open. K+ is still leaving the axon, which makes it more difficult to depolarize the cell
During normal depolarization (in the absence of accommodation),_______. This allows _______
- the inactivation gate of the sodium channel is closing as the activation gate is opening
- sodium to rush into the axon and generate the action potential.
With accommodation, the stimulus is applied slowly, causing the_______. As a result, _______
- the inactivation gate to close before the activation gate opens
- sodium cannot enter the cell and an action potential is not generated
Accomodation refers to
a nerve cell’s loss of excitability as a result of applying a stimulus gradually, rather than all at once
Threshold is
the membrane potential at which sodium and potassium influx and efflux, respectively, are equal. Or in other words, threshold is the membrane potential at which sodium and potassium currents are equal and opposite.
Threshold is achieved by
a slight initial depolarization of the axon
The threshold must be reached in order for _______
an action potential to be fired.
Once threshold is reached,
the potential can either be tipped in the direction of sodium or potassium equilibrium potentials
Because sodium channels are voltage gated, a momentary, slight influx of sodium will cause the potential to
tip in favor of the sodium equilibrium potential, causing more channels to open. Sodium will then rush into the cell and an action potential is generated
An action potential is generated due to
depolarization of an axon caused by sodium influx.
An action potential is an _______ mechanism because sodium channels are voltage gated.
explosive, positive-feedback
An action potential is an explosive, positive-feedback mechanism because _______
sodium channels are voltage gated
Once an axon is depolarized to threshold: Voltage gated sodium channels
begin to open
Once an axon is depolarized to threshold: Sodium
moves into the cell which further depolarizes the cel
Once an axon is depolarized to threshold: further depolarization causes
more voltage-gated sodium channels to open
