Flashcards in SDL-3 Action Potential Deck (19):
What are the five stages of an action potential?
I. Rising phase
IV. Falling phase
V. Hyperpolarization (Undershoot)
(T/F) The membrane potential remains negative throughout an action potential.
False. During the Overshoot phase, the membrane potential depolarizes past the threshold needed to elicit an action potential, peaking at approximately +30mV.
On average, the hyperpolarization phase lasts __-__ milliseconds.
A sudden influx of ___ ions causes the rising phase of the action potential.
____________ is a toxin found in puffer fish used to block Na+ channels for use in measurement of membrane permeabilities.
____________ is a toxin used to block K+ channels for use in measurement of membrane permeabilities.
How is an action potential propagated the length of an axon?
As Na+ ions enter the cell through voltage-gated Na+ channels, they cause eddy currents from outside to inside the membrane. The entering Na+ ions are attracted to the nearby negative region of the membrane. This in turn depolarizes the nearby region of the membrane, opening more Na+ channels. The newly entering Na+ ions continue the process further and further down the axon, allowing for propagation of the action potential.
How does a myelinated fiber increase action potential propagation?
In myelinated fibers, the eddy currents generated by Na+ ions skip the internodal myelinated portions, only depolarizing the membrane at the intervening nodes where Na+ channels are congregated. This process is referred to as saltatory conduction. Also, the voltage-gated K+ channels are sequestered underneath the myelinated portions of the fiber. This prevents hyperpolarization, allowing for generation of a new action potential sooner.
In myelinated fibers, repolarization of the membrane is due to ____________ that are not actively opened and thus, there is no hyperpolarization.
K+ leakage channels
Conduction of an action potential away from the soma is referred to as (antidromic/orthodromic).
Conduction of an action potential toward the soma is referred to as (antidromic/orthodromic).
Changes in membrane potential that occur in a small region of the cytoplasmic membrane are referred to as _____________.
The length of membrane at which an electrotonic potential is decreased to 1/e (about 37%) of it's initial amplitude is the membrane's ______________.
Length constant, λ (Lambda)
The time required for the amplitude of an action potential to decrease to 37% of its initial value is the membrane's _____________.
Time constant, τ (Tau)
On average, the time constant of a membrane is __-__ milliseconds.
Larger diameter nerve fibers have (smaller/larger) length constants and (smaller/larger) time constants due to their lower internal resistance to the flow of ions.
Larger length constants; smaller time constants
Larger diameter fibers have (lower/higher) thresholds for generation of an action potential. The opposite is true of smaller diameter fibers.
Larger diameter = lower threshold
Smaller diameter = higher threshold
A depolarizing stimulus that accumulates slowly but does not result in an action potential due to the inactivation of Na+ channels before a cascade may be reached is referred to as _______________ to the stimulus.