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60 Cards in this Set

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The membrane potential at which there is no net flux of an ion across the membrane is called that ion's ________.
equilibrium potential
The presence of the ________ prevents the dissipation of the concentration gradient for Na+.
Na+/K+ pump
Why is the electrical potential of a membrane at rest closest to potassium's equilibrium potential than to sodium's equilibrium potential?
more potassium channels are open, allowing more potassium to move out of the cell
As a membrane's permeability to a particular ion increases, membrane potential will move ________ that ion's ________.
closer to : equilibrium potential
True/False: The membrane potential of a cell is determined exclusively by that cell's sodium and potassium permeability.
false
True/False: The Nernst equation is used to calculate the resting membrane potential.
false
Whether a membrane is depolarized to threshold or above, the amplitude of the resulting action potential is the same; in other words, once threshold is reached, the action potential will take place. This concept is known as __________.
the "all-or-none principle"
A change in a cell's membrane potential, such that it becomes more positive, is referred to as a ________.
depolarization
The depolarization phase of the action potential is generated by a rapid ________.
opening of sodium channels
The repolarization phase of action potentials in neurons is due primarily to ________.
potassium flow out of the cell
During which of the following states are the majority of voltage-gated sodium channels closed and incapable of opening?
during the absolute refractory period
The all-or-none principle, associated with the action potential, states that ________.
once membrane potential reaches threshold, an action potential will be generated and that action potential will always be the same magnitude
In order for a neuron to move from the absolute to the relative refractory period, a majority of that neuron's sodium channels must have their ________.
inactivation gates open
In myelinated nerve fibers, where do action potentials occur?
nodes of Ranvier
True/False: The magnitude of the action potential is dependent upon the extent to which the change in membrane potential is above threshold.
false
Where in the neuron is an action potential initially generated?
axon hillock
Yes, this region (first part of the axon) receives local signals (graded potentials) from the soma and dendrites and has a high concentration of voltage-gated Na+ channels.
The depolarization phase of an action potential results from the opening of which channels?
voltage-gated Na+ channels
Yes, when the voltage-gated Na+ channels open, Na+ rushes into the cell causing depolarization.
The repolarization phase of an action potential results from __________.
the opening of voltage-gated K+ channels
Yes, as the voltage-gated K+ channels open, K+ rushes out of the cell, causing the membrane potential to become more negative on the inside, thus repolarizing the cell.
Hyperpolarization results from __________.
slow closing of voltage-gated K+ channels
Yes, the slow closing of the voltage-gated K+ channels means that more K+ is leaving the cell, making it more negative inside.
What is the magnitude (amplitude) of an action potential?
100 mV
Yes, the membrane goes from –70 mV to +30 mV. Thus, during the action potential, the inside of the cell becomes more positive than the outside of the cell.
The membranes of neurons at rest are very permeable to _____ but only slightly permeable to _____.
K+; Na+
Yes, more K+ moves out of the cell than Na+ moves into the cell, helping to establish a negative resting membrane potential.
During depolarization, which gradient(s) move(s) Na+ into the cell?
both the electrical and chemical gradients
Yes, a positive ion is driven into the cell because the inside of the cell is negative compared to the outside of the cell, and Na+ is driven into the cell because the concentration of Na+ is greater outside the cell.
What is the value for the resting membrane potential for most neurons?
-70mV
Yes, the resting membrane potential for neurons depends on the distribution of both Na+ and K+ across the cell membrane. The potential is closer to the equilibrium potential of K+ because the cell is more permeable to K+.
The Na+–K+ pump actively transports both sodium and potassium ions across the membrane to compensate for their constant leakage. In which direction is each ion pumped?
Na+ is pumped out of the cell and K+ is pumped into the cell
Yes, Na+ is pumped out of the cell against its electrochemical gradient and K+ is pumped into the cell against its concentration gradient.
The concentrations of which two ions are highest outside the cell.
Na+ and Cl–
Yes, both Na+ and Cl– are in higher concentrations outside the cell.
What is the approximate resting membrane potential of neurons?
-70mV
Which of the following best describes the electrochemical forces acting on sodium and potassium ions at the resting membrane potential?
a. the force on sodium ions move out of the cell, and the force of potassium ions is to move into the cell
b. the force of sodium ions is to move into the cell, and the force on potassium ions is to move out of the cell.
c. there is no force on either ion to move
d. forces on both sodium and potassium ions are to move out of the cell
e. forces on both sodium and potassium ions are to move into the cell
b. the force of sodium ions is to move into the cell, and the force on potassium ions is to move out of the cell.
At the resting membrane potential, the membrane is most permeable to ________, which moves ________ the cell due to its electrochemical gradient.
potassium : out of
If, under resting conditions, the membrane is much more permeable to sodium than potassium, what would happen to the resting membrane potential?
approach sodium's equilibrium potential
If we apply an electrical stimulus to a muscle cell to cause it to contract, the magnitude of that stimulus must be strong enough to reach a critical value that is essential in initiating the process of contraction. This critical value is known as __________.
threshold
Which of the following represents a state of depolarization of a neuron?
-70mv to +30mV
A change in a cell's membrane potential, such that it becomes more negative, is referred to as a ________.
hyperpolarization
A ________ is a subthreshold change in membrane potential within the cell body that decays as it travels away from its point of origin.
graded potential
If the graded potential remains above threshold once it reaches the ________, an action potential will be generated.
axon hillock
The opening of sodium channels causes a rapid ________ of sodium that ________ the neuron's membrane.
influx : depolarizes
The repolarization phase of the action potential in a neuron is driven by the ________.
closure of sodium channels and opening of potassium channels
For the sodium channel to open and allow sodium into the cell, ________.
the activation and inactivation gates must be both opened
The jumping of an action potential from node-to-node is called ________.
saltatory conduction
True/False: Under resting conditions, the sodium channel responsible for generating an action potential is closed and incapable of opening.
false
Where do most action potentials originate?
initial segment
The first part of the axon is known as the initial segment. The initial segment is adjacent to the tapered end of the cell body, known as the axon hillock.
What opens first in response to a threshold stimulus?
Voltage-gated Na+ channels
The activation gates of voltage-gated Na+ channels open, and Na+ diffuses into the cytoplasm
What characterizes depolarization, the first phase of the action potential?
The membrane potential changes from a negative value to a positive value.
The plasma membrane, which was polarized to a negative value at the RMP, depolarizes to a positive value.
What characterizes repolarization, the second phase of the action potential?
Once the membrane depolarizes to a peak value of +30 mV, it repolarizes to its negative resting value of -70 mV.
The plasma membrane was depolarized to a positive value at the peak of the first phase of the action potential. Thus, it must repolarize back to a negative value.
What event triggers the generation of an action potential?
The membrane potential must depolarize from the resting voltage of -70 mV to a threshold value of -55 mV.
This is the minimum value required to open enough voltage-gated Na+ channels so that depolarization is irreversible.
What is the first change to occur in response to a threshold stimulus?
Voltage-gated Na+ channels change shape, and their activation gates open.
The activation gates of voltage-gated Na+ channels open very rapidly in response to threshold stimuli. The activation gates of voltage-gated K+ channels are comparatively slow to open.
What type of conduction takes place in unmyelinated axons?
continuous conduction
An action potential is conducted continuously along an unmyelinated axon from its initial segment to the axon terminals. The term continuous refers to the fact that the action potential is regenerated when voltage-gated Na+ channels open in every consecutive segment of the axon, not at nodes of Ranvier.
An action potential is self-regenerating because __________.
depolarizing currents established by the influx of Na+ flow down the axon and trigger an action potential at the next segment
The Na+ diffusing into the axon during the first phase of the action potential creates a depolarizing current that brings the next segment, or node, of the axon to threshold.
Why does regeneration of the action potential occur in one direction, rather than in two directions?
The inactivation gates of voltage-gated Na+ channels close in the node, or segment, that has just fired an action potential.
At the peak of the depolarization phase of the action potential, the inactivation gates close. Thus, the voltage-gated Na+ channels become absolutely refractory to another depolarizing stimulus.
What is the function of the myelin sheath?
The myelin sheath increases the speed of action potential conduction from the initial segment to the axon terminals.
The myelin sheath increases the velocity of conduction by two mechanisms. First, myelin insulates the axon, reducing the loss of depolarizing current across the plasma membrane. Second, the myelin insulation allows the voltage across the membrane to change much faster. Because of these two mechanisms, regeneration only needs to happen at the widely spaced nodes of Ranvier, so the action potential appears to jump.
What changes occur to voltage-gated Na+ and K+ channels at the peak of depolarization?
Inactivation gates of voltage-gated Na+ channels close, while activation gates of voltage-gated K+ channels open.
Closing of voltage-gated channels is time dependent. Typically, the inactivation gates of voltage-gated Na+ channels close about a millisecond after the activation gates open. At the same time, the activation gates of voltage-gated K+ channels open.
In which type of axon will velocity of action potential conduction be the fastest?
Myelinated axons with the largest diameter
The large diameter facilitates the flow of depolarizing current through the cytoplasm. The myelin sheath insulates the axons and prevents current from leaking across the plasma membrane.
Ions are unequally distributed across the plasma membrane of all cells. This ion distribution creates an electrical potential difference across the membrane. What is the name given to this potential difference?
Resting membrane potential (RMP)
The resting membrane potential is the baseline potential that can be recorded across the plasma membrane of an excitable cell prior to excitation.
Sodium and potassium ions can diffuse across the plasma membranes of all cells because of the presence of what type of channel?
Leak channels
Leak channels for Na+ and K+ are ubiquitous, and they allow for the diffusion of these ions across plasma membranes.
On average, the resting membrane potential is -70 mV. What does the sign and magnitude of this value tell you?
The inside surface of the plasma is much more negatively charged than the outside surface.
The inside surface of the plasma membrane accumulates more negative charge because of the presence of Na+ and K+ gradients and the selective permeability of the membrane to Na+ and K+.
The plasma membrane is much more permeable to K+ than to Na+. Why?
There are many more K+ leak channels than Na+ leak channels in the plasma membrane.
More leak channels translates into more leakiness. Thus the outward flux of K+ is greater than the inward flux of Na+.
The resting membrane potential depends on two factors that influence the magnitude and direction of Na+ and K+ diffusion across the plasma membrane. Identify these two factors.
The presence of concentration gradients and leak channels
The concentration gradient and the large number of K+ leak channels allow for rather robust K+ diffusion out of a cell. In contrast, the concentration gradient and the relatively few Na+ leak channels allow for much less Na+ diffusion into a cell.
What prevents the Na+ and K+ gradients from dissipating?
Na+-K+ ATPase
Also known as the Na+-K+ pump, or simply the pump, this transporter moves three Na+ out of the cell and two K+ into the cell for every ATP it hydrolyzes. This pumping action prevents the Na+ and K+ gradients from running down as these ions passively move through leak channels.
Which ion(s) is/are higher in concentration inside the cell compared to outside?
potassium
Voltage-regulated channels are located
in the membranes of axons
Action potentials occur in the membrane of
axons