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49 Cards in this Set

  • Front
  • Back
Synaptic activity results in _____________

A. the electrical impulse that propagates along the surface of the axon
B. the production of graded potentials in the plasma membrane of the postsynaptic cell
C. a stimulus that temporarily causes a localized change in the resting potential
D. the moment to moment variation of the transmembrane potential in all living cells
B. the production of graded potentials in the plasma membrane of the postsynaptic cell
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?
A. Action potential
B. Positive membrane potential
C. Resting membrane potential (RMP)
D. Threshold potential
C. resting membrane potential (RMP)
Sodium and potassium ions can diffuse across the plasma membranes of all cells because of the presence of what type of channel?
A. Voltage-gated channels
B. Ligand-gated channels
C. Leak channels
D. Sodium-potassium ATPases
C. leak channels
On average, the resting membrane potential is -70 mV. What does the sign and magnitude of this value tell you?
A. The inside surface of the plasma membrane is much more negatively charged than the outside surface.
B. There is no electrical potential difference between the inside and the outside surfaces of the plasma membrane.
C. The outside surface of the plasma membrane is much more negatively charged than the inside surface.
D. The inside surface of the plasma membrane is much more positively charged than the inside surface.
A. The inside surface of the plasma membrane 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?
A. There are many more voltage-gated K+ channels than voltage-gated Na+ channels.
B. Ligand-gated cation channels favor a greater influx of Na+ than K+.
C. There are many more K+ leak channels than Na+ leak channels in the plasma membrane.
D. The Na+-K+ pumps transport more K+ into cells than Na+ out of cells.
C. There are many more K+ leak channels than Na+ leak channels in the plasma membrane.

*more leaks 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.
A. The presence of concentration gradients and leak channels
B. The presence of concentration gradients and Na+-K+ pumps
C. The presence of a resting membrane potential and leak channels
D. The presence of concentration gradients and voltage-gated
A. 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?
A. Na+ cotransporter
B. Na+-K+ ATPase
C. H+-K+ ATPase
D. Na+ and K+ leaks
B. 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**
The membranes of neurons at rest are very permeable to _____ but only slightly permeable to _____.
A. K+; Na+
B. Na+; K+
C. Na+; Cl–
D. K+; Cl–
A. K+; Na+


**more K+ moves out of the cell than Na+ moves into the cell, helping to establish a negative resting membrane potential**
During polarization. which gradient moves sodium into the cell?
A. both the electrical and chemical gradients
B. sodium does not move into the cell. Sodium moves out of the cell
C. only the electrical gradient
D. only the chemical gradient
A. both the electrical and chemical gradients


**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?
A. -70mV
B. -90mV
C. +30mV
A. -70mV


**The potential is closer to the equilibrium potential of K+ because the cell is more permeable to K+.**
The concentrations of which two ions are highest outside the cell.
A. K+ and A– (negatively charged proteins)
B. Na+ and A– (negatively charged proteins)
C. K+ and Cl–
D. Na+ and Cl–
D. Na+ and Cl–
In a neuron, sodium and potassium concentrations are maintained by the sodium-potassium exchange pump such that __________.

A. both sodium and potassium concentrations are higher outside the cell compared to inside.
B. the sodium concentration is higher inside the cell than outside the cell and the potassium concentration is higher outside the cell than inside the cell.
C. the sodium concentration is higher outside the cell than inside the cell and the potassium concentration is higher inside the cell than outside the cell.
D. the concentration of sodium outside the cell is equal to the concentration of potassium inside the cell.
C. the sodium concentration is higher outside the cell than inside the cell and the potassium concentration is higher inside the cell than outside the cell.

**Because the sodium-potassium exchange pump moves sodium and potassium ions in opposite directions, the pump generates concentration gradients for these ions that are opposite in direction. The opposite direction of these concentration gradients explains why the equilibrium potentials for those ions are opposite in sign (that is, -90 mV for potassium and +66 mV for sodium).**
The sodium-potassium exchange pump transports potassium and sodium ions in which direction(s)?
A. Sodium ions are transported out of the cell. Potassium ions are transported into the cell.
B. Sodium and potassium ions are both transported out of the cell.
C. Sodium ions are transported into the cell. Potassium ions are transported out of the cell.
D. Sodium and potassium ions are both transported into the cell.
A. Sodium ions are transported out of the cell. Potassium ions are transported into the cell.

*The energy of ATP is used to actively transport potassium and sodium ions against their electrochemical gradients. Potassium and sodium ions diffuse in the opposite direction through channels.*
Leak channels allow the movement of potassium and sodium ions by what type of membrane transport?
A. facilitated diffusion
B. channel-mediated diffusion
C. simple diffusion
D. active transport
B. channel-mediated diffusion

*Ions move through leak channels because of chemical and electrical gradients.**
The electrochemical gradient for potassium ions when the transmembrane potential is at the resting potential (-70 mV) is caused by what?
A. chemical and electrical gradients both going into the cell
B. a chemical gradient going into the cell and an electrical gradient going out of the cell
C. a chemical gradient going out of the cell and an electrical gradient going into the cell
D. chemical and electrical gradients both going out of the cell
C. a chemical gradient going out of the cell and an electrical gradient going into the cell

*The higher concentration of potassium inside the cell than outside the cell results in an outward chemical gradient. However, the electrical gradient is in the opposite direction (inward) because, at the resting potential, the inside of the cell is more negative, which is attractive to the positively charged potassium ions.*
What is the electrochemical gradient of an ion?
A. the sum of the electrical and chemical gradients for that ion
B. the difference between the concentrations of an ion inside and outside the cell
C. the transmembrane potential at which the electrical and chemical gradients are equal in magnitude, but opposite in direction
D. The electrochemical gradient is the direction an ion would diffuse (either outward or inward) when the neuron is at rest, regardless of the transmembrane potential.
A. the sum of the electrical and chemical gradients for that ion

**Together, these two gradients determine the net movement of a particular ion across the plasma membrane
The events that occur at a functioning cholinergic synapse cause _____________ .

A. strengthening of the synapse
B. synaptic delay
C. flow of acetylcholine (ACh) into the synaptic cleft that is removed only by simple diffusion
D. loss of transmission of the action potential
B. synaptic delay

*Due to the time involved in calcium influx and neurotransmitter release, the transmission of an action potential is delayed at the synaptic cleft*
Which type of ion channel is always open?
A. passive
B. mechanically gated
C. chemically gated
D. voltage-gated
A. passive
The sodium-potassium exchange pump stabilizes resting potential at about __________.
A. -70 mV
B. +66 mV
C. -90 mV
D. -10 mV
A. -70 mV
Where do most action potentials originate?
A. Axon terminal
B. Nodes of Ranvier
C. Cell body
D. Initial segment
D. Initial segment
What opens first in response to a threshold stimulus?
A. Voltage-gated Na+ channels
B. Voltage-gated K+ channels
C. Ligand-gated cation channels
D. Ligand-gated Cl- channels
A. 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?
A. The membrane potential changes to a less negative (but not a positive) value.
B. The membrane potential reaches a threshold value and returns to the resting state.
C. The membrane potential changes to a much more negative value.
D. The membrane potential changes from a negative value to a positive value.
D. 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?
A. Before the membrane has a chance to reach a positive voltage, it repolarizes to its negative resting value of approximately -70 mV.
B. Once the membrane depolarizes to a threshold value of approximately -55 mV, it repolarizes to its resting value of -70 mV.
C. As the membrane repolarizes to a negative value, it goes beyond the resting state to a value of -80 mV.
D. Once the membrane depolarizes to a peak value of +30 mV, it repolarizes to its negative resting value of -70 mV.
D. 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?

A. The membrane potential must depolarize from the resting voltage of -70 mV to a threshold value of -55 mV.
B. The membrane potential must hyperpolarize from the resting voltage of -70 mV to the more negative value of -80 mV.
C. The membrane potential must depolarize from the resting voltage of -70 mV to its peak value of +30 mV.
D. The membrane potential must return to its resting value of -70 mV from the hyperpolarized value of -80 mV.
A. 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?
A. Voltage-gated Na+ channels change shape, and their activation gates open.
B. Voltage-gated Ca2+ channels change shape, and their activation gates open.
C. Voltage-gated Na+ channels change shape, and their inactivation gates close.
D. Voltage-gated K+ channels change shape, and their activation gates open.
A. 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?
A. Synaptic transmission
B. Electrical conduction
C. Saltatory conduction
D. Continuous conduction
D. 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 __________.
A. repolarizing currents established by the efflux of Na+ flow down the axon and trigger an action potential at the next segment
B. depolarizing currents established by the influx of K+ flow down the axon and trigger an action potential at the next segment
C. depolarizing currents established by the influx of Na+ flow down the axon and trigger an action potential at the next segment
D. repolarizing currents established by the efflux of K+ flow down the axon and trigger an action potential at the next segment
C. 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?
A. The inactivation gates of voltage-gated Na+ channels close in the node, or segment, that has just fired an action potential.
B. The inactivation gates of voltage-gated K+ channels close in the node, or segment, that has just fired an action potential.
C. The activation gates of voltage-gated Na+ channels close in the node, or segment, that has just depolarized.
D. The activation gates of voltage-gated K+ channels open in the node, or segment, that has just depolarized.
A. 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?
A. The myelin sheath decreases the speed of action potential conduction from the initial segment to the axon terminals.
B. The myelin sheath increases the insulation along the entire length of the axon.
C. The myelin sheath increases the speed of action potential conduction from the initial segment to the axon terminals.
D. The myelin sheath decreases the resistance of the axonal membrane to the flow of charge.
C. 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?
A. Inactivation gates of voltage-gated Na+ channels close, while inactivation gates of voltage-gated K+ channels open.
B. Activation gates of voltage-gated Na+ channels close, while activation gates of voltage-gated K+ channels open.
C. Activation gates of voltage-gated Na+ channels close, while inactivation gates of voltage-gated K+ channels open.
D. Inactivation gates of voltage-gated Na+ channels close, while activation gates of voltage-gated K+ channels open.
D. Inactivation gates of voltage-gated Na+ channels close, while activation gates of voltage-gated K+

**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?
A. Myelinated axons with the largest diameter
B. Unmyelinated axons with the largest diameter
C. Myelinated axons with the smallest diameters
D. Unmyelinated axons of the shortest length
A. 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.**
Where in the neuron is an action potential initially generated?
A. axon hillock
B. soma and dendrites
C. anywhere on the axon
A. axon hillock

**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?
A. voltage-gated K+ channels
B. voltage-gated Na+ channels
C. chemically gated Na+ channels
D. chemically gated K+ channels
B. voltage-gated Na+ channels
The repolarization phase of an action potential results from __________.
A. the opening of voltage-gated Na+ channels
B. the closing of voltage-gated K+ channels
C. the opening of voltage-gated K+ channels
D. the closing of voltage-gated Na+ channels
C. the opening of voltage-gated K+ channels

**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 __________.
A. slow closing of voltage-gated Na+ channels
B. slow closing of voltage-gated K+ channels
C. fast closing of voltage-gated K+ channels
B. slow closing of voltage-gated K+ channels

**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?
A. 70 mV
B. 100 mV
C. 30 mV
B. 100 mV

**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.**
Action potential propagation begins (is first generated at) what region of a neuron?
A. initial segment
B. node
C. myelin
D. dendrite
A. initial segment
Where are action potentials regenerated as they propagate along an unmyelinated axon?
A. at the nodes
B. at the internodes
C. at myelin
D. at every segment of the axon
D. at every segment of the axon


***In unmyelinated axons, the action potential is regenerated continuously along every segment of the axon (continuous propagation). In humans, only small diameter axons (for example, type C fibers) are unmyelinated. These neurons carry low-priority information, such as smell (olfaction) and temperature sensations.***
The movement of what ion is responsible for the local currents that depolarize other regions of the axon to threshold?
A. voltage-gated sodium (Na+) channels
B. calcium (Ca2+)
C. sodium (Na+)
D. Potassium (K+)
C. sodium (Na+)


***Sodium ions enter the cell during the beginning of an action potential. Not only does this (further) depolarize the membrane where those channels are located, but it also sets up local currents that depolarize nearby membrane segments. In the case of myelinated axons, these local currents depolarize the next node, 1-2 mm away.***
In an unmyelinated axon, why doesn't the action potential suddenly "double back" and start propagating in the opposite direction?
A. New action potential generation near the soma repels previously generated action potentials.
B. The previous axonal segment is refractory.
C. Positive charges only move in one direction.
D. The extracellular sodium concentration is too low around the previous axonal segment for an action potential to be (re)generated.
B. The previous axonal segment is refractory.

**A propagating action potential always leaves a trail of refractory membrane in its wake. The trailing membrane takes some time to recover from the action potential it just experienced, largely because the membrane's voltage-gated sodium channels are inactivated. By the time this membrane segment is ready to (re)generate another action potential, the first propagating action potential is long gone.***
Approximately how fast do action potentials propagate in unmyelinated axons in humans?
A. 1 meter per second
B. 120 meters per second
C. 12 meters per second
D. 0.1 meters per second
A. 1 meter per second


**While 1 m per second (2 mph) seems slow, most axons are short, and these speeds are fast enough for low-priority information such as smell (olfaction), temperature, and general touch sensations. Unmyelinated type C fibers have propagation speeds in this range.**
In contrast to the internodes of a myelinated axon, the nodes __________.
A. are wrapped in myelin
B. have lower membrane resistance to ion movement
C. have higher membrane resistance to ion movement
D. only occur at the beginning and end of the axon
B. have lower membrane resistance to ion movement


***In a myelinated axon, action potential regeneration occurs at the nodes where myelin is absent. Here, the ion channels associated with the action potential provide a low resistance pathway for ions to cross the axon membrane. In contrast, the myelin surrounding the internode regions makes it difficult for ions to cross the membrane. Therefore, membrane resistance at the internodes is higher than membrane resistance at the nodes. Conversely, membrane resistance at the nodes is lower than membrane resistance at the internodes.**
Where are action potentials regenerated as they propagate along a myelinated axon?
A. at the internodes
B. at the nodes
C. at every segment of the axon
D. at myelin
B. at the nodes


**In myelinated axons, voltage-gated sodium channels are largely restricted to the nodes between myelinated internodes. Therefore, action potentials only regenerate at the nodes. The high membrane resistance of the internodes ensures that local currents generated at one node will quickly bring the next node to threshold, even though it is 1-2 mm away.***
The node-to-node "jumping" regeneration of an action potential along a myelinated axon is called __________.
A. local propagation
B. myelinated propagation
C. saltatory propagation
D. continuous propagation
C. saltatory propagation
How do action potential propagation speeds in myelinated and unmyelinated axons compare?
A. Propagation is faster in myelinated axons.
B. Propagation in myelinated axons is faster over short distances, but slower over long distances.
C. Propagation is faster in unmyelinated axons.
D. Propagation speeds are similar in both axon types.
A. Propagation is faster in myelinated axons.

**The internode segments of myelinated axons allow local currents to travel quickly between nodes where the action potential is regenerated. This leaping of action potentials from node to node is several times faster than the continuous propagation found in unmyelinated axons. Myelinated axons also tend to have larger diameters, which enhances propagation speed.***
Multiple sclerosis (MS) is a disease that stops action potential propagation by destroying the myelin around (normally) myelinated axons. Which of the following best describes how MS stops action potential propagation?
A. Without myelin, the internode membrane resistance increases, preventing local currents from reaching adjacent nodes.
B. Without myelin, the internode membrane is depolarized more easily.
C. Without myelin, the node membrane more easily becomes refractory.
D. Without myelin, the internode membrane resistance decreases, preventing local currents from reaching adjacent nodes.
D. Without myelin, the internode membrane resistance decreases, preventing local currents from reaching adjacent nodes.



**Myelin increases the membrane resistance of the axon section it surrounds, allowing local currents to travel between nodes, even though they are 1-2 mm apart. Removing myelin decreases the membrane resistance of internode regions. This shortens the distance that local currents travel because more charge now exits at the internode regions before it reaches the next node***
During propagation of the action potential, __________.
A. local currents depolarize a spot adjacent to the active zone
B. after threshold is reached, sodium channels open rapidly
C. the axon hillock depolarizes the initial segment
D. All of these events occur during propagation of the action potential.
D. All of these events occur during propagation of the action potential.
Compared to type A axons, type C axons are __________.

A. smaller diameter
B. unmyelinated
C. slower propagating
D. Type C axons have all of these characteristics
D. Type C axons have all of these characteristics
Which of these axons will conduct an action potential most quickly?
A. Type C fiber
B. Type B fiber
C. Type A fiber
D. All fibers have the same propagation speed.
C. type A fiber