ap chpt 11

What prevents the Na+ and K+ gradients from dissipating? Hints Na+ and K+ leaks Na+-K+ ATPase H+-K+ ATPase Na+ cotransporter

Na+-K+ ATPase

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? Hints Threshold potential Positive membrane potential Resting membrane potential (RMP) Action potential

resting membrane potential

What event triggers the generation of an action potential? Hints The membrane potential must return to its resting value of -70 mV from the hyperpolarized value of -80 mV. The membrane potential must depolarize from the resting voltage of -70 mV to its peak value of +30 mV. The membrane potential must depolarize from the resting voltage of -70 mV to a threshold value of -55 mV. The membrane potential must hyperpolarize from the resting voltage of -70 mV to the more negative value of -80 mV.

The membrane potential must depolarize from the resting voltage of -70 mV to a threshold value of -55 mV.

Hypothetically, what would be the most immediate effect of doubling the number of Na+ leakage channels in the plasma membrane? Hints The resting membrane potential would become more negative. The outward concentration gradient for K+ would become smaller. The inward concentration gradient for Na+ would become larger. The resting membrane potential would become less negative (more positive).

The resting membrane potential would become less negative (more positive).

Action potentials (nerve impulses) are changes in the membrane potential that, once started, will affect the entire excitable membrane. The first action potential is usually generated at the initial segment of the neuron's axon. This activity will test your understanding of the sequence of events that occur at the membrane of the initial segment of the axon during generation of an action potential. Place the events involved in generation of an action potential in the correct order of occurrence from left to right.

Threshold stimulus Na+ channels open Na+ influx Depolarization Na+ channels close K+ channels open K+ efflux Repolarization Hyperpolarization K+ channels close

A molecule that carries information across a synaptic cleft is a Hints neurotransmitter. synaptic cleft. sending neuron. synapse. receiving neuron.

neurotrasmitter

1. This neuron is most depolarized at ? 2. This neuron spends approximately ?in a hyperpolarized state. 3. The ion ? is crossing the cell's plasma membrane at 1.5 msec. 4. This cell reaches threshold at approximately ?

1. +30mV 2. 2.5msec 3. k+ 4. 0.6 msec

Cl− is a common, negatively charged extracellular ion. Predict the effect on the RMP if many Cl− gated channels are suddenly opened. Hints The membrane would become hypopolarized or have less charge separation across the membrane. The RMP would become more positive. A more negative RMP would result. There would be no change in the RMP.

A more negative RMP would result.

Assume you have a membrane with only potassium leak channels. The RMP is -90mV. Predict the RMP if we add Na+ leak channels. The most likely RMP value of Na+ is __________. Hints -50 mV +70 mV +90 mV -90 mV -70 mV

-70mV

What is the value for the resting membrane potential for most neurons? Hints -90 mV +30 mV -70 mV

-70mV

On average, the resting membrane potential is -70 mV. What does the sign and magnitude of this value tell you? Hints The inside surface of the plasma membrane is much more negatively charged than the outside surface. The outside surface of the plasma membrane is much more negatively charged than the inside surface. There is no electrical potential difference between the inside and the outside surfaces of the plasma membrane. The inside surface of the plasma membrane is much more positively charged than the outside surface.

The inside surface of the plasma membrane is much more negatively charged than the outside surface.

What characterizes depolarization, the first phase of the action potential? Hints The membrane potential reaches a threshold value and returns to the resting state. The membrane potential changes to a less negative (but not a positive) value. The membrane potential changes to a much more negative value. The membrane potential changes from a negative value to a positive value.

The membrane potential changes from a negative value to a positive value.

What is the function of the myelin sheath? Hints The myelin sheath increases the insulation along the entire length of the axon. The myelin sheath decreases the speed of action potential conduction from the initial segment to the axon terminals. The myelin sheath decreases the resistance of the axonal membrane to the flow of charge. The myelin sheath increases the speed of action potential conduction from the initial segment to the axon terminals.

The myelin sheath increases the speed of action potential conduction from the initial segment to the axon terminals

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. Hints The presence of a resting membrane potential and leak channels The presence of concentration gradients and voltage-gated channels The presence of concentration gradients and leak channels The presence of concentration gradients and Na+-K+ pumps

The presence of concentration gradients and leak channels

An action potential is self-regenerating because __________. Hints depolarizing currents established by the influx of K+‎ flow down the axon and trigger an action potential at the next segment repolarizing currents established by the efflux of Na+‎ flow down the axon and trigger an action potential at the next segment repolarizing currents established by the efflux of K+‎ flow down the axon and trigger an action potential at the next segment depolarizing currents established by the influx of Na+‎ flow down the axon and trigger an action potential at the next segment

depolarizing currents established by the influx of Na+‎ flow down the axon and trigger an action potential at the next segment

The membranes of neurons at rest are very permeable to _____ but only slightly permeable to _____. Hints K+; Cl- K+; Na+ Na+; K+ Na+; Cl-

k, na+

Sodium and potassium ions can diffuse across the plasma membranes of all cells because of the presence of what type of channel? Hints Ligand-gated channels Voltage-gated channels Sodium-potassium ATPases Leak channels

leak channels

What is the major role of the Na+-K+ pump in maintaining the resting membrane potential? Hints maintaining the concentration gradients for Na+ and K+ across the cell membrane making the membrane potential negative by moving more Na+ ions out of the cell than K+ ions into the cell permitting Na+ and K+ ions to diffuse across the plasma membrane hydrolyzing ATP

maintaining the concentration gradients for Na+ and K+ across the cell membrane

Complete the following sentence. The operation of the Na+−K+ ATPase pump __________. Hints releases 3 K+ to the ECF moves 2 Na+ to the ECF and 3 K+ to the cytoplasm moves 3 Na+ to the ECF and 2 K+ to the cytoplasm releases 1 Na+ to the ECF and 1 K+ to the cytoplasm

moves 3 Na+ to the ECF and 2 K+ to the cytoplasm

The concentrations of which two ions are highest outside the cell. Hints K+ and Cl- Na+ and Cl- Na+ and A- (negatively charged proteins) K+ and A- (negatively charged proteins)

na+ and cl-

Imagine you changed the concentration of K+ outside a neuron such that the resting membrane potential changed to -80 mV (from the normal resting value of -70 mV). What have you changed? Hints the electrical gradient for K+ the concentration gradient for K+ the electrical gradient for K+ and the concentration gradient for K+ the electrical gradients and concentration gradients for both Na+ and K+.

the electrical gradient for K+ and the concentration gradient for K+

If a signal from a sending neuron makes the receiving neuron more negative inside, Hints the sending neuron becomes more negative inside. the receiving neuron is more likely to generate an action potential. the receiving neuron is less likely to generate an action potential. the sending neuron becomes more positive inside. the receiving neuron immediately generates an action potential.

the receiving neuron is less likely to generate an action potential.

The resting membrane potential is maintained by Na+-K+ pumps that actively transport ? into and ? out of the cell. The membrane is more permeable to ?. The concentration of ? is higher outside than inside the cell. The concentration of ? is higher inside than outside the cell.

1. k+, na+ 2. k+ 3. Na+ 4. k+

Which of the following is the clearest example of a neuronal membrane's selective permeability? Hints K+ ions can diffuse across the membrane more easily than Na+ ions. The Na+-K+ pump only transports Na+ and K+ ions. The concentration gradient for Na+ ions is inward, but the concentration gradient for K+ ions is outward. Diffusion of K+ ions out of the neuron causes the membrane potential to become more negative.

K+ ions can diffuse across the membrane more easily than Na+ ions.

Events Involved in Continuous Propagation of an Action Potential The propagation of an action potential (AP) in an unmyelinated axon is called continuous propagation. This activity will test your understanding of the sequence of events that occur during continuous propagation. Place the events involved in the propagation of an action potential in the correct order of occurrence from left to right. Hints

Local current flows to axon segment Axon segment depolarized to threshold Voltage-gated Na+ channels open Influx of Na+ AP regenerated in adjacent axon segment

In which type of axon will velocity of action potential conduction be the fastest? Hints Myelinated axons with the smallest diameters Unmyelinated axons of the shortest length Unmyelinated axons with the largest diameter Myelinated axons with the largest diameter

Myelinated axons with the largest diameter

he 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? Hints Na+ is pumped out of the cell and K+ is pumped into the cell. Both Na+ and K+ are pumped out of the cell. Both Na+ and K+ are pumped into the cell. K+ is pumped out of the cell and Na+ is pumped into the cell.

Na+ is pumped out of the cell and K+ is pumped into the cell.

What characterizes repolarization, the second phase of the action potential? Hints Once the membrane depolarizes to a threshold value of approximately -55 mV, it repolarizes to its resting value of -70 mV. Once the membrane depolarizes to a peak value of +30 mV, it repolarizes to its negative resting value of -70 mV. As the membrane repolarizes to a negative value, it goes beyond the resting state to a value of -80 mV. Before the membrane has a chance to reach a positive voltage, it repolarizes to its negative resting value of approximately -70 mV.

Once the membrane depolarizes to a peak value of +30 mV, it repolarizes to its negative resting value of -70 mV.

Which of the following best describes the Na+ and K+ concentrations across a neuron's plasma membrane? Hints The Na+ concentration is higher inside the cell compared to outside. The K+ concentration is higher outside the cell compared to inside. The Na+ concentration is higher outside the cell compared to inside. The K+ concentration is higher inside the cell compared to outside. Both Na+ and K+ concentrations are higher outside the cell compared to inside. Both Na+ and K+ concentrations are higher inside the cell compared to outside.

The Na+ concentration is higher outside the cell compared to inside. The K+ concentration is higher inside the cell compared to outside.

imagine that the cell membrane from the previous problem becomes more permeable to Na+. Predict how this will affect the RMP. Hints The RMP will be zero. The RMP will be unaffected. The RMP will be more negative. The RMP will be more positive.

The RMP will be more positive.

You are going to record RMP from a cell using an electrode. You place your electrode and record a resting membrane potential every millisecond. You record an initial value of -70mV; however, over time you notice that your recordings become more and more positive until the RMP reaches 0mV. Assuming that Na+ and K+ are the major determinants of RMP in this cell, which of the following could best explain your results? Hints The cell's K+ leak channels have stopped functioning. The cell's Na+-K+ ATPase pumps have stopped functioning. The cell is becoming depleted of Na+. The cell is becoming depleted of K+. The cell's Na+ leak channels have stopped functioning.

The cell's Na+-K+ ATPase pumps have stopped functioning.

Why does regeneration of the action potential occur in one direction, rather than in two directions? Hints The inactivation gates of voltage-gated K+‎ channels close in the node, or segment, that has just fired an action potential. The inactivation gates of voltage-gated Na+‎ channels close in the node, or segment, that has just fired an action potential. The activation gates of voltage-gated K+‎ channels open in the node, or segment, that has just depolarized. The activation gates of voltage-gated Na+‎ channels close in the node, or segment, that has just depolarized

The inactivation gates of voltage-gated Na+‎ channels close in the node, or segment, that has just fired an action potential.

Suppose a drug is developed that blocks K+ leakage channels. The drug prevents ions from passing through those channels. If this drug was applied to a neuron, what would be the most immediate effect on that neuron? Hints The resting membrane potential would become less negative (more positive). The resting membrane potential would become more negative. The concentration gradient for K+ would decrease. The concentration gradient for Na+ would decrease.

The resting membrane potential would become less negative (more positive).

The plasma membrane is much more permeable to K+ than to Na+. Why? Hints There are many more voltage-gated K+ channels than voltage-gated Na+ channels. There are many more K+ leak channels than Na+ leak channels in the plasma membrane. The Na+-K+ pumps transport more K+ into cells than Na+ out of cells. Ligand-gated cation channels favor a greater influx of Na+ than K+.

There are many more K+ leak channels than Na+ leak channels in the plasma membrane.

What is the first change to occur in response to a threshold stimulus? Hints Voltage-gated K+ channels change shape, and their activation gates open. Voltage-gated Ca2+ channels change shape, and their activation gates open. Voltage-gated Na+ channels change shape, and their activation gates open. Voltage-gated Na+ channels change shape, and their inactivation gates close.

Voltage-gated Na+ channels change shape, and their activation gates open.

During depolarization, which gradient(s) move(s) Na+ into the cell? Hints Na+ does not move into the cell. Na+ moves out of the cell. only the electrical gradient both the electrical and chemical gradients only the chemical gradient

both electrical and chemical gradients

What type of conduction takes place in unmyelinated axons? Hints Synaptic transmission Saltatory conduction Continuous conduction Electrical conduction

continuous conduction

What changes occur to voltage-gated Na+ and K+ channels at the peak of depolarization? Hints Activation gates of voltage-gated Na+‎ channels close, while inactivation gates of voltage-gated K+‎ channels open. Activation gates of voltage-gated Na+‎ channels close, while activation gates of voltage-gated K+‎ channels open. Inactivation gates of voltage-gated Na+‎ channels close, while activation gates of voltage-gated K+‎ channels open. Inactivation gates of voltage-gated Na+‎ channels close, while inactivation gates of voltage-gated K+‎ channels open.

inactivation gates of voltage-gated Na+‎ channels close, while activation gates of voltage-gated K+‎ channels open

Where do most action potentials originate? Hints Cell body Initial segment Axon terminal Nodes of Ranvier

initial segment

When neurotransmitter molecules bind to receptors in the plasma membrane of the receiving neuron, Hints the receiving neuron becomes more positive inside. ion channels in the plasma membrane of the sending neuron open. ion channels in the plasma membrane of the receiving neuron open. the receiving neuron becomes more negative inside. vesicles in the synaptic terminal fuse to the plasma membrane of the sending neuron.

ion channels in the plasma membrane of the receiving neuron open.

Which of the following would increase the membrane permeability to K+? Hints more negative membrane potential a greater concentration gradient for K+ more Na+ leakage channels more K+ leakage channels

more k+ leakage channels

Saltatory propagation occurs in _________ axons, in which action potentials _________. Select the best answer. Hints unmyelinated; move from one node of Ranvier to another myelinated; move continuously along the axon toward the axon hillock unmyelinated; spread by depolarizing the adjacent region of the axon membrane myelinated; move from one node of Ranvier to another

myelinated; move from one node of Ranvier to another

The small space between the sending neuron and the receiving neuron is the Hints calcium channel. vesicle. neurotransmitter. synaptic cleft. synaptic terminal.

synaptic cleft

What is the electrochemical gradient of an ion? Hints the sum of the electrical and concentration gradients for that ion the difference between the inside and outside concentrations of that ion the direction an ion would tend to diffuse based on the membrane potential the membrane potential at which the electrical gradient and concentration gradient for that ion are equal in magnitude, but opposite in direction

the sum of the electrical and concentration gradients for that ion

When calcium ions enter the synaptic terminal, Hints they cause an action potential in the sending neuron. the inside of the receiving neuron becomes more positive. the inside of the receiving neuron becomes more negative. they cause vesicles containing neurotransmitter molecules to fuse to the plasma membrane of the sending neuron. neurotransmitter molecules are quickly removed from the synaptic cleft.

they cause vesicles containing neurotransmitter molecules to fuse to the plasma membrane of the sending neuron.

Which choice best characterizes K+ leak channels? Hints transmembrane channels that use energy to allow the movement of K+ across the membrane chemically gated K+ channels that open and close according to the binding of other molecules common transmembrane channels that are always open for any ion to move through in the presence of K+ transmembrane protein channels that are always open to allow K+ to cross the membrane without the additional input of energy

transmembrane protein channels that are always open to allow K+ to cross the membrane without the additional input of energy

The generation of an action potential in a neuron requires the presence what type of membrane channels? Select the best answer. Hints leakage channels voltage-gated channels chemically gated channels membrane channels are not required

volage gates channels

What opens first in response to a threshold stimulus? Hints Ligand-gated cation channels Voltage-gated Na+ channels Ligand-gated Cl- channels Voltage-gated K+ channels

voltage gated na channels