Chapter 11 Homework

Which of the cell types shown helps determine capillary permeability in the CNS?

Which of the cell types shown is most associated with the production and flow of cerebrospinal fluid (CSF)?

Which of the neuroglial cell types shown form myelin sheaths within the CNS?

Which of the neuroglial cell types shown are found in the peripheral nervous system (PNS)?

What is the structure at A?

What structural classification describes this neuron?

Which areas of this neuron would be classified as receptive regions?

Which of these materials or structures would be found in greatest amounts or numbers at E?

In which area of the neuron is an action potential initially generated?

The membranes of neurons at rest are very permeable to _____ but only slightly permeable to _____.

During depolarization, which gradient(s) move(s) Na+ into the cell?

What is the value for the resting membrane potential for most neurons?

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?

The concentrations of which two ions are highest outside the 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?

Sodium and potassium ions can diffuse across the plasma membranes of all cells because of the presence of what type of channel?

On average, the resting membrane potential is -70 mV. What does the sign and magnitude of this value tell you?

The plasma membrane is much more permeable to K+ than to Na+. Why?

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.

What prevents the Na+ and K+ gradients from dissipating?

Which of the following best describes the Na+ and K+ concentrations across a neuron's plasma membrane?

What is the major role of the Na+-K+ pump in maintaining the resting membrane potential?

Which of the following is the clearest example of a neuronal membrane's selective permeability?

Which of the following would increase the membrane permeability to K+?

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?

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?

What is the electrochemical gradient of an ion?

Hypothetically, what would be the most immediate effect of doubling the number of Na+ leakage channels in the plasma membrane?

You are working on a new medication to selectively kill cancer cells. You test the drug on a culture of normal neurons to check for any side effects. Despite the presence of the drug, a normal resting membrane potential of ?70 mV is maintained. Look at each of the figures below to analyze how the drug might be affecting the neuron. Figure A shows neuron activity under normal, or control, conditions (without the drug). Figure B shows neuron activity that has been altered due to exposure to the drug. Based on these results, the drug is most likely __________.

The concentrations of which two ions are highest outside the cell?

Let's consider a scenario in which the resting membrane potential changes from ??70 mVmV to +70 mVmV, but the concentrations of all ions in the intracellular and extracellular fluids are unchanged. Predict how this change in membrane potential affects the movement of Na+Na+. The electrical gradient for Na+Na+ would tend to move Na+Na+ __________ while the chemical gradient for Na+Na+ would tend to move Na+Na+ __________.

Which choice best characterizes K+ leakage channels?

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

Imagine that the cell membrane from the previous problem becomes more permeable to Na+. Predict how this will affect the RMP.

Complete the following sentence. The operation of the Na+?K+ ATPase pump __________.

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+Na+ and K+K+ are the major determinants of RMP in this cell, which of the following could best explain your results?

Cl? is a common, negatively charged extracellular ion. Predict the effect on the RMP if many Cl? gated channels are suddenly opened.

Where in the neuron is an action potential initially generated?

The depolarization phase of an action potential results from the opening of which channels?

The repolarization phase of an action potential results from __________.

Hyperpolarization results from __________.

What is the magnitude (amplitude) of an action potential?

How is an action potential propagated along an axon?

Why does the action potential only move away from the cell body?

The velocity of the action potential is fastest in which of the following axons?

Where do most action potentials originate?

What opens first in response to a threshold stimulus?

What characterizes depolarization, the first phase of the action potential?

What characterizes repolarization, the second phase of the action potential?

What event triggers the generation of an action potential?

What is the first change to occur in response to a threshold stimulus?

What type of conduction takes place in unmyelinated axons?

An action potential is self-regenerating because __________.

Why does regeneration of the action potential occur in one direction, rather than in two directions?

What is the function of the myelin sheath?

What changes occur to voltage-gated Na+ and K+ channels at the peak of depolarization?

In which type of axon will velocity of action potential conduction be the fastest?

During the action potential of a neuron, which ion is primarily crossing the membrane during the depolarization phase, and in which direction is the ion moving?

What is happening to voltage-gated channels at this point in the action potential?

During what part of the action potential do voltage-gated Na+ channels begin to inactivate (their inactivation gates close)?

The repolarization phase of the action potential, where voltage becomes more negative after the +30mV peak, is caused primarily by __________.

During an action potential, hyperpolarization beyond (more negative to) the resting membrane potential is primarily due to __________.

During the hyperpolarization phase of the action potential, when the membrane potential is more negative than the resting membrane potential, what happens to voltage-gated ion channels?

Tetraethylammonium (TEA) blocks voltage-gated K+ channels such that K+ cannot pass even when the channels are open. However, TEA leaves K+ leakage channels largely unaffected. How would you expect the action potential to change if you treated a neuron with TEA?

The diffusion of what ion, across the neuronal membrane, is responsible for the local currents that depolarize regions of the axon to threshold?

An action potential in one segment of axon causes adjacent sections of axon membrane to reach threshold through what mechanism?

During action potential propagation in an unmyelinated axon, why doesn't the action potential suddenly "double back" and start propagating in the opposite direction?

In a myelinated axon, how do the nodes of Ranvier differ from other segments of the same axon?

Where are action potentials regenerated as they propagate along a myelinated axon?

How do action potential propagation speeds compare in myelinated and unmyelinated axons?

The node-to-node "jumping" regeneration of an action potential along a myelinated axon is called __________.

The myelin on myelinated neurons can be degraded or destroyed in diseases such as multiple sclerosis-a process called demyelination. If a myelinated neuron was affected by demyelination, how would this affect action potentials in that neuron?

The generation of an action potential in a neuron requires the presence what type of membrane channels?

Saltatory propagation occurs in _________ axons, in which action potentials _________.

What is the resting membrane potential of the neuron used in the experiment?

At which membrane potential, given the graphs shown, do a sufficient number of the voltage-gated Na+ channels start to open?

Which of the stimuli in this experiment would be considered a threshold stimulus?

Which of the following events would be directly affected if a neuron had a mutation that prevented the production of voltage-gated Na+ channels?

What change in a neuron is being measured in the graph?

At which point of the illustrated action potential would voltage-gated Na+ channels be mostly open but voltage-gated K+ channels be mostly closed?

Which of the following correctly states the direction followed by the specified ions when their voltage-gated channels open?

Which of the following mechanisms is most significant in returning the ion concentrations to the resting state (from point D to point E)?

At which of the points along the illustrated action potential can a second action potential be produced, but only with a stimulus significantly greater than the one that produced the first?

In a synapse, neurotransmitters are stored in vesicles located in the __________.

An action potential releases neurotransmitter from a neuron by opening which of the following channels?

Binding of a neurotransmitter to its receptors opens __________ channels on the __________ membrane.

Binding of the neurotransmitter to its receptor causes the membrane to __________.

The mechanism by which the neurotransmitter is returned to a presynaptic neuron's axon terminal is specific for each neurotransmitter. Which of the following neurotransmitters is broken down by an enzyme before being returned?

Which of the following best characterizes depolarization?

When an action potential arrives at the end of the axon terminal, a series of events take place that result in the release of neurotransmitter from the presynaptic axon. Select the answer that correctly describes the primary stimulus for vesicles to move toward the cell membrane and eventually release their contents.

Which statement best describes exocytosis?

What condition will increase the diffusion of molecules, such as neurotransmitters?

If the membrane of a postsynaptic dendrite is setting up a graded potential, what must have happened after neurotransmitter was released by the presynaptic terminal? The neurotransmitter __________.

Which of the following choices best represents synaptic transmission?

Predict the possible effect of a drug that totally blocks the neurotransmitter receptor on the postsynaptic membrane. For example, curare is a neurotoxin used by several South American cultures. The primary effect of curare is that acetylcholine, a major neuromuscular neurotransmitter, cannot bind at its receptor because curare is blocking it. Predict the possible effects of curare on the postsynaptic membrane and muscle.

What ion is entering the axon terminal at A, and what effect does it have?

By which method does the structure at B release neurotransmitter?

Which of the following statements most accurately describes the effect caused by binding of the neurotransmitter (green dots) to the structure labeled C?

The box labeled D illustrates three mechanisms by which the effects of a neurotransmitter may be terminated. Which of the following mechanisms is NOT included in the figure?

How would the receptors at C best be classified?

A postsynaptic cell can be a neuron, a muscle cell, or a secretory cell. What is an example of a presynaptic cell?

Which component has a role in the postsynaptic cell during synaptic activity?

What is the role of calcium in synaptic activity?

What is the direct role of neurotransmitter at a chemical synapse?

Neurotransmitter is released from presynaptic neurons through what mechanism?

What type of channel on the postsynaptic membrane binds neurotransmitter?

In addition to diffusion, what are two other mechanisms that terminate neurotransmitter activity?

Events that occur during synaptic activity are listed here, but they are arranged in an incorrect order. Choose the correct order of these events below. (a) Voltage-gated calcium channels open (b) Neurotransmitter binds to receptors (c) Action potential arrives at axon terminal (d) Neurotransmitter is removed from the synaptic cleft (e) Neurotransmitter released into synaptic cleft (f) Graded potential generated in postsynaptic cell

Which of the following statements is true of both membrane potential responses shown in the graphs?

Which of the following stimuli caused the reaction in the graph on the left?

Which of the following is expected to occur first if the membrane potential increase shown in the graph on the left were to reach the threshold value indicated at ?55 mV?

Suppose that both stimuli seen in these graphs happened equally at the same time on a postsynaptic membrane as a result of two different synapses. Which of the following best describes the result?

Choose the correct response to this statement: Presynaptic neurons synapse on the ________ of the postsynaptic neuron.

In the animation's analogy of "Fire!" and "Don't Fire!" of the neuron, what physiological response is implied?