Chapter 12 (CVP)
What are the similarities and differences among the channels in the voltage-gated channel superfamily?
All the voltage-gated channels have principal subunits with extensive sequence homology and thus are evolutionarily related. Voltage-gated Na+ and Ca2+ channels have four domains, whereas the voltage-gated K+ channel has one domain that is homologous to one of the domains on the Na+ channel.
Compare and contrast the techniques of patch clamping and voltage clamping.
Both patch clamping and voltage clamping provide experimental information about membrane currents, especially during an action potential. The patch-clamp technique uses a micropipette to record single channel currents, whereas the voltage-clamp technique shows whole cell ionic currents.
What are glial cells and how do they aid in the function of the nervous system?
Glial cells are the support cells of the nervous system. They function in forming myelination, which increases action potential velocity. They surround capillaries and act as metabolic intermediaries between neurons and their circulatory supply. They also serve immune and scavenging functions in order to protect surrounding neurons.
Describe the significance of myelination.
Myelination greatly increases conduction velocity of an axon by increasing the membrane resistance while decreasing the membrane capacitance. In other words, conduction velocity is increased by increasing the length constant without increasing the time constant. Action potentials occur only at the nodes of Ranvier, in a process that is called saltatory conduction.
Compare and contrast nervous systems and endocrine systems.
Neural and endocrine systems are both systems for communication within the body. Nervous systems are faster and capable of much finer temporal and spatial control, whereas endocrine systems typically control more widespread and prolonged activities
Explain in mechanistic terms how the action potential is an all-or-none phenomenon.
The action potential is initiated only when a threshold depolarization is reached near the axon hillock. That is, a certain critical number of voltage-gated Na+ channels have to open in order to cause a depolarization that is strong enough to initiate the Hodgkin cycle and, by definition, perpetuate the further opening of voltage-gated Na+ channels via their own depolarization. If the threshold is not reached, there will be no Hodgkin cycle or action potential.
Since the bulk solutions that make up the intracellular and extracellular fluids maintain charge neutrality, how does the cell produce membrane potentials?
The charge separation producing the membrane potential is an extraordinarily local phenomenon. According to textbook Figure 12.11, in a small 1 µm3 section around each side of the membrane, of the 110,000 cations and 110,000 anions in each fluid compartment, only six pairs of ions need to sit on the membrane and charge its capacitance to produce a membrane potential of -90 mV.
2. Describe the startle response in the cockroach.
The cockroach's startle response is a reflex. Sound waves or air vibrate the filiform hair receptors, which generate impulses in sensory neurons. The sensory neurons excite the giant interneurons that synapse with leg motor neurons. Once excited, the leg motor neurons activate the leg muscles.
Compare and contrast current and voltage with respect to the cell membrane.
The net movement of charge constitutes an electric current. The separation of positive and negative charges constitutes a voltage. In terms of the cell membrane, the current would be a flow of ions through channels in the membrane, whereas the voltage would be the separation of charges across the membrane.
Explain in mechanistic terms why the action potential can travel a great distance along an axon without degrading.
The same mechanism that is responsible for the rising phase of the action potential also aids in its perpetuation along the axon without degradation. The action potential on one location on the axon can itself initiate an action potential at a neighboring location, and the induced action potential will have the same all-or-none amplitude as the original.
Which of the following is the best explanation for the absolute refractory period of the action potential? a. Inactivated voltage-gated sodium channels b. Closed voltage-gated sodium channels c. Open slow calcium channels d. Inactivated voltage-gated potassium channels e. The passive properties of the axon membrane Answer: a
a. Inactivated voltage-gated sodium channels
In the figure, the _______ decreases with distance. a. graded potential b. action potential c. membrane potential d. membrane current e. membrane capacitance
a. graded potential
Which arrow best represents the point where the permeability to sodium is the highest? a. A b. B c. C d. D e. E
a. A
Which term best describes the movement of ions across a membrane? a. Current b. Voltage c. Resistance d. Capacitance e. Membrane potential
a. Current
Which of the following statements regarding the action potential is false? a. In an extremely long axon, the action potential eventually will degrade. b. During the "falling" phase, K+ permeability increases. c. During the "rising" phase, Na+ moves into the neuron. d. The action potential lasts about 3 ms. e. In the recovery phase, Na+ channels are closed.
a. In an extremely long axon, the action potential eventually will degrade.
Which of the following statements regarding the ions in intracellular and extracellular fluids is false? a. Na+ leaks into the cell rapidly because its electrochemical gradient is large. b. K+ leaks out of the cell slowly because the electrochemical gradient is small. c. Cl- may be at passive equilibrium in some cells. d. The Na+‒K+ pump actively transports Na+ out of the cell and K+ into the cell. e. All of the above are true, none is false.
a. Na+ leaks into the cell rapidly because its electrochemical gradient is large.
Which of the following statements about an animal's nervous system is false? a. Neurotransmitter is released throughout the body via the blood. b. Signal transmission rate is relatively fast. c. Neurons form highly discrete lines of communication. d. Action potential signals do not degrade over distance. e. A neuron must normally make synaptic contact with another cell in order to exert control.
a. Neurotransmitter is released throughout the body via the blood.
Which technique was used to collect the data in the bottom panel? a. Patch-clamp b. Voltage-clamp c. Current-clamp d. Potential recording e. Hodgkin clamp
a. Patch-clamp
_______ are responsible for extending the time of the cardiac action potential relative to a neural action potential. a. Slow Ca2+ channels b. Slow Na+ channels c. Slow frequency of action potentials to the pacemaker d. Slow K+ channels e. Voltage-gated Na+ channels
a. Slow Ca2+ channels
The figure shows that the membrane potential results a. from relatively few charges sitting on the membrane. b. from many individual charges sitting on the membrane. c. in significant changes in intra- and extra cellular ion concentrations. d. in a complete change of ions from one side of the membrane to the other. e. from ion changes on only a specific portion of the membrane
a. from relatively few charges sitting on the membrane.
_______ prevents bidirectional propagation of action potentials. a. The inactivation of Na+ channels b. The increased permeability to K+ c. A decrease in membrane resistance d. Myelination e. The K+ channel
a. The inactivation of Na+ channels
Which of the following statements about glial cells is false? a. They integrate cell membrane potentials to enhance or inhibit action potentials. b. They increase the velocity of nerve-impulse propagation. c. They act as metabolic intermediaries between capillaries and neurons. d. They help supply metabolic substrates to neurons. e. They mediate immune responses in neurons.
a. They integrate cell membrane potentials to enhance or inhibit action potentials.
A decrease in the absolute value of the membrane potential toward zero is called a. depolarization. b. an action potential. c. hyperpolarization. d. a membrane potential. e. voltage.
a. depolarization.
Myelination by Schwann cells increases the velocity of action potential propagation by a. increasing the resistance and decreasing the capacitance, allowing the action potential to "jump" over the myelinated area. b. decreasing the resistance and increasing the capacitance, allowing the action potential to "jump" over the myelinated area. c. increasing the diameter of the neuron. d. increasing the number of voltage-gated sodium channels. e. increasing the resistance and increasing the capacitance, allowing the action potential to "jump" over the myelinated area. Answer: a
a. increasing the resistance and decreasing the capacitance, allowing the action potential to "jump" over the myelinated area.
Which of the following is not a factor in the Nernst Equation? a. The gas constant, R b. Capacitance c. Temperature d. The valence of the ion species e. The ion concentrations on the two sides of the membrane
b. Capacitance
Which of the following statements about membrane capacitance is false? a. It is in series with membrane resistance. b. In a cell, the membrane separates only similarly charged ions. c. It is measured in farads. d. It is a function of the insulating properties of the membrane. e. All of the above are true, none is false.
b. In a cell, the membrane separates only similarly charged ions.
The plasma membrane of a resting neuron is most permeable to which of the following ions? a. Na+ b. K+ c. Cl- d. Ca2+ e. Mg2+ Answer: b
b. K+
Which of the following glial cells are found in the peripheral nervous system? a. Oligodendrocytes b. Schwann cells c. Astrocytes d. Both a and b e. Both a and c Answer: b
b. Schwann cells
If a current pulse is generated on the membrane and creates a passive potential, which of the following will be true? a. The change in the membrane potential will increase as the distance from the current pulse increases. b. The change in the membrane potential will decrease as the distance from the current pulse increases. c. The change in the membrane potential will remain constant throughout the length of the membrane. d. The change in the membrane potential will fluctuate depending on the strength of the initial current pulse. e. There will be no change in membrane potential. Answer: b
b. The change in the membrane potential will decrease as the distance from the current pulse increases.
How would the trace on the right look if the neuron was soaking in TEA? a. The inward ionic current would disappear. b. The outward ionic current would disappear. c. The trace would look exactly like the trace in the left panel. d. The inward ionic current would be amplified. e. The outward ionic current would be amplified.
b. The outward ionic current would disappear.
How do nonspiking neurons function even though their depolarization signal significantly degrades with distance? a. Voltage-gated Na+ channels are replaced by ligand-gated Na+ channels. b. These neurons are very short, so there is no major signal decrement. c. There are sufficient numbers of voltage-gated Na+ channels to convey the signal without major decrement. d. These neurons do not release neurotransmitters, so signal degradation is not a problem. e. Voltage-gated K+ channels compensate for the lack of voltage-gated Na+ channels. Answer: b
b. These neurons are very short, so there is no major signal decrement.
What allows the action potential to return to a repolarized state? a. K+ leaks into cells. b. Voltage-gated Na+ channels become inactivated. c. Voltage-gated K+ channels become inactivated. d. Na+ reaches equilibrium across the neural membrane and stops leaking in. e. Voltage-gated Na+ channels close. Answer: b
b. Voltage-gated Na+ channels become inactivated.
What occurs when the membrane is clamped at -100 mV? a. Voltage-gated ion channels behave in a similar manner as in the diagram. b. Voltage-gated ion channels do not open at all. c. There is a brief shift in ions and then a flat current at -100 mV. d. Only ligand-gated channels work at this point. e. There is a steady clamped voltage at 0 mV.
b. Voltage-gated ion channels do not open at all.
_______ channels are responsible for the undershoot at point D of the figure. a. Voltage-gated sodium b. Voltage-gated potassium c. Ligand-gated potassium d. Voltage-gated calcium e. Sodium
b. Voltage-gated potassium
Label A of the figure represents _______ currents through voltage-gated _______ channels. a. outward; Na+ b. inward; Na+ c. outward; K+ d. inward; K+ e. inward; Ca2+
b. inward; Na+
According to the Goldman equation, the contribution of each ion to the membrane potential depends the most on a. its size. b. its membrane permeability. c. its activation energy. d. temperature. e. the resting membrane potential.
b. its membrane permeability.
The neuron converts an electrical signal to a chemical signal in the a. dendrite. b. presynaptic terminal. c. axon. d. cell body. e. axon hillock.
b. presynaptic terminal.
If stimulating current pulse 9 (not shown) was both stronger and longer than stimulating current pulse 8, then a. action potentials would cease. b. the train of action potentials would continue for the length of the stimulating current. c. action potentials would increase in amplitude. d. action potentials would first increase in frequency and then decrease. e. the line at stimulus 9 would look exactly same as the line at stimulus 8.
b. the train of action potentials would continue for the length of the stimulating current.
How many separate current pulses cause the membrane potential to reach the threshold? a. 1 b. 2 c. 3 d. 5 e. 8
c. 3
What would likely occur if stimulus 3 and 6 were performed simultaneously? a. Membrane potential would be around -100 mV. b. An action potential would likely occur. c. An action potential would likely not occur. d. Multiple action potentials would likely occur. e. The threshold voltage would likely decrease.
c. An action potential would likely not occur.
Which of the following statements about a voltage clamp of a neuron to 0 mV is false? a. Once clamped, the voltage remains at 0 mV. b. Voltage-gated potassium channels open. c. Apart from the initial current shift from the clamp, no other current is produced. d. Voltage-gated sodium channels open e. An inward ionic current is produced during the opening of voltage-gated sodium channels.
c. Apart from the initial current shift from the clamp, no other current is produced.
. In a typical neuron, which of the following ions is in passive equilibrium across the cell membrane? a. Na+ b. K+ c. Cl- d. Both Na+ and K+ e. Both Na+ and Cl-
c. Cl-
Which of the following is not one of the likely factors affecting the various velocities at which axons conduct action potentials? a. Myelination b. Temperature c. Length d. Diameter e. The number of voltage-gated Na+ channel per unit surface area
c. Length
Which of the following statements about the startle response of the cockroach is false? a. Vibrations of hairs generate nerve impulses in sensory neurons. b. Sound waves or air currents vibrate the filiform hairs. c. Sensory neurons synapse with and excite the dorsal hollow spinal cord. d. At the metathoracic ganglion, the interneurons synaptically excite leg motor neurons. e. The motor neurons activate leg muscles.
c. Sensory neurons synapse with and excite the dorsal hollow spinal cord.
Which of the following would not occur if ouabain was used to block Na+-K+-ATPase pumps? a. Na+ would go to equilibrium across the cell membrane. b. The membrane potential would become less negative. c. The concentration of K+ would be equal on both sides of the membrane. d. The cell would no longer be in a steady state. e. Cl- would go to equilibrium across the cell membrane.
c. The concentration of K+ would be equal on both sides of the membrane.
Which of the following statements regarding cardiac pacemaker cells is false? a. They spontaneously generate action potentials. b. The frequency of action potential generation can be modified by neural input. c. The pacemaker cells are modified neural tissue. d. They are connected to myocardium via gap junctions. e. They have a current that is inward and activated by hyperpolarization. Answer: c
c. The pacemaker cells are modified neural tissue.
_______ channels govern the generation of an action potential. a. Ligand-gated Na+ b. Ligand-gated K+ c. Voltage-gated Na+ d. Voltage-gated K+ e. K+ Answer: c
c. Voltage-gated Na+
Which of the following is most responsible for the all-or-none property of the action potential? a. Myelination b. Voltage-gated K+ channels c. Voltage-gated Na+ channels d. Leakage of K+ channels e. Acetylcholine
c. Voltage-gated Na+ channels
The separation of positive and negative charges constitutes a. resistance. b. an electric current. c. a voltage. d. capacitance. e. a depolarization.
c. a voltage.
The figure depicts a a. neuronal action potential. b. muscle contraction. c. cardiac action potential. d. pacemaker potential. e. graded potential
c. cardiac action potential.
During the falling phase of an action potential, the K+ leak channel on the axon is _______, the voltage-gated Na+ channel is _______, and the voltage-gated K+ channel is _______. a. open; inactivated; closed b. closed; inactivated; closed c. open; inactivated; open d. closed; closed; closed e. open; closed; closed
c. open; inactivated; open
. In the figure, _______in the center of the cell. a. there would be a slight negative charge b. there would be a strong negative charge c. the overall charge neutrality would be maintained independently of the membrane potential d. there would be a slight positive charge e. there would be a strong positive charge
c. the overall charge neutrality would be maintained independently of the membrane potential
According to the Nernst equation, which of the following will depolarize Vm, the membrane potential? a. A decrease in temperature b. An increase in the valence of the ion species involved c. A decrease in the electromotive force of the ion d. A decrease in the concentration of anions inside the membrane e. An increase in Faraday's constant
d. A decrease in the concentration of anions inside the membrane
In a cell, the difference in ion concentration between the intracellular and extracellular fluids results from a. active ion transport. b. passive diffusion of ions. c. bulk movements of intracellular and extracellular fluids. d. Both a and b e. All of the above
d. Both a and b
What is occurring to the membrane? a. Depolarization b. Hyperpolarization c. Redistribution of charges during a current pulse d. Both a and c e. All of the above
d. Both a and c
What is the best explanation for the plateau shown in the figure? a. Voltage-gated Na+ channels remain open. b. Voltage-gated Ca2+ channels remain open. c. Voltage-gated K+ channels delay opening. d. Both b and c e. All of the above Answer: d
d. Both b and c
Which arrow best represents the point where the voltage-gated sodium channels are inactivated? a. A b. C c. D d. C and D e. C, D, and E
d. C and D
Why do the channels at B of the figure stay open longer than those at label A? a. Channels at A are responding to a depolarization, whereas channels at B are responding to a hyperpolarization. b. The depolarization is a faster event compared to the repolarization. c. Channels at A are less sensitive to voltage compared to channels at B. d. Channels at A become inactivated, whereas channels at B close due to membrane voltage. e. All of the above
d. Channels at A become inactivated, whereas channels at B close due to membrane voltage.
Considering the cycle of an action potential, when is the permeability to K+ at its greatest? a. During the resting membrane potential b. During the rising phase of the action potential c. At the peak of the action potential d. During the falling phase of the action potential e. The permeability of K+ remains the same throughout the action potential cycle. Answer: d
d. During the falling phase of the action potential
Conduction velocity shows a(n) _______ axon diameter. a. proportional relationship to b. proportional relationship to the square root of c. exponential relationship to d. Either a or b, depending on the type of axon e. Either a or c, depending on the type of axon
d. Either a or b, depending on the type of axon
Which of the following statements regarding the structure of the voltage-gated Na+ channels is false? a. P loops mediate ion selectivity. b. Segment 4 of each domain is the voltage sensor. c. It has 4 domains with extensive sequence homology. d. The channel protein changes its primary structure in response to membrane depolarization. e. A cytoplasmic loop is thought to inactivate the channel by blocking the opening. Answer: d
d. The channel protein changes its primary structure in response to membrane depolarization.
Which of the following is the best explanation for the difference between the middle panel and the lower panel? a. The membrane in the lower panel is producing a lower current. b. There is a lower resistance in the lower panel at the point where voltage is measured. c. There is a greater capacitance in the lower panel at the point where voltage is measured. d. The membrane voltage measured in the lower panel is farther away from the current pulse. e. In the lower panel the action potential dissipates by the time it reaches the location of the electrode.
d. The membrane voltage measured in the lower panel is farther away from the current pulse.
Neurons that relay sensory signals to integrative centers of the CNS are called a. interneurons. b. synaptic neurons. c. efferent neurons. d. afferent neurons. e. motor neurons.
d. afferent neurons.
The treatment difference between the membranes shown in the graphs is that the membrane on the left is _______, while the membrane on the right is being _______. a. a control depolarization; depolarized while soaking in Na+-free seawater b. a control depolarization; depolarized while soaking in TEA c. a control depolarization; depolarized while soaking in a solution with the same concentration of Na+ as the concentration inside the cell d. being hyperpolarized; depolarized e. being depolarized; hyperpolarized
d. being hyperpolarized; depolarized
A stimulating depolarizing current that depolarizes the axon hillock just slightly negative to the threshold will a. not change the overall membrane potential at all. b. produce an action potential. c. produce a very small action potential. d. produce a temporary graded potential. e. produce a small action potential that increases in amplitude as it travels along the axon. Answer: d
d. produce a temporary graded potential.
The time constant (τ) depends on the a. resistance of the membrane. b. capacitance of the membrane. c. resistance and voltage of the membrane. d. resistance and capacitance of the membrane. e. resistance, capacitance, and voltage of the membrane. Answer: d
d. resistance and capacitance of the membrane.
The properties shown in the figure can be measured in which of the following? a. Neurons b. Pacemaker cells c. Muscle cells d. Both a and b e. All of the above
e. All of the above
Which of the following statements about a local circuit in an axon is false? a. Na+ ions move into the cell through open Na+ channels. b. Ions flow in intracellular fluid, carrying current to more distant parts of the membrane. c. At the membrane, the ion movements change the distribution of charges on the membrane capacitance. d. An ionic current completes the local circuit as cations move toward the locus of the action potential and anions move away. e. Anions migrate into the membrane interior.
e. Anions migrate into the membrane interior.
Which of the following statements about ion permeability as shown in the figure is true? a. Ca2+ permeability is at its highest at time point 0. b. K+ permeability is at its lowest very close to the membrane potential peak. c. K+ permeability is at its highest very close to the membrane potential peak. d. Na+ permeability is at its lowest very close to the membrane potential peak. e. Na+ permeability is at its highest very close to the membrane potential peak. Answer: e
e. Na+ permeability is at its highest very close to the membrane potential peak.
Which of the following is not a type of glial cell?
e. Neurocytes
Which of the following is a shared characteristic between a spiking neuron and a nonspiking neuron? a. High concentration of voltage-gated Na+ channels at the axon hillock b. The Hodgkin cycle c. A graded potential down the entire length of the axon d. An action potential down the entire length of the axon e. Neurotransmitter secretion based on a change in membrane potential
e. Neurotransmitter secretion based on a change in membrane potential
Which of the following is not likely to affect the conduction velocity of an action potential? a. Axon diameter b. Myelination c. Membrane surface area to volume ratio d. Temperature e. None of the above; all affect the velocity of an action potential. Answer: e
e. None of the above; all affect the velocity of an action potential.
Which of the following does not contribute to the cell's membrane potential? a. Permeability to K+ b. Permeability to Na+ c. The overall resistance of the membrane d. Electrogenic ion pumps e. None of the above; all contribute to membrane potentials. Answer: e
e. None of the above; all contribute to membrane potentials.
Which of the following does not contribute to the passive electrical properties of a cell? a. Membrane resistance b. Membrane capacitance c. The time constant d. Length constants e. The resting membrane current
e. The resting membrane current
Which technique was used to collect the data shown in the figure? a. Patch-clamp b. Hodgkin clamp c. Current-clamp d. Potential recording e. Voltage-clamp Answer: e
e. Voltage-clamp
Initiation of the action potential usually occurs _______of the neuron. a. in the cell body b. on the dendrites c. at the synapse d. on the axon e. at the axon initial segment
e. at the axon initial segment
In myelinated axons, action potentials occur a. all along the axon. b. only at the internodes. c. only at the initial segment of the axon. d. at the internodes and nodes of Ranvier. e. only at the nodes of Ranvier.
e. only at the nodes of Ranvier.
For an axon at resting membrane potential, the K+ leak channel is _______, the voltage-gated Na+ channel is _______, and the voltage-gated K+ channel is _______. a. open; inactivated; closed b. closed; inactivated; closed c. open; inactivated; open d. closed; closed; closed e. open; closed; closed
e. open; closed; closed
For a hormone to elicit a specific response from a cell, the cell must possess a. a synapse. b. integration. c. a cell body. d. dendrites specific to the hormone. e. receptor proteins specific to the hormone.
e. receptor proteins specific to the hormone.
. In the lower panel, the difference between the dashed line and the observed red line is due to a. membrane resistance. b. the fact that one represents a depolarization and the other represents a hyperpolarization. c. the difference in applied current pulses. d. the difference in applied voltage. e. the capacitive properties of the membrane.
e. the capacitive properties of the membrane.