NEUR 306 CH2 Practice Questions
Ion channels that are involved in generation of action potentials open or close in response to A) voltage. B) neurotransmitters. C) second messengers. D) mechanical stimulation. E) temperature.
A
The squid giant axon is useful in neuronal studies because a. its axon is easy to penetrate with recording electrodes because it is so long. b. the cytoplasm in the axon can be extruded, thus allowing studies of its composition. c. multiple synapses between the nerve cells make them easy to study. d. its giant ion channels allow insertion of recording electrodes into the channels. e. the axon has fewer ion channels, which simplifies the analysis of observations.
Answer: b.
Which property of the action potential do the graphs in the figure illustrate? A) Refractoriness B) All-or-none C) High frequency D) Polarized propagation E) None of the above
B
The _______ most directly affects the rate of information processing within the central nervous system. A) number of sodium channels along an axon B) number of potassium channels along an axon C) propagation speed of action potentials D) threshold voltage of neurons E) ratio of sodium to potassium channels
C
Which current corresponds to a flow of Na+ in response to a depolarizing stimulus in a giant axon of a squid? A) Inward capacitive current B) Outward capacitive current C) Transient inward current D) Delayed outward current E) Prolonged outward current
C
Which property is characteristic of Na+ channels but not K+ channels? A) Ion permeability B) Ion selectivity C) Voltage sensitivity D) Ability to inactivate E) Ability to bind neurotoxins
D
An action potential travels in only one direction along the axon because of its _______ property. A) refractory B) all-or-none C) passive D) active E) transient
A
Which current is produced in response to a hyperpolarizing stimulus in a giant axon of a squid? A) Inward capacitive current B) Outward capacitive current C) Transient inward current D) Delayed outward current E) Prolonged outward current
A
Work done by _______ and _______ elucidated changes in membrane permeability that underlie an action potential. A) Alan Hodgkin B) Bernard Katz C) Walther Nernst D) Kenneth Cole E) David Goldman F) Andrew Huxley
A and F
Suppose you are recording a neuron's resting membrane potential. If you add KCl to the external medium, what will happen to the resting potential? Compare this to what will happen if you add the same amount of NaCl. What can be concluded from this comparison?
Adding KCl will cause the resting potential to become less negative. Adding NaCl to the external medium will have a small effect because membrane permeability to Na+ is low. We can conclude that the resting membrane potential is primarily due to/attributable to the product of K+ permeability
. A student new to neuroscience research is practicing recording resting membrane potentials from giant squid axons. During one of the trials, the resting membrane potential, which is normally around -60 mV, measured -15 mV. Which statement best describes what might have occurred during the experiment? a. The student added too much potassium to the extracellular solution. b. The student added too much sodium to the extracellular solution. c. The student did not add enough potassium to the extracellular solution. d. The student did not add enough sodium to the extracellular solution. e. The student added too little potassium and too much sodium to the extracellular solution.
Answer: a
A dull probe stimulates a Pacinian corpuscle. An electrode is placed midway down the axon, and action potentials are recorded. After one second, the probe is pushed with greater force. What change will occur in the recording? a. The height of action potentials will increase. b. The frequency of action potentials will increase. c. The frequency of action potentials will decrease. d. The resting membrane potential will increase. e. The threshold potential level will increase.
Answer: b
6. Which of the following is not necessary for neurons to communicate electrically? a. Consumption of metabolic energy b. Use of active transporters to create ionic gradients c. Separation of large amounts of electrical charge, with excess positive charges stored inside the cell d. Selective permeability of the cell membrane via different kinds of ion channels e. Changes in membrane potential caused by the movement of ions across the cell membrane
Answer: c
Which stimulus is most likely to evoke an action potential? a. Small hyperpolarizing current pulse b. Large hyperpolarizing current pulse c. Small depolarizing current pulse d. Large depolarizing current pulse e. Microelectrode insertion
D
Which technique would you use to study the effects of the extracellular environment on ion channel activity? A) Conventional voltage clamp B) Whole-cell patch clamp C) Inside-out patch clamp D) Outside-out patch clamp E) Cell-attached patch clamp
D
In the following figure, which of the following is the key event at a membrane potential of 0 mV? A) The late outward current increases in magnitude B) The late outward current decreases in magnitude C) The early current reverses its polarity D) The early and late currents flow inward E) The early current is at its maximum
E
Voltage clamp data, in which investigators analyzed membrane conductances during action potentials, showed all of the following except A) the sodium current was rapidly activated by depolarization. B) the potassium current activates on a comparatively slow time scale of a few ms. C) at certain potentials, there can be zero current even with a large conductance. D) depolarization leads to a time-dependent inactivation of the sodium current. E) depolarization leads to a time-dependent inactivation of the potassium current.
E
Which observation is not evidence that helped to identify sodium as the early current of the action potential? A) The current declined when there was decreased driving force on sodium fluxes. B) The current disappeared near the Nernst potential for sodium. C) The early current was blocked by tetrodotoxin D) The early current was unaffected by tetraethylammonium E) When the late current was blocked, the reversal potential of the inward current shifted to a negative membrane potential.
E
Which statement regarding refractory periods is true? A) They allow neurons to fire an unlimited number of action potentials per unit of time. B) During the refractory period the cell requires a less intense stimulus to reach threshold. C) The refractory period arises in part due to the increase in sodium conductance across the membrane. D) The refractory period arises in part due to the decrease in potassium conductance across the membrane. E) The refractory period ends when the sodium channels are no longer inactivated.
E
What is electrochemical equilibrium?
Electrochemical equilibrium is the state of balance between the concentration and electrical gradients at which there is no net flow of charge or ions.
There is an excess of _______ in the extracellular compartment, relative to the intracellular compartment. a. Na+ only b. K+ only c. Na+ and Ca2+ only d. Na+ and Cl- only e. Na+, Cl-, and Ca2+
e. Na+, Cl-, and Ca2+
Which intervention will disrupt the function of the Na+/K+ ATPase pump? A) Removal of extracellular K+ B) Removal of extracellular Na+ C) Removal of extracellular ATP D) Removal of cytoplasmic Ca2+ E) Application of tetrodotoxin
A
Which treatment was shown to eliminate the early inward current in squid giant axons? A) Removal of external sodium B) Doubling of external sodium C) Removal of external potassium D) Doubling of external potassium E) Removal of all external cations
A
Hodgkin and Katz proposed that sodium was the predominant ion associated with the firing of an action potential because a. the membrane potential approaches the Na+ Nernst potential during the rising phase. b. the membrane potential approaches the Na+ Nernst potential during the falling phase. c. sodium ions can move more quickly than other ionic species. d. sodium ions are the only ions that can flow into the nerve cell body. e. the sodium gradient explains the rising phase, falling phase, and overshoot of the action potential.
Answer: a
Which statement about ionic distributions in nerve cells is true? a. Potassium is higher outside cells than inside cells. b. Sodium is higher outside cells than inside cells. c. Chloride is higher inside cells than outside cells. d. Calcium is higher inside cells than outside cells. e. The concentrations of all ionic species are the same for all nerve cells in all animals.
Answer: b
Which channel(s) is(are) implicated in inherited forms of epilepsy? A) Ca2+ and Na+ only B) K+, Ca2+, and Na+ C) K+ and Ca2+ only D) K+ only E) Ca2+ only
B
Which ion is transported down its concentration gradient by transporters? A) H+ B) Na+ C) K+ D) Cl- E) Ca2+
B) Na+
In the following figure, which of the following is the key event at a membrane potential of 52 mV? A) The late outward current increases in magnitude B) The late outward current decreases in magnitude C) The early current reverses its polarity D) The early and late currents flow inward E) The early current is at its maximum
C
Which transporter plays a key role in maintaining the concentration gradients of ions in the brain that are critical for generating electrical signals? A) SERCA B) PMCA C) Na+/K+ ATPase pump D) Na+/Ca2+ exchanger E) Na+/K+/Cl- co-transporter
C
Which statement about voltage-gated ion channels is true? A) Without sodium channels, no current flows out B) Without potassium channels, no current flows in C) Na+ channels open after a short delay D) K+ channels close after a short delay E) Na+ and K+ channels can work independently of one another
E
How would you explain the statement, "Ion channels and ion pumps have complementary functions"?
: Ion pumps move ions against ion concentration gradients while ion channels allow the flow of ions in the direction of the concentration gradient.
How is stimulus strength encoded by graded potentials? How is stimulus strength encoded by action potentials?
Stimulus strength is encoded by graded potentials by amplitude, and encoded by action potentials in frequency.
During which phase of an action potential does membrane permeability to Na+ exceed membrane permeability to K+? a. Rising phase only b. Rising and overshoot phases c. Overshoot phase only d. Overshoot and falling phases e. All of the phases of the action potential
b. Rising and overshoot phases
In a two-compartment model of a cell with a K+- and Na+-permeable membrane and a 10-fold excess of K+ in the inside compartment, how would the membrane potential change if all K+ ions were replaced by Na+ ions? a. It would double. b. It would be reduced by half. c. It would not change. d. It would become positive. e. No potential would be generated.
c
In a two-compartment model of a cell with a K+-permeable membrane, at K+ equilibrium potential, there is _______ flux of K+ ions. a. a large inward b. a large outward c. no net d. a small inward e. a small outward
c
An action potential occurs if the current is injected into a neuron _______ the neuron to reach _______ potential. a. depolarizes; synaptic b. hyperpolarizes; synaptic c. depolarizes; threshold d. hyperpolarizes; threshold e. hyperpolarizes; resting
c. depolarizes; threshold
Subthreshold current injected into an axon flows _______ along the axon and _______ with distance from the site of injection. a. actively; remains constant b. actively; decays c. actively; grows d. passively; remains constant e. passively; decays
e. passively; decays
A neuron has received enough stimulation to fire an action potential; it also has been treated with TEA, a K+ channel blocker. Which outcome is possible? A) The cell will initially depolarize, but repolarization will take much longer because it relies only on ion pumps. B) The cell will initially depolarize and will continue to do so until the cell reaches the equilibrium potential for Na+. C) The cell will initially hyperpolarize and will return to resting membrane potential after a delay. D) There will be no change in membrane potential in the cell. E) There will be no change in membrane potential in the cell initially, but will it depolarize after a delay.
A
A patient presents with migraines that usually last about 48 hours and are accompanied by vomiting. Two of his immediate relatives show similar symptoms. Which ion channel would you expect to be dysfunctional in this patient? A) Voltage-gated calcium channel B) Voltage-gated sodium channel C) Ligand-gated chloride channel D) Voltage-gated potassium channel E) Ligand-gated sodium channel
A
A researcher conducts a voltage clamp experiment on a giant squid axon. She clamps a typical neuron at 0mV. Which graph in the figure below represents the current changes she will observe? A B C D E
A
In the following figure, which of the following is the key event at a membrane potential of -26 mV? A) The late outward current increases in magnitude B) The late outward current decreases in magnitude C) The early current reverses its polarity D) The early and late currents flow inward E) The early current is at its maximum
A
In the phase labeled B, the voltage-gated sodium channels are ________ and the voltage-gated potassium channels are ________. A) open; closed B) closed; open C) open; open D) inactivated; open E) closed; inactivated
A
In what way are ion channels similar to active transporters? A) Both are proteins. B) Both actively move ions from one side of the membrane to the other. C) Both create ion concentration gradients. D) Both maintain ion concentration gradients. E) Both enable selective ion permeability.
A
Membrane potential depolarizes, Na+ channels open, Na+ current increases, _______. A) K+ channels open B) Na+ channels close C) Na+ current decrease D) Na+ current decrease E) membrane potential hyperpolarizes
A
Under which circumstances is the Goldman equation equivalent to the Nernst equation? a. When a membrane is permeable to only one ion b. When a membrane is permeable to multiple ions c. When the membrane is permeable to positively charged ions only d. When the membrane is permeable to negatively charged ions only e. When permeability of the membrane is different for different ions
A
What is the net charge transported by one cycle of the Na+/ K+ ATPase pump? A) One positive charge leaves the cell B) Two positive charges leave the cell C) Three positive charges leave the cell D) One positive charge enters the cell E) There is no net change in charge
A
What would occur if the ATPase pumps in a neuron stopped functioning? A) Concentration gradients would not be maintained across the membrane B) At rest, sodium would continuously depolarize the cell C) At rest, potassium would continuously depolarize the cell D) During the action potential, the sodium channel would not inactivate E) During the action potential, the voltage-gated ion channels would remain closed
A
Which statement describes one of the features of Hodgkin and Huxley's mathematical model? A) The action potential can be reconstructed based entirely on the time course and amplitudes of the ionic conductances. B) The fast-rising phase can be accounted for by selective potassium entry. C) The model is unable to mimic the experimentally measured refractory period. D) The falling phase can be at least partially accounted for by the inactivation of the potassium current. E) The undershoot can be accounted for by the time course of sodium current reactivation.
A
What is the magnitude of a typical neuron's resting membrane potential? Why do neurons and other cells have a negative resting membrane potential?
A typical neuron's resting membrane potential is approximately -65 mV. It is negative because resting membrane is permeable mainly to K+, and there is a concentration gradient for K+ across the plasma membrane with roughly a 13-fold excess of K+ inside the cell.
Which process(es) underlie(s) the refractory period? A) The slow time course of turning off K+ conductance activation B) The persistence of Na+ conductance inactivation C) The slow time course of turning off K+ conductance D) activation and the persistence of Na+ conductance inactivation E) The delay in K+ conductance activation F) Rapid activation of Na+ conductance
A) and B)
Which conclusion can be drawn from Hodgkin and Huxley's studies of K+ and Na+ conductances? A) Both conductances exhibit the property of time-dependent activation. B) Both conductances depend on voltage. C) K+ conductance reaches its maximum with a pronounced delay. D) Unlike K+ conductance, Na+ conductance reaches its maximum and inactivates rapidly. E) Both K+ conductance and Na+ conductance reach their maximums and then inactivate rapidly.
A, B, C, D
Based on the observations made by Hodgkin and Huxley, one can expect ion channels to A) allow ions to move across the membrane quickly. B) work with the electrochemical gradients to pass ions. C) exist in distinct variants, allowing different types of ions to pass. D) respond to changes in the membrane potential. E) exist in distinct variants, and are non-specific with respect to ions.
A, B, C, and D
A friend has taken a job in a neuroscience research lab, and is studying neurons in a freshwater snail. He has been told to calculate the equilibrium potential of K+. Which equation will he use and what other information will he need? a. Nernst equation; concentration of K+ inside and outside of the cell b. Nernst equation; concentration of K+ inside and outside of the cell and permeability of K+ c. Goldman equation; concentration of K+ inside and outside of the cell d. Goldman equation; concentration of K+ inside and outside of the cell and permeability of K+ e. Nernst equation; concentration of K+, Na+, and Cl- inside and outside of the cell
Answer: a
Studies of the ionic basis of the action potential in squid giant axon found that a. decreasing sodium outside the cell decreases the size of the action potential. b. decreasing sodium outside the cell increases the size of the action potential. c. decreasing potassium outside the cell decreases the size of the action potential. d. decreasing potassium outside the cell increases the size of the action potential. e. manipulating sodium has large effects on both the size of the action potential and the resting membrane potential.
Answer: a
Which statement about electrochemical equilibrium is true? a. It involves the movement of a relatively large number of ions, altering the concentrations of permeant ions. b. It occurs when the potential across the membrane exactly offsets the concentration gradient. c. The size of the potential is inversely proportional to the size of the ion gradient. d. The fluxes of ion that are required to generate the membrane potential disrupt chemical electroneutrality. e. For a given ion concentration gradient, the resulting potential is independent of the number of charges on the ion.
Answer: b
Which statement regarding membrane potential and equilibrium potential is true? a. Membrane potential is affected by ion concentration in- and outside of the cell; equilibrium potential is affected only by ions inside the cell. b. Equilibrium potential is affected by the concentration and electrical gradients of one ion; membrane potential is affected by gradients of all ions. c. Both membrane and equilibrium potentials change during an action potential. d. Equilibrium potentials are affected by membrane permeability; membrane potentials are not. e. Equilibrium potentials are the same for all neurons; membrane potentials can be different depending on the neuron.
Answer: b
9. Which statement about active ion transporters is true? a. They are selectively permeable to certain ions. b. They are functionally similar to ion channels. c. They allow ion movement down the concentration gradient. d. They move all ions against the concentration gradient. e. They move certain ions against the concentration gradient.
Answer: e
The current flowing through individual ion channels was visualized with the advent of the voltage clamp in 1956. A) exhibits the same time course across all individual sodium channels. B) reflects the passage of thousands of ions per millisecond. C) has a different voltage dependence than the macroscopic ionic current has. D) has a different reversal potential than the macroscopic ionic current has.
B
The figure below depicts a normal action potential (left) and an action potential altered by application of a toxin (right). Mechanistically, how does this toxin affect the action potential? A) Blocks the pore of Na+ channels B) Slows the inactivation of Na+ channels C) Shifts the voltage dependence of the Na+ channel activation D) Blocks the pore of K+ channels E) Slows the inactivation of K+ channels F) Shifts the voltage dependence of the K+ channel activation
B
Which evidence supports the assertion that the macroscopic Na+ current is the sum of many microscopic Na+currents? A) The probability of a Na+ channel opening increases as the membrane is hyperpolarized. B) The averaged collective response of single channels resembles the time course of the macroscopic current. C) Opening and closing of Na+ channels is concentration-dependent. D) Tetrodotoxin blocks macroscopic, but not microscopic, currents. E) Tetraethylammonium chloride (TEA or TEAC) blocks macroscopic, but not microscopic, currents.
B
Which statement about Na+ permeability during an action potential is most accurate? A) It is long-lasting. B) It is responsible for the rising phase of the action potential. C) It is responsible for the falling phase of the action potential. D) It restores the membrane potential to its usual level following the action potential.
B
Which statement about myelination is false? A) Myelin sheaths are created by glial cells. B) Myelin serves to sharply increase the time constant of the axon. C) Multiple layers of closely opposed glial membranes wrap the axon and serve as an electrical insulator. D) Myelin is absent at the nodes of Ranvier. E) Sodium and potassium channels are clustered at the nodes of Ranvier.
B
Which statement correctly differentiates between the passive and active current in a myelinated axon? A) The passive current flows only in the nodes of Ranvier, unlike the active current. B) The active current flows only in the nodes of Ranvier, unlike the passive current. C) The passive current flows in one direction along the axon, unlike the active current. D) The action potential propagation depends on the passive current only. E) The action potential propagation depends on the active current only.
B
Which statement is a common, defining feature of membrane-bound active ion transporters? A) All transport two or more different ions. B) All are able to move at least one ion against its concentration gradient. C) All catalyze the conversion of ATP to ADP. D) All are electrogenic. E) All move sodium across the membrane.
B
Which substance binds only at the extracellular domain of a ligand-gated ion channel? A) H+ B) Neurotransmitter C) Ca2+ D) cAMP E) cGMP
B
Which statement does not stem from the application of Ohm's law to ionic conductances? A) The driving force on the ionic current is the difference between the membrane potential and the ion's Nernst potential. B) The conductance for an ion is inversely proportional to the resistance of the membrane to the passage of that ion. C) All permeant ions experience an identical driving force at each time point during the course of an action potential. D) The conductance for each ion can be calculated based on the measured ionic currents and the calculated driving force. E) The calculations stemming from Ohm's law can be used to derive a mathematical description of the action potential.
C
Which symptom(s) is characteristic of patients with multiple sclerosis? A) Bilateral blindness due to lesions of the optic nerve B) Unilateral motor weakness due to lesions of the corticospinal tracts C) Abnormal somatic sensations due to lesions of somatosensory pathways D) Seizures from kindling of action potentials in adjacent neurons due to loss of insulation around axons
C
19. How does membrane permeability to K+ (PK) and Na+ (PNa) change during an action potential? a. PNa always exceeds PK; permeability does not change for either ion. b. PK always exceeds PNa; permeability does not change for either ion. c. PNa exceeds PK at rest; PK temporarily increases during the action potential. d. PK exceeds PNa at rest; PNa temporarily increases during the action potential. e. PK exceeds PNa at rest; PNa increases during the action potential and remains higher than PK until the next action potential, then it quickly drops.
D
In a two-compartment model of a cell with a K+- and Cl--permeable membrane and a 10-fold excess of K+ in the inside compartment, how would the membrane potential change if all K+ ions were replaced by Cl- ions? a. It would double. b. It would be reduced by half. c. It would not change. d. It would become positive e. No potential would be generated.
D
In the experiments conducted by Hodgkin and Huxley, the early current disappeared if the membrane was clamped at _______ mV. A) -26 B) 0 C) + 26 D) +52 E) +65
D
In the following figure, which of the following is the key event at a membrane potential of +65 mV? A) The late outward current increases in magnitude B) The late outward current decreases in magnitude C) The early current reverses its polarity D) The early and late currents flow outward E) The early current is at its maximum
D
In the phase labeled D, the voltage-gated sodium channels are ________ and the voltage-gated potassium channels are ________. A) open; closed B) closed; open C) open; open D) inactivated; open E) closed; inactivated
D
The proteins that establish ionic gradients are called A) ligand-gated ion channels. B) voltage-gated ion channels. C) passive transporters. D) active transporters. E) permeability transition pores.
D
The voltage clamp apparatus has _______ electrodes, and the _______ compares the actual membrane potential with the command potential. A) two; amplifier B) two; reference electrode C) two; recording electrode D) three; amplifier E) three; reference electrode
D
What do microscopic and macroscopic Na+ currents have in common? A) They flow through a single ion channel B) They flow through multiple ion channels C) They flow through a large area of neuronal membrane D) They represent a flow of many ions E) They have a magnitude of 1-10 pA
D
What is the primary pathophysiological mechanism associated with multiple sclerosis? A) Myelin loss B) Axon damage C) Immune cell infiltration D) Immune response within the nervous system E) Loss of trophic support of the axon
D
Which consequence of Na+ channels staying open, instead of closing after membrane depolarization, is most plausible? A) Action potentials would spread both ways, forward and backward. B) The refractory period would be longer. C) The refractory period would be shorter. D) The membrane would not repolarize (return to a negative value of membrane potential) following depolarization. E) None of the above
D
Which observation was not observed in Hodgkin and colleagues' voltage-clamp study of squid action potentials? A) Capacitive currents in response to hyperpolarizing voltage steps B) Capacitive currents in response to depolarizing voltage steps C) A transient inward current as a result of depolarization D) A sustained outward current as a result of hyperpolarization E) A delayed outward current as a result of depolarization
D
Which of the following is not a variant of the patch clamp technique? A) Inside-out patch B) Intracellular C) Whole cell D) Outside-out patch E) Cell attached
D
Which of the following is not integral to the action potential waveform? A) A change in permeability of the membrane to sodium B) A change in permeability of the membrane to potassium C) A transient increase in the sodium current D) An initial decrease in the potassium current E) A "self-activating" aspect to the rise in the sodium current
D
Which statement about passive current involved in action potential propagation is most accurate? A) It acts as a booster at each point along the axon. B) It flows through the voltage-dependent K+ channels. C) It flows through the voltage-dependent Na+ channels. D) It opens voltage-dependent Na+ channels in the adjacent region of axon. E) It opens voltage-dependent K+ channels in the adjacent region of axon.
D
Which statement on the rising or overshoot phase of the action potential is true? A) The time from threshold to maximum depolarization is essentially instantaneous (i.e., too fast to be measured accurately with current electronics). B) A negative feedback loop leads to a regenerative depolarization that would increase continuously if unchecked. C) The degree of depolarization is limited in part by the declining driving force on potassium entry. D) The degree of depolarization is limited in part by the inactivation time course for the sodium current. E) The degree of depolarization is limited in part by the inactivation time course of the potassium current.
D
Which technique is illustrated in the figure, and what can it be used to measure? A) Whole-cell patch-clamp; measures potentials from the entire cell B) Whole-cell patch-clamp; measures the current that flows through a single ion channel C) Cell-attached patch clamp; measures potentials from the entire cell D) Cell-attached patch clamp; measures the current that flows through a single ion channel E) Outside-out patch clamp; measures the current that flows through a single ion channel
D
Suppose a water-filled aquarium is divided into two compartments by a membrane that is impermeable to all ions. If KCl is added to one compartment, what will happen to the distribution of K+ and Cl-? Will there be a potential difference between the two compartments? What will happen to the membrane potential if the membrane suddenly becomes selectively permeable to K+ (but not to Cl-)?
If KCl is added to one compartment, nothing will happen because the membrane is impermeable. There will not be a potential difference between the two compartments. If the membrane suddenly becomes selectively permeable to K+ (but not to Cl-), it will reach equilibrium potential for K+.
In what situation would you use the Goldman equation instead of the Nernst equation?
If there is more than one permeant ion in the environment you would use the Goldman equation.
. In a two-compartment model of a cell with a K+-permeable membrane and a 10-fold excess of K+ in the inside compartment, how would K+ ions flow across the membrane? a. They would flow from the inside compartment to the outside compartment. b. They would flow from the outside compartment to the inside compartment. c. There would be no flow of K+ ions. d. They would flow in both directions at the same time in equal molar quantities. e. They would flow in both directions, but the flow would be negligible.
a
Which experimental model did Hodgkin and Katz use in their studies of the resting membrane potential? a. Living squid neuron b. Neurons of Aplysia species c. Mammalian neurons d. Mammalian brain slices e. Neurospheres
a. Living squid neuron
Which state of the plasma membrane does not occur during an action potential? a. Resting phase b. Rising phase c. Overshoot phase d. Falling phase e. Undershoot phase
a. Resting phase
1. The synaptic potential a. makes communication between nerve cells possible. b. occurs only in response to external stimuli. c. propagates along axons. d. determines the cell's resting potential. e. results in a long-term change in a cell's membrane potential.
a. makes communication between nerve cells possible.
In a two-compartment model of a cell with a K+- and Ca2+-permeable membrane and a 10-fold excess of K+ in the inside compartment, how would the membrane potential change if all K+ ions were replaced by Ca2+ ions? a. It would double. b. It would be reduced by half. c. It would not change. d. It would become positive. e. No potential would be generated.
b
In a two-compartment model of a cell with a K+-permeable membrane and a 10-fold excess K+ in the inside compartment, the membrane potential is experimentally made more negative than the K+ equilibrium potential. How would K+ ions flow across the membrane? a. They would flow from the inside compartment to the outside compartment. b. They would flow from the outside compartment to the inside compartment. c. There would be no flow of K+ ions. d. They would flow in both directions at the same time in equal molar quantities. e. They would flow in both directions, but the flow would be negligible.
b
Which statement best describes the Nernst equation? a. It relates the equilibrium potential of an ion to its intracellular concentration. b. It relates the equilibrium potential of an ion to its extracellular concentration. c. It relates the equilibrium potential of an ion to its intra- and extracellular concentrations. d. It relates the equilibrium potentials of multiple ions to their intracellular concentrations. e. It relates the equilibrium potentials of multiple ions to their intra- and extracellular concentrations.
c
During the overshoot phase of an action potential, membrane potential briefly reaches a value near _______ mV. a. -80 b. -65 c. 0 d. +50 e. +90
d. +50
Which factor is important in determining the membrane potential when there are multiple permeant ions? a. The concentration gradient of the individual ionic species b. The permeability of the membrane to the individual ionic species c. The sum total of all of the ions on both sides of the membrane d. Both a and b e. All of the above
d. Both a and b
In a two-compartment model of a cell with a K+-permeable membrane and a 10-fold excess of K+ in the inside compartment, how would the membrane potential change if all K+ ions were replaced by Na+ ions? a. It would double. b. It would be reduced by half. c. It would not change. d. It would become positive. e. No potential would be generated.
e
Concentrations of which ion, inside and outside of a neuron, have the greatest effect on the resting membrane potential? a. K+ b. Na+ c. Ca2+ d. Cl- e. PO43-
a
What is the major determinant of the permeability of a membrane to a specific ion? a. Size of the ion b. Concentration of the ion inside the cell c. Concentration of the ion outside the cell d. Electrical charge of the ion e. Number of open ion channels specific for that ion
Answer: e
A researcher conducts a voltage clamp experiment on a giant squid axon and collects the data shown in the graph. At what membrane potential was the cell clamped? A) 0 mV B) Sodium's equilibrium potential C) -65 mV D) Potassium's equilibrium potential E) -110 mV
B
In the following figure, which of the following is the key event at a membrane potential of 26 mV? A) The late outward current increases in magnitude B) The late outward current decreases in magnitude C) The early current reverses its polarity D) The early and late currents flow inward E) The early current is at its maximum
B
In which way do potassium channels in the squid giant axon differ from sodium channels? A) The summing of the individual potassium channels does not reconstruct the macroscopic current. B) Once the potassium channels open in response to a voltage step command, they tend to remain open. C) The potassium channels pass only a few ions per second. D) The potassium channels show little voltage dependence. E) The potassium channels open in response to hyperpolarization of the membrane.
B
Nodes of Ranvier represent A) points where two axons connect. B) gaps in myelin wrapping. C) areas of high synaptic density. D) segments of axon where only K+ channels are located. E) segments of axon where passive current flows.
B
Practically speaking, how would you determine that Na+ influx into a cell underlies the early current? A) Replace intracellular Na+ with its radioactive form and trace its movement across the membrane. B) Remove Na+ from the extracellular compartment and assess the early current under new conditions. C) Use the voltage clamp method to measure the current. D) Remove K+ from the intracellular compartment and assess the early current under the new conditions. E) Treat the cell with tetraethylammonium.
B
The classic voltage clamp technique would be suitable for which application? A) Indirect measurement of unidirectional current flowing through cell membrane B) Direct measurement of current flowing through the cell membrane C) Measurement of current flowing through a single ion channel D) Study of the ionic composition of the intracellular environment E) Evaluation of effects of large intracellular molecules on the function of ion channels
B
. The resting membrane potential typically ranges from _______ to _______. a. -90 mV; 90 mV b. 40 mV; 90 mV c. 40 V; 90 V d. -40 mV; -90 mV e. 0 mV; 90 mV
D
How does the resting membrane potential of a typical neuron compare to the equilibrium potential (calculated by the Nernst equation) for potassium? a. The resting membrane potential is not exactly equal to the equilibrium potential for potassium because of variation among neurons. b. The resting membrane potential is not exactly equal to the equilibrium potential for potassium because rapid fluctuations in membrane potential prevent accurate measurements. c. The resting membrane potential is not exactly equal to the equilibrium potential for potassium because the membrane has some resting permeability to species other than potassium. d. The resting membrane potential is not exactly equal to the equilibrium potential for potassium because potassium does not contribute to the resting membrane potential. e. The resting membrane potential is exactly equal to the equilibrium potential for potassium.
Answer: c
Which statement best describes the electrical properties of nerve cells? a. They are exceptionally good conductors of electricity (much better than copper wires). b. They are similar in their electrical conduction properties to copper wires. c. In comparison to copper wires, they are relatively poor conductors of electricity. d. They are unable to conduct electricity under any circumstances. e. They are electron sinks; they absorb many electrons, but no electricity comes out of them.
Answer: c
4. Which statement best describes the action potential? a. An action potential is specialized to transmit signals over only very short distances. b. An action potential is a brief change in membrane potential from positive to negative. c. An action potential is elicited by hyperpolarization. d. An action potential occurs when the cell's membrane potential reaches threshold. e. The level of depolarization is graded in proportion to the magnitude of the stimulus.
Answer: d
For which reason was the development of the voltage clamp critical to investigations of the ionic basis of the action potential? A) Voltage changes in the cell cannot be seen without voltage clamp. B) Ionic conductances can be activated only in cells that have been voltage clamped. C) Voltage clamping allows simultaneous control of membrane potential and measurement of permeability changes. D) Sodium and potassium currents are activated in non-overlapping voltage regimes. E) Voltage clamping does not require specialized equipment.
C
The resting potential of a cell is negative because a. there is an excess of K+ outside of the cell at rest. b. at rest there is an excess of K+ outside of the cell, and the membrane is permeable chiefly to K+. c. at rest there is an excess of K+ inside the cell, and the membrane is permeable chiefly to K+. d. at rest there is an excess of K+ inside the cell, but the membrane is permeable to all ions. e. there is an excess of Cl- ions outside of the cell at rest.
C
When current is injected into an axon, an action potential is evoked before the current has spread any distance from the point of injection. A) the current will spread in only one direction. B) the current will spread passively only if it is a depolarizing current. C) the current will decay exponentially with increasing distance from the injection site (if no action potential is present). D) the current will propagate as an oscillating wave independently of its polarity.
C
Which of the following is the main reason that the opening of sodium channels causes a very rapid depolarization of most neurons? A) Sodium channels pass sodium and chloride ions in opposite directions causing a large charge separation at the membrane. B) Sodium ion diffusion proceeds so quickly that whenever sodium channels are open, there is a rapid directional flux across the membrane. C) Because of the large sodium gradient created by membrane transporters, a rapid depolarization occurs whenever sodium channels are opened in resting neurons. D) Compared to the movement of other cations, the movement of a sodium ion produces a larger voltage change. E) None of these answers are correct.
C
Which phenomenon explains the unidirectional propagation of action potentials? A) The voltage dependence of the sodium channels B) The voltage dependence of the potassium channels C) The presence of a refractory period at a location where an action potential has just passed D) Sufficient "leakiness" of the axons, such that backward propagation of action potentials is prevented E) The polarized orientation of microtubules within the axon
C
