Univ. of Illinois, Urbana-Champaign
Bio/Neuro 303
Chapter 4 - Study Questions
74. A neuron is said to be polarized because
a. the action potential can travel in one direction only.
b. the soma is always at one extremity of the cell.
*c. there is a difference of electrical potential across its membrane.
d. it tends to cluster with other neurons in nuclei.
75. Axons generally have which of the following concentrations of ions
INTERNALLY (relative to extra-cellular space)?
a. High K+, high Na+, low Cl-.
*b. High K+, low Na+, low Cl-.
c. Low K+, high Na+, low Cl-.
d. Low K+, low Na+, low Cl-.
76. The extracellular space around axons generally has which of the following
concentrations of ions (relative to intracellular concentrations)?
*a. Low K+, high Na+, high Cl-.
b. Low K+, high Na+, low Cl-.
c. High K+, low Na+, low Cl-.
d. High K+, low Na+, high Cl-.
77. The membrane of a typical resting neuron is largely impermeable to
*a. Na+.
b. K+.
c. Cl-.
d. none of the above.
78. When voltage-gated ion channels open, ions move through these channels
under the influence of the
a. electrical field of the membrane potential only.
b. concentration gradients of the ions only.
*c. combined influence of the electrical field of the membrane potential
and the concentration gradients of the ions.
d. metabolic pumps for the moving ions.
79. Calculation of the "net" potential of an ion (the difference between the
resting membrane potential and the equilibrium potential) tells you
*a. how much "force" (in electrical terms), and its direction, is acting on
an ion in a resting neuron.
b. how much "force" (in electrical terms), and its direction, is acting on
an ion in an active neuron.
c. the potential difference across the membrane necessary just to balance
the concentration gradient.
d. the total potential that drives the ion during the peak of the action
potential.
80. Changing the temperature of a squid giant axon from 20oC to 40oC would
change the K+ equilibrium potential (Nernst potential) from about -75 mV to
about
a. -150 mV.
b. -37.5 mV
*c. -80 mV.
d. changing the temperature wouldn't affect the K+ equilibrium potential.
81. Imagine a hypothetical neuron that is only permeable to K+ ions. If the
EXTRAcellular K+ concentration were 10 TIMES GREATER than the INTRAcellular
K+ concentration, then the resting membrane potential for this hypothetical
cell at standard temperature (20oC) would be about:
*a. +58 mV.
b. 0 mV.
c. -58 mV.
d. -90 mV.
82. The formula for the Nernst Equation is
RT [ion]out
a. Em = ---- ln ----------
FZ [ion]in
RT [ion]in
b. Eion = ---- ln ----------
FZ [ion]out
RT [ion]in
c. Em = ---- ln ----------
FZ [ion]out
RT [ion]out
*d. Eion = ---- ln ----------
FZ [ion]in
83. The Nernst Equation is used to find
a. the resting membrane potential.
b. the contribution to the membrane potential made by a particular ion.
*c. the equilibrium potential of an ion.
d. the effect on the membrane potential of changing the concentration of
an ion.
84. The Nernst equation ______ be used to calculate the membrane potential
because ______
a. can; it allows you to calculate the equilibrium point for each ion,
which must be the resting potential.
*b. cannot; it tells you only what the equilibrium potential for an
individual ion is, not what the summed effect of all ions is on the
membrane potential.
c. can; it allows you to calculate the balance of forces acting on each
ion as it contributes to membrane potential.
d. cannot; it does not take into account such variables as temperature.
85. The equilibrium potential of an ion
*a. may be calculated by the Nernst equation.
b. must be determined experimentally.
c. may be calculated by the Goldman equation.
d. is dependent on the membrane potential of the cell.
86. The equilibrium potential of an ion represents
a. its contribution toward an action potential.
b. its contribution toward a post-synaptic potential.
c. the electrical charge just required to balance the concentration
differences of all the ions across the membrane.
*d. the electrical charge just required to balance the concentration
difference of one specific ion across the membrane.
87. The equilibrium potential of an ion is the potential
a. at which there is no movement at all of that ion across the membrane.
*b. which just balances the concentration difference of the ion across the
membrane.
c. at the peak of the action potential where ion influx and efflux are
at equilibrium.
d. at which the equilibrium forces net inward movement.
88. If you experimentally increase the permeability of an axonal membrane to
sodium ions, the equilibrium potential for sodium in the cell will
a. increase, because the influx of sodium depolarizes the neuron.
b. decrease, because the influx of sodium depolarizes the neuron.
c. decrease, because the efflux of potassium that follows sodium influx
repolarizes the membrane.
*d. remain unchanged.
89. Consider the squid giant axon at rest with normal intracellular and
extracellular ion concentrations. If the membrane permeability to K+
ions is increased, the K+ equilibrium potential (Nernst potential)
a. will become more positive.
b. will become more negative.
*c. will stay the same.
d. the effect can't be predicted.
90. Consider the squid giant axon at rest with normal intracellular and
extracellular ion concentrations. If the membrane permeability to K+
ions is increased, then over the short term (a few minutes)
a. the K+ equilibrium potential will become more positive.
b. the K+ equilibrium potential will become more negative.
*c. the K+ equilibrium potential will stay the same.
d. the effect on the K+ equilibrium potential cannot be predicted.
91. Suppose that in a neuron ECl- is -60 mV and the resting membrane potential
is -65 mV. Given a typical distribution of the ion, then if chloride
channels are opened in this neuron by the action of a transmitter
substance, there will be
a. a net inward movement of Cl- ions.
*b. a net outward movement of Cl- ions.
c. no net movement of Cl- ions.
d. nothing! The premises of the question are wrong, since you cannot have
an ECl- of -60 mV if the membrane potential is -65 mV.
92. Suppose that in a neuron ECl- is -60 mV and the resting membrane potential
is -65 mV. In such a neuron, an inhibitory effect ______ be brought about by
the opening of Cl- channels because
a. could; chloride would move into the neuron, thereby depolarizing it.
b. could not; chloride would move out of the cell, thereby depolarizing
it.
*c. could; chloride would move into the cell once the membrane potential
became more positive than -60 mV.
d. could not; the effect of the presence of a simultaneous EPSP would be
to prevent any net movement of chloride.
93. In molluscan neurons, the carrier of inward current during the rising phase
of the action potential is usually calcium. This ion has an unusually
steep concentration gradient. Given the values below, what is the
equilibrium potential for Ca2+ at 20oC? (Consider the options carefully.)
[Ca2+]o = 10-2 M
[Ca2+]i = 1.7 x 10-7 M
[Ca2+]o
log --------- = 4.77
[Ca2+]i
[Ca2+]i
log --------- = -4.77
[Ca2+]o
a. +274 mV
b. -274 mV
*c. +137 mV
d. -137 mV
94. In resting neuron the EK+ is greater (-75 mV) than Em (-60 mV). The
consequence of this is that
*a. there is a net tendency for K+ to leak from the cell.
b. there is a net tendency for K+ to leak into the cell.
c. there is no net movement of K+.
d. The cell has no true resting potential.
95. A decrease (i.e., depolarization) in the resting membrane potential can be
brought about by
*a. increasing the external K+ concentration.
b. increasing the external Na+ concentration.
c. decreasing the external K+ concentration.
d. decreasing the external Na+ concentration.
96. The resting membrane potential of neurons is primarily determined by
a. the resting membrane permeability to sodium.
*b. the resting membrane permeability to potassium.
c. the resting membrane permeability to chloride.
d. the resting membrane permeability to organic anions.
97. The resting neuron is sometimes referred to as a
a. sodium battery, because sodium drives the action potential.
b. calcium battery, because calcium is necessary for synaptic transmission.
c. sodium battery, because sodium is excluded from the cell.
*d. potassium battery, because the resting potential is nearly proportional
to external K+ concentration.
98. Ignoring constants, it is accurate to say that the Goldman equation
*a. allows you to calculate the membrane potential for a neuron, based on
the concentrations and permeabilities of the major ions.
b. allows you to calculate the membrane potential for a neuron, based only
on the concentrations of the major ions.
c. allows you to calculate the equilibrium potential for an ion, based on
the concentrations and permeabilities of the ion.
d. allows you to calculate the equilibrium potential for an ion, based
only on the concentrations of the ion.
99. Extracellular recording is so called because
a. two electrodes are used, one being called the "extra" electrode.
b. such recordings are from more than one (the "extra") nerve cell.
*c. such recording requires placement of the electrodes extracellular to
the nerve cell.
d. extracellular refers to the glia in the extracellular space.
100. If one records extracellularly with two wire electrodes from an axon while
one replaces the normal extracellular fluid with saline with a high
potassium content, one would see (consider all options before you select
the best one)
a. a shift in the membrane potential (Em) toward zero, because the
increased K+ would depolarize the axon.
b. no shift in Em because no shift takes place.
c. a shift in Em away from zero because the increased K+ would
hyperpolarize the axon.
*d. no shift in Em because one cannot record Em by using this kind of
extracellular recording.
101. In intracellular recording, the reference electrode (the one against which
potential is measured; i.e., the ground electrode) is
a. inside the cell.
b. pressed against the cell membrane.
c. not used, since the recording electrode is inside the cell.
*d. outside the cell but not touching it.
102. In intracellular recording, the potential ______ is measured.
a. across the synapse
*b. across the cell membrane
c. along the length of the axon
d. between the soma and the spike initiation zone
103. Increasing the external concentration of potassium to twice its normal
level around a squid giant axon will
a. do nothing to the membrane potential because disturbing the equilibrium
potential cannot affect the membrane potential of the cell.
b. increase the membrane potential (hyperpolarize the cell) because the
presence of extra potassium outside the cell will make the potassium
equilibrium potential more negative.
c. increase the membrane potential because the excess positive charge on
the outside of the cell makes the inside relatively more negative.
*d. decrease the membrane potential (depolarize the cell) because the
reduction in the equilibrium potential for potassium will mean less
potassium will diffuse out of the cell, leaving the interior more
positive than before.
104. Cutting in half the external concentration of sodium around a squid giant
axon at rest will
*a. have very little effect on the membrane potential because the cell
membrane has an extremely low permeability to sodium.
b. decrease the membrane potential (depolarize the cell) because the
presence of less sodium outside the cell will decrease the activity of
the sodium-potassium exchange pump, leaving more positively charged
potassium inside the cell.
c. increase the membrane potential (hyperpolarize the cell) because the
reduction in exterior positive charge will change the potassium
equilibrium potential, allowing more potassium to leak out of the cell
and making the interior more negative.
d. decrease the membrane potential because the reduction in positive
charges around the outside of the cell leaves the interior less
negative relative to the outside than it was before.
105. In most neurons, the internal concentration of K+ is about 10 times as
great as the external concentration. If one then doubled the external
potassium concentration around such a neuron, the membrane potential would
a. stay the same.
b. go to zero.
*c. move toward zero but not reach it.
d. move away from zero.
106. In a squid giant axon, if one reduced the external concentration of Na+
around a neuron, the membrane potential would quickly
*a. stay the same.
b. go to zero.
c. move appreciably toward zero, but not reach it.
d. move appreciably away from zero.