Excitable Tissues Online Feedback Quiz 2011 -
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Department of Physiology
Excitable Tissues Online Feedback Quiz 2011
Total score: 20 out of 20, 100%
Thank you for completing the Excitable Tissues online feedback quiz.
Please review your feedback and revise any areas of weakness.
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You can then accesss the Physiology 1A page and take the assessment again
if you wish.
1)
Which ONE of the following statements regarding membrane transport processes is
CORRECT?
The Ca 2+/Na+ exchanger (counter-transporter) that couples Ca 2+ efflux with Na +
influx, directly utilizes ATP as an energy source.
The hormone insulin is released from pancreatic beta-cells into the bloodstream by
endocytosis.
A K+ ion can only move through an ion channel in a direction that is down its
electrochemical gradient.
The Na +/K +/ATPase is an example of a secondary active transporter.
The SGLT protein that couples Na + influx with the movement of glucose into cells
against its concentration gradient is an example of a facilitated diffusion protein.
1 out of 1
This is correct. An ion channel is an example of facilitated diffusion, so the
substance always moves down its chemical gradient (if solute is
uncharged) or electrochemical gradient (if solute is charged).
2)
The diagram below shows the ionic currents in a typical nerve axon recorded using
the voltage clamp technique and in response to depolarization from about -100 mV to
0 mV, which begins at time = 0. The current trace labelled A corresponds to the
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response obtained in typical physiological solutions in the absence of any drug. Which
ONE of the following statements provides the MOST CORRECT explanation for
traces B and/or C?
Trace B was obtained when internal K+ was replaced by an impermeant ion.
Trace C was obtained in the presence of tetrodotoxin (TTX).
Trace C was obtained when external Na+ was replaced by an impermeant ion.
Trace B was obtained when external Na+ was replaced by an impermeant ion.
Both B and C were obtained when external Na+ was replaced by an impermeant
ion.
1 out of 1
This is correct. Trace B shows the outward K+ currents which can be
separated from the inward Na+ current (trace C) by removing all the
external Na+ ions.
3)
Which ONE of the following statements regarding electrical signals in excitable cells
is CORRECT?
Electrical signals occur as the influx of a cation across the membrane occurs
simultaneously with the influx of an anion.
Movement of electrons in the lipid bilayer results in electrical signals passing from
one cell to another.
The plasma membrane can be represented electrically as a resistor and capacitor
in parallel.
The lipids that comprise the plasma membrane have a high conductance, or low
resistance, to current flow.
The intracellular solution of a nerve cell always has the same electrical potential as
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the extracellular solution.
1 out of 1
This statement is correct. The lipid bilayer gives rise to the capacitive
component while the ion channels give rise to the resistive component.
4)
A nerve cell in the visual cortex of the brain is quiescent (not firing action potentials)
with a steady resting membrane potential of -70 mV. A flash of light is detected by the
eye which results in an action potential being produced in this nerve cell. In regard to
this nerve cell, which ONE of the following options is INCORRECT?
In its resting state (i.e. before receiving the light-evoked signal) the membrane of
the nerve cell is likely to be more permeable to K+ as compared to Na +.
The light caused the membrane potential of the nerve cell to cross the threshold
for activation of voltage-dependent Na + and K+ channels.
As long as the nerve cell has a continuous supply of energy (ATP) it will maintain a
higher intracellular concentration of K+ than compared to the K+ in the extracellular
solution.
The nerve cell was hyperpolarized in response to the light which resulted in the
action potential occurring.
The response of the eye was transmitted to the nerve cell via propagation of action
potentials.
1 out of 1
This is the incorrect statement. The nerve cell was excited by the light
stimulus hence it was depolarized by the stimulus.
5)
The diagram below shows a typical Action Potential in a nerve cell in the brain. In
regards to this action potential, which ONE of the following is MOST CORRECT?
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A strong stimulus causes a larger amplitude action potential as compared to one
produced by a weak stimulus.
The action potential consists of a rapid hyperpolarization, followed by a slower
depolarization and then an afterhyperpolarization.
The afterhyperpolarization results primarily from increased pumping activity of the
Na+/K+/ATPase.
The duration of the action potential is about 1-3 milliseconds, with an amplitude of
about 100 mV.
At the peak of the action potential the membrane potential is about -40 mV.
1 out of 1
This is correct.
6)
A healthy young man drinks a sports supplement containing glucose and creatine
which is advertised to “enhance muscle endurance by increasing intracellular ATP and
Na-pump activity”. Assuming this “Na-pump” refers to the Na+/K+/ATPase, which
ONE of the following options is MOST CORRECT?
The Na+/K+/ATPase will transport glucose (along with K+) into the muscle fibre to
generate ATP and Na+.
A sustained and significant increased in the activity of the Na+/K+/ATPase would
not have any effect on the intracellular ion concentrations.
An increase in Na+/K+/ATPase activity would be expected to lead to a decrease in
the intracellular free Ca2+ concentration due to an increased activity of a secondary
active transporter that exchanges Na+ influx for Ca2+ efflux.
The Na+/K+/ATPase actively transports K+ ions out of a cell and Na+ ions into the
cell.
Increased ATP concentration allows a greater passive flux of K+ and Na+ via the
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Na+/K+/ATPase.
1 out of 1
This is correct. An increase in Na+/K+/ATPase activity should result in
increased pumping out of Na+ thus generating a greater electrochemical
force for Na+/ Ca2+ exchange. In fact, blocking the Na+/K+/ATPase can
be used to increase intracellular Ca2+ and aid cardiac muscle contraction
in congestive heart disease.
7)
Consider you work in a health / sports clinic and a client comes to discuss with you
their symptoms of muscle weakness. Their neurologist has diagnosed that the motor
nerve EMG is normal and that the muscle weakness results from an abnormal
sequence of events occurring at the neuromuscular junction. Which ONE of the
following options MOST CORRECTLY lists the sequence of events that occur at the
neuromuscular junction, and in the correct order?
Exocytosis of neurotransmitter, influx of Ca2+ into the presynaptic nerve terminal,
activation of postsynaptic receptors.
Generation of an end-plate potential, presynaptic release of acetylcholine, diffusion
across the synaptic cleft of the neurotransmitter.
Release of glutamate from the nerve terminal, activation of postsynaptic glutamate
receptors, generation of an end-plate potential.
Activation of nicotinic acetylcholine receptors, generation of an end-plate potential,
enzymatic breakdown of the neurotransmitter.
Influx of K+ into the end-plate, spread of the postsynaptic depolarization through
the muscle, endocytosis of acetylcholine into the muscle.
1 out of 1
This is correct.
8)
A nerve cell contains intracellular K+ and Na + concentrations of 140 mM and 10 mM,
respectively. It is surrounded by an extracellular solution containing K+ and Na +
concentrations of 4 mM and 150 mM, respectively. The only open ion channels in the
nerve cell are selective for K+. Given that R= the Gas constant, T = temperature in
Kelvins, F = Faraday’s constant and z = valence, the nerve cell’s membrane potential
can be calculated as:
(RT) / (zF) multiplied by log e [(150 mM + 4 mM) / (10 mM + 140 mM)]
(RT) / (zF) multiplied by log e [(10 mM + 140 mM) / (4 mM + 150mM)]
(RT) / (zF) multiplied by log e (4 mM / 140 mM)
(RT) / (zF) multiplied by log e (140 mM / 4 mM)
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(RT) / (zF) multiplied by log e (10 mM / 150 mM)
1 out of 1
This is correct. The cell is only permeable to K +, so the membrane
potential will quickly go to the K + equilibrium potential, given by the Nernst
equation.
9)
Which ONE of the following statements regarding action potential propagation in
nerve cells is INCORRECT?
Action potentials are initiated in the axon hillock and can then propagate both
forward towards the axon terminal and backwards into the nerve dendrites.
There is a greater leak of local current flow across the cell membrane in an
unmyelinated axon as compared to a myelinated axon.
In a normal unmyelinated axon, the action potential amplitude gets progressively
smaller as it travels along the axon towards the nerve terminal.
Saltatory conduction, where the action potential “jumps” from node to node, only
occurs in myelinated axons.
Myelination increases the conduction velocity of action potential propagation.
1 out of 1
This is the incorrect statement. The action potential is a regenerative or “all
or nothing” response that is of about the same amplitude throughout the
axon.
10 )
Recent research demonstrated that humans with a specific type of epilepsy had a
decrease amplitude of inhibitory postsynaptic potentials (IPSPs) between two neurons
in a particular part of the brain. Which ONE of the following statements would be
MOST CONSISTENT with this finding?
The decreased IPSP may result from an increase in the neurotransmitter
dependent Cl- flux into the postsynaptic neuron.
A decrease in release of glutamate from the presynaptic terminal could cause the
decrease IPSP amplitude
An increase in the response of GABAA receptors in the brain may be the cause of
the decreased IPSP amplitude.
The firing rate of the postsynaptic neuron is likely to be decreased as a result of
the decreased IPSP amplitude.
There is a decrease in the number of K+ channels that open in response to
activation of an inhibitory metabotropic receptor.
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1 out of 1
This is correct. Slow IPSPs typically result from efflux of K+ through K+
channels activated by metabotropic receptors.
11 )
Which ONE of the following statements regarding communication between cells of the
body is CORRECT?
At the mammalian neuromuscular junction, the neurotransmitter is released from
nerve terminals by a Na + dependent counter-transporter.
Gap junction proteins are critical elements in neurotransmitter-mediated
communication between adjacent cells.
At the mammalian neuromuscular junction, enzymatic breakdown plays a major
role in terminating the actions of acetylcholine on its receptors.
The same neurotransmitter can only signal via either metabotropic or ionotropic
receptors.
Chemical communication can occur via metabotropic or ionotropic signaling with
metabotropic signaling being more suited for very fast (1-2 ms) synaptic
communication between nerve cells.
1 out of 1
This is correct. The enzyme acetylcholinesterase breaks down acetycholine
and is the main mechanism by which the neurotransmitter's actions are
terminated (there is also some lateral diffusion away from the synapse).
12 )
If the K+ equilibrium (Nernst) potential is -90 mV and a nerve cell has a resting
membrane potential of -60 mV, then:
Opening of more K+ channels will depolarize the membrane.
There is no electrochemical driving force acting on K+ ions in this resting state.
The extracellular concentration of K+ is higher than the intracellular concentration.
Opening of more K+ channels will hyperpolarize the membrane.
Only K+ channels are open in this resting state.
1 out of 1
This is correct. More K + leaves and Vm tends towards the Nernst potential
for K +.
13 )
At the neuromuscular junction, the motor nerve communicates with the skeletal
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muscle by releasing a chemical neurotransmitter. In regard to this neuromuscular
transmission which ONE of the following typically occurs?
Binding of the neurotransmitter to the muscle receptor generates an inhibitory
postsynaptic receptor potential (IPSP).
The neurotransmitter acts on gap junctions to cause a synchronized contraction.
The neurotransmitter released by the nerve terminal is adrenaline.
A metabotropic receptor mediates a slow postsynaptic response to the
neurotransmitter.
Acteylcholinesterase helps to terminate the response by metabolising the
neurotransmitter.
1 out of 1
This is correct.
14 )
Choose the MOST CORRECT option. With regard to the ion channels underlying the
action potential in a typical nerve axon:
Voltage-dependent K+ channels activate before the voltage-dependent Na +
channels.
The voltage-dependent Na + channels are inactivated when the action potential
threshold is reached.
Background or “leak” K+ channels are closed during the depolarization phase.
Voltage-dependent K+ channels are open during the repolarization phase.
Voltage-dependent K+ channels are closed during the afterhyperpolarization
phase.
1 out of 1
This is correct. Efflux of K + through these open channels is what causes
the repolarization.
15 )
If a solute is moving from inside a cell to outside via simple diffusion then which ONE
of the following is CORRECT?
Its transport rate is directly proportional to the solute’s lipid solubility (partition coefficient).
If the solute is uncharged, then its extracellular concentration must be greater than
its intracellular concentration.
Its transport is likely to be mediated by exocytosis of a vesicle containing the
solute.
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Its transport across the membrane requires coupling to the transport of a second
solute down this (second) solute’s pre-existing electrochemical gradient.
Its transport rate is slower across a small cell (smaller surface area) compared to a
large cell (with larger surface area).
1 out of 1
This is correct (from Fick's Law).
16 )
Consider an experiment where a small amount of blue-coloured copper sulphate
(CuSO4 ) salt is added to a mixture of water and paraffin oil and the solution is shaken
so that the molecules making up the salt become hydrated by some of the other
molecules in this solution. Complete the sentence with ONE of the following options:
The CuSO4 becomes hydrated by:
non-polar oil molecules giving rise to Cu 2+ anions and SO 4 2- cations.
polar water molecules giving rise to Cu 2+ cations and SO 4 2- anions.
polar water molecules giving rise to Cu 2+ anions and SO 4 2- cations.
non-polar water molecules giving rise to Cu 2+ cations and SO 4 2- anions.
polar oil molecules giving rise to Cu 2+ anions and SO 4 2- cations
1 out of 1
This is the correct statement.
17 )
Consider a skeletal muscle or nerve cell that is bathed in an extracellular and
intracellular solution containing the same concentration of a cation, i.e. the cation
concentration inside the cell = its concentration outside the cell. Regarding the
electrochemical forces on this cation, which ONE of the following options is
CORRECT?
When the membrane potential of the cell is -70 mV, there is no electrochemical
force causing the ion to move across the membrane.
When the membrane potential of the cell is -70 mV, a chemical force acts on the
ion to cause cation influx.
When the membrane potential of the cell is +30 mV, an electrochemical force acts
on the ion to favour cation efflux.
At - 70 mV, no cations would move through a cation selective channel as there is
no driving force for cation movement.
The equilibrium potential for the ion would be approximately -90 mV at 37°C.
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1 out of 1
This is correct. There is an electrochemical force exerted on the cation
which acts to push the cation out, ie efflux.
18 )
The schematic diagram below shows a model of epithelial transport in the kidney
proximal tubule. The cell is at rest with typical ion concentrations in the extracellular
and intracellular solutions. The membrane transport protein labeled “X”, which
transports Na +, K+ and Cl - into the cell as shown, is an example of a:
Primary active transporter.
Secondary active transporter (exchanger).
Ion channel.
Facilitated diffusion transporter.
Secondary active transporter (co-transporter).
1 out of 1
This is correct. The transporter uses a Na+ gradient set up by active
transport to transport K+ ions against their electrochemical gradient. Na+
and K+ are transported in the same direction (hence co-transport)
19 )
Which ONE of the following statements about ion channels is INCORRECT?
Ion channels allow transport of an ion against its chemical gradient, if the electrical
driving force is sufficient.
Ion channels may be opened by stretch of the cell membrane.
Ion channels can be opened either directly or indirectly by neurotransmitters.
Ion channels have gates that may be opened by intracellular ligands.
Ion channels allow transport of an ion against its electrochemical gradient.
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1 out of 1
This is the incorrect statement. Ion channels are passive (facilitated
diffusion) transporters so that ions can only flow down their electrochemical
gradients.
20 )
The diagram below shows a schematic nerve cell bathed in intracellular and
extracellular solutions at 37°C and with the concentrations of Na+ and K+ as shown.
The cell membrane contains a population of K+-selective ion channels and a
separate population of Na+-selective ion channels as indicated. An electrode is
inserted into the cell that measures the membrane potential (Vm). The Nernst
equation for ion x at 37°C, can be simplified to: Ex = 62 mV log10 [ionoutside] /
[ioninside].
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If initially (at rest) only the K+ channels are open, and then the Na+ channels also
open, which ONE of the following options MOST CLOSELY describes the membrane
potential (Vm):
Resting Vm = -62 mV, when the Na+ channels open, Vm becomes depolarized.
Resting Vm = +62 mV, when the Na+ channels open, Vm becomes depolarized.
Resting Vm = 0 mV, no change when Na+ channels open.
Resting Vm = -62 mV, when the Na+ channels open, Vm becomes hyperpolarized.
Resting Vm = +62 mV, when the Na+ channels open, Vm becomes
hyperpolarized.
1 out of 1
This is correct.
Link...
Copyright (c) Department of Physiology, University of New South Wales, Sydney, Australia 2010
Should you encounter a problem please notify:L.Ulman@unsw.edu.au
Perception is licensed to The University of New South Wales
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