Campbell Biology in Focus, 2e (Urry)
Chapter 37 Neurons, Synapses, and Signaling
37.1 Multiple-Choice Questions
1) A simple nervous system
A) must include chemical senses and vision.
B) includes sensory information but no effectors.
C) has information flow in only one direction: toward an integrating center.
D) has information flow in only one direction: away from an integrating center.
E) includes sensory information, an integrating center, and effectors.
2) Most of the neurons in the human brain are
A) sensory neurons.
B) motor neurons.
C) interneurons.
D) nerves.
3) The nucleus and most of the organelles in a neuron are located in the
A) dendrites.
B) axon hillock.
C) axon.
D) cell body.
E) axon terminals.
4) The point of connection between two communicating neurons is called the
A) axon hillock.
B) dendrite.
C) synapse.
D) cell body.
E) axon.
5) In a simple synapse, neurotransmitter chemicals are released by
A) the dendritic membrane.
B) the presynaptic membrane.
C) axon hillocks.
D) cell bodies.
6) Somatic motor neurons are used to transmit motor signals to muscles. For example, a somatic
motor neuron carries a signal from your spinal cord to your biceps brachii so that you can flex
your arm at the elbow. In this example, what is the correct sequence of neuronal structures that
this signal would travel through in the motor neuron?
A) dendrites, cell body, axon, axon hillock, synaptic terminals, biceps brachii
B) dendrites, cell body, axon hillock, axon, synaptic terminals, biceps brachii
C) axon, cell body, synaptic terminals, dendrites, axon hillock, biceps brachii
D) synaptic terminals, dendrites, cell body, axon, axon hillock, biceps brachii
7) Although the membrane of a “resting” neuron is highly permeable to potassium ions, its
membrane potential does not exactly match the equilibrium potential for potassium because the
neuronal membrane is also
A) fully permeable to sodium ions.
B) slightly permeable to sodium ions.
C) fully permeable to calcium ions.
D) impermeable to sodium ions.
E) highly permeable to chloride ions.
8) The operation of the sodium-potassium “pump” moves
A) sodium and potassium ions into the cell.
B) sodium and potassium ions out of the cell.
C) sodium ions into the cell and potassium ions out of the cell.
D) sodium ions out of the cell and potassium ions into the cell.
E) sodium and potassium ions into the mitochondria.
9) A cation that is more abundant as a solute in the cytosol of a neuron than it is in the interstitial
fluid outside the neuron is
A) HCO3–.
B) Cl–.
C) Ca2+.
D) Na+.
E) K+.
10) The membrane potential that exactly offsets an ion’s concentration gradient is called the
A) graded potential.
B) threshold potential.
C) equilibrium potential.
D) action potential.
E) inhibitory postsynaptic potential.
11) ATP hydrolysis directly powers the movement of
A) K+ out of cells.
B) Na+ out of cells.
C) Na+ into cells.
D) Ca2+ into cells.
E) Cl– into cells.
12) Two fundamental concepts about the ion channels of a “resting” neuron are that the channels
A) are always open, but the concentration gradients of ions frequently change.
B) are always closed, but ions move closer to the channels during excitation.
C) open and close depending on stimuli and are specific as to which ion can traverse them.
D) open and close depending on chemical messengers and are nonspecific as to which ion can
traverse them.
E) open in response to stimuli and then close simultaneously, in unison.
13) Opening all of the sodium channels, with all other ion channels closed — which is an
admittedly artificial setting — on an otherwise typical neuron should move its membrane
potential to
A) -90 mV.
B) -70 mV.
C) 0 mV.
D) +30 mV.
E) +62 mV.
14) The selectivity of a particular ion channel refers to its
A) permitting passage by positive but not negative ions.
B) permitting passage by negative but not positive ions.
C) ability to change its size depending on the ion needing transport.
D) binding with only one type of neurotransmitter.
E) permitting passage only to a specific ion.
15) Tetraethylammonium (TEA) is a potent neurotoxin that results in death from respiratory
failure within 10 to 30 minutes. When a neuron is incubated with TEA, researchers observed that
action potentials could be generated, but the membrane potential remained positive and never
returned to the resting membrane potential. What channel is TEA likely acting on?
A) voltage-gated sodium channels
B) voltage-gated potassium channels
C) sodium potassium pumps
D) chloride channels
16) Tetraethylammonium (TEA) is a potent neurotoxin that results in death from respiratory
failure within 10 to 30 minutes. When a neuron is incubated with TEA, researchers observed that
action potentials could be generated, but the membrane potential remained positive and never
returned to the resting membrane potential. What channels could be opened that would counter
the effects of TEA and allow the neuron to return to resting membrane potential?
A) chloride channels
B) calcium channels
C) sodium channels
D) There are no channels that can oppose the effects of TEA.
17) For a neuron with an initial membrane potential at -70 mV, an increase in the movement of
potassium ions out of that neuron’s cytoplasm would result in the
A) depolarization of the neuron.
B) hyperpolarization of the neuron.
C) replacement of potassium ions with sodium ions.
D) replacement of potassium ions with calcium ions.
E) neuron switching on its sodium-potassium pump to restore the initial conditions.
18) A graded hyperpolarization of a membrane can be induced by
A) increasing its membrane’s permeability to Na+.
B) decreasing its membrane’s permeability to H+.
C) decreasing its membrane’s permeability to Cl–.
D) increasing its membrane’s permeability to Ca2+.
E) increasing its membrane’s permeability to K+.
19) Self-propagation and refractory periods are typical of
A) action potentials.
B) graded hyperpolarizations.
C) excitatory postsynaptic potentials.
D) inhibitory postsynaptic potentials.
E) resting potentials.
20) The “threshold” potential of a membrane is the
A) maximum depolarization needed to operate sodium-potassium pumps.
B) lowest frequency of action potentials a neuron can produce.
C) minimum hyperpolarization needed to prevent the occurrence of action potentials.
D) minimum depolarization needed to operate the voltage-gated sodium and potassium channels.
E) peak amount of depolarization seen in an action potential.
21) Action potentials move along axons
A) more slowly in axons of large diameter as compared to those of small diameter.
B) by the direct action of acetylcholine on the axonal membrane.
C) by activating the sodium-potassium “pump” at each point along the axonal membrane.
D) more rapidly in myelinated than in nonmyelinated axons.
E) by reversing the concentration gradients for sodium and potassium ions.
22) A toxin that binds specifically to voltage-gated sodium channels in axons would be expected
to
A) prevent the hyperpolarization phase of the action potential.
B) prevent the depolarization phase of the action potential.
C) prevent graded potentials.
D) increase the release of neurotransmitter molecules.
E) have most of its effects on the dendritic region of a neuron.
23) After the depolarization phase of an action potential, the resting potential is restored by
A) the opening of voltage-gated sodium channels.
B) the opening of voltage-gated potassium channels and the closing of sodium channels.
C) a decrease in the membrane’s permeability to potassium and chloride ions.
D) a brief inhibition of the sodium-potassium pump.
E) the opening of more voltage-gated sodium channels.
24) The “undershoot” phase of after-hyperpolarization is due to
A) slow opening of voltage-gated sodium channels.
B) sustained opening of voltage-gated potassium channels.
C) rapid opening of voltage-gated calcium channels.
D) slow restorative actions of the sodium-potassium ATPase.
E) ions that move away from their open ion channels.
25) Immediately after an action potential passes along an axon, it is not possible to generate a
second action potential; thus, we state that the membrane is briefly
A) refractory.
B) fully depolarized.
C) above threshold.
D) at the equilibrium potential.
26) An action potential can start in the middle of an axon and proceed to both opposite directions
when
A) the neuron is an inhibitory neuron and operating normally.
B) only the middle section of the axon has been artificially stimulated by an electrode.
C) the dendritic region fires an action potential.
D) it is in its typical refractory state.
E) its membrane potential is above the threshold.
27) The fastest possible conduction velocity of action potentials is observed in
A) thin, nonmyelinated neurons.
B) thin, myelinated neurons.
C) thick, nonmyelinated neurons.
D) thick, myelinated neurons.
28) In the sequence of permeability changes for a complete action potential, the first of these
events that occurs is the
A) activation of the sodium-potassium “pump.”
B) inhibition of the sodium-potassium “pump.”
C) opening of voltage-gated sodium channels.
D) closing of voltage-gated potassium channels.
E) opening of voltage-gated potassium channels.
29) Saltatory conduction is a term applied to
A) conduction of impulses across electrical synapses.
B) an action potential that skips the axon hillock when it moves from the dendritic region to the
axon terminal.
C) the rapid movement of an action potential reverberating back and forth along a neuron.
D) jumping from one neuron to an adjacent neuron.
E) jumping from one node of Ranvier to the next in a myelinated neuron.
30) Two fundamental principles that characterize gated ion channels in the neuronal membrane
are that the channels
A) are always open, but the concentration gradients of ions frequently change.
B) are always closed, but ions move closer to the channels during excitation.
C) open and close depending on stimuli and are specific as to which ion can traverse them.
D) open and close depending on chemical messengers and are nonspecific as to which ion can
traverse them.
E) open in response to stimuli and then close simultaneously, in unison.
31) Researchers created a genetic strain of mice that were lacking both genes for MyRF, a
transcription factor that is required for oligodendrocytes to function normally. What is the most
likely effect that this would have on the mice?
A) loss of salutatory conduction
B) thicker myelin sheaths
C) impaired ability for potassium ions to cross neuronal membranes
D) growth of dendrites
32) Action potentials are normally carried in only one direction: from the axon hillock toward
the axon terminals. If you experimentally depolarize the middle of the axon to threshold, then
A) no action potential will be initiated.
B) an action potential will be initiated and proceed only in the normal direction toward the axon
terminal.
C) an action potential will be initiated and proceed only back toward the axon hillock.
D) two action potentials will be initiated, one going toward the axon terminal and one going back
toward the hillock.
E) an action potential will be initiated, but it will die out before it reaches the axon terminal.
33) The nervous system can alter the activities of skeletal muscle fibers because
A) it is electrically coupled by gap junctions to the muscles.
B) its signals bind to receptor proteins on the muscles.
C) its signals reach the muscles via the blood.
D) its light pulses activate contraction in the muscles.
E) it is connected to the internal neural network of the muscles.
34) In a simple synapse, neurotransmitter chemicals are received by
A) the postsynaptic dendritic membrane.
B) the presynaptic membrane.
C) axon hillocks.
D) cell bodies.
35) The surface on a neuron that discharges the contents of synaptic vesicles is the
A) dendrite.
B) axon hillock.
C) node of Ranvier.
D) postsynaptic membrane.
E) presynaptic membrane.
36) Neural transmission across a mammalian synapse is accomplished by
A) the movement of sodium and potassium ions from the presynaptic neuron into the
postsynaptic neuron.
B) impulses traveling as electrical currents across the synapse.
C) impulses causing the release of a chemical signal and its diffusion across the synapse.
D) impulses ricocheting back and forth across the synapse.
E) the movement of calcium ions from the presynaptic into the postsynaptic neuron.
37) The observation that the acetylcholine released into the junction between a motor neuron and
a skeletal muscle binds to a sodium channel and opens it is an example of a
A) voltage-gated sodium channel.
B) voltage-gated potassium channel.
C) ligand-gated sodium channel.
D) second-messenger-gated sodium channel.
E) chemical that inhibits action potentials.
38) An inhibitory postsynaptic potential (IPSP) occurs in a membrane made more permeable to
A) potassium ions.
B) sodium ions.
C) calcium ions.
D) ATP.
39) The following steps refer to various stages in transmission at a chemical synapse.
1. Neurotransmitters bind with receptors associated with the postsynaptic membrane.
2. Calcium ions rush into the neuron’s cytoplasm.
3. An action potential depolarizes the membrane of the axon terminal.
4. The ligand-gated ion channels open.
5. The synaptic vesicles release neurotransmitters into the synaptic cleft.
Which sequence of events is correct?
A) 1 → 2 → 3 → 4 → 5
B) 2 → 3 → 5 → 4 → 1
C) 3 → 2 → 5 → 1 → 4
D) 4 → 3 → 1 → 2 → 5
E) 5 → 1 → 2 → 4 → 3
40) The activity of acetylcholine in a synapse is terminated by its
A) active transport out of the synaptic cleft.
B) diffusion across the presynaptic membrane.
C) active transport across the postsynaptic membrane.
D) diffusion across the postsynaptic membrane.
E) degradation by a hydrolytic enzyme in the synaptic cleft.
41) Ionotropic receptors are found at synapses operated via
A) ligand-gated ion channels.
B) metabotropic receptors.
C) inhibitory, but not excitatory, synapses.
D) excitatory, but not inhibitory, synapses.
42) Neurotransmitters categorized as inhibitory are expected to
A) act independently of their receptor proteins.
B) close potassium channels.
C) open sodium channels.
D) close chloride channels.
E) hyperpolarize the membrane.
43) When several excitatory postsynaptic potentials (EPSPs) arrive at the axon hillock from
different dendritic locations and then depolarize the postsynaptic cell to threshold for an action
potential, this is an example of
A) temporal summation.
B) spatial summation.
C) a normal action potential.
D) an action potential with an abnormally high peak of depolarization.
44) When several inhibitory postsynaptic potentials (IPSPs) arrive at the axon hillock rapidly in
sequence from a single dendritic location, hyperpolarizing the postsynaptic cell more and more
and thus preventing an action potential, this is an example of
A) temporal summation.
B) spatial summation.
C) a normal action potential.
D) an action potential with an abnormally high peak of depolarization.
45) Assume that a single IPSP has a negative magnitude of -0.5 mV at the axon hillock and that a
single EPSP has a positive magnitude of +0.5 mV. For a neuron with an initial membrane
potential of -70 mV, the net effect of the simultaneous arrival of six IPSPs and two EPSPs would
be to move the membrane potential to
A) -72 mV.
B) -71 mV.
C) -70 mV.
D) -69 mV.
E) -68 mV.
46) Receptors for neurotransmitters are of primary functional importance in assuring one-way
synaptic transmission because they are mostly found on the
A) axonal membrane.
B) axon hillock.
C) postsynaptic dendritic membrane.
D) presynaptic membrane.
47) Functionally, which cellular location is the neuron’s “decision-making site” as to whether or
not an action potential will be initiated?
A) axonal membrane
B) axon hillock
C) dendritic membrane
D) presynaptic membrane
48) Neurotransmitters affect postsynaptic cells by
A) initiating signal transduction pathways in the cells.
B) causing molecular changes in the cells.
C) affecting ion-channel proteins.
D) altering the permeability of the cells.
E) all of the above.