Deck 37: Neurons, Synapses, and Signaling

Question 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.

Answer 1

E

Question 2

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.

Answer 2

D

Question 3

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.

Answer 3

C

Question 4

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.

Question 5

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.

Question 6

In a simple synapse, neurotransmitter chemicals are released by

A) the dendritic membrane.
B) the presynaptic membrane.
C) axon hillocks.
D) cell bodies.

Question 7

The point of connection between two communicating neurons is called the

A) axon hillock.
B) dendrite.
C) synapse.
D) cell body.
E) axon.

Question 8

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.

Question 9

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.

Question 10

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

Question 11

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

Question 12

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+.

Question 13

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.

Question 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.

Question 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 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.

Question 16

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+.

Question 17

Most of the neurons in the human brain are

A) sensory neurons.
B) motor neurons.
C) interneurons.
D) nerves.

Question 18

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.

Question 19

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.

Question 20

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.

Question 21

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.

Question 22

In a simple synapse, neurotransmitter chemicals are received by

A) the postsynaptic dendritic membrane.
B) the presynaptic membrane.
C) axon hillocks.
D) cell bodies.

Question 23

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.

Question 24

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.

Question 25

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.

Question 26

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.

Question 27

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.

Question 28

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.

Question 29

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.

Question 30

An inhibitory postsynaptic potential (IPSP) occurs in a membrane made more permeable to

A) potassium ions.
B) sodium ions.
C) calcium ions.
D) ATP.

Question 31

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.

Question 32

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

Question 33

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.

Question 34

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.

Question 35

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

Question 36

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.

Question 37

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.

Question 38

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.

Question 39

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.

Question 40

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.

Question 41

Most of the synapses in vertebrates conduct information in only one direction

A) as a result of the nodes of Ranvier.
B) as a result of voltage-gated sodium channels found only in the vertebrate system.
C) because vertebrate nerve cells have dendrites.
D) because only the postsynaptic cells can bind and respond to neurotransmitters.
E) because the sodium-potassium pump moves ions in one direction.

Question 42

The botulinum toxin inhibits the synaptic release of

A) acetylcholine.
B) epinephrine.
C) endorphin.
D) nitric oxide.
E) GABA.

Question 43

Please use the following information to answer the question(s) below.
Curare is a potent neurotoxin extracted from the Strychnos toxifera plant in Central and South America. Indigenous peoples of South America apply curare to arrows, which they used to hunt and kill animals. Curare acts at synapses between motor neurons and skeletal muscle cells. When a motor neuron synapses with a skeletal muscle cell, the skeletal muscle cell may be stimulated or inhibited just like postsynaptic neurons are. Curare acts by binding temporarily to acetylcholine receptors on the postsynaptic cell and prevents acetylcholine from binding.
Which of the following could be an effective treatment for curare poisoning?

A) a drug that promotes acetylcholine reuptake into the presynaptic cells
B) a drug that removes acetylcholine receptors from the postsynaptic cell
C) a drug that inhibits acetylcholinesterase
D) a drug that activates acetylcholinesterase

Question 44

Motor neurons alter skeletal muscle activities by releasing neurotransmitters because

A) they are electrically coupled by gap junctions to the muscles.
B) their signals bind to receptor proteins on the muscles.
C) their signals reach the muscles via the blood.
D) their light pulses activate contraction in the muscles.
E) they are connected to the internal neural network of the muscles.

Question 45

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.

Question 46

An amino acid that operates at inhibitory synapses in the brain is

A) acetylcholine.
B) epinephrine.
C) endorphin.
D) nitric oxide.
E) GABA.

Question 47

A neuropeptide that might function as a natural analgesic is

A) acetylcholine.
B) epinephrine.
C) endorphin.
D) nitric oxide.
E) GABA.

Question 48

The heart rate decreases in response to the arrival of

A) acetylcholine.
B) epinephrine.
C) endorphin.
D) nitric oxide.
E) GABA.

Question 49

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.

Question 50

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.

Question 51

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.

Question 52

The major inhibitory neurotransmitter of the human brain is

A) acetylcholine.
B) epinephrine.
C) glutamate.
D) nitric oxide.
E) GABA.

Question 53

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.

Question 54

Please use the following information to answer the question(s) below.
Curare is a potent neurotoxin extracted from the Strychnos toxifera plant in Central and South America. Indigenous peoples of South America apply curare to arrows, which they used to hunt and kill animals. Curare acts at synapses between motor neurons and skeletal muscle cells. When a motor neuron synapses with a skeletal muscle cell, the skeletal muscle cell may be stimulated or inhibited just like postsynaptic neurons are. Curare acts by binding temporarily to acetylcholine receptors on the postsynaptic cell and prevents acetylcholine from binding.
What effect does curare likely have on the postsynaptic cell?

A) prevents voltage-gated sodium channels from opening
B) hyperpolarizes the postsynaptic cell
C) stimulates muscle contraction
D) depolarizes the presynaptic cell

Question 55

Assume that excessive consumption of ethanol increases the influx of negative chloride ions into "commonsense" neurons whose action potentials are needed for you to act appropriately and not harm yourself or others. Thus, any resulting poor decisions associated with ethanol ingestion are likely due to

A) increased membrane depolarization of "commonsense" neurons.
B) increased membrane hyperpolarization of "commonsense" neurons.
C) more action potentials in your "commonsense" neurons.
D) more EPSPs in your "commonsense" neurons.
E) fewer IPSPs in your "commonsense" neurons.

Question 56

A chemical that affects neuronal function but is not stored in presynaptic vesicles is

A) acetylcholine.
B) epinephrine.
C) endorphin.
D) nitric oxide.
E) GABA.

Question 57

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

Question 58

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.

Question 59

Figure 37.1
In Figure 37.1, the membrane potential is closest to the equilibrium potential for potassium at label

A) A.
B) B.
C) C.
D) D.
E) E.

Question 60

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.

Question 61

In Figure 37.1, the neuronal membrane is at its resting potential at label

A) A.
B) B.
C) C.
D) D.
E) E.

Question 62

Please use the following information to answer the question(s) below.
The Arizona bark scorpion is the most venomous scorpion in North America, and its bite will cause extensive pain to a human that lasts up to three days. However, the southern grasshopper mouse is essentially immune to the sting of this scorpion and actually eats the scorpions as prey. Researchers have recently elucidated the neuronal reason for why the southern grasshopper mouse does not feel pain from bark scorpion venom.
The southern grasshopper mouse essentially does not feel pain when stung by the bark scorpion. What type of neuron is most likely blocked in this scenario?

A) interneuron
B) motor neuron
C) sensory neuron
D) glial cells

Question 63

Please use the following information to answer the question(s) below.
The Arizona bark scorpion is the most venomous scorpion in North America, and its bite will cause extensive pain to a human that lasts up to three days. However, the southern grasshopper mouse is essentially immune to the sting of this scorpion and actually eats the scorpions as prey. Researchers have recently elucidated the neuronal reason for why the southern grasshopper mouse does not feel pain from bark scorpion venom.
When mice feel pain on their bodies, they lick that part of their body. Researchers injected bark scorpion venom into the hind paws of the common house mouse and the southern grasshopper mouse; they also injected 0.9% saline (essentially salt water) as a control. The researchers then observed how long the mice licked their paws. What data do you think the researchers collected?

A) A
B) B
C) C
D) D

Question 64

Which of the following is a direct result of depolarizing the presynaptic membrane of an axon terminal?

A) Voltage-gated calcium channels in the membrane open.
B) Synaptic vesicles fuse with the membrane.
C) Ligand-gated channels open, allowing neurotransmitters to enter the synaptic cleft.
D) An EPSP or IPSP is generated in the postsynaptic cell.

Question 65

In Figure 37.1, the minimum graded depolarization needed to operate the voltage-gated sodium and potassium channels is indicated by the label

A) A.
B) B.
C) C.
D) D.
E) E.

Question 66

What happens when a resting neuron's membrane depolarizes?

A) There is a net diffusion of Na+ out of the cell.
B) The equilibrium potential for K+ (EK) becomes more positive.
C) The neuron's membrane voltage becomes more positive.
D) The cell's inside is more negative than the outside.

Question 67

Suppose a particular neurotransmitter causes an IPSP in postsynaptic cell X and an EPSP in postsynaptic cell Y. A likely explanation is that

A) the threshold value in the postsynaptic membrane is different for cell X and cell Y.
B) the axon of cell X is myelinated, but that of cell Y is not.
C) only cell Y produces an enzyme that terminates the activity of the neurotransmitter.
D) cells X and Y express different receptor molecules for this particular neurotransmitter.

Question 68

Researchers injected bark scorpion venom in mouse neurons (both a common house mouse and the southern grasshopper mouse) and measured the flow of sodium ions across the cell membrane. Their data is shown below. Based on these data, what effect do you think the venom is having on the grasshopper mouse?

A) The venom is blocking voltage-gated sodium channels.
B) The venom is blocking voltage-gated potassium channels.
C) The venom is opening voltage-gated sodium channels.
D) The venom is opening voltage-gated potassium channels.

Question 69

Researchers injected bark scorpion venom in mouse neurons (both a common house mouse and the southern grasshopper mouse) and measured how many action potentials were generated after the venom was introduced. Their data is shown below. Based on these data, what effect do you think the venom is having on the grasshopper mouse?

A) The venom is blocking voltage-gated sodium channels.
B) The venom is blocking voltage-gated potassium channels.
C) The venom is opening voltage-gated sodium channels.
D) The venom is opening voltage-gated potassium channels.

Question 70

The period in which voltage-gated potassium channels are open and hyperpolarization has yet to occur is at label

A) A.
B) B.
C) C.
D) D.
E) E.

Question 71

Where are neurotransmitter receptors located?

A) the nuclear membrane
B) the nodes of Ranvier
C) the postsynaptic membrane
D) synaptic vesicle membranes

Question 72

Figure 37.2
Figure 37.2 shows many channels in a cell membrane. The channel third from the left is a voltage-gated sodium channel. What would happen if this channel became blocked and thus unable to function?

A) The cell's membrane potential would not change.
B) The cell would hyperpolarize.
C) The cell would depolarize.
D) There is not enough information to make a conclusion.

Question 73

Why are action potentials usually conducted in one direction?

A) Ions can flow along the axon in only one direction.
B) Voltage-gated Na+ channels are inactivated during the refractory period.
C) The axon hillock has a higher membrane potential than the terminals of the axon.
D) Voltage-gated channels for both Na+ and K+ open in only one direction.

Question 74

In Figure 37.1, the membrane's permeability to sodium ions is at its maximum at label

A) A.
B) B.
C) C.
D) D.
E) E.

Question 75

In Figure 37.1, at what point in the graph are sodium channels closed (or closing) and potassium channels opened?

A) A.
B) B.
C) C.
D) D.
E) E.

Question 76

A common feature of action potentials is that they

A) cause the membrane to hyperpolarize and then depolarize.
B) can undergo temporal and spatial summation.
C) are triggered by a depolarization that reaches threshold.
D) move at the same speed along all axons.