Deck 37: Neurons, Synapses, and Signaling

Question 1

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) Ca++.
D) Na+.
E) K+.

Answer 1

E

Question 2

The nucleus and most of the organelles in a neuron are located in the

A) dendritic region.
B) axon hillock.
C) axon.
D) cell body.
E) axon terminals.

Answer 2

D

Question 3

The point of connection between two communicating neurons is called the

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

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

Self-propagation and refractory periods are typical of

A) action potentials.
B) graded hyperpolarizations.
C) excitatory postsynaptic potentials.
D) threshold potentials.
E) resting potentials.

Question 6

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 7

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 8

A simple nervous system

A) must include chemical senses, mechanoreception, and vision.
B) includes a minimum of 12 effector neurons.
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.

Question 9

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 10

ATP hydrolysis directly powers the movement of

A) K+ out of cells.
B) Na+ out of cells.
C) Na+ into cells.
D) Ca++ into cells.
E) Cl- into cells.

Question 11

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 12

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 Ca++.
E) increasing its membrane's permeability to K+.

Question 13

Most of the neurons in the human brain are

A) sensory neurons.
B) motor neurons.
C) interneurons.
D) auditory neurons.
E) peripheral neurons.

Question 14

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 15

In a simple synapse, neurotransmitter chemicals are released by

A) the dendritic membrane.
B) the presynaptic membrane.
C) axon hillocks.
D) cell bodies.
E) ducts on the smooth endoplasmic reticulum.

Question 16

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 17

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.

Question 18

After the depolarization phase of an action potential, the resting potential is restored by

A) the opening of sodium activation gates.
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 19

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 20

The "threshold" potential of a membrane is the

A) point of separation from a living to a dead neuron.
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 21

The activity of acetylcholine in a synapse is terminated by its

A) active transport across the presynaptic membrane.
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 on the postsynaptic membrane.

Question 22

Saltatory conduction is a term applied to

A) conduction of impulses across electrical synapses.
B) an action potential that skips the axon hillock in moving 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 23

The release of acetylcholine from the terminal of a motor neuron is most directly linked to the

A) entry of potassium into the axon terminal.
B) exit of potassium from the axon terminal.
C) entry of sodium into the axon terminal.
D) exit of sodium from the axon terminal.
E) entry of calcium into the axon terminal.

Question 24

An action potential can start in the middle of an axon and proceed in 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 25

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 26

An example of ligand-gated ion channels is

A) the spreading of action potentials in the heart.
B) acetylcholine receptors at the neuromuscular junction.
C) cAMP-dependent protein kinases.
D) action potentials on the axon.
E) graded hyperpolarization.

Question 27

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 28

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 29

The following steps refer to various stages in transmission at a chemical synapse. 1. Neurotransmitter binds 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 neurotransmitter 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 30

Neurotransmitters are released from axon terminals via

A) osmosis.
B) active transport.
C) diffusion.
D) transcytosis.
E) exocytosis.

Question 31

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 32

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

A) potassium ions.
B) sodium ions.
C) calcium ions.
D) ATP.
E) all neurotransmitter molecules.

Question 33

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 34

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 35

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) hyperexcitable.
B) refractory.
C) fully depolarized.
D) above threshold.
E) at the equilibrium potential.

Question 36

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 37

Ionotropic receptors are found at synapses operated via

A) ligand-gated ion channels.
B) second-messenger-gated ion channels.
C) electrical synapses.
D) inhibitory, but not excitatory, synapses.
E) excitatory, but not inhibitory, synapses.

Question 38

The somatic nervous system can alter the activities of its targets, the 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 39

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 40

In a simple synapse, neurotransmitter chemicals are received by

A) the dendritic membrane.
B) the presynaptic membrane.
C) axon hillocks.
D) cell bodies.
E) ducts on the smooth endoplasmic reticulum.

Question 41

When several 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) tetanus.
D) the refractory state.
E) an action potential with an abnormally high peak of depolarization.

Question 42

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 43

A neuropeptide that might function as a natural analgesic is

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

Question 44

The major inhibitory neurotransmitter of the human brain is

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

Question 45

For the following questions, refer to the graph of an action potential in Figure 37.1.
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 46

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 these options are correct.

Question 47

For the following questions, refer to the graph of an action potential in Figure 37.1.
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 48

For the following questions, refer to the graph of an action potential in Figure 37.1.
Figure 37.1
The neuronal membrane is at its resting potential at label

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

Question 49

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 50

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

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

Question 51

Functionally, which cellular location is the neuron's "decision-making site" as to whether or not an action potential will be initiated?

A) axonal membranes
B) axon hillocks
C) dendritic membranes
D) mitochondrial membranes
E) presynaptic membranes

Question 52

When several EPSPs arrive at the axon hillock from different dendritic locations, depolarizing the postsynaptic cell to threshold for an action potential, this is an example of

A) temporal summation.
B) spatial summation.
C) tetanus.
D) the refractory state.
E) an action potential with an abnormally high peak of depolarization.

Question 53

For the following questions, refer to the graph of an action potential in Figure 37.1.
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 54

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 55

The botulinum toxin reduces the synaptic release of

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

Question 56

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) dendritic membrane.
D) mitochondrial membrane.
E) presynaptic membrane.

Question 57

For the following questions, refer to the graph of an action potential in Figure 37.1.
Figure 37.1
The cell is not hyperpolarized; however, repolarization is in progress, as the sodium channels are closing or closed, and many potassium channels have opened, at label

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

Question 58

The heart rate decreases in response to the arrival of

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

Question 59

For the following questions, refer to the graph of an action potential in Figure 37.1.
Figure 37.1
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 60

Motor neurons alter skeletal muscle activities by releasing neurotransmitter 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 61

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, using an electronic probe, 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 62

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.
E) require the diffusion of Na+ and K+ through ligand-gated channels to propagate.

Question 63

Why are action potentials usually conducted in one direction?

A) The nodes of Ranvier conduct potentials in one direction.
B) The brief refractory period prevents reopening of voltage gated Na+ channels.
C) The axon hillock has a higher membrane potential than the terminals of the axon.
D) Ions can flow along the axon in only one direction.
E) Voltage-gated channels for both Na+ and K+ open in only one direction.

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) The postsynaptic cell produces an action potential.
D) Ligand-gated channels open, allowing neurotransmitters to enter the synaptic cleft.
E) An EPSP or IPSP is generated in the postsynaptic cell.

Question 65

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 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 neuron is less likely to generate an action potential.
E) 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) cell Y forms chemical synapses, whereas cell X forms electrical synapses.
C) the axon of cell X is myelinated, but that of cell Y is not.
D) only cell Y produces an enzyme that terminates the activity of the neurotransmitter.
E) cells X and Y express different receptor molecules for this particular neurotransmitter.

Question 68

Where are neurotransmitter receptors located?

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