Deck 48: Neurons, Synapses, and Signalling

Question 1

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 1

D

Question 2

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.

Answer 2

B

Question 3

Which is the correct order for processing and integrating sensory stimuli?

A)stimuli → sensory neuron → sensory nerve → CNS → PNS
B)stimuli → sensory nerve → sensory neuron → PNS → CNS
C)stimuli → sensory neuron → sensory nerve → PNS → CNS
D)stimuli → sensory nerve → sensory neuron → CNS → PNS
E)sensory nerve → stimuli → sensory neuron → PNS → CNS

Answer 3

C

Question 4

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 5

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 6

The point of connection between two communicating neurons is called

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

Question 7

The somatic nervous system can alter the activities of its targets, the skeletal muscle fibres, 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 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 centre.
D)has information flow in only one direction: away from an integrating centre.
E)includes sensory information, an integrating centre, and effectors.

Question 9

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 10

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 11

In certain large animals, this type of neuron can extend beyond 1 metre in length.

A)glial cell in the brain
B)a sensory neuron
C)an interneuron
D)a glial cell at a ganglion
E)a neuron that controls eye movements

Question 12

Most of the neurons in the human brain are

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

Question 13

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 14

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 15

In the communication between a motor neuron and a skeletal muscle

A)the motor neuron is considered the presynaptic cell and the skeletal muscle is the postsynaptic cell.
B)the motor neuron is considered the postsynaptic cell and the skeletal muscle is the presynaptic cell.
C)action potentials are possible on the motor neuron but not the skeletal muscle.
D)action potentials are possible on the skeletal muscle but not the motor neuron.
E)the motor neuron fires action potentials but the skeletal muscle is not electrochemically excitable.

Question 16

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⁺.

Question 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

A)the depolarization of the neuron.
B)the hyperpolarization of the neuron.
C)the replacement of potassium ions with sodium ions.
D)the replacement of potassium ions with calcium ions.
E)the neuron switching on its sodium-potassium pump to restore the initial conditions.

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

In a typical mammalian cell, if the [K⁺]ₒᵤtsᵢdₑ = 5mM and [K⁺]ᵢnsᵢdₑ = 140mM, what is the Nernst potential?

A)+62mV
B)-90mV
C)+90mV
D)-62mV
E)-1.4mV

Question 20

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 21

A "resting" motor neuron is expected to

A)release lots of acetylcholine.
B)have high permeability to sodium ions.
C)be equally permeable to sodium and potassium ions.
D)exhibit a resting potential that is more negative than the "threshold" potential.
E)have a higher concentration of sodium ions on the inside of the cell than on the outside.

Question 22

Neurotransmitters are released from axon terminals via

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

Question 23

One possible disadvantage to a nerve net is that it might conduct impulses in two directions from the point of the stimulus. 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 24

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 25

Neural transmission across a mammalian synaptic gap is accomplished by

A)the movement of sodium and potassium ions from the presynaptic neuron into the postsynaptic neuron.
B)impulses travelling as electrical currents across the gap.
C)impulses causing the release of a chemical signal and its diffusion across the gap.
D)impulses ricocheting back and forth across the gap.
E)the movement of calcium ions from the presynaptic into the postsynaptic neuron.

Question 26

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 27

In response to a stimulus, Na⁺ and K⁺ channels open, allowing for depolarization. The channels respond independently, with

A)both Na⁺ and K⁺ channels opening simultaneously and both remaining active until the end of the action potential.
B)the K⁺ channel opening first, then the Na⁺ channel opening, and only the Na⁺ channel remaining active until the end of the action potential.
C)the Na⁺ channel opening first, then K⁺ channel opening and only the K⁺ channel remaining active until the end of the action potential.
D)both Na⁺ and K⁺ channels opening simultaneously, with the K⁺ channel closing before the Na⁺ channel.
E)the Na⁺ channel opening first, then the K⁺ channel opening, and both remaining active until the end of the action potential.

Question 28

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 29

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 30

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 31

The fastest possible conduction velocity of action potentials is observed in

A)thin, non-myelinated neurons.
B)thin, myelinated neurons.
C)thick, non-myelinated neurons.
D)thick, myelinated neurons.

Question 32

Upon pricking your finger with a pin, which of the following variables change during the conduction of the produced action potential?

A)magnitude
B)frequency
C)duration
D)amplitude
E)threshold

Question 33

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)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 34

When Na⁺ moves into a cell and K⁺ moves out of a cell, this activates which type of gated ion channel?

A)voltage-gated ion channel
B)ligand-gated ion channel
C)stretch-activated ion channel
D)temperature-gated channel
E)mechanosensitive ion channels

Question 35

In the sequence of permeability changes for a complete action potential, the first of these events that occurs is

A)the activation of the sodium-potassium "pump."
B)the inhibition of the sodium-potassium "pump."
C)the opening of voltage-gated sodium channels.
D)the closing of voltage-gated potassium channels.
E)the opening of voltage-gated potassium channels.

Question 36

The primary means by which a neuron can communicate to a second neuron is by

A)the frequency of its action potentials.
B)the peak of the depolarization phase of an action potential.
C)the peak of the undershoot/hyperpolarization of an action potential.
D)varying how much neurotransmitter it releases for a given action potential.
E)remaining in the depolarization phase of the action potential for an extended interval.

Question 37

Action potentials move along axons

A)more slowly in axons of large than 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 non-myelinated axons.
E)by reversing the concentration gradients for sodium and potassium ions.

Question 38

The "threshold" potential of a membrane

A)is the point of separation from a living to a dead neuron.
B)is the lowest frequency of action potentials a neuron can produce.
C)is the minimum hyperpolarization needed to prevent the occurrence of action potentials.
D)is the minimum depolarization needed to operate the voltage-gated sodium and potassium channels.
E)is the peak amount of depolarization seen in an action potential.

Question 39

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 40

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 41

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 42

An example of the action of metabotropic receptors occurs when

A)voltage-gated ion channels open.
B)voltage-gated ion channels close.
C)acetylcholine-gated sodium channels open.
D)cAMP-linked ion channels open.
E)the undershoot/after-hyperpolarization occurs.

Question 43

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 44

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)a voltage-gated potassium channel.
C)a ligand-gated sodium channel.
D)a second-messenger-gated sodium channel.
E)a chemical that inhibits action potentials.

Question 45

The major inhibitory neurotransmitter of the human brain is

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

Question 46

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 47

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 48

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 49

Botulinum toxin inhibits the presynaptic release of acetylcholine. If inhibition occurs at a neuromuscular junction, then

A)the synaptic cleft will close.
B)muscle contraction will cease.
C)the post-synaptic cell will die.
D)muscles will spasm.
E)receptor ion channels will remain open.

Question 50

The primary neurotransmitter from the parasympathetic system that influences its autonomic targets is

A)acetylcholine.
B)adenosine.
C)norepinephrine.
D)adrenaline.
E)dopamine.

Question 51

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 52

The activity of acetylcholine in a synapse is terminated by

A)its active transport across the presynaptic membrane.
B)its diffusion across the presynaptic membrane.
C)its active transport across the postsynaptic membrane.
D)its diffusion across the postsynaptic membrane.
E)its degradation by a hydrolytic enzyme on the postsynaptic membrane.

Question 53

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 54

The major excitatory neurotransmitter of the human brain is

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

Question 55

Adjacent neurons with direct (non-neurotransmitter)action potential transfer are said to have electrical synapses, based on the presence of

A)tight junctions at their point of contact.
B)gap junctions at their point of contact.
C)leaky junctions at their point of contact.
D)anchoring junctions at their point of contact.
E)desmosomes at their point of contact.

Question 56

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 57

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 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 58

A neuropeptide that might function as a natural analgesic is

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

Question 59

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 60

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 61

For the following questions, refer to the graph of an action potential.

The membrane's permeability to sodium ions is at its maximum at label

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

Question 62

Use the following information to answer the next few questions.
Over the course of a year, you notice that you are more frequently losing your balance, are unable to keep your train of thought, and occasionally have double vision. After visiting several specialists, you are diagnosed with multiple sclerosis (MS), the hardening and ultimate loss of the myelin sheath which insulates axons.
The onset of these symptoms follows the loss of the myelin sheath, leading to

A)a loss in conduction speed of action potentials
B)an increase in conduction speed of action potentials.
C)consistent depolarization at the nodes of Ranvier.
D)increased saltatory conduction.
E)an increased diameter of the axon.

Question 63

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

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

Question 64

The heart rate decreases in response to the arrival of

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

Question 65

For the following questions, refer to the graph of an action potential.

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 66

Use the following information to answer the next few questions.
The baseball career of Lou Gehrig, a first baseman for the New York Yankees, ended once he became afflicted with amyotrophic lateral sclerosis (ALS). This disease causes the degeneration of motor neurons in the CNS, leading to rapidly progressive weakness, muscle spasticity, and atrophy. Research into the disease has shown that individuals with ALS have higher levels of the neurotransmitter glutamate in their serum and spinal fluid when compared to normal individuals.
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

Question 67

Use the following information to answer the next few questions.
The baseball career of Lou Gehrig, a first baseman for the New York Yankees, ended once he became afflicted with amyotrophic lateral sclerosis (ALS). This disease causes the degeneration of motor neurons in the CNS, leading to rapidly progressive weakness, muscle spasticity, and atrophy. Research into the disease has shown that individuals with ALS have higher levels of the neurotransmitter glutamate in their serum and spinal fluid when compared to normal individuals.
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 68

Use the following information to answer the next few questions.
The baseball career of Lou Gehrig, a first baseman for the New York Yankees, ended once he became afflicted with amyotrophic lateral sclerosis (ALS). This disease causes the degeneration of motor neurons in the CNS, leading to rapidly progressive weakness, muscle spasticity, and atrophy. Research into the disease has shown that individuals with ALS have higher levels of the neurotransmitter glutamate in their serum and spinal fluid when compared to normal individuals.
The excitatory effect of glutamate can be found in

A)postsynaptic cells.
B)the synapse
C)the glia.
D)axon hillocks.
E)the nodes of Ranvier.

Question 69

Use the following information to answer the next few questions.
The baseball career of Lou Gehrig, a first baseman for the New York Yankees, ended once he became afflicted with amyotrophic lateral sclerosis (ALS). This disease causes the degeneration of motor neurons in the CNS, leading to rapidly progressive weakness, muscle spasticity, and atrophy. Research into the disease has shown that individuals with ALS have higher levels of the neurotransmitter glutamate in their serum and spinal fluid when compared to normal individuals.
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 the 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 70

Assume that excessive consumption of ethanol increases the influx of negative chloride ions into "common sense" 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 "common sense" neurons.
B)decreased membrane depolarization of "common sense" neurons.
C)more action potentials in your "common sense" neurons.
D)more EPSPs in your "common sense" neurons.
E)fewer IPSPs in your "common sense" neurons.

Question 71

For the following questions, refer to the graph of an action potential.

The membrane potential is closest to the equilibrium potential for potassium at label

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

Question 72

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 73

The botulinum toxin reduces the synaptic release of

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

Question 74

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 75

Use the following information to answer the next few questions.
The baseball career of Lou Gehrig, a first baseman for the New York Yankees, ended once he became afflicted with amyotrophic lateral sclerosis (ALS). This disease causes the degeneration of motor neurons in the CNS, leading to rapidly progressive weakness, muscle spasticity, and atrophy. Research into the disease has shown that individuals with ALS have higher levels of the neurotransmitter glutamate in their serum and spinal fluid when compared to normal individuals.
Temporal summation always involves

A)both inhibitory and excitatory inputs.
B)synapses at more than one site.
C)inputs that are not simultaneous.
D)electrical synapses.
E)multiple inputs at a single synapse.

Question 76

Use the following information to answer the next few questions.
The baseball career of Lou Gehrig, a first baseman for the New York Yankees, ended once he became afflicted with amyotrophic lateral sclerosis (ALS). This disease causes the degeneration of motor neurons in the CNS, leading to rapidly progressive weakness, muscle spasticity, and atrophy. Research into the disease has shown that individuals with ALS have higher levels of the neurotransmitter glutamate in their serum and spinal fluid when compared to normal individuals.
Riluzole, an approved drug for ALS, blocks glutamate transporters, which inhibits the activation of

A)voltage-gated ion channels.
B)ligand-gated channels.
C)stretch-activated ion channels.
D)temperature-gated channels.
E)mechanosensitive ion channels.

Question 77

For the following questions, refer to the graph of an action potential.

The neuronal membrane is at its resting potential at label

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

Question 78

For the following questions, refer to the graph of an action potential.

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 79

Use the following information to answer the next few questions.
Over the course of a year, you notice that you are more frequently losing your balance, are unable to keep your train of thought, and occasionally have double vision. After visiting several specialists, you are diagnosed with multiple sclerosis (MS), the hardening and ultimate loss of the myelin sheath which insulates axons.
Neurons and support cells in the CNS have a limited ability to repair themselves; however, those of the PNS have a higher capacity for reparation. To slow or inhibit the breakdown of the myelin sheath, which type of cell could remyelinate the neurons?

A)astrocytes
B)oligodendrocytes
C)microglia
D)Schwann cells
E)ependymal cells

Question 80

Use the following information to answer the next few questions.
The baseball career of Lou Gehrig, a first baseman for the New York Yankees, ended once he became afflicted with amyotrophic lateral sclerosis (ALS). This disease causes the degeneration of motor neurons in the CNS, leading to rapidly progressive weakness, muscle spasticity, and atrophy. Research into the disease has shown that individuals with ALS have higher levels of the neurotransmitter glutamate in their serum and spinal fluid when compared to normal individuals.
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.