Florida International University

BIO PCB 4023

Chapter 7

1)The central nervous system, which is composed of the brain and spinal cord, receives and processes information from both the external environment, known as            information and, the internal environment, which refers to information.

1. 1. somatic : visceral
   2. sensory : visceral
   3. peripheral : somatic
   4. somatic : autonomic
   5. special : somatic
2. In the peripheral nervous system,     neurons carry sensory and visceral information to the central nervous system, and         neurons leave the central nervous system and innervate organs, which are usually muscles or glands.
   1. efferent : afferent
   2. sensory : somatic
   3. somatic : sensory
   4. sympathetic : parasympathetic
   5. afferent : efferent
3. Which of the following accurately describes afferent neurons?
   1. They transmit information from the periphery to the CNS.
   2. The cell body is located in the ventral horn of the spinal cord.
   3. They are typically multipolar neurons.
   4. They transmit information from the CNS to the periphery.
   5. They are the most abundant class of neurons.
4. What two divisions of the autonomic nervous system have opposite effects on the organs they innervate?
   1. parasympathetic and sympathetic
   2. somatic and enteric
   3. afferent and efferent
   4. somatic and motor
   5. peripheral and central
5. What is the functional unit of the nervous system?
   1. the central nervous system
   2. axons
   3. the brain
   4. neurons
   5. glial cells
6. On what portion of the neuron do action potentials propagate?
   1. cell body B) axon C) soma D) dendrite E) nucleus

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7.               branch from the cell body and receive input from other neurons at specialized junctions called

             .

7. 1. Dendrites : synapses
   2. Somas : synapses
   3. Dendrites : axon terminals
   4. Axon hillocks : axon terminals
   5. Dendrites : cell bodies
8. An action potential originates at the    and travels along the axon until it reaches the  .
   1. dendrite : axon terminal
   2. axon terminal : axon hillock

8. 3. axon hillock : axon terminal
   4. axon hillock : dendrite
   5. dendrite : axon hillock
9. The movement of synaptic vesicles to the end of the axon terminal involves what type of transport?
   1. anterograde
   2. passive
   3. retrograde
   4. pinocytosis
   5. receptor-mediated
10. What type of ion channels in the membrane of neurons allows ions to move across the membrane at rest and thereby contribute to resting membrane potential?
    1. leak channels
    2. resting channels
    3. potential-gated channels
    4. voltage-gated channels
    5. ligand-gated channels
11. What type of ion channels in the membrane of neurons open or close in response to a neurotransmitter binding to its receptor?
    1. potential-gated channels
    2. ligand-gated channels
    3. synaptic channels
    4. leak channels
    5. voltage-gated channels

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12. In a neuron, where is the greatest concentration of voltage-gated sodium and voltage-gated potassium channels?
    1. axon terminal
    2. axon hillock
    3. soma
    4. axon
    5. dendrites
13. In a neuron, where are voltage-gated calcium channels located?
    1. axon hillock
    2. axon terminal
    3. soma
    4. axon
    5. dendrites
14. What is the structural classification of a neuron composed of a single axon and a number of dendritic projections from the nerve cell body?
    1. unipolar
    2. bipolar
    3. pseudo-unipolar
    4. multipolar
    5. polar
15. A group of nerve cell bodies in the peripheral nervous system are referred to as
    1. tracts.
    2. commissures.
    3. nuclei.
    4. pathways.

15. 5. ganglia.
16. What functional class of neurons accounts for 99 percent of the neurons in the body processing sensory information and carrying out complex functions?
    1. bipolar
    2. interneurons
    3. efferent
    4. visceral
    5. afferent  3
17. What type of cell enhances the velocity of electrical transmission of an action potential along an axon in the central nervous system?
    1. astrocyte
    2. oligodendrocyte
    3. ependymal cell
    4. microglia
    5. Schwann cell
18. Which of the following best describes the function of the myelin sheath?
    1. decrease ion permeability in the nodes of Ranvier
    2. increase a membrane's ion permeability
    3. reduce a membrane's ion permeability
    4. increase leakage of ions across the membrane
    5. decrease axonal conduction velocity
19. Most neurons have a resting membrane potential of

A) -70 mV. B) +30 mV. C) +100 mV. D) -55 mV. E) -5 mV.

20. Which of the following is the correct term for the movement of an electrical charge across a membrane?
    1. current
    2. transistor
    3. resistance
    4. capacitance
    5. potential difference
21. Which of the following determines the resistance to an ion's movement across a membrane?
    1. ion channels within the membrane
    2. receptors on the cell membrane
    3. enzymes on the surface of the cell membrane
    4. the resting membrane potential
    5. the ions present on either side of the membrane
22. What is the inverse of resistance?
    1. current
    2. impedance
    3. voltage
    4. conductance
    5. flux  4
23. Which of the following best describes the electrochemical forces acting on sodium and potassium ions at the resting membrane potential?
    1. The force on sodium ions is to move into the cell, and the force on potassium ions is to move out of the cell.
    2. Forces on both sodium and potassium ions are to move into the cell.

23. 3. The force on sodium ions is to move out of the cell, and the force on potassium ions is to move into the cell.
    4. Forces on both sodium and potassium ions are to move out of the cell.
    5. There is no force on either ion to move.
24. At the resting membrane potential, the membrane is most permeable to                         , which moves     the cell due to its electrochemical gradient.
    1. sodium : into
    2. sodium : out of
    3. chloride : into
    4. potassium : out of
    5. potassium : into
25. At the resting membrane potential, the electrochemical gradient for sodium across the membrane is such that the net flux for sodium movement is directed      , thereby causing the cell's membrane potential to become more                                .
    1. outward : positive
    2. at equilibrium : positive
    3. inward : positive
    4. outward : negative
    5. inward : negative
26. The              maintains the resting membrane potential.
    1. Na+/K+ pump
    2. Na+/H+ antiporter
    3. Na+/Ca2+ exchanger
    4. action potential
    5. equilibrium potential
27. What equation is used to calculate the membrane potential based on ion concentration gradients and permeabilities?
    1. Fick's equation
    2. Nernst equation
    3. NAD equation
    4. GHK equation
    5. None of the answers is correct.

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28. The fact that a cell has an electrical potential difference across its membrane makes that cell
    1. polarized.
    2. polar.
    3. hyperpolarized.
    4. depolarized.
    5. repolarized.

29. A change in a cell's membrane potential, such that the inside of the cell becomes more positive, is referred to as a                                                                                              whereas if it becomes more negative it is referred to as                                                               .
    1. hyperpolarization : depolarization
    2. hypopolarization : repolarization
    3. depolarization : hyperpolarization
    4. repolarization : resting membrane potential
    5. polarization : depolarization
30. Saxitoxin (STX) is the most well-known paralytic shellfish toxin caused by the phenomenon known as "red tide." Which statement below best describes why this neurotoxin causes paralysis?
    1. It prevents the synaptic vesicles from migrating to the axon terminal; therefore, no action potentials

are generated.

1. 2. It acts on the potassium channels within a neuron, hyperpolarizing the cell membrane; therefore, no action potential can be generated.
   3. It acts by blocking voltage-gated sodium channels which are needed to generate an action potential.
   4. It acts on the hypothalamus of the brain, shutting down all neurological functions.
   5. It blocks ligand-gated channels on the postsynaptic membrane, which blocks signals leaving the central nervous system.

31. What determines the strength of a graded potential?
    1. the diameter of the axon
    2. the size of the stimulus
    3. the amount of cytoplasmic resistance within the soma of the neuron
    4. the amount of leak channels open in the neuron
    5. the amount of voltage-gated channels in the neuron
32. A(n)               is a subthreshold change in membrane potential within the cell body that decays as it travels away from its point of origin.
    1. polarization
    2. graded potential
    3. depolarization
    4. hyperpolarization
    5. action potential

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33. The direction of change in membrane potential, in response to a stimulus that initiates a graded potential, is dependent upon
    1. the gating of sodium channels only.
    2. the ion channels that are opened or closed.
    3. the changes in ion concentration across the membrane.
    4. the gating of potassium channels only.
    5. that membrane's threshold potential.
34. Which statement best describes how graded potentials determine whether an action potential will be generated or not?
    1. when the axon hillock is repolarized
    2. when electrotonic conduction occurs within the soma of the neuron
    3. when an excitatory depolarization reaches threshold
    4. when sodium enters the soma of a cell
    5. when the neuron is hyperpolarized
35. If the soma of a neuron became more permeable to potassium, which statement below best describes the graded potential that would be generated in the soma?
    1. Potassium would enter the cell, causing the membrane to depolarize and reach threshold.
    2. Potassium would reach its equilibrium potential and the voltage inside the cell would not change.
    3. Potassium is a cation; therefore, it would cause an excitatory depolarization.
    4. Potassium is an inhibitory second messenger; therefore, it would cause amplification of the graded potential.
    5. Potassium would leave the cell, causing the membrane to hyperpolarize.
36. When a weak stimulus is applied in rapid succession, it will often reach threshold due to
    1. spatial summation.
    2. excitatory summation.
    3. inhibitory summation.
    4. voltage potential.
    5. temporal summation.

37. Which of the following is an example of spatial summation?
    1. Two rapid stimuli from the same source produce graded potentials on the neurons that sum.
    2. Two action potentials occur at the same time and sum.
    3. An action potential occurs at the same time as a graded potential, and they sum.
    4. Two stimuli from two sources produce graded potentials on the same neuron at the same time such that the two potentials sum.
    5. A neuron sends out information through collaterals to several target cells.

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38. Which of the following changes in membrane potential is considered excitatory?
    1. hyperpolarization only
    2. depolarization only
    3. repolarization only
    4. both hyperpolarization and depolarization
    5. both hyperpolarization and repolarization
39. If the graded potential remains above threshold once it reaches the   , an action potential will be generated.
    1. axon
    2. cell body
    3. axon hillock
    4. nucleus
    5. dendrite
40. The opening of sodium channels causes a rapid of sodium that           the neuron's membrane.
    1. efflux : hyperpolarizes
    2. efflux : depolarizes
    3. influx : repolarizes
    4. influx : depolarizes
    5. influx : hyperpolarizes
41. The depolarization phase of the action potential is generated by a rapid
    1. closure of potassium channels.
    2. opening of sodium channels.
    3. closure of sodium channels.
    4. opening of potassium channels.
    5. opening of chloride channels.
42. The repolarization phase of the action potential in a neuron is driven by the
    1. closure of potassium channels.
    2. opening of calcium channels.
    3. opening of sodium channels.
    4. opening of sodium channels and closure of potassium channels.
    5. closure of sodium channels and opening of potassium channels.
43. The repolarization phase of action potentials in neurons is due primarily to
    1. increased activity of the Na+/K+ pump.
    2. sodium flow out of the cell.
    3. sodium flow into the cell.
    4. potassium flow into the cell.
    5. potassium flow out of the cell.

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44. In myelinated axons, sodium and potassium channels would be concentrated in what area?
    1. axon terminal
    2. dendrites

44. 3. nodes of Ranvier
    4. nucleus
    5. axon hillock
45. The depolarization of the membrane due to a stimulus is a regenerative mechanism meaning that, once sodium gates begin to open, even more sodium gates will be activated leading to a larger inflow of sodium ions and more depolarization until it is terminated when sodium gates close. This is an example of
    1. negative feedback.
    2. positive feedback.
    3. excitatory graded potentials.
    4. electrotonic conduction.
    5. inhibitory graded potentials.
46. A subthreshold stimulus will not generate an action potential whereas a suprathreshold stimulus does generate an action potential. This is an example of
    1. electrotonic conduction.
    2. negative feedback.
    3. the all-or-none principle.
    4. a refractory period.
    5. positive feedback.

47. The magnitude of depolarization at the peak of an action potential is dependent on what factor?
    1. the concentration of sodium and potassium ions
    2. the strength of the electrochemical gradient for sodium and potassium ions relative to their permeability to these ions
    3. the length of the refractory period
    4. the size of the stimulus
    5. the size of the graded potential
48. In order to generate an action potential, the magnitude of the inward sodium current must be large enough to overcome which of the following?
    1. outward sodium current
    2. inward chloride current
    3. outward calcium current
    4. outward potassium current
    5. inward potassium current

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49. During which of the following states are the majority of voltage-gated sodium channels closed and incapable of opening?
    1. at the resting membrane potential
    2. during depolarization
    3. during the absolute refractory period
    4. during the after-hyperpolarization
    5. during the relative refractory period
50. The all-or-none principle, associated with the action potential, states that
    1. there is a positive feedback loop for sodium channels that results in a rapid membrane depolarization.
    2. following an action potential, the membrane will be repolarized by the opening of a potassium channel.
    3. the positive feedback loop for the sodium channel is terminated by the inactivation gate.
    4. once membrane potential reaches threshold, an action potential will be generated and that action potential will always be the same magnitude.
    5. all of the action potentials will be generated from the axon hillock.
51. Toward the end of the relative refractory period, the continued decrease in stimulus intensity required to

initiate an action potential is caused by

51. 1. the number of sodium channels whose inactivation gate has not opened.
    2. decreased sodium permeability.
    3. closure of the sodium activation gate.
    4. decreased potassium permeability.
    5. increased potassium permeability.
52. Which statement below best describes why action potentials travel in only one direction?
    1. The all-or-none principle explains this.
    2. They have a refractory period.
    3. Only sodium- and potassium-gated channels are found on the axon.
    4. The diameter of the axon explains this.
    5. They have myelinated axons.
53. How can action potentials relay information about the intensity of a stimulus, such as distinguishing between a loud and soft sound?
    1. due to the decremental properties of graded potentials
    2. due to the frequency of action potentials
    3. due to electrotonic conduction
    4. due to summation of several action potentials
    5. due to the magnitude of action potentials

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54. What limits the maximum number of action potentials on an axon?
    1. whether the axon is myelinated or not
    2. the concentration of sodium within the cytoplasm of the cell
    3. the diameter of the axon
    4. the absolute refractory period
    5. the relative refractory period
55. For an unmyelinated axon, conduction velocity is primarily determined by the
    1. diameter of the axon.
    2. type of sodium channel activated.
    3. type of potassium channel activated.
    4. number of ion channels present on the membrane.
    5. permeability of the axonal membrane.
56. As an action potential is propagated away from the axon hillock, why does propagation continue in one direction?
    1. The region just in front of the action potential is in the relative refractory period.
    2. The region just behind the action potential is in the relative refractory period.
    3. The region just behind the action potential is in the absolute refractory period.
    4. They will travel the path of least resistance.
    5. The region just in front of the action potential is in the absolute refractory period.
57.               is the mechanism by which action potentials are propagated in unmyelinated axons.
    1. After-hyperpolarization
    2. Electrotonic conduction
    3. The all-or-none principle
    4. The regenerative mechanism
    5. Temporal summation
58. In myelinated nerve fibers, where do action potentials occur?
    1. nodes of Ranvier
    2. Schwann cell
    3. oligodendrocyte

58. 4. cell body
    5. underlying myelin sheath
59. The jumping of an action potential from node-to-node is called
    1. propagation.
    2. nodal conduction.
    3. nodal propagation.
    4. electrotonic conduction.
    5. saltatory conduction.

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60. Which of the following axons would have the fastest conduction velocity?
    1. diameter = 1 micron, myelinated
    2. diameter = 20 microns, myelinated
    3. diameter = 5 microns, unmyelinated
    4. diameter = 20 microns, unmyelinated
    5. diameter = 5 microns, myelinated
61. Which statement best describes how local anesthetics such as Novocaine work in numbing neurons?
    1. by making the cell membrane more permeable to sodium
    2. by blocking voltage-gated sodium channels
    3. by blocking voltage-gated potassium channels
    4. by making the cell membrane more permeable to potassium
    5. by binding to the enzyme sodiumase
62. Which of the following are common symptoms of peripheral neuropathy?
    1. numbness of the tongue, jaw, and ears
    2. dizziness, diarrhea, indigestion and impotence
    3. increased heart rate, excessive sweating, and red skin
    4. confusion, excessive thirst, dehydration, and frequent urination
    5. numbness, tingling sensation, or pain in the hands and feet
63. What percentage of people with diabetes develop peripheral neuropathy?
    1. 10 percent B) 5 percent C) 50 percent D) 30 percent E) 20 percent
64. Why do the distributions of sodium and potassium ions across the plasma membrane of neurons not change appreciably, even following hundreds of action potentials?
    1. The movement of sodium and potassium ions that occurs during an action potential is countered by the passive movement of these ions during the after-hyperpolarization.
    2. The movement of sodium and potassium ions that occurs during an action potential is countered by the active transport of these ions by the Na+/K+ pump.
    3. The movement of sodium and potassium ions that occurs during an action potential is countered by the passive movement of these ions during the repolarization phase.
    4. The movement of sodium and potassium ions that occurs during an action potential is countered by counter-transport of potassium with sodium during rest.
    5. The movement of sodium and potassium ions that occurs during an action potential is countered by the passive leak of these ions when a neuron is at rest.

65. What portion of the peripheral nervous system communicates to effector organs?
    1. spinothalmic tract
    2. afferent nervous system
    3. enteric nervous system
    4. central nervous system
    5. efferent nervous system

66. What portion of the peripheral nervous system transmits information from sensory receptors to the central nervous system?
    1. somatic nervous system
    2. central nervous system
    3. afferent nervous system
    4. autonomic nervous system
    5. efferent nervous system
67. What portion of the efferent branch of the nervous system communicates to glands and cardiac muscle?
    1. autonomic nervous system
    2. central nervous system
    3. afferent nervous system
    4. somatic nervous system
    5. enteric nervous system
68. The brain and spinal cord are part of which of the following branches of the nervous system?
    1. enteric nervous system
    2. afferent nervous system
    3. somatic nervous system
    4. efferent nervous system
    5. central nervous system
69. What portion of the efferent nervous system communicates with skeletal muscle?
    1. afferent nervous system
    2. autonomic nervous system
    3. somatic nervous system
    4. central nervous system
    5. enteric nervous system
70. What portion of the nervous system provides communication between peripheral organs and the brain and spinal cord?
    1. somatic nervous system
    2. central nervous system
    3. afferent nervous system
    4. peripheral nervous system
    5. efferent nervous system
71. What nervous system is found in the intestinal tract?
    1. efferent nervous system
    2. somatic nervous system
    3. enteric nervous system
    4. central nervous system
    5. afferent nervous system

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72. Which of the following potentials can sum?
    1. graded potentials
    2. threshold potentials
    3. action potentials
    4. both graded potentials and action potentials
    5. neither graded potentials nor action potentials
73. Which of the following potentials are affected by refractory periods?
    1. graded potentials
    2. threshold potentials
    3. action potentials

73. 4. both graded potentials and action potentials
    5. neither graded potentials nor action potentials
74. Which of the following potentials is a result of opening or closing of ion channels?
    1. graded potentials
    2. threshold potentials
    3. action potentials
    4. both graded potentials and action potentials
    5. neither graded potentials nor action potentials
75. Which of the following potentials dissipate in size as the potential moves away from the site of initiation?
    1. graded potentials
    2. threshold potentials
    3. action potentials
    4. both graded potentials and action potentials
    5. neither graded potentials nor action potentials
76. Which of the following potentials has an all-or-none response?
    1. graded potentials
    2. threshold potentials
    3. action potentials
    4. both graded potentials and action potentials
    5. neither graded potentials nor action potentials
77. Which of the following potentials can reach or exceed the sodium equilibrium potential?
    1. graded potentials
    2. threshold potentials
    3. action potentials
    4. both graded potentials and action potentials
    5. neither graded potentials nor action potentials

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Figure 7.1

78. Which statement best describes the event indicated by the letter "C" in Figure 7.1 and how that event is initiated?
    1. It is a suprathreshold graded potential resulting from the opening and closing of sodium and potassium channels.
    2. It is an excitatory potential that causes the relative refractory period.
    3. It is a subthreshold graded potential resulting from the opening of sodium channels, closure of potassium channels, or opening of ion channels for sodium and potassium.
    4. It is a suprathreshold depolarization representing an action potential.
    5. It is a hyperpolarization of the membrane due to the outward movement of potassium ions.
79. Which statement best describes the events responsible for the phase represented by the letter "A" in Figure 7.1?
    1. the opening of sodium channels
    2. the opening and closing of sodium channels
    3. the opening of potassium channels
    4. the closing of sodium channels and the opening of potassium channels
    5. the opening of potassium channels and the closing of sodium channels
80. Which statement best describes the events responsible for the phase represented by the letter "B" in Figure 7.1?
    1. the opening of sodium channels
    2. the opening and closing of sodium channels
    3. the opening of potassium channels

1. 4. the closing of sodium channels and the opening of potassium channels
   5. the opening of potassium channels and the closing of sodium channels

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81. Identify the type of summation that is occurring in Figure 7.1 where "S" refers to a stimulus from one source measured in the postsynaptic membrane.
    1. spatial
    2. subthreshold
    3. suprathreshold
    4. multiplier
    5. temporal
82. In Figure 7.1, if the direction of event "C" was reversed (hyperpolarization), how would this affect the ability of the postsynaptic membrane to generate an action potential?
    1. Hyperpolarization will reduce the likelihood that an action potential will be generated.
    2. Hyperpolarization only occur in graded potentials.
    3. Hyperpolarization only cause refractory periods.
    4. Hyperpolarization will cause an equilibrium potential to be reached between the intracellular fluid and the extracellular fluid.
    5. Hyperpolarization will increase the likelihood that an action potential will be generated.
83. In Figure 7.1, if S2 indicated a stimulus from a different source, and S1 occurred coincident with S2, what type of summation has been generated?
    1. subthreshold
    2. spatial
    3. suprathreshold
    4. multiplier
    5. temporal
84. Movement of what ion is responsible for event "D" in Figure 7.1?
    1. calcium (Ca++)
    2. phosphate (PO4-)
    3. potassium (K+)
    4. chloride (Cl-)
    5. sodium (Na+)
85. Information gathered about our internal environment (i.e., fullness of the stomach, blood pressure, etc.) is called          information.
    1. sensory B) efferent C) somatic D) afferent E) visceral
86. What is the most common neuronal cell type?
    1. interneuron
    2. bipolar neuron
    3. efferent neuron
    4. afferent neuron
    5. pseudo-unipolar neuron

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87. What is the only glial cell found outside of the central nervous system?
    1. astrocytes
    2. ependymal cells
    3. microglia
    4. Schwann cell
    5. oligodendrocytes
88. Which type of glial cell provides the myelin sheath for many axons in the central nervous system?

88. 1. astrocytes
    2. microglia
    3. ependymal cells
    4. oligodendrocytes
    5. Schwann cell
89. Once a membrane potential has been developed, the force that drives a particular ion across the membrane is its
    1. electrogenic pump.
    2. electrical gradient.
    3. concentration gradient.
    4. chemical gradient.
    5. electrochemical gradient.
90. What is the passive spread of current along a membrane called?
    1. refractory period
    2. action potential
    3. resistance
    4. electrotonic conduction
    5. graded potential
91. The fact that the opening of some sodium channels can induce several other sodium channels to open describes the property of these channels.
    1. suprathreshold
    2. refractory
    3. regenerative
    4. ligand
    5. all-or-none principle
92. What is the level of membrane depolarization required to induce the sodium channel's positive feedback loop called?
    1. axon terminal
    2. axon hillock
    3. subthreshold
    4. suprathreshold
    5. threshold  17
93. What type of ion channels is located along the axon?
    1. voltage-gated channels
    2. mechanical channels
    3. initiation channels
    4. ligand-gated channels
    5. propagation channels
94. In the peripheral nervous system, myelin is formed by  . In the central nervous system, myelin is formed by           .
    1. Schwann cells : astrocytes B) Schwann cells : oligodendrocytes

C) oligodendrocytes : Schwann cells D) Schwann cells : microglial cells

95. At rest, the plasma membrane is more permeable to which of the following ions?
    1. sodium (Na+)
    2. potassium (K+)
    3. chloride (Cl-)
    4. calcium (Ca++)
    5. phosphate (PO4-)

96. The resting membrane potential is close to the equilibrium potential of which of the following ions?
    1. sodium (Na+)
    2. potassium (K+)
    3. chloride (Cl-)
    4. calcium (Ca++)
    5. phosphate (PO4-)
97. During the rapid depolarization phase of an action potential, the plasma membrane is more permeable to which of the following ions?
    1. sodium (Na+)
    2. potassium (K+)
    3. chloride (Cl-)
    4. calcium (Ca++)
    5. phosphate (PO4-)
98. Increased permeability to what ion is responsible for the relative refractory period?
    1. sodium (Na+)
    2. potassium (K+)
    3. chloride (Cl-)
    4. calcium (Ca++)
    5. phosphate (PO4-)

99. Describe the organization of the nervous system, including a description of the different branches.

100. Describe the structure of a neuron and the important consequences of that arrangement.

101. Amyotrophic lateral sclerosis (ALS), often referred to as "Lou Gehrig's Disease," is a progressive neurodegenerative disease that affects the efferent division, particularly the motor neurons, of the nervous system. People with ALS have normal bodily functions and their ability to think, form memories, and to detect sensations is all normal. However, the progressive nature of this disease can lead to total paralysis. Based on your knowledge of the different divisions of the nervous system and the functioning of neurons, explain the symptoms of ALS.

102. Several ions are responsible for the resting membrane potential. Describe the forces that determine resting membrane potential.

103. Graded potentials develop in the cell body of neurons as well as in sensory receptor cells. In order for sensory information to reach the central nervous system that graded potential must be converted into an action potential. How are graded potentials created, and how are they different from action potentials?

104. Describe the voltage gating of ion channels and how this plays a role in an action potential.
105. Once an action potential is generated, there is a delay before another action potential can be generated. Name and describe the basis for the two refractory periods.

106. Describe how an action potential, originating at the axon hillock, is propagated along the axon. Include those factors that can alter conduction velocity.