Chapter 2. Pain Physiology Flashcards

1
Q
46. Which of the following nerves conduct nociceptive
stimuli?
(A) A-δ fibers and C fibers
(B) A-δ fibers and A-β fibers
(C) A-β fibers and C fibers
(D) B fibers and C fibers
(E) A-α fibers and A-β fibers
A
  1. (A) Nociceptors transmit impulses mainly
    through the A-δ and C fibers to the spinal cord.
    A-β fibers carry impulses generated from lowthreshold
    mechanoceptors. B fibers are mainly
    preganglionic autonomic (white rami and cranial
    nerves III, VII, IX, X).
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2
Q
  1. Arrange A-δ, A-β, B, C, and A-α nerves according
    to their conduction velocity (fastest to slowest):
    (A) A-α, A-β, A-δ, B, C
    (B) A-δ, C, B, A-β, A-α
    (C) C, B, A-δ, A-β, A-α
    (D) A-β, A-δ, C, B, A-α
    (E) B, C, A-β, A-α, A-δ
A
  1. (A) Conduction velocity is dependent on the
    size of the nerve fiber as well as myelination.
    Myelinated nerves conduct the impulse faster
    than unmyelinated nerves (C) due to jumping
    from one node to the next node of Ranvier
    (saltatory conduction).
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3
Q
48. The impulse traveling through the C fiber terminates
in the Rexed laminae:
(A) Laminae 1 and 5
(B) Laminae 1 and 2
(C) Laminae 1, 2, and 5
(D) Laminae 2 and 5
(E) Laminae 3 and 5
A
  1. (C) Impulses C fibers and their collaterals terminate

in the Rexed laminae L1, L2, and L5.

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4
Q
  1. Some of the naturally occurring chemicals
    involved in nociceptive input are hydrogen
    ions, serotonin (5-HT), and bradykinin. What
    effect do these have on the nociceptors?
    (A) Sensitize the nociceptors
    (B) Activate the nociceptors
    (C) Activate and sensitize the nociceptors
    (D) Block the nociceptors
    (E) Modify the nociceptors
A
  1. (B) The sensitization of nociceptors may be
    caused by prostaglandins and cytokines, whereas
    activation is caused by substance, such as
    hydrogen ions, serotonin, and bradykinin.
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5
Q
50. Substance P release from the dorsal horn neuronal
elements is blocked by
(A) endogenous opioids
(B) exogenous opioids
(C) both type of opioids
(D) anticonvulsant medications
(E) local anesthetics
A
  1. (C) Both, endogenous as well as exogenous
    opioids block the release of substance P in the
    dorsal horn there by providing analgesia.
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6
Q
  1. Arrange the visceral structures—hollow viscera,
    solid viscera, serosal membranes—in the order
    of increasing sensitivity to noxious stimuli:
    (A) Serosal membranes, hollow viscera, solid viscera
    (B) Hollow viscera, solid viscera, serosal membranes
    (C) Solid viscera, hollow viscera, serosalmembranes
    (D) Hollow viscera, serosal membranes,solid viscera
    (E) Serosal membranes, solid viscera, hollow viscera
A
  1. (C) The serosal membranes are the most sensitive
    and the solid viscera the least sensitive to
    noxious stimuli.
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7
Q
52. Visceral pain is typically felt as
(A) dull
(B) sharp
(C) vague
(D) all of the above
(E) A and C only
A
  1. (E) The visceral pain is felt as a vague, deep,
    dull pain as opposed to sharp and well-defined
    pain. It may mimic other
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8
Q
53. Hollow viscera can be painful during which
type of contractions?
(A) Isotonic
(B) Isometric
(C) Sustained
(D) Isotonic and isometric
(E) None of the above
A
  1. (B) Viscera can generate painful contraction in
    an isometric contraction state such as bowel
    and ureteral obstruction. Isotonic contractions
    usually are not painful.
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9
Q
  1. Certain nociceptors are termed “silent nociceptors.”
    These can be activated (“awakened”)
    by a prolonged noxious stimulus, such as
    inflammation. These types of receptors were
    initially identified in which structures?
    (A) Bones
    (B) Brain
    (C) Nails
    (D) Joints
    (E) Nerves
A
  1. (D) Sleeping or silent nociceptors are population
    of nociceptors that remain inactive under
    normal conditions. They are activated because
    of tissue injury, with consequent release of
    chemical mediators. They appear to be present
    in skin, joints, muscle, and visceral tissue.
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10
Q
55. Visceral referred pain with hyperalgesia can be explained by which of the following?
(A) Viscerovisceral convergence
(B) Viscerosomatic convergence
(C) Nociceptive perception
(D) Sympathetic stimulation
(E) Sympathetic transmission
A
  1. (B) The viscerosomatic convergence of signals
    within the spinal cord at the level of dorsal
    horn and at supraspinal levels within the
    brainstem, thalamus, and cortex; explains the
    phenomenon of referred pain to somatic structures.
    Viscerovisceral convergence on the other
    hand has been shown to exist between
    colon/rectum, bladder, vagina, and uterine
    cervix, and between heart and gallbladder.
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11
Q
56. Enkephalins and somatostatin – are these types
of neurotransmitters:
(A) Excitatory
(B) Inhibitory
(C) Gastrotransmitters
(D) Excitatory and inhibitory
(E) None of the above
A
  1. (B) Dopamine, epinephrine, and norepinephrine
    are considered to be excitatory neurotransmitters,
    whereas serotonin, GABA, and dopamine
    are the other inhibitory neurotransmitters.
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12
Q
57. There are several subtypes of N-methyl-Daspartate
(NMDA) receptors. They are
(A) NR1, NR2 (A, B, and C)
(B) NR1, NR2 (A, B, C, and D)
(C) NR1, NR2 (A, B, and C), and NR3
(A and B)
(D) NR1, NR2 (A, B, C, and D), and NR3
(A and B)
(E) NR1, NR2 (A, B, C, and D), NR3
(A and B), and NR4 (A and B)
A
  1. (D) There is accumulating evidence to implicate
    the importance of NMDA receptors to the
    induction and maintenance of central sensitization
    during pain states. However, NMDA
    receptors may also mediate peripheral sensitization
    and visceral pain. NMDA receptors are
    composed of NR1, NR2 (A, B, C, and D), and
    NR3 (A and B) subunits, which determine the
    functional properties of native NMDA receptors.
    Among NMDA receptor subtypes, the
    NR2B subunit– containing receptors appear particularly
    important for nociception, thus leading to the possibility that NR2B-selective antagonists
    may be useful in the treatment of chronic pain.
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13
Q
58. Sodium channels are also important in neurotransmission through the dorsal root ganglion (DRG). How many different types of sodium
channels have been identified?
(A) Four
(B) Eight
(C) Seven
(D) Five
(E) Nine
A
  1. (E) Voltage-gated sodium channels underlie
    the electrical excitability demonstrated by
    mammalian nerve and muscle. Nine voltagegated
    sodium channels are expressed in complex
    patterns in mammalian nerve and muscle.
    Six have been identified in the DRG. Three
    channels, Nav1.7, Nav1.8, and Nav1.9, are
    expressed selectively in peripheral damagesensing
    neurons. Nav1.8 seems to play a specialized
    role in pain pathways.
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14
Q
59. Ziconotide, found in snail venom, acts primarily
on which type of calcium channel?
(A) N-type
(B) T-type
(C) L-type
(D) P-type
(E) Q-type
A
  1. (A) The nonopioid analgesic ziconotide has been
    developed as a new treatment for patients with
    severe chronic pain who are intolerant of and/or
    refractory to other analgesic therapies. Ziconotide
    is the synthetic equivalent of a 25-amino-acid
    polybasic peptide found in the venom of the
    marine snail Conus magus. In rodents, ziconotide
    acts by binding to neuronal N-type voltagesensitive
    calcium channels, thereby blocking
    neurotransmission from primary nociceptive
    afferents. Ziconotide produces potent antinociceptive
    effects in animal models and its efficacy
    has been demonstrated in human studies.
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15
Q
  1. Pretreatment with an NMDA antagonist prior to inflammation has been shown to
    (A) enhance central sensitization
    (B) attenuate central sensitization
    (C) have no effect on central sensitization
    (D) enhance peripheral sensitization
    (E) attenuate peripheral sensitization
A
  1. (B) Pretreatment with an NMDA antagonist

attenuates the central sensitization from inflammation.

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16
Q
  1. NMDA receptor channels are usually inactive
    and blocked by zinc and magnesium ions.
    Adepolarization of the cell membrane removes
    these ions and allows influx of which ions?
    (A) Sodium
    (B) Calcium
    (C) Chloride
    (D) Sodium and calcium
    (E) Sodium and chloride
A
  1. (D) NMDA receptor ion channel has binding
    sites for zinc, magnesium, and phencyclidine,
    which are inhibitory. A depolarization causes
    removal of zinc and magnesium allowing
    largely calcium and to much lesser extent
    sodium ions to influx, initiating intracellular
    activity.
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17
Q
  1. Nociceptive stimuli cause increased activity in
    the cerebral cortex in
    (A) a focal area around the central gyrus
    (B) widespread areas in the temporal cortex
    (C) a focal area around the posterior cortical
    areas
    (D) widespread areas in the frontal cortex
    (E) a focal area in the thalamus
A
  1. (B) Noxious stimuli cause widespread activation
    of cortical area. Increasing stimulus intensity
    activates increasing number of areas within
    the cortex. Other areas of the brain are not
    involved in the interpretation of the noxious
    stimuli.
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18
Q
63. γ-Aminobutyric acid (GABA) receptors (a
type of cellular channel), are these types of ion
channels:
(A) Calcium
(B) Sodium
(C) Chloride
(D) Magnesium
(E) Potassium
A
  1. (C) Three major classes of chloride channels
    have been identified. The first class identified
    was the ligand-gated chloride channels, including
    those of the GABAA and glycine receptors.
    The ligand-gated chloride channels are common
    in dorsal horn neurons. The second class, also
    likely common spinal levels, is the voltage-gated
    chloride channels. The final chloride channel
    class is activated by cyclic adenosine monophosphate
    and may include only the cystic fibrosis
    transmembrane regulator. Activation of chloride
    currents usually produces inward movement
    of chloride to cells that hyperpolarize
    neurons; facilitation of these hyperpolarizing
    currents underlies the mechanisms of many
    depressant drugs. An important exception at
    spinal levels, however, is that GABAA receptors
    on primary afferent terminals gate a chloride
    channel that allows reflux of chloride with a net
    effect therefore of depolarizing primary afferent
    terminals.
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19
Q
  1. Nociceptors are present in
    (1) skin
    (2) subcutaneous tissue
    (3) joints
    (4) visceral tissue
A
  1. (E) Nociceptors are present in all of the above

tissues as well as in periosteum and muscles

20
Q
  1. Substance P is released by the activation of
    nociceptors and has the following effect(s):
    (1) Vasodilatation
    (2) Vasoconstriction
    (3) Mast cell activation
    (4) Decrease vascular permeability
A
  1. (B) Substance P activates and degranulates the
    mast cells, which in turn release histamine and
    serotonin.
21
Q
66. Visceral pain input terminates in the following
Rexed lamina(e):
(1) Lamina 1
(2) Lamina 2
(3) Lamina 5
(4) Lamina 10
A
  1. (E) The visceral afferents usually terminate in
    the Rexed laminae L1, L2, L5, and L10. These
    laminae receive input from the nerve fiber
    types A-δ and C.
22
Q
  1. The visceral pain may be felt as pain in
    (1) the midline
    (2) the unilateral
    (3) the bilateral
    (4) multiple patterns
A
  1. (E) Superficial and deep dorsal horn neurons
    are involved in pain perception from the
    abdominal visceral and may present it as vague
    unilateral, bilateral, and more commonly midline
    pain. The pattern may change with the
    course of the disease.
23
Q
68. Which of the following induce pain in hollow
viscera?
(1) Cutting
(2) Ischemia
(3) Burning
(4) Distension
A
  1. (C) Hollow viscera are insensitive to normally
    noxious stimuli that elicit pain in other somatic
    structures. However certain stimuli like ischemia,
    necrosis, inflammation, distension, and compression
    do elicit painful response from a viscus.
24
Q
69. Viscera are supplied by sympathetic nerves
which contribute to pain generation and transmission.
They release several chemical substances
including the following:
(1) Norepinephrine
(2) Histamine
(3) Serotonin
(4) Epinephrine
A
  1. (A) In the viscera, sympathetic nerve terminals,
    mast cells, and epithelial cells, including
    enterochromaffin cells in the gastrointestinal
    tract, release a variety of bioactive substances, including noradrenaline, histamine, serotonin,
    adenosine triphosphate (ATP), glutamate, NGF,
    and tryptase. Resident leukocytes and
    macrophages attracted to an area of insult collectively
    contribute products of cyclooxygenase
    and lipoxygenase, including prostaglandin I2,
    prostaglandin E2, hydroxyeicosatetraenoic acids
    (HETEs), and hydroperoxyeicosatetraenoic
    (HPETEs), and a variety of cytokines, reactive
    oxygen species, and growth factors. Some of
    these chemicals can directly activate visceral
    afferent terminals (eg, serotonin, ATP, and glutamate),
    whereas others probably play only a
    sensitizing role (eg, prostaglandins, nerve
    growth factor, and tryptase).
25
Q
  1. Neurotransmitters in the central nervous
    system (CNS) are classified into which of the
    following?
    (1) Excitatory
    (2) Inhibitory
    (3) Neuropeptides
    (4) Regulatory
A
  1. (A) There are three main classes of neurotransmitters;
    excitatory, inhibitory, and neuropeptides.
    Tissue injury results in the local release of
    numerous chemicals which either directly
    induce pain transduction by activating nociceptors
    or facilitate pain transduction by increasing
    the excitability of nociceptors. There are three
    classes of transmitter compounds; excitatory
    neurotransmitters, inhibitory neurotransmitters,
    and neuropeptides, that are found in three
    anatomical compartments; sensory afferent terminals,
    local circuit terminals, and descending
    (or ascending) modulatory circuit terminals.
26
Q
  1. These are some of the excitatory neurotransmitters:
    (1) Glutamate
    (2) Glycine
    (3) Aspartate
    (4) GABA
A
  1. (B) Glutamate and aspartate are the main excitatory
    neurotransmitters, whereas GABA and
    glycine are inhibitory neurotransmitters.
27
Q
  1. NMDA receptor blockade in the spinal cord
    causes
    (1) inhibition of pain transmission
    (2) modulation of pain transmission
    (3) reduction in pain transmission
    (4) does not have a role in pain transmission
A
  1. (B) NMDAreceptor activation causes increased
    pain transmission whereas its blockade attenuates
    pain transmission. There are four receptor
    types for glutamate and aspartate in the
    somatosensory system. The class of receptors
    best activated by NMDA is termed the NMDA
    receptor. The NMDAreceptor is usually considered
    as recruited only by intense and/or prolonged
    somatosensory stimuli. This characteristic
    is due to the NMDAreceptor’s well-known magnesium
    block that is only relieved by prolonged
    depolarization of the cell membrane.
28
Q
  1. The subunit most relevant in nociception is
    (1) NR2A
    (2) NR2B
    (3) NR3A
    (4) NR1
A
  1. (C) NMDA receptors are critically involved in
    the induction and maintenance of neuronal
    hyperexcitability after noxious events. Until
    recently, only central NMDA receptors were a
    primary focus of investigations. With the recognition
    of peripheral somatic and visceral
    NMDA receptors, it is now apparent that the
    role of NMDA receptors in pain is much greater
    than thought previously. Over the past decade,
    accumulating evidence has suggested that the
    NR2B subunit of NMDA receptor is particularly
    important for pain perception. Given the small
    side-effect profile and good efficacy of NR2Bselective
    compounds, it is conceivable that
    NR2B-selective blockade will emerge as a
    viable strategy for pharmacological treatment
    of pain.
29
Q
  1. Ketamine and Memantine are NMDA receptor
    (1) allosteric regulators
    (2) agonists
    (3) stimulators
    (4) blockers
A
  1. (D) Both are clinically used NMDA receptor
    blockers, causing analgesia. Clinically available
    compounds that are demonstrated to have
    NMDA receptor-blocking properties include
    ketamine, dextromethorphan, and memantine.
    Dextromethorphan, for example, is effective in
    the treatment of painful diabetic neuropathy
    and not effective in postherpetic neuralgia and
    central pain. NMDA receptor blockers may
    therefore offer new options in the treatment of
    pain.
30
Q
  1. The most important substances found in the
    descending inhibitory pathways of the CNS
    include
    (1) acetylcholine
    (2) serotonin
    (3) nitric oxide (NO)
    (4) norepinephrine (NE)
A
  1. (C) Nitric oxide is released in response to
    NMDAreceptor activation and is implicated in
    neuronal plasticity rather than antinociception.
    Amongst the substances found in the descending
    inhibitory pathways of the CNS are norepinephrine
    and serotonin.
31
Q
  1. There are several types of calcium channels.
    Which one is the most relevant to pain impulse
    transmission in the spinal cord?
    (1) L-type
    (2) R-type
    (3) T-type
    (4) N-type
A
  1. (D) The Ca2+ channel can be divided into subtypes
    according to electrophysiological characteristics,
    and each subtype has its own gene. The
    L-type Ca2+ channel is the target of a large
    number of clinically important drugs, especially
    dihydropyridine, and binding sites of Ca2+
    antagonists have been clarified.
    N-type calcium channels are primary targets
    for the calcium channel blockers with analgesic
    properties. The N-type calcium channel exhibits
    a number of characteristics that make it an attractive
    target for therapeutic intervention concerning
    chronic and neuropathic pain conditions.
32
Q
77. N-type calcium channels are highly concentrated
in which of the following areas?
(1) DRG
(2) Cerebral cortex
(3) Dorsal horn
(4) Postsynaptic terminals
A
  1. (B) N-type channels are highly concentrated in
    both DRG cell bodies and also in the synaptic terminals they make in dorsal horn of the spinal
    cord (laminae L1 and L2). Commonly they are
    found in presynaptic terminals. Critically, block
    of N-type currents inhibits the release of neuropeptides
    substance P and calcitonin generelated
    peptide (CGRP) from sensory neurons.
33
Q
  1. Windup is a phenomenon that occurs due to
    constant input of C-fiber activity to the spinal
    cord. This phenomenon defines
    (1) reduction in excitability of spinal neurons
    in the DRG
    (2) increase in excitability of spinal neurons
    in the DRG
    (3) reduction in excitability of spinal neurons
    in the dorsal horn
    (4) increase in excitability of spinal neurons
    in the dorsal horn
A
  1. (D) Windup refers to the progressive increase
    in the magnitude of C-fiber evoked responses
    of dorsal horn neurons produced by repetitive
    activation of C-fibers. Neuronal events leading
    to windup also produce some of the classical
    characteristics of central sensitization including
    expansion of receptive fields and enhanced
    responses to C but not A δ-fiber stimulation.
34
Q
79. Primary inhibitory neurotransmitters include
the following:
(1) Glycine
(2) Glutamate
(3) GABA
(4) Aspartate
A
  1. (B) Primary inhibitory neurotransmitters of the
    somatosensory system include the amino acids
    glycine and GABA. Glycine is particularly
    important at spinal levels, while GABA is the
    chief inhibitory transmitter at higher levels.
    Three types of GABA receptors have been identified.
    GABAA receptor is linked with a chloride
    channel and modulated by barbiturates, benzodiazepines,
    and alcohol. Selective GABAA
    agonists include muscimol and selective antagonists
    include gabazine. The GABAB receptor has
    been associated with both a potassium ionophore
    and G protein-linked complex. Baclofen is a selective
    GABAB receptor agonist and phaclofen is a
    selective antagonist. Finally the newly described
    GABAC receptor has also been described as associated
    with a potassium channel ionophore.
    Glutamate and aspartate are excitatory neurotransmitters.
35
Q
80. Excitatory neuropeptides in the CNS include
the following:
(1) Substance P
(2) Somatostatin
(3) Neurokinin A
(4) Dynorphin
A
  1. (B) The excitatory neuropeptides in the somatosensory system include substance P and neurokinin A. These peptides are especially concentrated in primary afferent fibers but also present in intrinsic neurons of the spinal dorsal horn and thalamus.
    The inhibitory neuropeptides at spinal levels
    include somatostatin, the enkephalins, and possibly
    dynorphin. These peptides are contained in
    both intrinsic neurons of the dorsal horn and in
    the fibers descending to the dorsal horn from various
    brainstem nuclei.
36
Q
  1. Serotonin is released as mediator as a result of
    tissue injury from which of the following?
    (1) Platelets
    (2) Muscle cells
    (3) Mast cells
    (4) White blood cells
A
  1. (B) Serotonin is one of many mediators that are
    released from platelets (rats and humans) and
    mast cells (rats) in injured and inflamed tissues.
    In situ hybridization, studies have shown that
    DRG neurons normally express mRNA for
    5-HT1B, 5-HT1D, 5-HT2A, 5-HT2B, 5-HT3B, and
    5-HT4 receptors. Many of the excitatory actions
    of serotonin have been ascribed to the ligandgated
    5-HT3 receptor, but there is good evidence
    that serotonin can activate and sensitize nociceptors
    by actions on G protein–coupled receptors.
    5-HT2 receptors are expressed largely
    in (calcitonin gene-related peptide) CGRPcontaining,
    small-diameter sensory neurons,
    and their activation produces thermal hyperalgesia.
    5-HT2 receptors are usually linked to
    the phospholipase C pathway. Activation of
    5-HT2 receptors depolarizes capsaicin-sensitive
    DRG neurons by reducing a resting potassium
    potential, and such an effect could contribute to
    both excitation and sensitization.
37
Q
82. Protease-activated receptors (PAR) were detected
in which of the following?
(1) Platelets
(2) Endothelial cells
(3) Fibroblasts
(4) Nervous system
A
  1. (E) Four types of G protein–coupled PARs have
    been identified (PAR1-PAR4). These receptors
    are activated by a unique mechanism whereby
    extracellular, soluble, or surface-associated proteases
    cleave at specific residues in the extracellular
    N-terminal domain of the G protein to
    expose a novel N-terminal sequence, which
    acts as a tethered ligand that activates the
    receptor by binding to other regions of the protein.
    These agonist effects can be mimicked by
    short synthetic peptides based on the sequence
    of the tethered ligands of the different PARs.
    PAR1, PAR2, and PAR4 are activated by thrombin
    produced during the blood-clotting cascade,
    while PAR3 activation is triggered by
    tryptase, which is known to be released from
    mast cells in inflammatory conditions, as well
    as the blood-clotting factors VIIa and Xa. In
    this way, PARs are activated as a result of tissue
    damage and inflammation. Because activation
    involves an irreversible enzymatic cleavage,
    restoration of PAR sensitivity requires internalization
    of the receptors and insertion of new
    receptor into the plasma membrane. PARs were
    initially detected in platelets, endothelial cells,
    and fibroblasts, but are now known to also be
    expressed in the nervous system. PAR1 and
    PAR2 are expressed on peripheral sensory neurons.
    PAR2 is expressed in about 60% of rat
    DRG neurons, where it is found mainly in the small to medium-sized neurons, with a significant
    number coexpressing substance P and
    CGRP.
38
Q
  1. Increased nerve growth factor (NGF) levels
    observed after inflammatory stimuli result
    from increased synthesis and release of NGF
    from cells in the affected tissue. Large number
    of stimuli can alter NGF production including:
    (1) 2IL-1β, IL-4, IL-5
    (2) Tumor necrosis factor α (TNF-α), transforming
    growth factor β (TGF-β)
    (3) Platelet-derived growth factor
    (4) Epidermal growth factor
A
  1. (E) NGF levels increase during inflammation.
    NGF is a critical mediator of inflammatory pain.
    NGF clearly has a powerful neuroprotective
    effect on small-diameter sensory neurons, and
    NGF levels have been shown to change in a
    number of models of nerve injury. However, its
    exact role in the development of neuropathic
    pain is at present unclear. Blocking NGF bioactivity
    (either systemically or locally) largely
    blocks the effects of inflammation on sensory
    nerve function. Elevated NGF levels have been
    found in a variety of inflammatory states in
    humans, including in the bladder of patients
    with cystitis, and there are increased levels in
    synovial fluid from patients with arthritis.
39
Q
  1. Endogenous opioid peptides are important in
    nociceptive perception and modulation. These
    include which of the following?
    (1) Leucine-enkephalin
    (2) Dynorphin
    (3) Methionine-enkephalin
    (4) Nociceptin
A
  1. (E) The contribution of endogenous opioid
    peptides to pain modulation was first suggested
    by reports that stimulation-produced
    analgesia in animals and humans is reduced by
    the narcotic antagonist naloxone. Naloxone
    also worsens postoperative pain in patients
    who have not received exogenous opioid therapy,
    thus establishing the relevance of endogenous
    opioids to common clinical situations.
    Peptide transmitters and hormones are derived
    by the cleavage of larger, usually inactive,
    precursor. Met- and leu-enkephalin are derived
    from a common precursor, preproenkephalin,
    each molecule of which generates multiple
    copies of met-enkephalin and one of leuenkephalin.
    β-Endorphin is cleaved from a
    larger precursor protein, proopiomelanocortin,
    which also gives rise to adrenocorticotrophic
    hormone and several copies of melanocytestimulating
    hormone. Two copies of dynorphin
    (A and B) and α-neoendorphin are generated
    from a third endogenous opioid precursor molecule
    (preprodynorphin).
40
Q
  1. Nociceptors are specific receptors within the

superficial layers of the skin. T/F

A
  1. (F) Nociceptors are free nerve endings and do
    not have any specific receptors, but are activated
    by a tissue injury due to mechanical,
    thermal, or chemical stimuli.
41
Q
  1. Conduction velocity of A-δ fibers is faster than

the C fibers. T/F

A
  1. (T) “A-δ” fibers are myelinated fibers and conduct
    the impulses faster (5-20 m/s) than the C
    fibers, which are unmyelinated (< 2 m/s).
42
Q
  1. Nociceptive impulse terminates in nociceptive—
    specific as well as wide dynamic range
    (WDR) neurons. T/F
A
  1. (T) WDR neurons respond to nociceptive as
    well as nonnociceptive stimuli transmitted by
    the peripheral nerves. These types of receptors
    are located in the dorsal horn of the spinal grey
    matter
43
Q
  1. Hyperalgesia can only occur with somatic nociceptive

stimuli and not visceral stimuli. T/F

A
  1. (F) Visceral pain is usually felt as referred pain.
    This type of pain can be “with hyperalgesia” or
    “without hyperalgesia.” Most structures elicit
    a midline or bilateral pain; however, certain
    structures such as kidneys and ureters can produce
    unilateral pain. Referred pain with hyperalgesia
    is termed “true parietal” pain and
    usually extends to the muscles, but can extend
    up to the skin
44
Q
  1. NMDAreceptor in the spinal cord dorsal horn
    is essential for central sensitization, the central
    facilitation of pain transmission produced by
    peripheral injury T/F
A
  1. (T) NMDAreceptors are involved in the induction
    and maintenance of certain pathological
    pain states produced by peripheral nerve
    injury, possibly by sensitizing dorsal horn neurons.
    These receptors have been implicated in
    the phenomenon of windup and related
    changes such as spinal hyperexcitability that
    enhance and prolong sensory transmission
45
Q
  1. Neuropeptides are only excitatory in nature. T/F
A
  1. (F) There are multiple neuropeptides that contribute
    to signaling of somatosensory information.
    Some of these could be classified as
    excitatory compounds and others as inhibitory.
    Neuropeptides tend to have more gradual
    onset of effects as well as much more prolonged
    duration of action once released.