Chapter 2. Pain Physiology Flashcards Preview

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Flashcards in Chapter 2. Pain Physiology Deck (45):

46. Which of the following nerves conduct nociceptive
(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

46. (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).


47. 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

47. (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).


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

48. (C) Impulses C fibers and their collaterals terminate
in the Rexed laminae L1, L2, and L5.


49. 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

49. (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.


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

50. (C) Both, endogenous as well as exogenous
opioids block the release of substance P in the
dorsal horn there by providing analgesia.


51. 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

51. (C) The serosal membranes are the most sensitive
and the solid viscera the least sensitive to
noxious stimuli.


52. Visceral pain is typically felt as
(A) dull
(B) sharp
(C) vague
(D) all of the above
(E) A and C only

52. (E) The visceral pain is felt as a vague, deep,
dull pain as opposed to sharp and well-defined
pain. It may mimic other


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

53. (B) Viscera can generate painful contraction in
an isometric contraction state such as bowel
and ureteral obstruction. Isotonic contractions
usually are not painful.


54. 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

54. (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.


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

55. (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.


56. Enkephalins and somatostatin – are these types
of neurotransmitters:
(A) Excitatory
(B) Inhibitory
(C) Gastrotransmitters
(D) Excitatory and inhibitory
(E) None of the above

56. (B) Dopamine, epinephrine, and norepinephrine
are considered to be excitatory neurotransmitters,
whereas serotonin, GABA, and dopamine
are the other inhibitory neurotransmitters.


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)

57. (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.


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

58. (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.


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

59. (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.


60. 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

60. (B) Pretreatment with an NMDA antagonist
attenuates the central sensitization from inflammation.


61. 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

61. (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


62. 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
(D) widespread areas in the frontal cortex
(E) a focal area in the thalamus

62. (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


63. γ-Aminobutyric acid (GABA) receptors (a
type of cellular channel), are these types of ion
(A) Calcium
(B) Sodium
(C) Chloride
(D) Magnesium
(E) Potassium

63. (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


64. Nociceptors are present in
(1) skin
(2) subcutaneous tissue
(3) joints
(4) visceral tissue

64. (E) Nociceptors are present in all of the above
tissues as well as in periosteum and muscles


65. 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

65. (B) Substance P activates and degranulates the
mast cells, which in turn release histamine and


66. Visceral pain input terminates in the following
Rexed lamina(e):
(1) Lamina 1
(2) Lamina 2
(3) Lamina 5
(4) Lamina 10

66. (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.


67. The visceral pain may be felt as pain in
(1) the midline
(2) the unilateral
(3) the bilateral
(4) multiple patterns

67. (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.


68. Which of the following induce pain in hollow
(1) Cutting
(2) Ischemia
(3) Burning
(4) Distension

68. (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.


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

69. (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).


70. Neurotransmitters in the central nervous
system (CNS) are classified into which of the
(1) Excitatory
(2) Inhibitory
(3) Neuropeptides
(4) Regulatory

70. (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.


71. These are some of the excitatory neurotransmitters:
(1) Glutamate
(2) Glycine
(3) Aspartate
(4) GABA

71. (B) Glutamate and aspartate are the main excitatory
neurotransmitters, whereas GABA and
glycine are inhibitory neurotransmitters.


72. NMDA receptor blockade in the spinal cord
(1) inhibition of pain transmission
(2) modulation of pain transmission
(3) reduction in pain transmission
(4) does not have a role in pain transmission

72. (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.


73. The subunit most relevant in nociception is
(1) NR2A
(2) NR2B
(3) NR3A
(4) NR1

73. (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.


74. Ketamine and Memantine are NMDA receptor
(1) allosteric regulators
(2) agonists
(3) stimulators
(4) blockers

74. (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


75. The most important substances found in the
descending inhibitory pathways of the CNS
(1) acetylcholine
(2) serotonin
(3) nitric oxide (NO)
(4) norepinephrine (NE)

75. (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.


76. 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

76. (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.


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

77. (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.


78. 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

78. (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.


79. Primary inhibitory neurotransmitters include
the following:
(1) Glycine
(2) Glutamate
(3) GABA
(4) Aspartate

79. (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.


80. Excitatory neuropeptides in the CNS include
the following:
(1) Substance P
(2) Somatostatin
(3) Neurokinin A
(4) Dynorphin

80. (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.


81. 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

81. (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.


82. Protease-activated receptors (PAR) were detected
in which of the following?
(1) Platelets
(2) Endothelial cells
(3) Fibroblasts
(4) Nervous system

82. (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


83. 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

83. (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.


84. 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

84. (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


85. Nociceptors are specific receptors within the
superficial layers of the skin. T/F

85. (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.


86. Conduction velocity of A-δ fibers is faster than
the C fibers. T/F

86. (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).


87. Nociceptive impulse terminates in nociceptive—
specific as well as wide dynamic range
(WDR) neurons. T/F

87. (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


88. Hyperalgesia can only occur with somatic nociceptive
stimuli and not visceral stimuli. T/F

88. (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


89. NMDAreceptor in the spinal cord dorsal horn
is essential for central sensitization, the central
facilitation of pain transmission produced by
peripheral injury T/F

89. (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


90. Neuropeptides are only excitatory in nature. T/F

90. (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.