SOMATIC SENSATION Flashcards
two types of afferent fibers in the distal axons
of primary sensory neurons
very fine, unmyelinated, slowly conducting C fiber
(0.3 to l.l).l in diameter);
the other is the thinly myelinated,
more rapidly conducting A-8 fiber (2 to s.u in diameter).
Three
categories of free endings or receptors are recognized:
mechanoreceptors, thermoreceptors, and polymodal
nociceptors
mechanoeffects are transmitted by both ______
and the thermal effects mostly by ______
A-8 and C fibers
C fibers
The peripheral afferent pain fibers of both A-8 and
C types have their cell bodies in the_______
dorsal root ganglia
The
pain afferents occupy mainly the _________of the root
entry zone
lateral part
That the ____________ is predominantly
a pain pathway is shown (in animals) by
the ipsilateral segmental analgesia that results from its
transection but it contains deep sensory or propriospinal
fibers as well
tract of Lissauer
_________ fibers terminate principally in
lamina I of Rexed (marginal cell layer of Waldeyer) and
also in the outermost part of lamina II;
Thinly myelinated (A-0)
some A-8 pain
fibers penetrate the dorsal gray matter and terminate
in the lateral part of ______
lamina V.
Unmyelinated (C) fibers
terminate in _________
lamina II (substantia gelatinosa)
Excitatory amino acids __________ and
nucleotides such as adenosine triphosphate (ATP) are the
putative transmitters at terminals of primary A-8 sensory
afferents.
(glutamate, aspartate)
Also,________ afferents, when stimulated,
release several neuromodulators that play a role in the
transmission of pain sensation
A-8 pain
animals, __________
excites nociceptive dorsal root ganglion and dorsal hom neurons; furthermore, destruction of substance P fibers
produces analgesia. In
substance P
Opiate receptors of three types are found on
both presynaptic primary afferent terminals and postsynaptic dendrites of small neurons in_______
lamina II.
axons of secondary neurons that
sub-serve pain sensation originate in laminae ________ of the spinal gray matter.
I, II, V, V.ll,
and Vlll
It is of clinical consequence that the axons carrying pain
impulses from each dermatome decussate __________ rostral to the level of root entry
one to three
segments
a fast-conducting pathway that projects directly to the
thalamus-the anterolateral fasciculus of the cord contains
several more slowly conducting, medially placed
systems of fibers.
spinoreticulothalamic
or paleospinothalamic pathway
The conduction of diffuse, poorly localized pain arising
from deep and visceral structures (gut, periosteum,
peritoneum) has been ascribed to _______________
these slow-conducting, indirect pathways
it is the direct spinothalamic
pathway, which projects to the _______ and thence to discrete areas of the sensory cortex, that subserves the sensorydiscriminative aspects of pain
ventroposterolateral
(VPL) nucleus of the thalamus
The direct spinothalamic fibers separate into two bundles as they approach the thalamus. The lateral division
terminates in the ventrobasal and posterior groups of
nuclei, the most important of which is the _______
VPL nucleus.
The medial contingent terminates mainly in the __________of nuclei and in the nucleus submedius
intralaminar
complex
__________ project onto the medial intralaminar (primarily parafascicular and centrolateral) thalamic nuclei; i.e., they overlap with the terminations of the medially projecting direct spinothalamic pathway.
Spinoreticulothalamic (paleospinothalamic) fibers
The ventrobasal thalamic complex and the ventroposterior group of nuclei project to two main cortical areas:
the ________ (a small number terminate in the precentral cortex) and the ________
primary sensory (postcentral) cortex
upper bank of the
sylvian fissure.
The ______ which also project
to the hypothalamus, amygdaloid nuclei, and limbic cortex,
probably mediate the arousal and affective aspects of
pain and autonomic responses.
intralaminar nuclei,
In skeletal muscle, pain
is caused by ischemia (the basis of intermittent claudication),
necrosis, hemorrhage, and injection of irritating
solutions as well as by injuries of ______
connective tissue sheaths.
Joints are insensitive to pricking,
cutting, and cautery; but pain can be produced in the
_______ by inflammation and by exposure to
hypertonic saline.
synovial membrane
Distention
of________ as occurs with thrombotic or embolic
occlusion, may be sources of pain;
arteries or veins,
These pain-producing substances-which include ____________
as well as potassium ions-elicit pain when they
are injected intraarterially or applied to the base of a
blister
histamine,
prostaglandins, serotonin, and similar polypeptides,
It causes erythema by dilating
cutaneous vessels and edema by releasing histamine
from mast cells; it also acts as a chemoattractant for
leukocytes. This reaction, called neurogenic inflammation
Substance P
persons. Inflammation lowers the threshold
for perception of pain by a process called_________
sensitization.
Strong emotion (fear or rage) suppresses pain, presumably by activation of the above-described \_\_\_\_\_\_\_\_\_\_
descending
noradrenergic system
In human subjects,
stimulation of the ___________r
through stereotactically implanted electrodes has also
produced a state of analgesia, though not consistently
midbrain periaqueductal gray matte
Opiates also act pre- and postsynaptically on the
neurons of laminae I and V of the dorsal hom, suppressing afferent pain impulses from both ______
the A-8 and C fibers.
Prolonged pain and fear are the
most powerful activators of this _______
endogenous opioid-mediated
modulating system.
most studied endorphins
B-endorphin, a peptide sequence of the pituitary
hormone /3-lipotropin, and two other peptides, enkephalin and dynorphin.
A demonstrable reduction in pain perception
(i.e., an elevated threshold) associated with an increased
reaction to the stimulus once it is perceived, is sometimes
referred to as ________
hyperpathia
there is an excessive reaction
to all stimuli, even those (such as light touch) that normally
do not evoke pain, a symptom termed ________
allodynia
Skin pain is of two types:
Together they constitute the ________
a pricking pain, evoked immediately on penetration of the skin by a needle point, or a stinging or burning pain that follows in a second or two
“double response”
_________has indefinite boundaries and its location is distant from the visceral structure involved.
It tends to be referred not to the skin overlying
the viscera of origin but to other areas innervated by the
same spinal segment (or segments) .
Deep pain
The convergence of deep and cutaneous afferents on the same dorsal hom cells, coupled with the fact that cutaneous afferents are far more numerous than visceral afferents and have direct connections with the thalamus, is probably responsible
for the phenomenon
referred pain.
The regions of projection of pain that originate in
the bones and adjacent ligamentous structures
“sclerotomes
alteration of the physiologic status of the
pools of neurons in adjacent segments of the spinal cord.
aberrant reference
One hypothesis proposes that in an injured nerve,
the unmyelinated sprouts of A-8 and C fibers become
capable of spontaneous ectopic excitation and afterdischarge
and are susceptible to ephaptic activation
C h ro n i c Pa i n
ephapse
(nerve-to-nerve cross-activation) is thought to be the
basis of causalgia (persistent burning and aching pain in
the territory of a partially injured nerve and beyond) and
its associated____________
reflex sympathetic dystrophy;
chronic
pains that fall into one of four categories:
( 1 ) pain
from an obscure medical disease, the nature of which
has not yet been disclosed by diagnostic procedures;
(2) pain associated with disease f the central or priphral
nervous system (i.e., neurogeruc, or neuropathic pam);
(3) pain associated with psychiatric disease; and (4) pain
of unknown cause.
These terms are generally used interchangeably t o designate
pain that arises from direct stimulation of nervous
tissue itself, central or peripheral, exclusive of pain as a
consequence of stimulation of C fibers by lesions of other
bodily structures
N e u rogenic, or N e u ropathic Pa i n
The sensations that characterize neuropathic pain
vary and are often multiple-__________________ qualities are described
burning, gnawing, aching,
and shooting or lancinating
mechanism of peripheral nerve pain
denervation hypersensitivity,
Regenerating axonal sprouts, as in a ___________ are
also hypersensitive to mechanical stimuli.
neuroma,
accumulate at the site of a neuroma and all along the
axon after nerve injury, and that this gives rise to ectopic and spontaneous activity of the sensory nerve cell and
its axon.
voltage-gated sodium channels
Spontaneous activity in ____________s is thought to give rise to burning pain;
firing of large myelinated A fibers is believed to produce _____________ induced by tactile stimuli
nociceptive C fiber
dysesthetic pain
Evidence that the sodium channel can generate neural
pain is given by the extraordinary disease ________
mutation of the sodium channel
gene, ________, leads to the early onset of paroxysmal autonomic changes and attacks of excruciating deep burning pain in the rectum, eye, or jaw,
“paroxysmal
extreme pain disorder” also known as “familial rectal
pain syndrome
SCN9A
It is characterized by persistent, severe
pain in the hand or foot, most pronounced in the digits,
palm of the hand, or sole.
The pain has a burning qualityand frequently radiates beyond the territory of the injured nerve.
causalgia
pathophysiology of causalgia
the result of an artificial
connection between efferent sympathetic and somatic
afferent pain fibers at the point of the nerve injury
__________has been
reported after limb and bone injury but in the absence of evident damage to adjacent nerves.
reflex sympathetic dystrophy
Alterations in _________, ___________
and changes in gabanergic inhibition in the dorsal
horns are all implicated in RSD
N-methyl-o-aspartate (NMDA) receptors,
induction of cyclooxygenase and prostaglandin synthesis,
_________ in which a fixed
dystonic posture is engrafted on a site of causalgic pain
causalgia- dystonia syndrome (Bhatia et al)
Complaints
of weakness and fatigue, depression, anxiety; insomnia,
nervousness, irritability, palpitations, etc., are woven into
the clinical syndrome,
Pa i n in Associati on with Psych iatric Diseases
Intractable pain may also be the leading symptom of
both ___________
somatization and conversion reactions.
Experienced
physicians are familiar with the patient who has undergone
multiple surgical procedures to address painful
complaints _________
so-called Briquet disease) .
Lesions of the ________ regions of one cerebral
hemisphere sometimes have peculiar effects on the
patient’s capacity to feel and react to pain. Under the title of ___________
parietooccipital
pain hemiagnosia,
There are also two varieties of rare individuals who
from birth are totally indifferent to pain coupled with
anhidrosis_______________or are
incapable of feeling pain___________
(“congenital insensitivity to pain”)
(“universal analgesia”).
mutation in the neural tyrosine kinase receptor, a nerve growth factor receptor;
(“congenital insensitivity to pain”)
suffer from either a congenital lack of pain neurons in
dorsal root ganglia, or to a mutation in the sodium channel
(“universal analgesia”)
The phenomenon of _________ is another
rare and unusual condition wherein the patient, although capable of distinguishing the different types of pain
stimuli from one another and from touch,
asymbolia for pain
The current
interpretation of asymbolia for pain is that it represents a particular type of __________ and ____________
agnosia (analgognosia) or apractagnosia
A useful way in which to undertake the management
of chronic pain that affects several parts of the body, as
in the patient with metastases, is with____________ taken together with aspirin, acetaminophen, or another nonsteroidal antiinflammatory drug (NSAID), or
tramadol.
codeine or oxycodone
__________ are sometimes useful drugs with which to begin, because of their effectiveness by mouth and the relatively slow development of tolerance
Methadone and levorphanol
provide relief for 24 to 72 h and which we have found
particularly useful in the treatment of pain from brachial
or lumbosacral plexus invasion by tumor and of painful
neuropathies such as those caused by diabetes and systemic
amyloidosis.
fentanyl
________are believed to prevent the activation of
nociceptors by inhibiting the synthesis of prostaglandins
in skin, joints, viscera, and other structures in the
peripheral nervous system.
Aspirin and
other NSAIDs
produce analgesia by acting as “false” neurotransmitters
at opiate receptor sites in the posterior horns of the spinal
cord-sites that are normally activated by endogenous
opioid peptides
Morphine and meperidine
Opioids not only
act directly on the central pain-conducting sensory systems
but also exert a powerful action on the ________
affective
component of pain.
Tricyclic antidepressants, especially the ___________ (imipramine, amitriptyline, and doxepin), block
serotonin reuptake and thus enhance the action of this
neurotransmitter at synapses and putatively facilitate the
action of the intrinsic opiate analgesic system
methylated
forms
The ____________
seem not to be as effective for the treatment of
chronic neuropathic pain
specific serotonin reuptake inhibitors (SSRI) antidepressants
A common combination for chronic pain
is the addition ____________________ and perhaps not surprisingly, this was superior
to either drug alone in a crossover trial in patients with
postherpetic neuralgia and diabetic neuropathy
of gabapentin to an opioid such as
morphine,
Concoctions such as
topical Ketamine mixed in soy lecithin to produce a gel
with drug concentration of 5 mg/ml, have been reportedly
useful in treating_________
post herpetic neuralgia
Aspirin mixed with_________in cold cream is said to
be very effective in the topical treatment of post herpetic
neuralgia,
chloroform
Only when a variety of analgesic medications
______________ and only when certain practical
measures, such as regional analgesia or anesthesia, have
completely failed, should one turn to neurosurgical procedures.
(including opioids
Spinothalamic tractotomy, in which the anterior half
of the spinal cord on one side is sectioned at an upper
thoracic level, effectively relieves pain in the __________
pposite leg
and lower trunk.
__________is also feasible
but with greater risk of loss of sphincteric control and,
at higher levels, of respiratory paralysis.
Bilateral tractotomy
Lesions placed in the ventroposterior
nucleus are said to diminish pain and thermal sensation
over the contralateral side of the body while leaving the
patient with ____________
all the misery or affective experience of pain
