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.