The Somatosensory System Flashcards
The somatosensory system reports the body’s interactions with its immediate surroundings via “touch and feel” sensing of ______ against the skin, and via _____ sensations
contact pressure; thermal
Its peripheral receptors are “tuned” to _____ among different qualities of the various stimuli to which they are responsive, e.g. texture and shape, hot vs. cold, innocuous vs. noxious
discriminate
the structural organization that gives rise to “somatotopic mapping” ensures
that _____ of the stimulus as applied to the body can be accurately identified
location
somatosensory reporting relies upon two “design characteristics”: _____ and _____.
Discrimination and location of the stimulus
somatotopic mapping → gives rise to _____, but note that location of individual receptive
fields within each dermatome is also mapped
dermatomes
peripheral somatosensory neurons are located in the ______, and is classified as?
dorsal root ganglia; pseudo-unipolar
the ______fiber travels as part of a peripheral nerve to enter the spinal cord via a dorsal root
afferent sensory
whereas somatosensory signals from the skin project into the brain via _____, allowing precise perception of location on the body surface
labeled lines
What does not use the labeled line concept to provide sensory inputs to the brain?
Visceral receptors
_____ receptors are broadly distributed, but they give rise to relatively few centrally projecting fibers
visceral
non-nociceptive and nociceptive fibers arising from the viscera therefore have a relatively large receptive field, which means _____ discrimination of the precise location
poor
in addition, _____ afferent fibers tend to synapse on spinal relay neurons that also convey somatic (body surface) sensory input
visceral
visceral stimuli may therefore be perceived as originating from a _____ site → our brain may refer neural signaling arising from visceral receptors to a _____ location
somatic
This is why people who is having heart problems will show signs of shoulder and neck pain
Even for heart attack, the brain perceives the signal as signal from the _____ of the body, where as it’s from the heart. “Shoulder and neck pain”
surface
peripheral fibers conveying _____ somatosensory afferent
signals are classified alphabetically (“A” and “C”)
non-proprioceptive
What fiber type?
-large diameter, heavy myelin sheath (fastest conducting)
− these may also be referenced as _____.
A-alpha; “Type 1”
What fiber type?
-medium diameter, myelinated
− these may also be referenced as _____.
A-beta; “Type 2”
What fiber type?
-small diameter, myelinated
A-delta
What fiber type?
-unmyelinated (slowest conducting)
C fibers
fibers conveying PROPRIOCEPTIVE afferent signals from muscle are classified numerically [from type I (_____) to type IV (_____)]
largest; smallest
Large Aα and Aβ (or Type 1 and 2) somatosensory fibers convey _____ information from the skin
Mechanical
smaller Aδ and unmyelinated C somatosensory fibers convey _____ information and _____.
thermal; pain
Mechanoreceptors in the skin provide our sensation of _____ and _____.
touch; feel
glabrous skin of the hands and feet contain four types of mechanoreceptors:
Superficial? (2)
Deep? (2)
Superficial: Merkel’s disk and Meissner’s corpuscle
Deep: Ruffini corpuscle and Pacinian corpuscle
Superficial receptors (Merkel's disk and Meissner's corpuscle): Give rise to \_\_\_\_\_afferent fibers. -Have no end organ
Aα (Type1)
Deep receptors (Ruffini corpuscle and Pacinian corpuscle) •give rise to \_\_\_\_\_afferent fibers. • are embedded within an end organ structure (sensory nerve ending).
Aβ (Type2)
the receptive field is the _____ to which an applied stimulus will
trigger signaling along a particular afferent sensory fiber
spatial domain
The size (surface area) of the Type 1 (Aa) fibers of the receptive field is determined by the distribution of the multiple receptors that collectively feed into one particular fiber, which are _____ exposed to the stimulus energy (force of applied pressure).
DIRECTLY
The size (surface area) of the Type 2 (Aβ) fibers of the receptive field is determined by the _____ within which the sensory nerve ending is embedded, through which the stimulus energy (applied pressure) is transmitted to the sensory nerve ending.
end-organ structure
The cutaneous mechanoreceptors are also classified as either _____ or _____ adapting to “report” different characteristics of the applied stimulus
slowly; rapidly
slowly adapting:
• _____ signaling (at a relatively steady frequency) throughout the duration that the stimulus is applied
• continued reporting → the stimulus is _____
maintains; sustained
rapidly adapting:
• maintains signaling just while the
stimulus intensity is _____
• reports “_____” and “_____”, and more generally, variations in the stimulus intensity
changing; “stimulus on” and “stimulus off”
Merkel’s disk and Meisner’s corpuscle are _____ mechanoreceptors.
superficial
Which type of mechanoreceptors consist of a individual mechanosensitive nerve terminals associated with a small
flattened non-neural epithelial cell (the “end organ”)?
Superficial mechanoreceptors: Merkel’s disk and Meisner’s corpuscle
Which type of mechanoreceptor’s receptive field for both types is relatively small, providing relatively fine spatial
resolution → good discrimination of location?
Superficial mechanoreceptors: Merkel’s disk and Meisner’s corpuscle
Superficial mechanoreceptors: Merkel’s disk and Meisner’s corpuscle
• afferent fibers are classified as either ___ or _____.
Aα; Type 1
Merkel’s disks are ______: responsive to continually applied pressure
slowly adapting (SA1)
Meissner’s corpuscles are \_\_\_\_\_: responsive to repetitive, low frequency stimuli (sensitivity is to light touch)
rapidly adapting (RA1)
Pacinian and Ruffini corpuscles are _____ mechanoreceptors.
Deep
Which type of mechanoreceptors has a large, specialized end organ that creates a relatively LARGE receptive field?
deep mechanoreceptors: Pacinian and Ruffini corpuscles
deep mechanoreceptors: Pacinian and Ruffini corpuscles
• afferent fibers are classified as either _____ or _____.
Aβ; Type 2
Ruffini’s corpuscles are ______: signaling sustained pressure
slowly adapting (SA2)
Pacinian corpuscles are ______: signaling changes in pressure (e.g. vibrations)
rapidly adapting (RA2)
slowly adapting mechanoreceptors report steady applied pressures, to enable discrimination of the _____ and _____ of objects pressing against the skin
shape; size
the _____ of signaling reports the intensity of the stimulus (i.e. how forceful the pressure is being applied to the skin surface)
frequency
_____ adapting mechanoreceptors report changing stimulus energy, e.g.
that caused by vibration or motion
rapidly
somatotopic mapping and transmission of sensory information from each receptive field via labeled lines contributes to discernment of? (2)
- points of contact with the object being grasped
* the size and shape of objects that we grasp
the mixed population of receptor types allows discernment of (2)
- surface texture
* movements of the object relative to the surface of the fingers and hand
Hair follicle receptors:
• each follicle is innervated by _____ nerve ending
• deformation (bending) induces a _____ potential
• may be both slowly and rapidly adapting
a single; generator
Cutaneous thermoreceptors individually respond to changes within a _____ range of surface (skin) temperature
limited
T/F: individual thermoreceptors respond to either heat (↑ temperature) or cold
(↓ temperature), but not to both; more so to cold than to heat
TRUE
Thermoreceptors are limited in their individual response ranges, based
upon skin temperature (Ts):
– heat receptors [warm to hot]: 95 to 110°F (___ fibers) – cold receptors [cool to cold]: 85 to 60°F (___ fibers)
C; Aδ
thermoreceptors are most sensitive to changes in temperature; most adapt _____ to sustained temperature
rapidly
___ threshold cold receptors detect rapid drops in temperature below 88°F; ___ threshold cold receptors/nociceptors detect rapid drops in temperature in the lower range (down to and below 32°F)
low; high
Warm receptors report increases in temperature above 97°F, but are _____ rapidly adapting that cold receptors, are also much _____ sensitive to temperature change than cold receptors, providing _____ sensitivity to warming than to cooling
less
separate cold and heat nociceptors generate the perception of _____ to either cold [Ts below 60°F] or heat [Ts above 110°F]
pain
We are only aware of _____ in temperature, thermoreceptors are _____ adapting.
change; rapidly
Thermoreceptors can also be fired off by ______.
botanics/chemicals (hot peppers)
Pain is the perception of _____ (tissue damaging) stimuli
noxious
nociceptors transduce painful stimuli arising from all three somatosensory
modalities:
• _____ → both sharp and sustained pressure
• _____ → hot (Ts > 110°F) and cold (Ts < 60° F)
• _____ → irritants, e.g. acid, inflammatory molecules
mechanical; thermal; chemical
_____ nociceptors are responsive to a combination of the above modalities.
Polymodal
_____generally consist of free nerve endings with little or no
specialized structures. There is little to no “modulation” (either focusing or spreading out) through an accessory structure to the receptor
Nociceptors
What differentiates a nociceptor from a non-nociceptive somatosensory receptor is the receptor’s _____
stimulus threshold
Nociceptors have a _____ stimulus threshold, compared to non- nociceptive receptors
higher
a greater stimulus intensity is therefore required to initiate signaling from _____
nociceptors
nociceptive signaling is conveyed from the periphery into the CNS via ___ and ___ fibers
Aδ; C
Nociceptive signaling: -Aδ fibers arise from mechanical and thermal nociceptors; convey _____sensation of pain
sharp (short lasting)
Nociceptive signaling: -C fibers arise from polymodal receptors; convey ___ or ___ pain
dull; diffuse
______ → is reflected as the strength of the nervous signaling that the receptor generates in response to a given strength of stimulus intensity.
receptor sensitivity
Mechanoreceptor normally respond to that amount of force by signaling at 10 Hz:
• if the response is now 14 Hz → _____ sensitivity
• if the response is now 7 Hz → _____ sensitivity
increased; decreased
Receptor sensitivity is determined by the receptor’s stimulus threshold:
• lower stimulus threshold→______ sensitivity
•higher stimulus threshold→______ sensitivity
higher (more responsive) ; lower (less responsive)
_____ → sensitization (an increase in the receptor sensitivity)
• in effect, the stimulus threshold for these receptors is reduced, which leads to:
− a perception that a given stimulus is more painful than normal
− what is normally a non-noxious stimulus may now be perceived as painful
hyperalgesia
_____ → desensitization (a reduction in the receptor sensitivity)
in effect, the stimulus threshold for these receptors is elevated, which leads to:
− a perception that a given stimulus is less painful than normal
− what is normally a noxious stimulus may now be perceived as non-painful
analgesia
_____ hyperalgesia may arise from sensitization of peripheral nociceptors, e.g. by various chemical substances
primary
Secondary hyperalgesia may arise from a change in the strength of _____ of peripheral afferent signals arising from the nociceptors to the second order relay neurons
synaptic transmission
released neuropeptides such as substance P and CGRP may also stimulate inflammation by sensitizing and/or activating surrounding nociceptors.
→ ______
neurogenic inflammation
During hyperalgesia; uninjured tissue’s nociceptor stimulus threshold are relatively _____
High
During hyperalgesia; injured tissue’s nociceptor stimulus threshold are _____
reduced
The SURROUNDING mechanical hyperalgesia may be due to sensitization of C-fiber nociceptors, as well as from _____ sensitization of C-fiber neurotransmission within the spinal cord.
secondary (2nd order neurons) Surrounding= Not localized/within the area, into spinal cord
secondary hyperalgesia may arise from sensitization of the dorsal horn synaptic relay for _____nociceptive signaling
ascending
Analgesia is _____ sensitivity to a painful stimulus
reduced
_____: pain due to a stimulus that does not normally provoke pain
→ usually due to sensitization within the CNS, causing non-nociceptive inputs (e.g. light touch) to activate pain pathways via spinal interneurons
allodynia
______: pain initiated or caused by a primary lesion or dysfunction within the central nervous system
→ disease, trauma, or space-occupying lesions that alter normal function of tracts, nuclei and cell bodies of the nervous system in a way that stimulate nociceptive pain pathways
central pain
_____: pain in the distribution of a nerve or nerves
→ typically described as lancinating (tearing, darting, sharply cutting) or paroxysmal (sudden recurrence, spasms), occurring spontaneously or triggered in response to minimal stimuli (allodynia)
neuralgia
_____: pain initiated or caused by a primary lesion, dysfunction, or transitory perturbation in the peripheral or central nervous system
→ normally resulting from sensitization of nociceptors, dorsal root ganglia, and dorsal horn neurons and interneurons, presenting clinically as spontaneous pain, hyperalgesia, and allodynia
neurogenic pain
