The Somatosensory System

Question 1

The somatosensory system reports the body’s interactions with its immediate surroundings via “touch and feel” sensing of ______ against the skin, and via _____ sensations

Answer 1

contact pressure; thermal

Question 2

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

Answer 2

discriminate

Question 3

the structural organization that gives rise to “somatotopic mapping” ensures
that _____ of the stimulus as applied to the body can be accurately identified

Answer 3

location

Question 4

somatosensory reporting relies upon two “design characteristics”: _____ and _____.

Answer 4

Discrimination and location of the stimulus

Question 5

somatotopic mapping → gives rise to _____, but note that location of individual receptive
fields within each dermatome is also mapped

Answer 5

dermatomes

Question 6

peripheral somatosensory neurons are located in the ______, and is classified as?

Answer 6

dorsal root ganglia; pseudo-unipolar

Question 7

the ______fiber travels as part of a peripheral nerve to enter the spinal cord via a dorsal root

Answer 7

afferent sensory

Question 8

whereas somatosensory signals from the skin project into the brain via _____, allowing precise perception of location on the body surface

Answer 8

labeled lines

Question 9

What does not use the labeled line concept to provide sensory inputs to the brain?

Answer 9

Visceral receptors

Question 10

_____ receptors are broadly distributed, but they give rise to relatively few centrally projecting fibers

Answer 10

visceral

Question 11

non-nociceptive and nociceptive fibers arising from the viscera therefore have a relatively large receptive field, which means _____ discrimination of the precise location

Answer 11

poor

Question 12

in addition, _____ afferent fibers tend to synapse on spinal relay neurons that also convey somatic (body surface) sensory input

Answer 12

visceral

Question 13

visceral stimuli may therefore be perceived as originating from a _____ site → our brain may refer neural signaling arising from visceral receptors to a _____ location

Answer 13

somatic

This is why people who is having heart problems will show signs of shoulder and neck pain

Question 14

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”

Answer 14

surface

Question 15

peripheral fibers conveying _____ somatosensory afferent

signals are classified alphabetically (“A” and “C”)

Answer 15

non-proprioceptive

Question 16

What fiber type?
-large diameter, heavy myelin sheath (fastest conducting)
− these may also be referenced as _____.

Answer 16

A-alpha; “Type 1”

Question 17

What fiber type?
-medium diameter, myelinated
− these may also be referenced as _____.

Answer 17

A-beta; “Type 2”

Question 18

What fiber type?

-small diameter, myelinated

Answer 18

A-delta

Question 19

What fiber type?

-unmyelinated (slowest conducting)

Answer 19

C fibers

Question 20

fibers conveying PROPRIOCEPTIVE afferent signals from muscle are classified numerically [from type I (_____) to type IV (_____)]

Answer 20

largest; smallest

Question 21

Large Aα and Aβ (or Type 1 and 2) somatosensory fibers convey _____ information from the skin

Answer 21

Mechanical

Question 22

smaller Aδ and unmyelinated C somatosensory fibers convey _____ information and _____.

Answer 22

thermal; pain

Question 23

Mechanoreceptors in the skin provide our sensation of _____ and _____.

Answer 23

touch; feel

Question 24

glabrous skin of the hands and feet contain four types of mechanoreceptors:
Superficial? (2)
Deep? (2)

Answer 24

Superficial: Merkel’s disk and Meissner’s corpuscle

Deep: Ruffini corpuscle and Pacinian corpuscle

Question 25

``` Superficial receptors (Merkel's disk and Meissner's corpuscle): Give rise to _____afferent fibers. -Have no end organ ```

Answer 25

Aα (Type1)

Question 26

``` Deep receptors (Ruffini corpuscle and Pacinian corpuscle) •give rise to _____afferent fibers. • are embedded within an end organ structure (sensory nerve ending). ```

Answer 26

Aβ (Type2)

Question 27

the receptive field is the _____ to which an applied stimulus will trigger signaling along a particular afferent sensory fiber

Answer 27

spatial domain

Question 28

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).

Answer 28

DIRECTLY

Question 29

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.

Answer 29

end-organ structure

Question 30

The cutaneous mechanoreceptors are also classified as either _____ or _____ adapting to “report” different characteristics of the applied stimulus

Answer 30

slowly; rapidly

Question 31

slowly adapting: • _____ signaling (at a relatively steady frequency) throughout the duration that the stimulus is applied • continued reporting → the stimulus is _____

Answer 31

maintains; sustained

Question 32

rapidly adapting: • maintains signaling just while the stimulus intensity is _____ • reports “_____” and “_____”, and more generally, variations in the stimulus intensity

Answer 32

changing; “stimulus on” and “stimulus off”

Question 33

Merkel’s disk and Meisner’s corpuscle are _____ mechanoreceptors.

Answer 33

superficial

Question 34

Which type of mechanoreceptors consist of a individual mechanosensitive nerve terminals associated with a small flattened non-neural epithelial cell (the “end organ”)?

Answer 34

Superficial mechanoreceptors: Merkel’s disk and Meisner’s corpuscle

Question 35

Which type of mechanoreceptor's receptive field for both types is relatively small, providing relatively fine spatial resolution → good discrimination of location?

Answer 35

Superficial mechanoreceptors: Merkel’s disk and Meisner’s corpuscle

Question 36

Superficial mechanoreceptors: Merkel’s disk and Meisner’s corpuscle • afferent fibers are classified as either ___ or _____.

Answer 36

Aα; Type 1

Question 37

Merkel’s disks are ______: responsive to continually applied pressure

Answer 37

slowly adapting (SA1)

Question 38

``` Meissner’s corpuscles are _____: responsive to repetitive, low frequency stimuli (sensitivity is to light touch) ```

Answer 38

rapidly adapting (RA1)

Question 39

Pacinian and Ruffini corpuscles are _____ mechanoreceptors.

Answer 39

Deep

Question 40

Which type of mechanoreceptors has a large, specialized end organ that creates a relatively LARGE receptive field?

Answer 40

deep mechanoreceptors: Pacinian and Ruffini corpuscles

Question 41

deep mechanoreceptors: Pacinian and Ruffini corpuscles | • afferent fibers are classified as either _____ or _____.

Answer 41

Aβ; Type 2

Question 42

Ruffini’s corpuscles are ______: signaling sustained pressure

Answer 42

slowly adapting (SA2)

Question 43

Pacinian corpuscles are ______: signaling changes in pressure (e.g. vibrations)

Answer 43

rapidly adapting (RA2)

Question 44

slowly adapting mechanoreceptors report steady applied pressures, to enable discrimination of the _____ and _____ of objects pressing against the skin

Answer 44

shape; size

Question 45

the _____ of signaling reports the intensity of the stimulus (i.e. how forceful the pressure is being applied to the skin surface)

Answer 45

frequency

Question 46

_____ adapting mechanoreceptors report changing stimulus energy, e.g. that caused by vibration or motion

Answer 46

rapidly

Question 47

somatotopic mapping and transmission of sensory information from each receptive field via labeled lines contributes to discernment of? (2)

Answer 47

* points of contact with the object being grasped | * the size and shape of objects that we grasp

Question 48

the mixed population of receptor types allows discernment of (2)

Answer 48

* surface texture | * movements of the object relative to the surface of the fingers and hand

Question 49

Hair follicle receptors: • each follicle is innervated by _____ nerve ending • deformation (bending) induces a _____ potential • may be both slowly and rapidly adapting

Answer 49

a single; generator

Question 50

Cutaneous thermoreceptors individually respond to changes within a _____ range of surface (skin) temperature

Answer 50

limited

Question 51

T/F: individual thermoreceptors respond to either heat (↑ temperature) or cold (↓ temperature), but not to both; more so to cold than to heat

Answer 51

TRUE

Question 52

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)

Answer 52

C; Aδ

Question 53

thermoreceptors are most sensitive to changes in temperature; most adapt _____ to sustained temperature

Answer 53

rapidly

Question 54

___ 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)

Answer 54

low; high

Question 55

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

Answer 55

less

Question 56

separate cold and heat nociceptors generate the perception of _____ to either cold [Ts below 60°F] or heat [Ts above 110°F]

Answer 56

pain

Question 57

We are only aware of _____ in temperature, thermoreceptors are _____ adapting.

Answer 57

change; rapidly

Question 58

Thermoreceptors can also be fired off by ______.

Answer 58

botanics/chemicals (hot peppers)

Question 59

Pain is the perception of _____ (tissue damaging) stimuli

Answer 59

noxious

Question 60

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

Answer 60

mechanical; thermal; chemical

Question 61

_____ nociceptors are responsive to a combination of the above modalities.

Answer 61

Polymodal

Question 62

_____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

Answer 62

Nociceptors

Question 63

What differentiates a nociceptor from a non-nociceptive somatosensory receptor is the receptor’s _____

Answer 63

stimulus threshold

Question 64

Nociceptors have a _____ stimulus threshold, compared to non- nociceptive receptors

Answer 64

higher

Question 65

a greater stimulus intensity is therefore required to initiate signaling from _____

Answer 65

nociceptors

Question 66

nociceptive signaling is conveyed from the periphery into the CNS via ___ and ___ fibers

Answer 66

Aδ; C

Question 67

Nociceptive signaling: -Aδ fibers arise from mechanical and thermal nociceptors; convey _____sensation of pain

Answer 67

sharp (short lasting)

Question 68

Nociceptive signaling: -C fibers arise from polymodal receptors; convey ___ or ___ pain

Answer 68

dull; diffuse

Question 69

______ → is reflected as the strength of the nervous signaling that the receptor generates in response to a given strength of stimulus intensity.

Answer 69

receptor sensitivity

Question 70

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

Answer 70

increased; decreased

Question 71

Receptor sensitivity is determined by the receptor’s stimulus threshold: • lower stimulus threshold→______ sensitivity •higher stimulus threshold→______ sensitivity

Answer 71

higher (more responsive) ; lower (less responsive)

Question 72

_____ → 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

Answer 72

hyperalgesia

Question 73

_____ → 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

Answer 73

analgesia

Question 74

_____ hyperalgesia may arise from sensitization of peripheral nociceptors, e.g. by various chemical substances

Answer 74

primary

Question 75

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

Answer 75

synaptic transmission

Question 76

released neuropeptides such as substance P and CGRP may also stimulate inflammation by sensitizing and/or activating surrounding nociceptors. → ______

Answer 76

neurogenic inflammation

Question 77

During hyperalgesia; uninjured tissue's nociceptor stimulus threshold are relatively _____

Answer 77

High

Question 78

During hyperalgesia; injured tissue's nociceptor stimulus threshold are _____

Answer 78

reduced

Question 79

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.

Answer 79

secondary (2nd order neurons) Surrounding= Not localized/within the area, into spinal cord

Question 80

secondary hyperalgesia may arise from sensitization of the dorsal horn synaptic relay for _____nociceptive signaling

Answer 80

ascending

Question 81

Analgesia is _____ sensitivity to a painful stimulus

Answer 81

reduced

Question 82

_____: 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

Answer 82

allodynia

Question 83

______: 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

Answer 83

central pain

Question 84

_____: 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)

Answer 84

neuralgia

Question 85

_____: 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

Answer 85

neurogenic pain