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PSYCH 367 > Topic 15: The Cutaneous Senses > Flashcards

Topic 15: The Cutaneous Senses Flashcards

1
Q

Somatosensory System

A

the system that includes the cutaneous senses (senses involving the skin), proprioception (the sense of position of the limbs), kinesthesis (sense of movement of the limbs), haptic perception and the vestibular system

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2
Q

Cutaneous Senses

A

the ability to perceive sensations, such as touch and pain, that are based on the stimulation of receptors in the skin

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3
Q

Kinesthesis

A

the sense that enables us to feel the motions and positions of limbs and body

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4
Q

Epidermis

A

the outer layer of the skin, including a layer of dead skin cells

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5
Q

Dermis

A

the layer of skin below the epidermis

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6
Q

Mechanoreceptors

A

receptor that responds to mechanical stimulation of the skin, such a pressure, stretching, or vibration

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7
Q

Merkel Receptor

A

a disk-shaped receptor in the skin associated with slowly adapting fibers and the perception of fine details

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8
Q

Meissner Corpuscle

A

a receptor in the skin, associated with RA1 mechanoreceptors

it has been proposed that the Meissner corpuscle is important for perceiving tactile slip and for controlling the force needed to group objects

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9
Q

Rapidly Adapting (RA1) Fiber

A

fiber in the cutaneous system that adapts rapidly to a stimulus and so responds briefly to tactile stimulation

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10
Q

Ruffini Cyclinder

A

a receptor structure in the skin associated with slowly adapting fibers

it has been proposed that the Ruffini cylinder is involved in perceiving “stretching”

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11
Q

SA2

A

a slowly adapting fiber in the cutaneous system that is associated with the Ruffini cylinder and is located deeper in the skin than the SA1 fiber

this fiber also responds continuously to a tactile stimulus

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12
Q

Pacinian Corpuscle

A

a receptor with a distinctive elliptical shape associated with RA2 mechanoreceptors

it transmits pressure to the nerve fiber inside it only at the beginning or end of a pressure stimulus and is responsible for our perception of vibration and fine textures when moving the fingers over a surface

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13
Q

RA2

A

fiber in the skin associated with Pacinian corpuscle receptors that is located deeper in the skin than RA1 fibers

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14
Q

Medial Lemniscal Pathway

A

a pathway in the spinal cord that transmits signals from the skin toward the thalamus

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15
Q

Spinothalamic Pathway

A

one of the nerve pathways in the spinal cord that conducts nerve impulses from the skin to the somatosensory area of the thalamus

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16
Q

Secondary Somatosensory Cortex (S2)

A

the area in the parietal lobe next to the primary somatosensory area (S1) that processes neural signal related to touch, temperature, and pain

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17
Q

Homunculus

A

Latin for “little man”

refers to the topographic map of the body in the somatosensory cortex

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18
Q

Tactile Acuity

A

the smallest details that can be detected on the skin

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19
Q

Two-Point Threshold

A

the smallest separation between two points on the skin that is perceived as two points

a measure of acuity on the skin

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20
Q

Surface Texture

A

the visual and tactile quality of physical surface created by peaks and valleys

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21
Q

Duplex Theory of Texture Perception

A

the idea that texture perception is determined by both spatial and temporal cues that are detected by two types of receptors

originally proposed by David Katz and now called the “duplex theory”

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22
Q

Spatial Cues

A

in tactile perception, information about the texture of a surface that is determined by the size, shape, and distribution of surface elements such as bumps and grooves

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23
Q

Temporal Cues

A

in tactile perception, information about the texture of a surface that is provided by the rate of vibrations that occur as we move our finger across the surface

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24
Q

Active Touch

A

touch in which the observer plays an active role in touching and exploring an object, usually with his or her hands

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25
Q

Passive Touch

A

a situation in which a person passively receives tactile stimulation

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26
Q

Haptic Perception

A

the perception of three-dimensional objects by touch

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27
Q

Exploratory Procedures (EPs)

A

people’s movements of their hands and fingers while they are identifying three-dimensional objects by touch

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28
Q

Interpersonal Touching

A

one person touching another person, a.k.a. social touch

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29
Q

CT Afferents

A

unmyelinated nerve fibers found in hairy skin, which have been shown to be involved in social touch

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30
Q

Microneurography

A

technique used to record neural signals that involves inserting a metal electrode with a very fine tip just under the skin

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31
Q

Social Touch Hypothesis

A

hypothesis that CT afferents and their central projection are responsible for social touch

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32
Q

Discriminative Functions of Touch

A

functions of the touch system such as sensing details, texture, vibration, and objects

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33
Q

Affective Function of Touch

A

the eliciting of emotions by touch

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34
Q

Inflammatory Pain

A

pain caused by damage to tissues, inflammation of joints, or tumor cells

this damage releases chemicals that create an “inflammatory soup” that activates nociceptors

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35
Q

Neuropathic Pain

A

pain caused by lesions or other damage to the nervous system

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36
Q

Nociceptive Pain

A

this type of pain, which serves as a warning of impending damage to the skin, is caused by activation of receptors in the skin called nociceptors

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37
Q

Nociceptors

A

a fiber that responds to stimuli that are damaging to the skin

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38
Q

Direct Pathway Model of Pain

A

the idea that pain occurs when nociceptor receptors in the skin are stimulated and send their signals to the brain

this model does not account for the fact that pain can be affected by other factors in addition to stimulation of the skin

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39
Q

Phantom Limbs

A

a person’s continued perception of a limb, such as an arm or a leg, even though the limb has been amputated

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40
Q

Gate Control Model

A

Melzack and Wall’s idea that perception of pain is controlled by a neural circuit that takes into account the relative amount of activity in nociceptors, mechanoreceptors, and central signals

this model has been used to explain how pain can be influenced by factors other than stimulation of receptors in the skin

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41
Q

Transmission Cells

A

according to the gate control theory, the cell that receives (+) and (-) inputs from cells in the dorsal horn

T-cell activity determines the perception of pain

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42
Q

Placebo

A

a substance that a person believes will relive symptoms such as pain but that contains no chemicals that actually act on these symptoms

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43
Q

Placebo Effect

A

a relief from symptoms resulting from a substance that has no pharmacological effect

44
Q

Nocebo Effect

A

a negative placebo effect characterized by a negative response to negative expectations

45
Q

Multimodal Nature of Pain

A

the fact that the experience of pain has both sensory and emotional components

45
Q

Sensory Component of Pain

A

pain perception described with terms such as throbbing, prickly, hot, or dull

46
Q

Affective Component of Pain

A

the emotional experience associated with pain

for example, pain described as torturing, annoying, frightful, or sickening

47
Q

Opioids

A

a chemical such as opium, heroin, and other molecules with related structures that reduce pain and induce feelings of euphoria

48
Q

Naloxone

A

a substance that inhibits the activity of opiates

it is hypothesized that naloxone also inhibits the activity of endorphins and therefore can have an effect on pain perception

49
Q

Endorphins

A

chemical that is naturally produced in the brain and that causes analgesia

50
Q

Empathy

A

the ability to share and vicariously experience what someone else is feeling

51
Q

Social Pain

A

pain caused by negative social situations, such as rejection

52
Q

Physical-Social Pain Overlap Hypothesis

A

proposal that pain resulting from negative social experiences is processed by some of the same neural circuitry that processes physical pain

53
Q

Hand Dystonia

A

a condition which causes the fingers to curl into the palm

54
Q

Anosmia

A

loss of ability to smell due to injury or infection

55
Q

What are cutaneous senses?

A

based on mechanoreceptors in the skin

touch/tactile perception, vibration, texture, shape, warmth, cold, itch, & pain

56
Q

What is proprioception?

A

sensing position of the body and limbs

57
Q

What is kinesthesis?

A

sensing movement of the body and limbs

58
Q

What is haptic perception?

A

coordination of tactile and kinesthetic sensation

58
Q

What is vestibular sense?

A

equilibrioception

balance/spatial orientation (semicircular canals and vestibular sacs)

59
Q

What is the skin?

A

heaviest organ in human body: weighs 4 kg (8% of body mass)

on average, 1.8 m2 in area

thickness ranges from 0.5 mm (nose) to 4.0 mm (foot)

may be glabrous (non-hairy) or hairy

outer layer is epidermis, surface is corneum

inner layer is dermis

neural structures at the epi-/dermal boundary are believed to be receptors

60
Q

What is specificity theory?

A

one mechanoreceptor type proposed for each basic sensation

complex sensation supposedly comprised of “touch blends”

61
Q

What were the mechanoreceptor types proposed for each basic sensation in specificity theory?

A

warmth: Ruffini endings

cold: Krause end bulbs

touch: Meissner corpuscles

pain: free nerve endings

62
Q

What is punctate (“pointlike”) sensitivity?

A

if there’s a receptor under the skin at a location, there must be sensitivity to the associated sensation

63
Q

How was specificity theory determined?

A

stimulate skin, record sensation, determine which receptor type is responsible

microneurography: use electrode to find a nerve fiber (axon from receptor) triggered by the stimulus

histology: trace fiber back to the receptor

64
Q

What are the problems with specificity theory?

A

slightly problematic for participants

self-dissection: no correlation between structures and sensations; retest impossible

skin transmits kinetic and thermal energy over a distance from the point of stimulation; many receptor types affected by any stimulus

cornea has only free nerve endings, but all four sensations

sensory spots changed over time (e.g., touch in the morning, cold in the evening)

thermal grill illusion: simultaneous presentation of separate warm + cold stimuli = painfully hot

65
Q

What is the conclusion of specificity theory?

A

cannot determine which potential receptor structure associated with each sensation

66
Q

What is pattern theory?

A

the pattern of neural impulses from a number of receptors corresponds to a particular sensation

assumed that receptors differ in structure, but not in function

the same receptor can yield two different kinds of sensations, depending on the intensity of activation

e.g., mild pressure –> touch; more intense pressure –> pain

but why have so many different kinds of receptors?

67
Q

What is stimulus preference theory?

A

intermediate approach: each sensation arises from the firing of a number of receptor types, tuned to different aspects of a stimulus

68
Q

What was the Lowenstein & Skalak (1996)?

A

dissected Pacinian corpuscles (PCs)

1-4 mm long; have 20-40 layers

corpuscle around nerve fiber acts to absorb sustained pressure

fiber itself only stimulated at onset or offset of stimulus (or by changing stimulus)

69
Q

What recent evidence supports stimulus preference of other nerve fibers?

A

fibers are relatively specialized to certain stimulation, but may also respond (more weakly) to other stimuli

70
Q

What is the spinothalamic pathway?

A

smaller nerve fibres synapse in the spinal cord

ascends via spinal cord and brainstem to the ventral posterolateral nucleus (VPN) of the thalamus

projects to the anterior cingulate cortex (involved in pain), insular cortex (involved in emotion), and primary somatosensory cortex

carries primarily temperature and pain information

71
Q

What is the medial lemniscus pathway?

A

larger, longer nerve fibers synapse in the medulla

ascends via medial lemniscus to the thalamus

projects to the primary somatosensory cortex

conveys touch and proprioceptive information

72
Q

What is the evoked potential method for measuring the somatosensory cortex?

A

electrode on scalp measures cortical activity

different skin loci stimulated until activity produced at electrode

very time-consuming

73
Q

What is the stimulation method for measuring the somatosensory cortex?

A

operating to remove tumors

didn’t want to damage sensorimotor areas

stimulated cortex with low voltage, which produced sensations in awake patients

allowed mapping of sensory and motor cortexes

74
Q

What is the somatotopic organization of the cortex?

A

adjacent points on the skin have adjoining cortical representations (and columnar organization similar to visual cortex)

75
Q

What is the homunculus?

A

touch represented in somatosensory cortex as a body map, or homunculus (“little man”)

some parts of homunculus disproportionately large compared to corresponding body locus (e.g., lips)

these body areas are more sensitive, partly due to increased density of receptors

amount of cortical area can be changed via experience; even in adults; experience-dependent neural plasticity

there are multiple homunculi; each has a different function (e.g., discrimination of forms/shapes, textures, etc.)

76
Q

What is touch/tactile perception?

A

touch is constant pressure; vibration is changing pressure

stimulus containing kinetic energy causes an abrupt change in skin tension

soft touch signals go to insular cortex, which processes emotion

plays a major role in development, social cooperation, and affiliation

may be evolutionary holdover from social grooming, important for maintaining social relationships

77
Q

What was the Tiffany Field et al. (1986) study on touch perception?

A

premature babies massaged (vs. in incubator)

gained 47% more weight

more socially responsive, slept better

discharged 6 days earlier

78
Q

What is public distance?

A

for public speaking (over 3.5 m, 12 ft)

79
Q

What is social distance?

A

for interactions with stranger and acquaintances (1.2-3.5 m, 4-12 ft)

80
Q

What is personal distance?

A

for interactions with friends and family (45-120 cm, 1.5-4 feet)

81
Q

What is intimate distance?

A

for whispering, touching, or embracing intimate partners (15-45 cm, 6-18 inches)

82
Q

What is the Cruso & Wetzel (1984) study on touch perception?

A

waitresses at two restaurants in Oxford, Mississippi enlisted to investigate the effects of touch on tipping

touch manipulations: no touch, placed hand on diner’s shoulder, touched diner’s palm when giving change

results: smallest tips, 18% greater, 37% greater

83
Q

What is oxytocin?

A

hormones synthesized in the hypothalamus and stored in the pituitary gland

involved in contractions during labor and lactation

also released by touch and at orgasm in males and females; may cause endorphin release

84
Q

What was the Turner et al. (1999) study on oxytocin?

A

oxytocin levels measured in blood samples of 26 women

relaxation massage: oxytocin levels rose slightly

recollection of a negative emotion: oxytocin fell slightly

recollection of a positive emotion: no effect

85
Q

What are the ways of measuring touch threshold?

A

absolute threshold: von Frey hair pushed into skin until hair bends; each bends with a different amount of force; use stronger hairs until absolute threshold established

difference threshold is called two-point threshold: smallest separation between two points on the skin that can be perceived

86
Q

What is active touch?

A

actively handling an object aids identification

87
Q

What is the J.J. Gibson (1962) study on active touch?

A

observers had to identify shape of six cookie cutters, while blindfolded (e.g. teardrop, star, triangle)

pushed onto palm (passive): 29% correct

actively handed: 95% correct

88
Q

What are the different “exploratory procedures” that provide information on different stimulus features?

A

lateral motion and contour following: texture

pressure: hardness

static contact: temperature

unsupported holding: weight

enclosure: global shape, volume

enclosure and contour following: specific shape

89
Q

What is thermoception?

A

Dallenbach (1927): found no correspondence between spots that responded to cool and warm; warmth and cold are separate

90
Q

How is temperature encoded by two types of fibers?

A

warm fibers: 30-48 degrees

cold fibers: 20-45 degrees

thermal grill illusion simultaneously activates warm and cold fibers

91
Q

What is paradoxical cold?

A

hot stimulus (45-50 degrees) produces sensation of cold; may be due to activation of cold fibers

92
Q

What is thermal adaptation?

A

John Locke (1690): is local, not global

physiological zero: temperature at which receptors have become adapted; perception of temperature is relative at this point

only occurs completely within 29-37 degree range

takes ~20 min; depends on difference from normal temperature

93
Q

What is pain perception and nociception?

A

an unpleasant sensory or emotional experience associated with actual or potential tissue damage

nociception is neural encoding of impending or actual tissue damage; i.e., noxious stimulation

once thought to be result of excess of intensity, but is more complex than this

evolutionarily adaptive: tissue damage –> intense pain –> lots of motivation

affected by non-physical factors, including cultural background

94
Q

What is the specificity theory approach to pain perception?

A

nociceptors: receptors for noxious stimuli; peptide substance P released from C fibers

A delta fibers transmit sharp, pricking pain
C fibers transmit burning, throbbing pain

double pain: sharp pain, followed by dull pain

fibers enter spinal cord via dorsal horn, then to substantia gelatinosa

95
Q

What are the structures involved in the gate-control theory of pain perception?

A

SG is substantia gelatinosa (in spinal cord)

T is pain transmission cell (in spinothalamic pathway)

L-fibers are large diameter axons from mechanoreceptors

S-fibers are small diameter axons from nociceptors

central control is top-down signals from the brain

96
Q

What are the steps involved in the gate-control theory of pain perception?

A

activity in L fibers: closes gate
activates SG (-) –> T cell inhibited; no pain signal

activity in S fibers: opens gate
activates SG (+) –> T cell excited; pain signal sent

rubbing may reduce pain by activating A beta fibers

97
Q

What is the placebo effect?

A

person led to believe that a substance will relieve symptoms, feels no pain

98
Q

How may pain signals be attentuated?

A

may be due to endogenous opioids: natural analgesics in the brain; e.g., endorphins (pituitary) and enkephalin (CNS, intestines)

inhibit substance P

evidence: naloxone; narcotic antagonist (blocks opioids), wipes out effects of placebo and acupuncture, but not hypnosis

99
Q

What is synesthesia?

A

involuntary physical experience of a cross-modal association, in which stimulation of one sensory modality reliably causes a perception in one or more different senses

not the same as using a metaphor to describe an experience

100
Q

What is the experience of synesthesia like?

A

responses are generic and unelaborated (e.g., colors, simple shapes, textures, tastes)

one-way projections: a synesthete who sees colors when hearing spoken words does not necessarily hear words when viewing colors

idiosyncratic: different synesthetes have different experiences to same stimulus

101
Q

What is the more connections theory of synesthesia?

A

synesthetes have genetic overabundance of neural connections

increased wiring is due to insufficient pruning

this results in a breakdown in the modularity of perception, so that one modality “samples” an event in another

evidence: synesthetes found to have greater neural connectivity

102
Q

What is the less inhibition theory of synesthesia?

A

not due to abnormal connections

normally, excitation and inhibition in the brain are balanced

in synesthetes, there is less inhibition in feed-backward connections from high-level multisensory brain areas in single-sense areas

evidence: synesthesia may be induced in anyone by LSD or mescaline, which may activate existing pathways

103
Q

What are the implications of synesthesia?

A

may reveal aspects of top-down processing, the binding problem, sensory integration and conscious experience

PSYCH 367 (15 decks)

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