Midterm 3 - Topic 11 Flashcards
1
Q
Why is touch probably the most complex sense we have?
A
It covers our entire body
It is our largest sensory system
Unlike other senses, it is not only in one place
The sensitivity of skin varies, depending on its location
2
Q
How can touch be further divided?
A
Into three clusters that belong to what is called proprioception
3
Q
What three clusters belong to proprioception?
A
Temperature sense
Kinesthetic sense (muscular info)
Vestibular sense (motion perception topic)
Pain
4
Q
What sensory system is responsible for touch?
A
Skin
5
Q
How does skin have a very important protective value?
A
Protects from potential tissue damage when we feel pain
Protects us from extremely hot or extremely cold temperatures
6
Q
What type of skin covers most of our body? What does it contain?
A
Hairy skin
Either noticeable or almost invisible hairs
7
Q
What 3 layers is the skin divided in?
A
Epidermis (outer layer)
Dermis
Subcutaneous tissue
8
Q
What does the epidermis contain?
A
Dead skin
9
Q
Dermis
A
Makes new skin cells
10
Q
Subcutaneous tissue
A
Contains connective tissue and fat globules
11
Q
What does the skin contain in addition to the three layers
A
An array of glands, nerve endings and veins
12
Q
Name 2 receptors that the skin contains
A
Nerve fibre
Pacinian corpuscule
13
Q
Glaborous skin
A
Another type of skin that covers the palm of our hands, the sole of our feet and the smooth surfaces of our toes and fingers
14
Q
How are the two types of skin different?
A
Glaborous skin has a thicker outer layer and a more complex mixture of receptors
We use these areas to explore the physical qualities of objects
15
Q
Explain how the skin varies in thickness
A
Facial skin: about .5 mm
Skin on sole of feet: about 5 mm
16
Q
What two types can the skin receptor types be divided into?
A
Skin receptors with free nerve endings
Skin receptors with encapsulated endings
17
Q
What suggests that the different endings of the receptors might show functional differences?
A
Differences in the size, shape, and degree or organization of these endings
18
Q
Oldest theory about the skin senses
A
Specificity theory
19
Q
What does the specificity theory state?
A
That each of the different types of receptors responds only to one kind of physical stimulus (e.g., temperature)
Separate receptors for touch, cold, warmth, and pain
20
Q
Does most evidence support or argue against the specificity theory?
A
Argues against
21
Q
In a typical study, how do researchers study the skin sense?
A
Researchers poke a needle around on their own skin until they locate a region especially sensitive to pain
They then cut out that small region of skin and use a microscope to determine the type of receptors located beneath the surface
The results from this type of studies suggest the conclusion that the type of receptor is not related to the type of sensation
22
Q
What is a more recent theory about the skin sense?
A
Pattern theory
23
Q
What does the pattern theory suggest?
A
The pattern of nerve impulse determines sensation
24
Q
Explain the pattern theory
A
Each kind of receptor responds to many kinds of stimulation, but it responds more to some than to others
In final analysis, the brain can eventually interpret the relative strengths of the receptors’ responses as resulting from a specific complex sensation
25
Most recent theory about the skin sense
Developed by Melzack and Wall (1962)
26
Melzack and Wall theory - similarities to other theories
Incorporates some aspect of each theory
According to this theory, each kind of receptor can convert a particular kind of stimulus into a particular pattern of impulses
Like specificity theory: each receptor responds in a specific way to a specific stimulus
Like pattern theory be claiming that a specific pattern of impulse is produced for a particular stimulus
27
Melzack and Wall theory - differences from other theories
Unlike specificity theory: receptors respond to a wide variety of stimuli
Unlike pattern theory: receptors respond as much to different stimuli, but the pattern of the response varies from stimulus to stimulus and from receptor to receptor
28
Why is it difficult to discuss the neural pathways for the skin?
Since the receptors are distributed over the entire body
29
Through which two separate pathways is info about the sense of touch passed through?
Spinothalamic system
Lemniscal system
30
Which pathway is info about pain
The spinothalamic system
31
Spinothalamic system
Small nerve fibres, slow transmission, and a poor ability to localize a stimulus
32
Lemniscal system
Large and fast nerve fibres that allow a precise localization of the area stimulated
33
Where do the spinothalamic and lemniscal systems end up?
In the somatosensory cortex
34
How are the spinothalamic and lemniscal systems organized?
Contralaterally: Sensation for each hand goes to the contralateral hemisphere; there are no ipsilateral connections
35
What is touch?
A sensation arising from pressure on our skin
36
What does pressure on our skin produce?
A slight distortion of the skin, which is interpreted as a contact between the skin and an object
37
What is touch perception the product of?
The stimulation of several different types of receptors
38
What is the best understood of the touch receptors?
The Pacinian Corpuscle
39
What are Pacinian corpuscles?
Encapsulated nerve endings that consist of about 70 layers assembled in an onion-like fashion at the end of an axon
40
What are Pacinian corpuscles more sensitive to?
Changes in stimulation than to sustained stimulation
41
Are Pacinian corpuscles more sensitive to stimulus onset or stimulus offset?
Stimulus onset
42
How many channels transmit touch information?
Four
43
Other channels transmitting touch information
Rapidly Adapting (RA) fibers
Two types of Slowly Adapting (SA) fibers
44
Of the channels, which one(s) respond to changes in stimulation, but rapidly cease to respond to continuous pressure on the skin (rapidly adapt)
RA fibers and the Pacinian corpuscles
45
Of the channels, which ones continue to respond to steady pressure on the skin
SA fibers
46
How are the four channels distinguished?
By the size of their receptive fields
47
Receptive fields for touch
Area of the skin where pressing will cause a specific fiber to increase its firing rate
48
Border of RA and one type of SA
Small with distinct border
49
Border of Pacinian corpuscles and one type of SA
Large with less distinct border
50
Summary of transduction for touch
Stimulation of skin receptors produces action potentials in the nerves leading to the somatosensory cortex
51
Threshold mapping for the spinothalamic system
Studies on the relation between points on the body and points in the cortex have not been very successful as far as the spinothalamic system is concerned
52
Mapping of the lemniscal system
The amount of space occupied by a body part corresponds to its threshold (homunculus)
53
Passive touch
Placing an object on someone's skin
54
Active touch
Actively seeking interactions with objects by exploring and touching them
55
What are studies on passive touch typically concerned with?
The thresholds for detecting a single pressure point on the skin
56
What can the absolute threshold for passive touch be defined as?
The smallest detectable pressure on the skin
57
Classic experiment on passive touch
Weinstein (1968) measured the absolute threshold for men and women on different body parts using Von Frey hairs
58
Main finding from Weinstein's experiment
Different body parts have different sensitivities, which likely has to do with their functions
59
Results of Weinstein's (1968) experiment
Women are more sensitive to touch than men
Body parts vary in sensitivity (nose most sensitive; sole of foot, calf, less sensitive)
60
Are there any body parts for which women and men are equally sensitive? If so, which one(s)
Yes
Tongue
61
What is another way to study passive touch?
To measure the ability to notice that two points on our skin are touched
Two-point discrimination threshold (TPDT)
62
Explain TPDT
Assessed by using two narrow-diameter blunt prongs and placing them about 2 cm apart
Participants report whether they feel one or two stimuli
The method of limits is used
Results with this procedure parallel findings in absolute threshold studies
63
In everyday life, which type of touch is more common? Why?
Active touch
We move about and actively explore our environment by touching objects and people
64
What is a typical way to study active touch?
To present participants with objects that they are not allowed to see, and ask them to identify these objects by touching them
Haptic perception
65
How has active touch been widely used?
To assess lateralization of functions
66
Which typically shows lower thresholds: active or passive touch? Explain.
Active touch
People can detect a dot 1 micrometer on a surface
67
How has the ability of active touch been used productively?
To detect very small stimuli that has been applied to help blind people read
The Braille alphabet consists of raised dots
68
Why should we care about touch?
It has critical medical applications: physicians, detection of cancer
69
When does touch adaptation occur?
When the perceived intensity of a continuously presented stimulus decreases over time
70
What is adaptation due to?
Unlike other senses, adaptation is not due to fatigue of the touch receptors
Relates to the working of the touch receptors
71
Touch adaptation in relation to touch receptors
Pacinian corpuscles respond better to the onset of offset of stimulus pressure
Touch adaptation is only a reduction in response of the receptors under continuous stimulation
72
What is the adaptation of slowly adapting receptors due to?
Fatigue
73
What is pain defined as?
A state involving the perception of tissue damage and the subjective experience of unpleasantness
74
What components does pain have?
Sensory and emotional components
75
Why is pain not like other perceptions?
Because it is the product of internal stimulation
Tissue damage causes pain
76
How is pain a survival function?
It protects our body from further tissue damage
77
Are the sensory and emotional components of pain supported by data?
Seen clearly in neuroimaging data showing activation in areas associated with both aspects during the experience of pain
78
Pain threshold
Defined as the minimum stimulus intensity at which pain is reported
79
What do pain thresholds depend on?
Sensitivity and criterion
Body part
80
What do higher numbers of pain points reflect?
Lower thresholds
Greater sensitivity to pain
81
Are pain threshold and absolute threshold related? Give example. Why is this the case?
No
Tip of nose: Low AT high PT
Two independent systems at work
82
Gender differences in pain tolerance
Women have higher pain tolerance than men do
83
How is measurement of the pain threshold complicated?
By pain tolerance
84
Explain pain tolerance
Maximum level at which people voluntarily accept pain
Source of individual differences
85
How does signal detection theory relate to pain tolerance
Captures pain tolerance in criterion placement
High tolerance = strict criterion
86
When does pain adaptation occur?
Pain adaptation occurs only for mild pain, not for intense pain
87
Give example of intense pain
Pain from headache or injury
88
Give example of mild pain
Pain from initial immersion in a hot bath
89
To what temperature do we show pain adaption?
We show adaptation for hot water up to 46 deg C
90
Specificity theory for pain
Claims that pain is produced by the stimulation of specific pain receptors
91
Pattern theory for pain
States that pain is produced by specific patterns of stimulation
The stimulation of the receptors is added together and must reach a critical level for the pain to be perceived
92
Melzack's argument for pain theories
Specificity and pattern theories ignore the psychological and physiological aspects of pain
93
Downfall of specificity theory of pain perception
Pain should be perceived whenever enough damage is done to stimulate the pain receptors
However, severely wounded soldiers report very little pain, presumably as a result of psychological factors
94
Downfall of pattern theory of pain
Ignores physiological evidence by claiming that pain receptors do not exist
Specific receptors responding to pain have been found
95
Melzack's theory of pain perception
Proposed the gate-control theory of pain perception
96
What does the gate-control theory propose?
That pain perception involves an interaction between neural fibers and the brain
97
Gate control theory two types of fibers
Transmission cells are the line through which pain info is sent to the brain
Neural fibers also affect the substantia gelatinosa
98
What does the substantia gelatinosa serve as?
A gate for pain info
Gate closed when stimulated by large fibers
Gate opened when stimulated by small fibers
99
How does the gate contribute to the perception of pain?
By means of the transmission cells (TC)
Gate closed: Small contribution of TC: less pain
Gate opened: Large contribution of TC: more pain
100
What happens when significant large-fiber activity is present?
Perception of pain is decreased
101
What happens when significant small-fiber activity is present?
Perception of pain is increased
102
How can you increase large fiber activity? Why does this work?
By rubbing or applying heat to the area
Presumably closes the gate and alleviates pain
103
How can the brain affect pain perception?
Signals from the brain are sent to the gate control system, and affect whether the gate is opened or not
Cognitive effects
104
What is another thing that has a direct effect on the substantia gelatinosa?
The descending inhibitory control
105
How can we predict whether pain is perceived?
By knowing the amount of activity in the large and small fibers
106
What did Meldrum (2021) conclude?
Despite flaws in its presentation of neural architecture, the gate control theory is currently the only theory that most accurately accounts for the physical and psychological aspects of pain
107
Temperature sense phenomena
The perception of temperature is separate from touch because it does not involve mechanical pressure on the skin
Instead, it involves the effect the temperature of the air (or the object) has on our perception
108
How does our body adjust its temperature?
Our body uses info about the air temperature to adjust its temperature
It has a well tuned ability to regulate its own temperature to keep it at about 37 degC
109
How does our body react to cold air?
The blood vessels from the surface of our skin shrink their diameter so that less warmth from our blood will be lost on the surface
110
How does our body react to warm air?
Blood vessels increase their diameter so that more warmth from our blood will be lost on the surface
111
If we get very cold, how does our body compensate?
We start shivering to produce more heat, which generates muscle activity
112
To do the necessary adjustments, what does out body need?
A precise mechanism that registers the external temperature and adjusts to it
113
Basics of temperature threshold
We have two separate systems: one for warmth and one for cold
Some regions of our skin responds to cold stimuli (cold spots); other areas respond to warm stimuli (warm spots)
114
What size are the cold and warm spots on our skin?
They are about 1 mm in diameter
115
How is temperature coded in the NS?
By receptors similar to those used for touch
116
How do cold fibers signal a cooling of the skin?
Increase their firing rate
117
How do warm fibers signal a warming of the skin?
Increase their firing rate
118
What determines the perceived temperature?
The pattern of activity in warm and cold fibers
119
Do different areas on the body have different sensitivity to temperature?
Yes
120
What is the absolute threshold for temperature?
There isn't one, there is only a difference threshold
121
What region is most sensitive to changes in warmth?
Forehead
122
What regions are least sensitive to hear?
Arms, chest, shoulders, and calves
123
What body region is the most sensitive to cold?
The trunk
124
What body parts less sensitive to cold?
Arms and legs, followed by the cheeks
125
What body part is least sensitive to the cold?
The forehead
126
Why do the thresholds by body part vary?
Has to do with survival
127
What is the threshold for temperature affected by?
Size of the areas of skin exposed
Current skin temperature
Phase of menstrual cycle
Time of day
Stress
128
What can thermal adaption be defined as? Caveat?
A decrease in the perceived intensity of a hot or cold stimulus
As we saw earlier, it only happens for mild temperatures
129
How is temperature adaptation studied?
By putting a hot or cold stimulus on the skin and asking participants to indicate when the temperature sensation disappears
130
What is normal skin temperature?
About 33 degC
131
What temperature range do we seem to adapt completely to?
Between 29 degC to 37 degC
132
Explanation for temperature adaptation
No satisfactory explanation has been offered for temperature adaptation yet
