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Somatosensory Sensation Flashcards

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1
Q

What do cutaneous receptors respond to?

A

External stimuli

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2
Q

What do cutaneous receptors transmit information to?

A

CNS for processing and interpretation

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3
Q

What are mechanoreceptors?

A

A type of cutaneous receptor that respond to touch

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4
Q

What do cutaneous senses depend on?

A

Specialised sensory receptors responding to specific types of stimuli

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5
Q

What are the types of cutaneous sensory receptors?

A
  • Mechanoreceptors

- Thermoreceptors

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6
Q

What do cutaneous mechanoreceptors respond to?

A

Mechanical stimuli e.g skin compression/bending/stretching

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7
Q

What do cutaneous thermoreceptors respond to?

A

Changes in temperature at the site of the nerve ending

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8
Q

When do cutaneous thermoreceptors generally display some activity?

A

‘Normal’ skin temperatures but can be responsive to either cold/warm stimuli

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9
Q

What did the first skin practical compare?

A

The sensitivity of the skin on different parts of the body to somatosensory stimuli (touch in this case)

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10
Q

What is the distribution and density of cutaneous sensory receptors across different areas of the skin?

A

Heterogenous

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11
Q

What does the distribution and density of cutaneous sensory receptors across different areas of the skin being heterogeneous allow?

A

Comparison of different receptor densities at different skin sites, links to the different functions of each skin area

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12
Q

What are fine discriminatory touch sensations mainly mediated by?

A

Primary afferent neurones with fibres in Aα/β conduction velocity range

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13
Q

Where do primary afferent fibres in the Aα/β conduction velocity range terminate?

A

Specialised end organs

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14
Q

What are primary afferent fibres in the Aα/β conduction velocity range and their specialised end organs collectively known as?

A

Low threshold mechanoreceptors

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15
Q

What are examples of mechanoreceptor end organs? (4)

A
  • Pacinian corpuscles
  • Meissner’s corpuscles
  • Merkels disks
  • Ruffini ending /corpuscles
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16
Q

What are low threshold mechanoreceptor end organs activated by?

A

Light pressure applied to the skin

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17
Q

Why can low threshold mechanoreceptor end organs be activated by light pressure to the skin?

A

They have very low mechanical thresholds for activation

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18
Q

Define mechanical threshold

A

The minimum stimulus intensity which will elicit a response in a receptor or primary afferent neurone when applied to the receptive field, measured in the appropriate stimulus units

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19
Q

What are the stimulus units for mechanoreceptors?

A

N/m^2

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20
Q

Label the location of somatosensory receptors in the skin

A

See notes for diagram

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21
Q

How are the mechanoreceptor end organs different?

A
  • Different end specialisations
  • Different receptive field size
  • Rate of adaptation
  • Different response properties
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22
Q

What is receptive field?

A

Area of skin when stimulated gives rise to a response in a receptor/primary afferent neurone

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23
Q

What is rate of adaptation caused by?

A

A reduction in activity of a receptor/primary afferent neurone when a constant stimulus is applied

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24
Q

Match the receptor location and appearance to the type

A

See notes for diagram

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25
Which type of mechanoreceptor end organ has the largest receptive field?
Ruffini's corpuscle/ending
26
Which type of mechanoreceptor end organ has the 2nd largest receptive field?
Pacinian corpuscle
27
Which 2 types of mechanoreceptor end organs have the smallest and same size receptor fields? (2)
- Meissner's corpuscle | - Merkel's discs
28
Match the neural spike train to the receptor type
See diagram for notes
29
What is receptor field size largely related to?
Depth of the receptor from the skin surface
30
What is the depth of the receptor from the skin surface most likely due to? (2)
- Physical structure of the end organ | - Properties of the channels in nerve terminals transmitting the response
31
What different attributes of a mechanical stimulus do different types of low threshold mechanoreceptor signal? (3)
- Dynamic properties of the stimulus - Static properties of the stimulus - Precise location
32
What is the relationship between receptive field size and accuracy of stimulus localisation?
The smaller the receptive field, the more accurate the localization of the stimulus
33
Where does the combination of information necessary to detect the precise nature of stimulus applied need to be received from?
Both slowly adapting and rapidly adapting units
34
What is temperature sensed by?
Free nerve endings
35
How many types of stimulus do free nerve endings respond to?
3
36
List the types of free nerve ending receptors
- Cold receptor - Warm receptor - Pain receptor
37
When do cold receptors increase their rate of action potential production?
As skin is cooled
38
When do warm receptors increase their rate of action potential production?
As skin is warmed
39
What do both warm and cold receptors respond strongly to?
Changes in temperature
40
What are more numerous in any given area of the skin - cold or warm receptors? And by how much?
Cold receptors | 10-15x more
41
What 2 aspects of cold perception are greater than that of warm perception?
- Acuity | - Discrimination
42
Why does cold perception have greater acuity and discrimination than warm perception?
Cold receptors are 10-15 times more numerous than warm receptors in any given area of skin
43
What are the only 2 things that pain receptors are stimulated by?
Extreme cold/heat
44
What are pain receptors thought to respond to?
Temperature sensitive channels initiating action potentials over a range of temperatures at which the fibres respond
45
What range are ambient temperatures of the skin?
20-40c
46
What does the sensing of ambient temperatures at the skin require?
A comparison of input activity levels in warm and cold fibres
47
What do both warm and cold fibres show at ambient skin temperature ranges?
Ongoing activity
48
What requires more complicated processing - sensing of temperature/mechanical stimuli?
Temperature stimuli
49
Why does the sensing of mechanical stimuli require less complicated processing?
Activity is only present when a stimulus is given
50
What is required to sense the temperature at the skin and so means temperature stimuli detection requires more processing?
A combined processing of the information encoded by both the warm and the cold fibres and integration of their activity to produce temperature sensation
51
Where is information from the somatosensory system encoded?
Receptor/primary afferent neurone activity
52
Where does information from the somatosensory system go after being encoded?
Enters the spinal cord and travels up various pathways to the somatosensory cortex
53
What pathway are mechanical stimuli detected in?
Dorsal column
54
What pathway are temperature stimuli detected in?
Spinothalamic pathway
55
What interpretation does the discrimination of different stimuli require?
A greater degree of interpretation of primary afferent neurone activity by the central nervous system
56
What activation does two point discrimination of mechanical information require?
Multiple primary afferent neurones at distinct sites to identify 2 seperate points of contact
57
What is the discrimination of mechanical information aided by? (3)
- Increase in receptor density - Decrease in receptor field size - CNS processing
58
What does discrimination of different temperatures rely on?
CNS detecting relative changes in activity of both warm and cold fibres compared for different stimuli applied
59
In the somatosensation practical, how are the areas to be tested prepared?
- Shave hairs off test areas - Practice using ink stamp on paper/other skin areas - Use ink stamp to mark 10mm square in each area
60
What areas are tested in the somatosensation practical? (4)
- Tip of middle finger - Palm of hand - Forearm - Lumbar region of back
61
Why is it essential to remove hairs from test areas in the somatosensation practical to collect accurate data?
Hair follicles are very sensitive mechanoreceptors
62
Describe the method for mapping receptors (11)
- Blindfold the subject - Do not inform the subject which area will be tested - Very gently place the fine bristle (a von Frey hair) vertically onto the skin surface in one of the small (2mm) square - Apply pressure until the hair bends - Subject states when distinct touch sensation felt - Ticks=positive, Zero=nil - Move randomly between the four test areas and small squares - Test each small square twice - Score correct responses out of 50 and convert to % correct. - Remove blindfold: subject can see the area being stimulated - Only on the upper limb area, determine area least sensitive to touch by repeating it all with subject looking
63
Why does pressure need to be applied to the Von Frey hair until it bends?
Indicates that the correct amount of force has been applied
64
What is "two-point discrimination threshold" also known as?
Simultaneous spatial threshold
65
What is "two-point discrimination threshold"?
The minimum distance whereby two touch stimuli can be distinguished separately
66
How is two point discrimination tested?
- Blindfold subject - With dividers apply both points simultaneously and lightly to skin surface in each of the four test areas - The subject states if 2 points/1 point felt 4. Vary the distance between the points randomly and find the shortest separation distance that the subject can distinguish. Record your results in your lab book.
67
How is two point discrimination tested? (4)
- Blindfold subject - With dividers apply both points simultaneously and lightly to skin surface in each of the four test areas - The subject states if 2 points/1 point felt - Vary distance between points randomly - Find shortest separation distance that subject can distinguish
68
How are the results of the somatosensory practical displayed?
Fully-annotated scatter graphs of the mean percentages of correct touch responses against the minimum distance for two-point discrimination in the same skin area
69
Why do Ruffini's endings/corpsucles not provide much information on surface skin sensation?
They are very deep
70
Why is it important that different receptor types/somatosensory endings innervating skin are overlapping?
Different types of somatosensory information can be sensed
71
What receptors in superficial locations generally for?
Fine spacial detail
72
What type of skin is the only place where Meissner's corpuscles are found?
Glandular skin
73
What do Meissner's corpuscles have the same role as in hairy skin?
Hair follicle receptors
74
What type of receptors sense vibration?
Rapidly adapting receptors
75
Give 3 examples of rapidly adapting receptors
- Pacinian corpuscles - Meissner's corpuscles - Hair follicle afferents
76
Explain the structure of a rapidly adapting receptor (2)
- Axon surrounded by accessory structures | - Lamallae have viscous content
77
How do rapidly adapting receptors sense vibration? (3)
- Force on axon transported via viscocity to nerve ending - Causes it to fire APs - Pressure less on nerve endings causes firing to stop
78
What is adaptation?
Maintained stimulus of constant strength is applied to a sensory receptive terminal so the action potential frequency decreases with time

Dermatology (12 decks)

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