The somatosensory system Lecture 7

Question 1

What is enteroception?

Answer 1

Cutaneous sensations from skin like touch and temperature

Question 2

What is interoception?

Answer 2

Visceral sensations from internal organs

Question 3

What is proprioception?

Answer 3

Awareness of the position of limbs in space

Question 4

What is noxiception?

Answer 4

Pain- a protective mechanism

Question 5

Why is touch important?

Answer 5

For communication, object exploration, feedback mechanism for control of movement

Question 6

What are the two types of skin?

Answer 6

Hairy and glabrous

Question 7

Which fibres are associated with proprioception?

Answer 7

A alpha

Question 8

Which fibres are associated with mechanoreceptors of the skin?

Answer 8

A beta

Question 9

Which fibres are associated with pain nociception?

Answer 9

A delta

Question 10

Which fibres are associated with temperature, itching, pain and pleasurable sensations?

Answer 10

C fibres

Question 11

Which fibres are unmyelinated?

Answer 11

C fibres

Question 12

What is the speed of A alpha fibres?

Answer 12

80-120m/sec

Question 13

What is the speed of A beta fibres?

Answer 13

35-75m/sec

Question 14

What is the speed of A delta fibres?

Answer 14

5-30m/sec

Question 15

What is the speed of C fibres?

Answer 15

0.5-2m/sec

Question 16

What is the diameter of A alpha fibres?

Answer 16

13-20 micrometres

Question 17

What is the diameter of A beta fibres?

Answer 17

6-12 micrometres

Question 18

What is the diameter of A delta fibres?

Answer 18

1-5 micrometres

Question 19

What is the dimeter of C fibres?

Answer 19

0.2-1.5 micrometres

Question 20

Describe a rapidly adapting receptor fibre

Answer 20

One which fires for onset of stimulus but ceases with sustained stimulus. Fires with offset. This allows response to rapid changes in stimulus.

Question 21

Slowly adapting fibre

Answer 21

Fires on onset of stimulus and is sustained while stimulus is applied.

Question 22

What fibres are connected to the 4 receptors in glabrous skin?

Answer 22

A beta

Question 23

What threshold do all 4 of the receptors in glabrous skin have?

Answer 23

Low threshold mechanoreceptors

Question 24

What are the two superficial receptors in glabrous skin?

Answer 24

Meissner’s corpuscle and Merkel cells

Question 25

Which receptor in superficial glabrous skin is rapidly adapting?

Answer 25

Meissner's corpuscle

Question 26

Which receptor in superficial glabrous skin is slowly adapting?

Answer 26

Merkel cells

Question 27

What are the 2 deep receptors in glabrous skin?

Answer 27

Pacinian corpuscle and Ruffini's ending

Question 28

Which deep glabrous receptor is rapidly adapting?

Answer 28

Pacinian corpuscle

Question 29

Which deep glabrous receptor is slowly adapting?

Answer 29

Ruffini's ending

Question 30

What is the fifth receptor present in glabrous skin which is a high threshold mechanoreceptor?

Answer 30

Free nerve endings

Question 31

What are the two rapidly adapting receptors in glabrous skin?

Answer 31

Messner's corpuscle and Pacinian corpuscle.

Question 32

What are the two types of lanceolate endings in hairy skin?

Answer 32

Longitudinal and circumferential

Question 33

Which type of lanceolate endings can detect movement of hair in any direction?

Answer 33

Circumferential

Question 34

One of the longitudinal lanceolate endings is associated with a fibre that is rapidly adapting, which fibre is it?

Answer 34

A beta

Question 35

What are the two slowly adapting fibres?

Answer 35

Merkel cells and Ruffini's endings

Question 36

Which receptor is SA type 1?

Answer 36

Merkel cells

Question 37

Which receptor is SA type 2?

Answer 37

Ruffini's ending

Question 38

What are ruffini's endings mostly stimulated by?

Answer 38

Stretch across the skin, mostly along the line of the corpuscle

Question 39

What are Ruffini's endings corpuscles made of?

Answer 39

Collagen

Question 40

Which receptor is rapidly adapting type 1?

Answer 40

Meissner's corpuscle

Question 41

Which receptor is rapidly adapting type 2?

Answer 41

Pacinian corpuscle

Question 42

Describe the structure of Meissner's corpuscle?

Answer 42

Nerve fibres surrounded by Schwann cells, anchored to skin by collagen fibres

Question 43

What forms the corpuscle of Meissner's?

Answer 43

Schwann cells

Question 44

What forms the corpuscle of Pacinian?

Answer 44

Layers of lamellae

Question 45

What is the dimeter of thermoreceptors?

Answer 45

1mm

Question 46

What is the maximum sensitivity of cold receptors?

Answer 46

25-30 degrees C

Question 47

What is the maximum sensitivity of warm receptors?

Answer 47

40-43 degrees C

Question 48

Which thermoreceptor is highly sensitive to change?

Answer 48

Cold receptors

Question 49

What fibres are associated with cold receptors?

Answer 49

Small myelinated A delta fibres

Question 50

What fibres are associated with warm receptors?

Answer 50

C fibres- unmyelinated

Question 51

What are nociceptors receptive to?

Answer 51

Pin pricks, squeezing, crushing

Question 52

What fibres are nociceptors connected to?

Answer 52

A delta

Question 53

Which fibres and receptor detect the 'first pain'?

Answer 53

Nociceptors and A delta fibres

Question 54

Which fibres and receptor detects the second pain?

Answer 54

Mechano-thermal receptors and C fibres

Question 55

What is the sensitivity of mechano-thermal receptors?

Answer 55

below 5-10 and above 45 degrees

Question 56

As well as Meissner's corpuscle, what other receptor is RA-1?

Answer 56

A-beta LTMR longitudinal lanceolate endings

Question 57

What is the technique used to map out receptive fields?

Answer 57

Micro-neurography

Question 58

Describe mironeurography

Answer 58

Place an electrode into median nerve in arm until find a single nerve fibre. record from this nerve fibre when moving probes across surface of the hand. any area that elicits a response is the receptive field for that single nerve fibre.

Question 59

Which receptors have small discrete receptive fields with high density on fingertips?

Answer 59

The superficial receptors- Meissner's and Merkel cells

Question 60

What factors determine spatial resolution?

Answer 60

Receptor density and size of receptive fields

Question 61

Which receptors are important for a high spatial resolution?

Answer 61

The two superficial receptors- slowly adapting 1 and rapidly adapting 1- Merkel cells and Ruffini's endings

Question 62

Describe experiments on rapidly adapting receptors done by Mountcastle et al

Answer 62

They applied pressure at different frequencies and determined which receptor was detecting it. Found that Pacinian corpuscle is most sensitive at 300Hz- needs very little indentation to generate response. Meissners most sensitive at 50Hz but need strong indentation. Then did psychophysics experiment and found the curve was the same

Question 63

What is Meissner's corpuscle sensitive to?

Answer 63

Low frequency vibration, slip and shear- feedback for grip

Question 64

How many Meissner's receptors per cm2?

Answer 64

150- mainly on fingertips

Question 65

How many Merkel cells per cm2?

Answer 65

100

Question 66

What are Merkel cells sensitive to?

Answer 66

Texture and spatial details of an object, moving stimuli

Question 67

Which receptors have small receptive fields?

Answer 67

The two superficial receptors- Meissner's and Merkel

Question 68

Which receptors have large receptive fields?

Answer 68

Pacinian and Ruffinis

Question 69

How many Pacinian corpuscles in each finger and palm?

Answer 69

300 per finger, 800 in palm

Question 70

What are Pacinian corpuscles sesntive to?

Answer 70

High frequency vibration

Question 71

Which receptor is highly sensitive to stretch but not indentation

Answer 71

Ruffini's

Question 72

Which fibres relay pleasant sensations

Answer 72

C fibres- thought to be only for noxious stimuli