Somatosensory system Flashcards Preview

Foundations of Neuroscience > Somatosensory system > Flashcards

Flashcards in Somatosensory system Deck (65):
1

Describe a primary afferent neurone

Sensory receptor in skin
Axon fibre
Cell body on stalk
Cell body in dorsal root ganglia
Terminates in dorsal horn of spinal cord

2

What is the name of the area that a sensory neurone receives information from?

The receptive field

3

Where is an action potential generated in a primary afferent sensory neurone?

At the peripheral end of the axon

4

What are the four classifications of primary afferent axons?

Aalpha
Abeta
Adelta
C

5

Which is the thickest myelinated axon?

Aalpha

6

What is the classification of an unmyelinated axon?

C

7

Where will you find Aalpha axons?

Proprioceptors of skeletal muscle

8

Where will you find Abeta axons?

Mechanoreceptors of skin

9

Where will you find Adelta axons?

Pain, temperature

10

Where will you find C axons?

Temperature, pain, itch

11

Explain the relationship between nerves and receptive fields

Each nerve axon innervates a specific receptive field

12

Describe receptive fields

Can vary greatly in size
This determines precision of localisation

13

What defines the size of a receptive field?

2 point discrimination

14

What is 2 point discrimination?

The smallest distance between two points where you can still distinguish two stimuli

15

How does sensory localisation vary over the body?

Greatly
Fingers are very sensitive
Area like the back isn't

16

What in the brain relates to the sensory localisation?

The size of the cerebral cortex for that region of the body

17

What is a dermatome?

An area of skin that is innervated by afferent axon fibres
Signalling all its sensation via a signal nerve from a single spinal nerve root

18

What is an adequate stimulus?

The right size and type of stimulus for that nerve ending that will stimulate a response

19

Is threshold dependent on nerve endings?

Yes

20

What is the line code?

The CNS interprets incoming action potentials by the specific axon they arrived via

21

What is generated in the nerve ending of a sensory neurone?

A receptor potential

22

Stimulus strength determines what?

The size of the graded receptor potential

23

What creates the graded receptor potential?

Channels opening
Membrane depolarisation

24

Firing rate is proportional to...

...stimulus strength

25

What is a slow or non-adapting stimulus?

A stimulus that is always present
Important when maintaining information about a stimulus is valuable
e.g. amount of stretch or pain

26

What is a fast adapting stimulus?

Constantly changing stimulus
Useful where it is important to signal a change in stimulus
Also to stop paying attention to stimulus
e.g. touch

27

Name the three kinds of cutaneous sensory receptors

Mechanoreceptors
Thermoreceptors
Nociceptors

28

What do mechanoreceptors sense?

Touch
Pressure
Vibration

29

What do thermoreceptors sense?

Temperature

30

What do nociceptors sense?

Noxious stimulation
(Pain)

31

Name sensory organs (mechanoreceptors) found in human skin

Ruffini's corpuscle
Meissner's corpuscle
Pacinian corpuscle
Merkel's receptor

32

What classification of axon does a cutaneous mechanoreceptor have?

Abeta

33

The structure of sensory apparatus determines what?

Structure determines function
Function determines location

34

Group the mechanoreceptors of the skin by location

Superficial
Meissner's corpuscle
Merkel's receptor

Deep
Ruffini's corpuscle
Pacinian corpuscle

35

Describe Meissner's corpuscles

Found in papillary dermis
Rapidly adapting
Constantly changing stimulus required
Light touch
Vibration

36

Why does the need for constantly changing stimulus make a Meissner's corpuscle effective

Example:
Detect putting clothes on
Do not detect wearing the clothes

37

Describe Merkel's receptors

High density in epidermis of digits and lips
Lower density elsewhere (glabrous)
Very low density (hairy)
Slowly adapting
Light touch

38

What actually is a Merkel cell?

An adapted keratocyte

39

What stimuli do Merkel cells respond to?

Initial indentation of skin
Sustained pressure of up to a few seconds

40

What do Merkel's receptors allow us to perceive?

Form and texture

41

Describe Ruffini's corpuscle

Responds to lateral movement or stretching of skin
Deep touch

42

Describe the structure of a Ruffini's corpuscle

Network of collagen fibres

43

Describe a Pacinian corpuscle

Found in deeper layers of dermis
Rapidly adapting
Stronger stimulus
High frequency vibration

44

What is the structure of a Pacinian corpuscle

A fully encapsulated nerve ending
Onion structure
Relieves pressure on nerve ending

45

What does the activation of a Pacinian corpuscle feel like?

Vibration

46

Describe a hair follicle receptor

Light touch
Rapidly adapting
Constantly changing stimulus required

47

Describe a cutaneous thermoreceptor

Bare nerve endings
Slowly adapting sensory receptor

48

What are the two types of thermoreceptor?

Respond to cold
Respond to warm

49

What is important to remember about thermoreceptors?

They do not indicate absolute temperature
They are sensitive to change in temperature

50

How do we sense temperature?

Comparing signals from warm and cold receptors

51

What are thermoreceptor channels?

Non-specific cation channels
Nerve ending sensitivity dependant on which transducer channels are expressed

52

Describe TRPV3/4

Warm thermoreceptor
Channels open 29-45
Maximum 45

53

Describe TRPM8

Cold thermoreceptor
Channels open 8-38
Maximum 25
Also opened by menthol

54

Describe TRPA1

Cold thermoreceptor
Channels open <17

55

Cold receptors have what kind of axons?

C and Adelta

56

Warm receptors have what kind of axon?

C

57

What is paradoxical cold perception?

Cold receptors activated at very high temperatures
Feeling of cool at high temperatures

58

Describe cutaneous nociceptors

Bare nerve endings
Non-adapting sensory receptors
High threshold
Adequate stimulus must be capable of damaging tissue

59

Name the 2 types of nociceptors

High threshold mechanoreceptors
Polymodal nociceptor

60

Describe a high threshold mechanoreceptor

Pricking pain
Adelta fibre

61

Describe a polymodal nociceptor

Poorly localised burning pain
C fibre
Sensitive to mechanical stimulus, heat and chemicals

62

What is proprioception?

Detecting the mechanical status of the muscle-skeletal system

63

What do proprioceptors provide information about?

Joint position
Muscle length
Muscle movement
Acceleration
Tension/force

64

Describe a muscle spindle

Specialised muscle fibres in a fibrous capsule
Termed intrafusal fibres
1a afferents wrap around central portion
Firing contributes to muscle tone
Stretch sensitive = increased firing

65

Describe a golgi tendon organ

Located at the junction of the muscle and tendon
Made of collagen fibrils
Innervated by 1b sensory afferent neurone
Sensitive to tension generated by contraction
Its position is in series with the muscle