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Foundations of Neuroscience > Somatosensory system > Flashcards

Somatosensory system Flashcards

1
Q

Describe a primary afferent neurone

A 
Sensory receptor in skin
Axon fibre
Cell body on stalk
Cell body in dorsal root ganglia
Terminates in dorsal horn of spinal cord
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2
Q

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

A

The receptive field

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3
Q

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

A

At the peripheral end of the axon

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4
Q

What are the four classifications of primary afferent axons?

A

Aalpha
Abeta
Adelta
C

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5
Q

Which is the thickest myelinated axon?

A

Aalpha

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6
Q

What is the classification of an unmyelinated axon?

A

C

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7
Q

Where will you find Aalpha axons?

A

Proprioceptors of skeletal muscle

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8
Q

Where will you find Abeta axons?

A

Mechanoreceptors of skin

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9
Q

Where will you find Adelta axons?

A

Pain, temperature

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10
Q

Where will you find C axons?

A

Temperature, pain, itch

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11
Q

Explain the relationship between nerves and receptive fields

A

Each nerve axon innervates a specific receptive field

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12
Q

Describe receptive fields

A

Can vary greatly in size

This determines precision of localisation

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13
Q

What defines the size of a receptive field?

A

2 point discrimination

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14
Q

What is 2 point discrimination?

A

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

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15
Q

How does sensory localisation vary over the body?

A

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

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16
Q

What in the brain relates to the sensory localisation?

A

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

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17
Q

What is a dermatome?

A

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

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18
Q

What is an adequate stimulus?

A

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

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19
Q

Is threshold dependent on nerve endings?

A

Yes

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20
Q

What is the line code?

A

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

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21
Q

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

A

A receptor potential

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22
Q

Stimulus strength determines what?

A

The size of the graded receptor potential

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23
Q

What creates the graded receptor potential?

A

Channels opening

Membrane depolarisation

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24
Q

Firing rate is proportional to…

A

…stimulus strength

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25
Q

What is a slow or non-adapting stimulus?

A

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

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26
Q

What is a fast adapting stimulus?

A

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

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27
Q

Name the three kinds of cutaneous sensory receptors

A

Mechanoreceptors
Thermoreceptors
Nociceptors

28
Q

What do mechanoreceptors sense?

A

Touch
Pressure
Vibration

29
Q

What do thermoreceptors sense?

A

Temperature

30
Q

What do nociceptors sense?

A

Noxious stimulation

Pain

31
Q

Name sensory organs (mechanoreceptors) found in human skin

A

Ruffini’s corpuscle
Meissner’s corpuscle
Pacinian corpuscle
Merkel’s receptor

32
Q

What classification of axon does a cutaneous mechanoreceptor have?

A

Abeta

33
Q

The structure of sensory apparatus determines what?

A

Structure determines function

Function determines location

34
Q

Group the mechanoreceptors of the skin by location

A

Superficial
Meissner’s corpuscle
Merkel’s receptor

Deep
Ruffini’s corpuscle
Pacinian corpuscle

35
Q

Describe Meissner’s corpuscles

A 
Found in papillary dermis
Rapidly adapting
Constantly changing stimulus required
Light touch
Vibration
36
Q

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

A

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

37
Q

Describe Merkel’s receptors

A 
High density in epidermis of digits and lips
Lower density elsewhere (glabrous)
Very low density (hairy)
Slowly adapting
Light touch
38
Q

What actually is a Merkel cell?

A

An adapted keratocyte

39
Q

What stimuli do Merkel cells respond to?

A

Initial indentation of skin

Sustained pressure of up to a few seconds

40
Q

What do Merkel’s receptors allow us to perceive?

A

Form and texture

41
Q

Describe Ruffini’s corpuscle

A

Responds to lateral movement or stretching of skin

Deep touch

42
Q

Describe the structure of a Ruffini’s corpuscle

A

Network of collagen fibres

43
Q

Describe a Pacinian corpuscle

A

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

44
Q

What is the structure of a Pacinian corpuscle

A

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

45
Q

What does the activation of a Pacinian corpuscle feel like?

A

Vibration

46
Q

Describe a hair follicle receptor

A

Light touch
Rapidly adapting
Constantly changing stimulus required

47
Q

Describe a cutaneous thermoreceptor

A

Bare nerve endings

Slowly adapting sensory receptor

48
Q

What are the two types of thermoreceptor?

A

Respond to cold

Respond to warm

49
Q

What is important to remember about thermoreceptors?

A

They do not indicate absolute temperature

They are sensitive to change in temperature

50
Q

How do we sense temperature?

A

Comparing signals from warm and cold receptors

51
Q

What are thermoreceptor channels?

A

Non-specific cation channels

Nerve ending sensitivity dependant on which transducer channels are expressed

52
Q

Describe TRPV3/4

A

Warm thermoreceptor
Channels open 29-45
Maximum 45

53
Q

Describe TRPM8

A

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

54
Q

Describe TRPA1

A

Cold thermoreceptor

Channels open <17

55
Q

Cold receptors have what kind of axons?

A

C and Adelta

56
Q

Warm receptors have what kind of axon?

A

C

57
Q

What is paradoxical cold perception?

A

Cold receptors activated at very high temperatures

Feeling of cool at high temperatures

58
Q

Describe cutaneous nociceptors

A

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

59
Q

Name the 2 types of nociceptors

A

High threshold mechanoreceptors

Polymodal nociceptor

60
Q

Describe a high threshold mechanoreceptor

A

Pricking pain

Adelta fibre

61
Q

Describe a polymodal nociceptor

A

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

62
Q

What is proprioception?

A

Detecting the mechanical status of the muscle-skeletal system

63
Q

What do proprioceptors provide information about?

A 
Joint position
Muscle length
Muscle movement
Acceleration
Tension/force
64
Q

Describe a muscle spindle

A 
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
Q

Describe a golgi tendon organ

A

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

Foundations of Neuroscience (15 decks)

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