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LCRS 2 > Sensory Pathways: Touch and Proprioception > Flashcards

Sensory Pathways: Touch and Proprioception Flashcards

1
Q

What receptors are responsible for the sensory modalities of touch and proprioception?

A

Mechanoreceptors

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2
Q

Describe the structure of mechanoreceptors involved in touchand proprioception.

A

The receptor is NOT a separate entity but is actually the peripheral terminal of the peripheral axon of the primary sensory neuron.

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3
Q

What is the difference between slow adapting and fast adapting receptors?

A

Slow adapting receptors continue firing impulses for as long as thestimulus is present
Fast adapting receptors tend to fire at the start of the stimulus and sometimes when the stimulus switches off but they tend to fade in the middle

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4
Q

What type of receptors are mechanoreceptors?

A

Mixture of slow and fast adapting receptors

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5
Q

Describe how sensory neurons vary in their properties.

A

They vary in SIZE and CONDUCTION VELOCITY

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6
Q

What are the two classifications of axons?

A

Anatomical = based on axon diameter (labelled using LETTERS)
Physiological = based on conduction velocity (labelled using ROMAN NUMERALS)
As axon diameter and conduction velocity are related, there is a lot of overlap in the classifications

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7
Q

Describe the general structure of sensory neurons that convey touch and proprioceptive information.

A

They are LARGE and have a FAST conduction velocity

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8
Q

What is a receptive field?

A

An area of skin that is innervated by one sensory axon and its branches

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9
Q

Describe how the receptive fields in the lips and mouth vary from the receptive fields of the upper arm.

A

Lips and Mouth – high-density innervation with very small receptive fields
Upper arm – larger receptive fields and thinner innervation

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10
Q

Describe how neurons can code for the intensity of a stimulus.

A

It is coded by the FREQUENCY of the action potentials going down the sensory fibres

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11
Q

Which part of the spinal cord carries sensory axons for touch and proprioception?

A

Dorsal columns

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12
Q

What are the bundles of axons within the spinal cord that havecome from above and below the waist called? Describe their spatial arrangement within the spinal cord.

A 
Above the waist – Cuneate Fasciculus 
Below the waist – Gracile Fasciculus  
Axons from below the waist are packed more medially in the dorsal column and above the waist are more lateral
Lower = Medial 
Higher = Lateral
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13
Q

Where do these fasiculus neurons synapse?

A

They synapse in the Cuneate and Gracile Nuclei in the medulla

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14
Q

Describe what happens after these fasiculus neurons synapse and the tract that they run in.

A

The second order neurons then cross the midline (decussation) and continue up the brainstem in the MEDIAL LEMNISCUS

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15
Q

Which thalamic nucleus is responsible for relaying somatosensory information from the neck down?

A

Ventral Postero-lateral

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16
Q

Describe the passage of the third order sensory neuron.

A

The third order neurone travels from the ventral postero-lateral nucleus in the thalamus to the primary somatosensory cortex

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17
Q

What is the main sensory nerve of the face?

A

Trigeminal Nerve (CN V)

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18
Q

Where does the trigeminal nerve enter the brainstem and where does it synapse with a second order neuron?

A

Pons

It synapses at the trigeminal cranial nucleus

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19
Q

Describe the passage of the trigeminal sensory second order neuron.

A

The second order neuron crosses the midline (decussation) and joins the medial part of the median lemniscus

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20
Q

Which thalamic nucleus is responsible for relaying sensory information from the face?

A

Ventral Postero-medial

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21
Q

What is lateral inhibition?

A

Lateral inhibition takes place in the cuneate and gracile nuclei
Each axon has lateral branches that are inhibitory on neighbouringaxons
So each axon will stimulate a second order neuron and inhibit neighboring first order neurons

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22
Q

What is the purpose of lateral inhibition?

A

Improves the resolution of localising the stimulus

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23
Q

Name the three parts of the somatosensory cortex.

A

Primary Somatosensory Cortex (SI)
Secondary Somatosensory Cortex (SII)
Posterior Parietal Cortex

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24
Q

What is the posterior parietal cortex mainly involved in?

A

Spatial relationships

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25
Q

Damage to the touch and proprioception pathway will halt sensory information going up to the primary somatosensory cortex. What effects will this have?

A

Anaesthesia (complete cessation of sensation)

Parasthesia (sensation is there but it isn’t normal)

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26
Q

What is the most common cause of peripheral neuropathy?

A

Diabetes mellitus

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27
Q

List 4 major somatosensory modalities

A

Pain
Temperature
Touch
Proprioception

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28
Q

3 sensory neurones

A

A beta
A delta
C fibers

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29
Q

Define receptor

A

Transducers that convert environmental energy to neuronal action potentials

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30
Q

What is somatosensory function?

A 
Ability to interpret the bodily sensations
Mechanical 
Thermal
Proprioceptive
Nociceptive
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31
Q

Somatosensory system consists of

A

Receptors
Nerve cell tracts in body and spine
Parts of brain dealing with processing sensory information

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32
Q

Somatosensory modalities

A

Touch- mechanical stimuli
Thermal
Nociception
Proprioception

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33
Q

What is modified to determine what is being sensed

A

Nerve terminal

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34
Q

What do free nerve endings transduce

A

Nociceptors and thermoreceptors

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35
Q

What do enclosed nerve terminals transduce

A

Mechanoreceptors

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36
Q

Role of AB fibres

A

Innocuous mechanical stimulation

The fastest

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37
Q

Role of A delta fibres

A

Noxious mechanical and thermal stimulation

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38
Q

Role of c fibres

A

Noxious mechanical, thermal and itch stimulation

39
Q

Define receptors

A

Sensory receptors are transducers that convert environmental energy to neuronal action potentials

40
Q

Thermoreceptor fibres

A

A delta and C

41
Q

How do nerves determine temperature changes

A

Presence of Transient Receptor potential ion channels

4 heat activated and 2 cold activated ion channels which are activated by different temperatures

42
Q

5 different mechanoreceptors

A 
Hair follicle receptors 
Meissners corpuscle
Merkel cells
Pacinian corpuscle 
Ruffini endings
43
Q

Role of meissners corpuscles

A

Transduce low frequency vibration and fine discriminative touch

44
Q

Role of Merkel cells

A

Transduce light touch and superficial pressure

45
Q

Role of pacinian corpuscles

A

Transduce deep pressure
High frequency vibration
Tickling

46
Q

Role of ruffini endings

A

Transduce continuous pressure

Stretch

47
Q

Role of hair follicle receptors

A

Light touch

48
Q

Phasic receptors

A

Detect change in stimulus strength by transmitting impusle at start and end of a stimulus so when a change has occurred

49
Q

Example of phasic receptor

A

Pacinian receptor

Sudden pressure when excited then transmits signal when pressure released

50
Q

Feature of phasic receptor

A

Fast adapting

51
Q

Receptive field

A

Region of skin which causes activation of one signal sensory neurone

52
Q

Differences in receptor fields across body

A

On back is large fields so cells detect over a larger area for less precise perception
Whereas on fingers are densely packed mechanoreceptors with small receptor fields giving very precise perception

53
Q

2 point discrimination

A

Minimum distance at which 2 points are perceived as separate

54
Q

What is 2 point discrimination related to

A

Size of receptive field

55
Q

Where are cell bodies for receptors in body

A

Dorsal root ganglia at that spinal level

56
Q

Where are cell bodies for receptors found on face

A

Trigeminal ganglia

57
Q

Pathway for sensory information from upper limbs

A

Received at cervical level-> head up cuneate fasiculas tract (known as internal arculate fibres) then cross over at medulla-> form medial lemniscus tract-> thalamus

58
Q

Types of dorsal horn neurones

A

Axons that project to brain

Axons remaining in spinal chord (interneurones)

59
Q

Difference in distribution sensory neurones synapsing in dorsal horn

A

A delta and c more superficial

A beta deeper

60
Q

What is lateral inhibition

A

Can get overlapping of adjacent receptive fields making it hard to distinguish 2 stimulus locations. Lateral inhibition prevents this

61
Q

How does lateral inhibition work

A

Mediated by inhibitory interneuones within dorsal horn

62
Q

What pathway is touch and proprioception carried in

A

Dorsal column

63
Q

Path of first order neurones touch and proprioception

A

Cell body in dorsal root ganglion, travels up either cuneate or gracile tract to terminate in either cuneate or gracile nucleus in medulla

64
Q

Path of second order neurones

A

Decussate in caudal medulla then form contralateral medial leminiscus tract and synapse in the ventral posterior lateral nucleus

65
Q

Differences in termination of second order neurones depending on where they’ve come from

A

Lower parts of body are more lateral

66
Q

Somatosensory homunculus

A

Size of somatotropic area in brain is proportional to density of sensory receptors in that area

67
Q

Differences in localisation between noxious and inoxious

A

Inoxious much more precise localisation

68
Q

Location of somatosensory cortex

A

Found in posterior part of parietal lobe behind central gyrus

69
Q

Differences in ascension between pain, temperature and crude touch

A

Crude touch in anterior spinothalamic

Pain and temp in lateral spinothalamic

70
Q

Pathway of spinothalamic first order neurones

A

Terminate immediately in dorsal horn

71
Q

Pathway second order spinothalamic pathway neurones

A

Decussate at spinal level and travel in lateral or anterior spinothalamic tract before terminating in VPL in thalamus

72
Q

Topographic representation of body in VPL spinothalamic pathway

A

Lower extremities more lateral

73
Q

Quantitive sensory testing purpose

A

To test effectiveness of spinal tracts

74
Q

How quantitive sensory testing works

A

An quantified stimulus is applied either in form of heat and temperature for spinothalamic tract or 2 point stimulus for dorsal column and integrity is checked

75
Q

Cause of anterior spinal lesion

A

Blocked anterior spinal artery

76
Q

Effect on both tracts of anterior spinal artery blockage

A

Bilateral loss pain and temperate sensation below that spinal level
Normal touch and 2 point discrimination below that level

77
Q

Define pain

A

An unpleasant sensory or emotional experience associated with actual or potential tissue damage

78
Q

2 types of nociceptors

A

A delta and C

79
Q

Pain from a delta nociceptors

A

Sharp and intense first pain
Type 1- noxious mechanical
Type 2- noxious heat

80
Q

Pain from c fibre nociceptors

A

Dull and aching pain from all stimuli

81
Q

Spinal chord nociceptive processing NT

A

Glutamate is major pain signalling NT

It is released from sensory afferents in response to acute or persistent noxious stimuli

82
Q

First synapse in pain pathway

A

Gulatmergic synapse in superficial dorsal horn

83
Q

Parts of brain involved in pain reception

A

Amygdala
Prefrontal cortex
Cerebellum

84
Q

Gate control theory

A

There is inhibition of primary afferent inputs to brain via a beta neurone which excites and inhibitory neurone

85
Q

Descending control pathways

A

Use of strong emotions to inhibit pain

86
Q

How does descending control pathways work

A

Monoamines from descending pathways can inhibit nociceptive processing in the dorsal horn

87
Q

Examples of monoamines acting in descending control pathways

A

Serotonin and noradrenaline

88
Q

Chronic pain

A

Pain experienced for over 3 months

In the uk believed 28 million people

89
Q

Difference between nociceptive and neuropathic pain

A

Nociceptive to do with noxious stimulation of a somatic or visceral nociceptor but neuropathic a disease of somatosensory system

90
Q

Peripheral sensitisation

A

With tissue damage a lot of inflammatory molecules are released, these have been proven to increase the sensitivity of nociceptors in this area therefore reducing their threshold for stimuli

91
Q

Central sensitisation

A

Increased sensitisation of c fibres from periphery brings about a plasticity in the projection neurone in dorsal horn which affects adjacent cells such as the a delta fibre in dorsal horn

92
Q

Allodynia

A

Pain due to a stimulus that does not normally provoke pain

93
Q

Hyperalgaesia

A

Increased pain from a stimulus that does normally provoke pain

94
Q

Remembering 5 mechanoreceptors

A

PHRMM

LCRS 2 (44 decks)

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