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4. BIOL257 > Somatosensory system: > Flashcards

Somatosensory system: Flashcards

1
Q

somatosensory receptors: types

A
  • general somatic afferents (GSA)

- general visceral afferents (GVA)

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2
Q

somatosensory receptors: general somatic afferents

A
  • cutaneous = exteroceptors

- muscles, tendons, joints = proprioceptors

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3
Q

somatosensory receptors: general visceral afferents

A
  • internal organs (viscera) = enteroreceptor
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4
Q

cutaneous receptors: mechanoreceptors

A
  • touch
  • pressure
  • vibration
  • stretch
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5
Q

cutaneous receptors: thermoreceptors

A
  • hot

- cold

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6
Q

cutaneous receptors: nociceptors

A
  • intense mechanical
  • intense hot and cold
  • chemicals
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7
Q

mechanoreceptors (non-nociceptive): typical features

A
  • low threshold (highly sensitive)
  • glutamatergic
  • predominantly A-beta afferent nerve fibres (large, myelinated, fast)
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8
Q

hair follicle (peritrichial) receptors (RA1): features

A
  • detects bending of hairs (air movement, touch)
  • bending of hair stretches membrane
  • opens mechanically gated cation channels in membrane of afferent fibre
  • depolarisation –> action potentials
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9
Q

hair follicle (peritrichial) receptors (RA1): non-encapsulated endings

A
  • single process of an afferent sensory fibre, wrapped in spiral around base of hair
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10
Q

hair follicle (peritrichial) receptors (RA1): adapting

A

rapid adapting

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11
Q

hair follicle (peritrichial) receptors (RA1): receptive field

A

small receptive field

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12
Q

Meissner’s corpuscle (RA1): features

A
  • glabrous (hairless) skin only (eg. fingertips)
  • superficial location
  • sheath of ct, packed w pancake-like stack of pear-shaped Schwann cells (teloglia)
  • compression causes mechanically gated cation channels in membrane to open
  • depolarisation -> action potentials
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13
Q

Meissner’s corpuscle (RA1): good for and adapting

A
  • discriminative touch
  • grip
  • touch

rapid adapting

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14
Q

Meissner’s corpuscle (RA1): receptive field

A
  • encapsulated capsule

- small receptive field

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15
Q

Pacinian corpuscle (RA2): good for and adapting

A
  • pressure and vibration

- rapid adapting (sustained pressure dissipates)

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16
Q

Pacinian corpuscle (RA2): receptive field

A
  • large receptive field
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17
Q

Pacinian corpuscle (RA2): pressure causes

A
  • mechanically gated Na channels in afferent nerve ending to open-> depolarise cell -> AP
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18
Q

Pacinian corpuscle (RA2): features

A
  • concentric layers of flattened fibroblasts (ct)

- viscous fluid in btw

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19
Q

duplex theory: tactile texture perception - depends on

A
  • spatial cues

- temporal cues

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20
Q

duplex theory: tactile texture perception eg. spatial cue

A
  • size

- shape

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21
Q

duplex theory: tactile texture perception eg. temporal cues

A
  • rate of vibration as object moved across skin
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22
Q

duplex theory: tactile texture perception for fine texture

A
  • spatial cues alone can’t be used in static touch

- must move fingers across surface

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23
Q

duplex theory: tactile texture perception vibration sensitivity from

A
  • high freq vibration receptors (Pacinian corpuscles RA2)
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24
Q

Merkel cell - neurite complex (SA1): features and adapting

A
  • superficial (lips, fingertips)
  • discriminative touch and pressure
  • edges of objects (shape, curvature) texture
  • slow adapting
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25
Q

Merkel cell - neurite complex (SA1): receptive field

A
  • small receptive field
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26
Q

Merkel cell - neurite complex (SA1): mechanism

A
  • afferent fibre terminals (neurites) form disks which are mechanoreceptive
  • discs contact epidermal cells (Merkel)
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27
Q

Merkel cell - neurite complex (SA1): merkel cell job

A
  • also mechanoreceptive

- release NT glutamate onto afferent terminals (disks) -> depolarisation -> AP

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28
Q

Ruffini’s corpuscles (SA2): adapting and field

A
  • slow adapting

- large receptive field

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29
Q

Ruffini’s corpuscles (SA2): for and located

A
  • stretching of skin (ligs, tendons)
  • joint position (kinaesthesia and proprioception)
  • long axis along stretch lines of skin
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30
Q

Ruffini’s corpuscles (SA2): features

A
  • thin, cigar shaped capsule deep in skin
  • interior of capsule have ct
  • branched terminals of primary afferent sensory fibre lie btw strands
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31
Q

Ruffini’s corpuscles (SA2): mechanism

A
  • stretching compresses mechanoreceptive nerve terminals
  • opens cation channels
  • depolarises primary afferent -> AP
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32
Q

free nerve endings- mechanoreceptive (non-nociceptive): features

A
  • terminal branches of afferent fibres (Type C, unmyelinated) btw epidermal cells
  • membrane distortion opens mechanically gated cation channels
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33
Q

free nerve endings- mechanoreceptive (non-nociceptive): adaptive and receptive field

A
  • slow adapting

small field: pleasant touch

large field: crude ‘non-discriminative’ touch

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34
Q

free nerve endings-general visceral afferents: faetures

A
  • most visceral receptors are also free nerve endings

- mostly subconscious sensory pathways (visceral autonomic reflexes)

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35
Q

free nerve endings-general visceral afferents: types

A
  • mechanoreceptors
  • chemoreceptors
  • nociceptors
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36
Q

free nerve endings-general visceral afferents: mechanoreceptor eg

A

mechanoreceptor:

  • walls of hollow organs, blood v
  • eg. aortic arch
  • respond to increase in BP -> vasodilation and lower heart rate
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37
Q

free nerve endings-general visceral afferents: chemoreceptor eg

A
  • blood gases
  • blood pH
  • trigger compensatory respiratory and cardiovascular changes
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38
Q

free nerve endings-general visceral afferents: nociceptor eg

A
  • signal pain

- excessive distention of an organ

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39
Q

free nerve endings- thermoreceptors (RA2): adapting and receptive field

A
  • rapid adapting

- large receptive

40
Q

free nerve endings- thermoreceptors (RA2): features

A
  • superficial layers of skin

- transduction = temperature sensitive transient receptor potential (TRP) ion channels

41
Q

free nerve endings- thermoreceptors (RA2): non-nociceptive thermal sensation

A

warm: 29-45˚ maximal activity at 45˚
cold: 5-40˚ maximal activity at 25˚

42
Q

TRP channels and thermoreception: features

A
  • non specific cation channels (Ca, Na)
  • different TRP variants for dif temp
  • activation cause influx of cations and depolarisation of cell -> increase firing of AP
43
Q

TRP channels and thermoreception: TRP channel agonists

A
  • chilli and mint
44
Q

thermoreceptors: features

A
  • rapidly adapting (best when temp changes)

- signal direction of temp change

45
Q

thermoreceptors: eg. drop in temp

A
  • momentarily silences warm receptors while cold receptors show burst in firing
  • vice versa
46
Q

thermoreceptors: perceived temp

A

comparing relative activities of warm and cold receptors

- population coding

47
Q

proprioceptors: list types

A
  • muscle spindle Type Ia
  • muscle spindle Type II
  • golgi tendon organs
  • ruffini’s corpuscles
  • pacinian corpuscles
48
Q

proprioceptors: located in mm

A
  • muscle spindle Ia, II
49
Q

proprioceptors: located in tendons

A
  • golgi tendon organs
50
Q

proprioceptors: located in joint capsule

A
  • ruffini’s corpuscle

- pacinian corpuscle

51
Q

proprioceptors: modality- muscle spindles

A

Ia: rate of mm stretch

II: degree of mm stretch

52
Q

proprioceptors: modality- golgi tendon organs

A
  • tendon stretch
53
Q

proprioceptors: modality- ruffini’s and pacinian corpuscles

A
  • stretch in articular cap
54
Q

proprioceptors: adaptation slow

A
  • muscle spindle II
  • golgi tendon organs
  • ruffini’s corpuscles
55
Q

proprioceptors: adaptation fast

A
  • muscle spindle Ia

- pacinian corpuscles

56
Q

ascending sensory pathways: generalised circuit has

A
  • 1st, 2nd and 3rd order neurons
57
Q

ascending sensory pathways: generalised circuit - 1st order neuron

A
  • pseudounipolar
  • transmits sensory info from PNS to CNS
  • cell body usually in ganglion
  • synapse w 2nd order in spinal cord/ brainstem
58
Q

ascending sensory pathways: generalised circuit - 2nd order neuron

A
  • multipolar neuron
  • relay sensory info from spinal cord/ brainstem to thalamus
  • also (reticular system, limbic, cerebellum)
59
Q

ascending sensory pathways: generalised circuit - 3rd order neuron

A
  • multipolar

- relay sensory info from thalamus to cortex where conscious sensory perception occurs

60
Q

ascending sensory pathways: lateral spinothalamic (ALS) pathway for

A

body:

  • pain
  • temp
61
Q

ascending sensory pathways: anterior spinothalamic (ALS) pathway for

A

body:

  • crude (non-discriminative) touch
  • pressure
62
Q

ascending sensory pathways: dorsal column-medial lemniscal (DCML) for

A

body

  • discriminative touch
  • pressure
  • kinaesthesia
  • conscious proprioception
63
Q

ascending sensory pathways: face- discriminative touch and pressure, kinaesthesia

A
  • primary trigeminal (pons)
64
Q

ascending sensory pathways: face- pain, temp, crude touch, pressure

A

spinal trigeminal (cervical cord)

65
Q

ascending sensory pathways: pain and pressure in viscera

A

spinothalamic (ALS)

66
Q

ascending sensory pathways: subconscious

A
  • most proprioceptive info not processed consciously, directed to cerebellum without passing thalamus
67
Q

ascending sensory pathways: spinocerebellar, spinohypothalamic for

A
  • subconscious proprioception

- autonomic activation

68
Q

ascending sensory pathways: subconscious pathway/ target/ function- proprioceptors

A
  • post spinocerebellar
  • cerebellum
  • coordination of mm movements
  • maintain posture
69
Q

ascending sensory pathways: subconscious pathway/ target/ function- mechanoreceptors

A
  • ant spinocerebellar
  • cerebellum
  • coordination of mm movements
  • maintain posture
70
Q

ascending sensory pathways: subconscious pathway/ target/ function- nociceptors/ thermoreceptors in spinohypothalamic pathway

A
  • hypothalamus
  • autonomic (hormonal etc)
  • reflex and emotional aspects of pain
71
Q

ascending sensory pathways: subconscious pathway/ target/ function- nociceptors/ thermoreceptors in spinoreticular pathway

A
  • reticular formation
  • arousal
  • alertness
  • evading injury
72
Q

spinothalamic pathway: primary afferents

A

terminate in spinal cord (dorsal horn)

  • nociceptors
  • thermoreceptors
  • mechanoreceptors (crude touch, pressure)
73
Q

spinothalamic pathway: 2nd order neurons will

A
  • decussate in spinal cord, travel contralaterally and terminate in
  • thalamus (ventral-post complex)
  • reticular formation (arousal, alertness)
74
Q

spinothalamic pathway: 3rd order neurons will terminate in

A
  • primary somatosensory cortex (SI) - discrimination

- limbic cortex (cingulate gyrus, insular cortex) - hypothalamus - affective motivatinal

75
Q

dorsal column-medial lemniscal pathway: primary afferents

A
  • mechanoreceptors
  • proprioceptors
  • axons ascend ipsilaterally in dorsal columns and terminate in medulla:
  • cuneate nucleus (upper body)
  • gracile nucleus (lower body)
  • collaterals (reflexes) terminate in spinal cord (dorsal horn)
76
Q

dorsal column-medial lemniscal pathway: 2nd order

A
  • axons decussate forming medial lemniscus (sensory decussation)
  • terminate in thalamus (ventral post complex)
77
Q

dorsal column-medial lemniscal pathway: 3rd order

A
  • terminate in primary somatosensory cortex (SI) -> discrimination
78
Q

trigeminothalamic pathway: features

A
  • principal somatosensory nerve of head

- sensory info from face, nose, mouth, teeth, eyes, (excl. retina), dura, blood vessels

79
Q

trigeminothalamic pathway: branches

A
  • ophthalmic n
  • maxillary n
  • mandibular n
80
Q

trigeminothalamic pathway: primary afferents

A
  • converge in trigeminal n
81
Q

trigeminothalamic pathway: 1st soma

A

trigeminal ganglion (PNS)

82
Q

trigeminothalamic pathway: 2nd soma

A

various nuclei in brainstem and cervical spinal cord

83
Q

trigeminothalamic pathway: 3rd

A

thalamus (ventral post)

84
Q

parietal lobe: somatosensory cortex SI primary

A
  • postcentral gyrus
  • somatotopic organisation
  • raw somatosensory info from thalamus
  • encodes type, intensity, localisation of sensory input
85
Q

parietal lobe: somatosensory cortex SII secondary

A
  • parietal operculum/ upper lip of lateral sulcus
  • somatotopic organisation
  • high order somatosensory functions (sensorimotor integration, integration of bilateral sensory info, attention, learning, memory)
86
Q

sensory homunculus:

A
  • area of cortex devoted to given body region is proportional to sensory input (no. of sensory afferents) from that region vs physical SA
87
Q

dermatome: define

A
  • sensory region on surface of body that sends afferents via spinal n
88
Q

parietal lobe: primary somatosensory SI cortex functional organisation

A

divided into narrow strips -> relate to Brodmann’s areas 3a, 3b, 1, 2

  • different sensory receptor type
  • each area in SI has separate somatotopic map
89
Q

parietal lobe: somatosensory cortex columnar organisation

A
  • area 3b: functionally distinct (vertical columns) receive input from SA or RA skin receptors in same body region
90
Q

parietal lobe: somatosensory cortex hierarchal organisation

A
  • cortical neurons show increase in size of receptive field from area 3b - 1 - 2 - 4
  • increase complexity of somatosensory processing and intergration
91
Q

parietal lobe: somatosensory cortex -post parietal cortex

A
  • somatosensory association cortex areas 5, 7
  • receives input from SI and SII
  • stereognosis

integration of somatosensory and visual input:

  • dorsal ‘where’ stream
  • spatial vision
  • coordinates motor output via motor cortex
  • arm, hand, eye movements
92
Q

stereognosis:

A

haptic (tactile) perception

- perceive and recognise object by touch without visual/ auditory info

93
Q

stereognosis: cues

A
  • size
  • shape
  • texture
  • temp
94
Q

stereognosis: pathway and diagnostic test for

A
  • DC-ML mostly

- for integrity of parietal lobe: postcentral gyrus, parietal association area

95
Q

astereognosis:

A
  • Alzheimer’s disease
  • less in other forms of dementia
  • disturbance of associative links btw tactile info and memory

4. BIOL257 (18 decks)

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