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Brain and Behavior Exam 2 > Lec 14 Somatosensory System 1 and 2 > Flashcards

Lec 14 Somatosensory System 1 and 2 Flashcards

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1
Q

What are exteroreceptors?

A

receptors that receive stimuli on body surface

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2
Q

What are interoreceptors?

A

receptors receive stimuli from within body itself

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3
Q

What are proprioceptors?

A

interoreceptors that receive info about positive of body, head, limbs in space

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4
Q

What types of info about stimulus are encoded by neural code?

A
  • modality
  • intensity
  • location
  • duration
  • rate of change
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5
Q

How many type of sensory modality is each axon usually concerned with?

A

each axon is specific to single type of sensation

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6
Q

What are free nerve endings? what do they sense?

A
  • terminal branches of C fibers or A-delta fibers
  • not covered by anything [no myelin]
  • enter epidermis as superficially as stratum corneum
  • detect painful stimuli, warmth or cold, or mechanical displacement [stretching] of skin
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7
Q

What are hair receptors? What activates them?

A
  • unmyelinated branches that encircle the hair follicle
  • multiple for each hair follicle
  • terminal axon membrane embedded in the follicle membrane
  • activated by hair deflection
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8
Q

What is merkel’s corpuscle? What stimuli do they detect?

A
  • flattened disc formed from terminal axon branch
  • associated with modified epidermal merkel cell
  • some of merkel cell cytoplasm encloses terminal disk of axon
  • detect sustained pressure
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9
Q

What are encapsulated endings?

A
  • terminal axon ends inside tissue capsule

- capsule formed by overlapping processes of several cells [often fibroblast-like cells]

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10
Q

What are pacinian corpuscle

A

type of encapsulated ending in skin/joints

detect rapid vibrations

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11
Q

What are ruffini endings?

A

type of encapsulated ending in skin/joints

detect pressure

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12
Q

What do ruffini endings detect?

A

detect pressure

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13
Q

What do merkel’s corpuscle detect?

A

detect sustained pressure

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14
Q

What do pacinian corpuscles detect?

A

detect [rapid] vibrations

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15
Q

What do meissner corpuscles detect?

A

light touch

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16
Q

What type of encapsulate mechanoreceptor in skeletal muscle? in myotendinous junction?

A

skeletal: muscle spindle
myotendinous: golgi tendon organ [GTO]

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17
Q

How is intensity of stimulus encoded by mechanoreceptors?

A
  • by frequency of AP and number of fibers recruited
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18
Q

How is location encoded by mechanoreceptors?

A

by position and size of neuron’s receptive field

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19
Q

How is duration/rate of change determined by mechanoreceptors?

A
  • by discharge characteristics of axon

slowly adapting = will continue to discharge AP as long as stimulus applied

rapidly adapting = discharged during onset, offset, or change

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20
Q

What is difference slowly adapting vs rapidly adapting axons?

A

slowly adapting = encode for static processes [ex. Meissners]

rapidly adapting = only confer AP at onset or offset of stimulus – when they is a change

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21
Q

What do group 1 muscle fibers innervate?

A
  • group 1 = large diameter axon, heavily myelinated, fast conducting

1a –> primary endings in muscle spindles
1b –> golgi tendon organs

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22
Q

What do group 2 muscle fibers innervate?

A
  • secondary innervation for muscle fibers
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23
Q

Which types of fibers have large diameter axon, heavily myelinated, and fast conducting?

A

muscle afferents: group 1a, 1b, 2

cutaneous afferents: A-beta

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24
Q

What do group 3 and group 4 do?

A

pain and temperature in muscle

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25
Q

What is structure of group 3 and A-delta fibers?

A

thin axon, thin myelin, slow-conducting

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26
Q

What is structure of group 4 and C fibers?

A

thin axon, unmyelinated, slow-conducting

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27
Q

What are the two type of muscle nociceptors?

A

Group 3 and Group 4

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28
Q

What is function of alpha-delta/C fibers?

A

cutaneous pain and temp crude touch
thermoreceptors, nociceptors, small diameter mechano-receptors

many are free nerve endings

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29
Q

Which fibers are part of the medial division of dorsal root? function?

A

larger afferents
group 1, 2, and A-beta

they sense proprioception and low-threshold touch of cutaneous and and muscle

30
Q

Which fibers are part of lateral division of dorsal root? function?

A

smaller afferents
group 3, 4, A-delta, and C

sense pain and temp largely but also inputs from viscera and some high-threshold tactile input

31
Q

What 3 branches do medial-division fibers branch into when they enter dorsal spinal cord?

A
  1. white matter ascending tract [in f.gracilis if below T6, in f. cuneatus if above T6]
  2. local processing branch:
    - – if A-beta: terminates in nucleus proprius [laminae 3/5]
    - if group 1/2 in Clarke’s column [laminae VII] or motor neuron pools [laminae 9]
  3. fibers descend caudally in fasiculus interfascicularis/septomarginalis and terminate in nucleus proprius/clarkes/motor neuron pools a few segments below
32
Q

Where do dorsal column-medial lemniscus ascending fibers terminate?

A
  • ascend via f. gracilis [if below T6] or f. cuneatus [above T6]
  • terminate/synapse in nucleus gracilis or cuneatus in medulla
33
Q

What happens to lateral division fibers when they enter the spinal cord?

A
  • enter spinal cord ventrally
  • travel over 2-5 segments and form lissauer’s tract in central/lateral dorsal horn
  • terminate on second-order neurons of substantia gelatinosa [lamina 1 and 2]
34
Q

What two structures make up the dorsal column nuclei of the medulla [DCN]

A
  • gracile nucleus

- cuneate nucelsu

35
Q

What is the function of fibers in the dorsal-column medial lemniscal [DC-ML] path?

A
  • principal path of info about position, movement, touch, vibration
36
Q

What are characteristics of DC-ML pathway?

A
  • responsible for somatotopic info
  • retain modality and location specificity [little convergence of fibers, receptive field characteristics are transmitted]
  • synaptic security [rapid/reliable transmission]
  • proportional representation [more important body parts represented more]
37
Q

What is the path of DC-ML fibers after they reach the medulla?

A
  • synapse in F. gracilis/f. cuneatus of medulla
  • 2ndary neurons continue to ascend and cross midline via medial lemniscus tract = “the great sensory decussation” to reach contralateral thalamus
  • 2nd synapse in ventral posterolateral nucleus of thalamus
  • thalamic fibers project to somatosensory cortex S1, S2 [cortical layer 4]
38
Q

What is the path of spinothalamic fibers after they enter the spinal cord?

A
  • synapse in substantia gelatinosa in dorsal horn
  • secondary nerve fibers cross to the other side of the spinal cord via the anterior white commissure [between central canal and ventral median fissure]
  • fibers ascend thus contralaterally from their entrance site in the anterolateral funiculus to the thalamus
  • fibers terminate in the thalamus VPL
  • ensuing fibers project from thalamus to S1 ,S2 cortical layer 1
39
Q

What is difference between fibers in the lateral vs ventral spinothalamic tracts?

A
  • lateral spinothalamic tract = pain, temp

- ventral spinothalamic tract is more medial = crude touch

40
Q

What is difference DC-ML and spinothalamic fiber receptive fields?

A
  • spinothalamic = larger, more overlapping receptive fields

- cruder localization

41
Q

What are the collaterals in the spinothalamic system?

A
  • spinothalamic fibers have lots of collaterals that end in tectum of midbrain [spinotectal] and reticular formation of mid/pons/med [spinoreticular]
  • these collaterals are related to pain mechanisms
42
Q

What is the trigeminal system?

A
  • somatosensory info from face/head conveyed by V nerve fibers whose cell bodies are in the trigeminal ganglion
  • divided into large-diameter vs small-diameter the same as DC-ML vs spinothalamic
43
Q

What happens to large-diameter fibers in the trigeminal system? function?

A
  • convey touch/pressure/vibration
  • terminate in principal trigeminal nucleus in pons on same side = analogous to dorsal column nuclei
  • 2nd order neurons cross midline in pons and join ascending medial lemniscus on opposite side
  • 2nd synapse in VPM of thalamus
  • thalamic fibers project to S1, S2 [layer 4]
44
Q

What happens to small-diameter fibers in trigeminal system?

A
  • convey pain/temp from face
  • enter lateral to pons
  • travel caudally to medulla via ipsilateral spinal tract of V
  • fibers terminate in spinal nucleus of V
  • cross midline and join contralateral ascending spinothalamic tract
  • thalamic fiber project to S1, S2
45
Q

What structure is analogous to lissauer’s tract?

A

spinal tract of V

46
Q

What is brown-sequard syndrome?

A

lateral hemi-section of spinal cord lesion [injury in part but not all of spinal cord]

  • below the point of lesion have:
  • – contralateral reduced sensation of temp and pain [spinothalamic]
  • – ipsilateral reduced 2 point discrimination, vibration, proprioception [dorsal column]
    • ipsilateral spastic paralysis, hypertonia below lesion + babinski [cortical spinal, UMN]
    • ipsilateral flaccid paralysis, hypotonia, atrophy at the level of the lesion [anterior horn, LMN]
47
Q

What is sterogenesis? When is it defective?

A

ability to identify objects placed in hand or to recognize letter or numbers written in hand

defective when lesion of dorsal column

48
Q

What is tabes dorsalis? What is destroyed in tabes dorsalis? sign?

A
  • due to tertiary syphilis
  • dorsal column especially gracile fasiculus destroyed
  • illicits rombergs sign [can’t stand upright with eyes closed] = proprioception deficits
  • bilateral loss of mechonsensation below leiosn
  • no motor deficits
49
Q

What structure is equivalent to dorsal column nuclei?

A

principal sensory nucleus of V in pons

50
Q

What structure is equivalent to substantia gelatinosa?

A

spinal nucleus of V in medulla

51
Q

What fibers are responsible for the jaw jerk afferenct and efferent?

A

afferent: group 1, 2, proprioceptive fibers of CN V enter brainstem
- terminates at motor nucleus of 5
efferent: CN 5 motor nerves from motor nucleus go back and terminate on muscles of mastication

52
Q

What is syringomyelia?

A
  • cystic enlargement of central spinal canal [most common C8-T1] causes compression of anterior white commissure
  • get bilateral loss of pain/temp a few levels above and below the lesion in cape-like distribution
  • preservation of fine touch + mechanosensation
53
Q

What terminates in VPM vs VPL of thalamus?

A

big fibers of DC-ML terminate in VPL
big fibers of trigeminal mechanosensation terminate in VPM

fibers from spinothalamic/small fibers of trigeminal not as organized

54
Q

Is the medial lemniscus somatopically organized when it enters thalamus? What about the spinothalamic tracts at the point? how?

A
  • DC-ML organized from lateral to medial LTANF [legs, trunk, arms, neck, face]
  • spinothalamic not organized
55
Q

What is the purpose of the ventral posterior [VP] nucleus of thalamus?

A
  • major somatosensory relay nucleus of thalamus
  • only site of termination of medial lemniscus
  • major site of termination of spinothalamic fibers
56
Q

Where does the VP nucleus project to?

A

S1 [first somoatosensory cortex]

S2 [2nd somatosensory cortex]

57
Q

Where is S1 located? S2?

A

S1 = caudal part of central sulcus and postcentral gyrus

S2 = part of parietal operculum [ceiling of lateral fissure]

58
Q

What are the parts of the VP nucleus of thalamus?

A
  • VPM = medial, receives lemniscal input from contralateral trigeminal nucleus
  • VPL = lateral, lemniscal input from non-trigeminal
59
Q

What is the order from lateral to medial of somatosensory lemniscal representation in the ventral posterior nucleus?

A 
lateral
- legs
- torso
- arms
- neck
- face [head, face, inside mouth]
medial

technically face in VPM, rest is VPL

60
Q

What parts of body have highest representation of VPL/VPM lemniscal fibers?

A
  • foot, hands, and lips since these have highest density of innervation and thus greatest sensory acuity
61
Q

What are 3 properties of lemniscal relay neurons in thalamus?

A
  1. high synaptic security [reproduce faithful temporal AP pattern]
  2. modality and place specificity from specific receptor type
  3. neurons with same place and modality characteristics cluster together [LTANF]
  4. surround inhibition = activation of one group of neurons is accompanied by simultaneous inhibition of its neighbors
62
Q

What are the 2 types of neurons in thalamic nuclei?

A
  1. relay neurons – relay to mostly cortex, exhibit properties that mirror their input
  2. instrinsic inhibitory interneurons, use GABA
63
Q

What are 4 properties of spinothalamic input?

A
  1. pain/temp fibers terminate widely and diffusely across VP, not somatotopically organized
  2. low transmission fidelity —> need intense stimuli to drive AP
  3. large receptive fields [not as specific location info]
  4. not modality specific –> can respond to noxious [pain] stimuli, thermal, or both
64
Q

What are the 4 separate areas of S1 layer 4? How is each area structured?

A

area 3a, 3b, 1, 2

  • within each area there is a contralateral body-map with leg most medial, face/head most lateral, also have disproportionate rep. of feet/hands/lips like in VP
65
Q

What type of info is received by areas 3a and 2? fiber type?

A
  • proprioceptive info
  • group 1a, 1b, 2 fibers
  • also spinothalamic input

all contralateral

66
Q

What type of info is received by areas 1 and 3b? fiber type?

A
  • cutaneous tactile info
  • A-beta fibers
  • also spinothalamic input

all contralateral

67
Q

Which of the four S1 areas receive spinothalamic input?

A

all 4 areas

68
Q

How is the S1 cortex organized? where does DC-ML and spinothalamic terminate within?

A
  • 6 layers “cortical columns”
  • columns arranged by receptive field span/neuron response properties
  • information integrated across cortical columns by long-range axons running perpendicular
  • DC-ML input terminated in layer 4 across 4 areas
  • spinothalamic input distributes widely in layer 1 across all 4 areas
69
Q

What is function of S2? Where do the fibers in S2 come from?

A

process info during bimanual manipulation
represents both sides of body

fibers from contralateral body come from : branches of thalamic projection destined for S1 [via internal capsule]

fibers from ipsilateral body come from: contralateral S1 via corpus callosum

70
Q

What happens in destruction of S2?

A

loss of interhemispheric transfer of info

can’t discriminate objects on basis of size and texture

71
Q

Via what structure does VPM/VPL project to S1/S2?

A

via internal capsule

via corpus callosum from contralateral S1 for S2 ipsilateral info

Brain and Behavior Exam 2 (21 decks)

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