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Neuro II > Somatosensory I > Flashcards

Somatosensory I Flashcards

1
Q

what are the two main pathways in the somatosensory system

A

posterior column - medial lemniscal pathway

trigeminothalamic pathway

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2
Q

which pathway is involved in awareness of body positions and limb movement

A

posterior column - medial lemniscal pathway (PMCLS)

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3
Q

what are the characteristic features afferent fibers of the PCMLS

A

fast conduction velocity,

few synaptic relays

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4
Q

what system allows of to localize touch with accuracy

A

PCMLS

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5
Q

what is two-point discrimination and what system is responsible for if

A

ability to discriminate between two stimuli simulataneously

PCMLS

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6
Q

what aspect of the PCMLS is two-point discrimination related to?

A

peripheral nerve ending density

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7
Q

what regions of the body have increased density of tactile receptors

A

hands, perioral

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8
Q

do small receptive fields have high or low receptor density

A

high receptor density

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9
Q

what are the three parts of primary afferent fibers

A 
peripheral process (soma => periphery)
central process (soma => CNS)
pseudounipolar cell body
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10
Q

where is the afferent fiber cell body located

A

dorsal root ganglia

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11
Q

what information do large-diameter afferent fibers relay

A

discriminative touch
flutter vibration
proprioception

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12
Q

where do large-diameter afferent fibers enter the spinal cord

A

at the medial division of the posterior (AKA dorsal) root

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13
Q

what structure do the largest set of afferent fibers form superiorly?

A

posterior columns (fasciculus gracilis and cuneatus)

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14
Q

what two structures make up the posterior columns

A

fasciculus gracilis

fasciculus cuneatus

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15
Q

which part of the posterior column holds fibers from T6-sacrum

A

fasciculus gracile

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16
Q

which part of the posterior column holds fibers from cervical-T6

A

fasciculus cuneatus

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17
Q

how are afferent fibers within the posterior column organized?

A 
more inferior (sacral) fibers are medial
superior fibers are lateral
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18
Q

spinal cord lesions result in loss of tactile sensation where?

A

at and below segmental level of injury

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19
Q

what should you suspect if a patient presents with wide stance, stomping and absent DTRs

A

sensory ataxia, secondary to a SC lesion

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20
Q

where are nucleus gracile and nucleus cuneatus found

A

posterior medulla

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21
Q

where do nucleus gracile and nucleus cuneatus receive input from

A

primary afferents from the ipsilateral dorsal root ganglia via its corresponding fasciculus

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22
Q

what sensory information is received at the cores of nucleus gracilis and nucleus cuneatus

A

inputs from afferent fibers

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23
Q

what sensory information is received at the outer shells of nucleus gracilis and nucleus cuneatus

A

inputs from muscle spindles, joints and Pacinian corpuscles

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24
Q

where do second order neurons of the posterior column nuclei send their axons

A

through the midbrain, to the contralateral thalamus

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25
Q

within the medial lemniscus, how are fibers from the extremities organized

A

UE fibers lie medially

LE fibers lie laterally

26
Q

where does the medial lemniscus terminate

A

ventral posterolateral nucleus

27
Q

how would a patient with damage at the brainstem present

A

deficits in discriminative touch, sensation of position and vibration of the CONTRALATERAL side

28
Q

what is the wedge-shaped group of cells in the caudal thalamus

A

ventral posterior nuclei

29
Q

what separates the ventral posterolateral nucleus (VPL) from the ventral posteromedial nucleus (VPM)

A

fibers of the arcuate lamina

30
Q

what is the blood supply to the ventral posterior nuclei

A

thalamogeniculate branches of the PCA

31
Q

how would a patient present after compromise of the thalamogeniculate branches of the PCA

A

loss of all tactile sensation of contralateral and head

32
Q

what are the inhibitory neurons that influence the firing rates of third-order neurons?

A

local circuit interneurons

33
Q

a lesion to what structure would cause tactile loss over the contralateral upper body and face

A

MCA

34
Q

a lesion to what structure would cause tactile loss over the contralateral LE

A

ACA

35
Q

what are the subdivisions of the somatosensory cortex?

A 
Brodmann areas:
3a
3b
1
2
36
Q

from what structure does the secondary somatosensory cortex receive inputs

A

ipsilateral cortex

ventral posterior inferior nucleus of the thalamus

37
Q

what are the four trigeminal nuclei

A

main sensory nucleus (msT)
trigeminal motor nucleus (mT)
spinal nucleus
mesencephalic nucleus (mes)

38
Q

what information is carried by the main sensory nucleus

A

touch and pressure

39
Q

what information is carried by the trigeminal motor nucleus

A

muscles of mastication

40
Q

what information is carried by the spinal nucleus

A

pain and temperature

41
Q

what information is carried by the mesencephalic nucleus

A

proprioceptive afferents from the TMJ and masticatory ms

42
Q

what division of the main sensory nucleus receives afferent input from the oral cavity

A

dorsomedial division

43
Q

what division of the main sensory nucleus receives afferent input from V1, V2 and V3

A

ventrolateral division

44
Q

where do secondary fibers of the dorsomedial divison of the main sensory nucleus travel

A

ipsilaterally via the posterior trigeminothalamic tract

45
Q

where do secondary fibers of the ventrolateral divison of the main sensory nucleus travel

A

contralaterally via the anterior trigeminothalamic tract

46
Q

what is the target of the anterior and posterior trigeminothalamic tracts

A

the ventral posteromedial nucleus (VPM)

47
Q

where do third order from the VPM project

A

through the posterior limb of the internal capsule to the primary somatosensory cortex

48
Q

what are the sxs of a spinal cord lesion

A

proprioceptive defitics on one side and anestheia on the other

49
Q

what sxs would be seen in a lesion to area 1 of the SI

A

deficit in texture discrimination

50
Q

what sxs would be seen in a lesion to area 2 of the SI

A

loss of size and shape discrimination (astereognosis)

51
Q

what sxs would be seen in a lesion to area 3b of the SI

A

deficits in size, shape and texture discrimination

52
Q

lesion of the left posterior column at L1 produces what impairments?

A

loss of light touch, vibration, position sensation of the LEFT leg

53
Q

lesion of the left fasciculus cuneatus at C3 produces what impairments

A

loss of light tough, vibration and position sensation of the left arm and trunk

54
Q

afferents from what spinal levels make up the fasciculus gracilis

A

T6 and below

55
Q

afferents from what spinal levels make up the fasciculus cuneatus

A

T6 and above

56
Q

where are the 1st order neurons of the PCMLS

A

dorsal root ganglia

57
Q

where and what are the 2nd order neurons of the PCMLS

A

medulla - nuclei gracilis and cuneatus

58
Q

where and what are the 3rd order neurons of the PCMLS

A

thalamus, ventral posterior lateral (VPL) nucleus

59
Q

where do afferents from the PCMLS go after synapsing in the thalamus

A

to the primary and secondary somatosensory cortices (via corona radiata)

60
Q

from what vessels does the primary somatosensory cortex receive blood supply

A

ACA and MCA

Neuro II (16 decks)

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