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Somatosensory Paths Flashcards

1
Q

What does the posterior column transmit

A

Perception of mechanical stimuli
Size, shape, and texture discrimination, and recognition of 3D shape
Proprioception

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2
Q

What is 2 pt discrimination

A

Can discriminate b/w 2 stimuli simultaneously

Related to density of peripheral nerve endings

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3
Q

Density seen in a small receptive field?

Density send in a small receptive field?

A

High receptor density

Low receptor density

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4
Q

Where are the cell bodies of the primary afferent fibers?

Where do these cell bodies terminate?

A

Dorsal root ganglion

On neurons in spinal gray matter

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5
Q

Where do primary afferent fibers for the posterior columns enter the spinal cord?

A

Enter via medial division of the posterior root then branch

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6
Q

What does the fasciculus gracilis transmit?

A

Sensory info and proprioception from

BELOW T6

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7
Q

What does the fasciculus Cuneatus do?

A

Transmits sensory info from AT and ABOVE T6

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8
Q

As you go up fasciculus gracilis and Cuneatus, how are fibers added?

A

Sacral fibers medially

Rostral fibers laterally

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9
Q

What happens to the posterior columns if they are lesioned at the spinal cord?

A

Ipsilateral reduction or loss of discriminative, positional, and vibratory tactile sensation at and below segment lesion

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10
Q

What is sensory ataxia?

What 2 things could it be caused from?

A

Loss of muscle tendon reflexes
Loss of proprioception from extremities
Wide based stance and place feet with force

Lesion to posterior column
Neurosyphylis

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11
Q

Where are the nuclei for gracile and Cuneatus?

A

Posterior medulla

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12
Q

What are the gracile nucleus and cuneate nucleus supplied by?

A

Posterior spinal a.

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13
Q

Where do the posterior columns cross midline?

A

Internal arcuate fibers in medulla

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14
Q

After crossing in the medulla, how do the posteiror columns ascend?

A

Ascend as medial lemniscus

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15
Q

Topographically, how are the medial lemniscus fibers set up?

A

upper ext. = medial

Lower extr. = lateral

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16
Q

Where does the ML go to?

A

VPL nucleus in thalamus

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17
Q

What is the blood supply of ML?

A

Anterior spinal a.

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18
Q

Where are the ventral posterior nuclei?

What supplies them?

A

In caudal thalamus

Thalamogeniculate branches

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19
Q

WHat happens if there is a lesion of thalamogeniculate branches of PCA?

A

Loss of all tactile sensation over opposite body and head

Thalamogeniculate supplies ML - aka posterior columns

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20
Q

The third order neurons of posterior column go where?

A

Posterior limb of internal capsule

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21
Q

What is the final destination of the GF/CF/ML posterior column pathways?

A

Primary and seocndary somatosensory cortices

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22
Q

What makes up the primary somatosensory cortex?

What is is boarded by?

A

Post central gyrus and posterior paracentral gyrus

Central and post central sulcus

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23
Q

What is the primary somatosensory cortex divided into?

A

Brodmann areas

3a,3b, 1 and 2

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24
Q

What supplies the primary somatosensory cortex?

A

ACA and MCA

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25
Q

What would a lesion to MCA cause (looking to primary somatosensory cortex)?

A

Tactile loss over contralateral upper body and face

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26
Q

What would a lesion to ACA cause (looking to primary somatosensory cortex)?

A

Affect contralateral lower limb

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27
Q

Where is the secondary somatosensory cortex?

What sends it inputs?

A

Upper bank of lateral sulcus

Input from somatosensory cortex and VPI of thalamus

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28
Q

What can a lesion to the parietal cortical region produce?

A

Agnosia = contralateral body regions lost from body map, limbs are not recognized

(Sensory intact)

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29
Q

What does the Mesencephalic nucelsu?

A

Proprioceptive info from masticatory ms., extraocular ms. And periodontal l.

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30
Q

What does the principle sensory nucleus do?

A

Discriminative tactile and proprioceptive info

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31
Q

What supplies the prinicpal sensory nucleus?

A

SCA

Principle Sensory A.

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32
Q

What does the dorsomedial division of the principal sensory nucleus?

A

Oral cavity

Travels ipsilaterally via anterior trigeminothalamic tract

33
Q

What does the ventrolateral division of the principal sensory nucleus?

A

V1, V2, V3

Travels contralaterally via posterior trigeminothalamic tract

34
Q

Where do the principal sensory nucleus go?

A

VPM nucleus

35
Q

What is the somatotopic arrangement of the VPM nucleus?

A

Oral cavity medial

External face lateral

36
Q

What is the only nucleus within the CNS?

A

Mesencephalic nucleus

37
Q

Where does the Mesencephalic nucleus go to?

A

To principal sensory nucleus and spinal nucleus

38
Q

What is the jaw jerk reflex ?

What is the afferent limb?

What is the efferent limb?

A

Stretching masseter by downward tap on chin - causes it to contract bilaterally

A: Mesencephalic nucleus to trigeminal motor neurons

E: trigeminal motor neuron

39
Q

What is mononeuropathy?

A

Damage to a nerve outside outside the brain and spinal cord

40
Q

What is a dermatomal sensory loss?

A

Big overlap of dermatomal sensory distribution

41
Q

What is peripheral neuropathy?

How does it present?

Who does it commonly affect?

A

Symmetrical damage to peripheral nerves

Stocking-glove loss of sensation

Diabetes Mellitus

42
Q

How does hemisection of the spinal cord present?

A

Brown-sequard

Dorsal column lost = ipsilateral sensation body lost

ALS lost = contralateral loss of pain/temp

CST lost = ipsilateral paralysis

43
Q

what does the als convey?

A

Pain, temp, non-discriminative touch from body, itching

44
Q

What is the direct pathway of ALS?

A

Spinal Cord —> Lateral thalamus —> S1

45
Q

What is the indirect pathway of ALS?

A

SC —> RF —> ML —> cingulate, frontal and limbic cortices

46
Q

What are cutaneous nociceptors?

A

1st strustcutres that pick up the sensation transmitted

C fibers and a-delta

47
Q

How is sensation transmitted thru free nerve endings?

A

Ligand gated ion channels
Glutamate receptors
GPCRs

48
Q

How do free nerve endings enter the SC?

A

Lateral division of the posterior root

Body sensation was medial

49
Q

What are the targets of the ALS free nerve endings?

A

Lamina 1, 2, and 5 of the posterior horn

50
Q

After the free nerve endings of the ALS enter the SC where do they go?

A

Ascend and descend via Lissauer’s tract

51
Q

How does the ALS cross? And where?

Cross to what?

A

Cross anterior white commissure to ascend via ALS

2 levels above the fiber entry zone

52
Q

What does the direct ALS pathway target?

A

VPL of thalamus

53
Q

Where does the indirect ALS pathway terminate?

Where do those 3rd order neurons go?

A

Reticular formation

RF to intralaminar nuclei and posterior group nuclei

54
Q

Where do the spinothalamic fibers go?

A

Spine -> thalamus -> VPL

55
Q

Where do the spinomesencephalic fibers go?

A

Spine -> RF and PAG

56
Q

Where do the spinobulbar fibers go?

A

Spine —> various nuclei of brain

57
Q

Where do the spinohypothalamic fibers go?

A

Spine -> hypothalamus and other nuclei

58
Q

How is the ALS organized?

A

Arms- medial

Legs - lateral

59
Q

What would an intramedullar tumor cause?

A

Medial= arms hit first

60
Q

What would an extramedullary tumor cause?

A

Lateral = sacral and coccygeal and lumbar hit first

61
Q

How does Herpes zoster manifest?

A

Viral etiology that has dermatomal distribution

Can reactivate from NS when under stress

Postherpetic neuralgia

62
Q

What is syringomyelia?

How does this first present

A

Cystic cavitation of central regions of spinal gray matter

Can impinge on AWC and take out both ALS fibers

Patient unknowingly burns hands on stove, curling iron, etc.

63
Q

What is the blood supply to the ALS?

A

Arterial vasocorona

Sulcal branches of ASA

64
Q

What could happen if the arterial vasocorona or Sulcal branches of ASA is occluded?

Where would sxs show up?

A

Patchy loss of pain, temp., and touch of contralateral side of body

2 spinal segments below lesion

65
Q

What does a medial medulla lesion cause?

A

Contralateral loss of touch and vibratory

Still has pain and touch

66
Q

Lateral medullary syndrome presents how?

Caused by what?

A

PICA lesion

Spinal V lost - ipsilateral pain loss to face
ALS lost - contra pain loss to body

67
Q

What is the target of the spinal trigeminal pathway?

A

VPM of thalamus

68
Q

What is the blood supply to the trigeminal strucutres in the medulla?

A

PICA

69
Q

What are the division of the spinal V nucleus?

A

Pars caudalis
Pars oralis
Pars interpolaris

70
Q

where is the pars caudalis located?

A

Spinal cord C2, C3 to obex

71
Q

Where is the pars oralis?

A

Pons to superior medulla

72
Q

What is pars interpolaris?

A

From superior medulla to obex

73
Q

What happens if the spinal trigeminal tract is lesioned…
Caudally?

Rostrally?

A

Onion peel sensory loss

Caudal lesion - mouth okay

Rostral lesion - sensory loss at mouth and back of head

74
Q

What is the indirect pathway for Trigeminal pathway?

What does this facilitate?

A

Pain fibers to RF bilaterally as Trigeminoreticular fibers

Helps ascending RAS system in arousal and alertness

75
Q

What does a unilateral lesion of trigeminal n. Cause?

A

Loss of jaw jerk reflex
Atrophy of Ms. of ma stication
Anesthesia in trigeminal dermatomes
Loss of ipsilateral and consensual corneal reflex

76
Q

What could cause alternating analgesia?

A

Brainstem lesion in upper medulla

Damaging spinal V tract before it crosses

77
Q

What causes alternating trigeminal hemiplegia?

A

Unilateral destruction of trigeminal n. And CST in PONS

78
Q

What would a lesion to the trigeminal n. Or central nuclei cause?

A

Ipsilateral loss of pain, temp and touch sensation cause

Loss of sensation in mouth

Paralysis in masticatory Ms.

Could lose afferent limb of corneal reflex

79
Q

How does the corneal reflex work?

A

Aff. Limb to CN V

Travel on V1 to cell bodies in trigeminal ganglion

Trigeminothalamic fibers BILATERALLY to facial motor nucleus

Causes both eyes to blink

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