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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
What would a lesion to MCA cause (looking to primary somatosensory cortex)?
Tactile loss over contralateral upper body and face
26
What would a lesion to ACA cause (looking to primary somatosensory cortex)?
Affect contralateral lower limb
27
Where is the secondary somatosensory cortex? What sends it inputs?
Upper bank of lateral sulcus Input from somatosensory cortex and VPI of thalamus
28
What can a lesion to the parietal cortical region produce?
Agnosia = contralateral body regions lost from body map, limbs are not recognized (Sensory intact)
29
What does the Mesencephalic nucelsu?
Proprioceptive info from masticatory ms., extraocular ms. And periodontal l.
30
What does the principle sensory nucleus do?
Discriminative tactile and proprioceptive info
31
What supplies the prinicpal sensory nucleus?
SCA | Principle Sensory A.
32
What does the dorsomedial division of the principal sensory nucleus?
Oral cavity Travels ipsilaterally via anterior trigeminothalamic tract
33
What does the ventrolateral division of the principal sensory nucleus?
V1, V2, V3 Travels contralaterally via posterior trigeminothalamic tract
34
Where do the principal sensory nucleus go?
VPM nucleus
35
What is the somatotopic arrangement of the VPM nucleus?
Oral cavity medial | External face lateral
36
What is the only nucleus within the CNS?
Mesencephalic nucleus
37
Where does the Mesencephalic nucleus go to?
To principal sensory nucleus and spinal nucleus
38
What is the jaw jerk reflex ? What is the afferent limb? What is the efferent limb?
Stretching masseter by downward tap on chin - causes it to contract bilaterally A: Mesencephalic nucleus to trigeminal motor neurons E: trigeminal motor neuron
39
What is mononeuropathy?
Damage to a nerve outside outside the brain and spinal cord
40
What is a dermatomal sensory loss?
Big overlap of dermatomal sensory distribution
41
What is peripheral neuropathy? How does it present? Who does it commonly affect?
Symmetrical damage to peripheral nerves Stocking-glove loss of sensation Diabetes Mellitus
42
How does hemisection of the spinal cord present?
Brown-sequard Dorsal column lost = ipsilateral sensation body lost ALS lost = contralateral loss of pain/temp CST lost = ipsilateral paralysis
43
what does the als convey?
Pain, temp, non-discriminative touch from body, itching
44
What is the direct pathway of ALS?
Spinal Cord —> Lateral thalamus —> S1
45
What is the indirect pathway of ALS?
SC —> RF —> ML —> cingulate, frontal and limbic cortices
46
What are cutaneous nociceptors?
1st strustcutres that pick up the sensation transmitted C fibers and a-delta
47
How is sensation transmitted thru free nerve endings?
Ligand gated ion channels Glutamate receptors GPCRs
48
How do free nerve endings enter the SC?
Lateral division of the posterior root | Body sensation was medial
49
What are the targets of the ALS free nerve endings?
Lamina 1, 2, and 5 of the posterior horn
50
After the free nerve endings of the ALS enter the SC where do they go?
Ascend and descend via Lissauer’s tract
51
How does the ALS cross? And where? | Cross to what?
Cross anterior white commissure to ascend via ALS 2 levels above the fiber entry zone
52
What does the direct ALS pathway target?
VPL of thalamus
53
Where does the indirect ALS pathway terminate? Where do those 3rd order neurons go?
Reticular formation RF to intralaminar nuclei and posterior group nuclei
54
Where do the spinothalamic fibers go?
Spine -> thalamus -> VPL
55
Where do the spinomesencephalic fibers go?
Spine -> RF and PAG
56
Where do the spinobulbar fibers go?
Spine —> various nuclei of brain
57
Where do the spinohypothalamic fibers go?
Spine -> hypothalamus and other nuclei
58
How is the ALS organized?
Arms- medial | Legs - lateral
59
What would an intramedullar tumor cause?
Medial= arms hit first
60
What would an extramedullary tumor cause?
Lateral = sacral and coccygeal and lumbar hit first
61
How does Herpes zoster manifest?
Viral etiology that has dermatomal distribution Can reactivate from NS when under stress Postherpetic neuralgia
62
What is syringomyelia? How does this first present
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
What is the blood supply to the ALS?
Arterial vasocorona Sulcal branches of ASA
64
What could happen if the arterial vasocorona or Sulcal branches of ASA is occluded? Where would sxs show up?
Patchy loss of pain, temp., and touch of contralateral side of body 2 spinal segments below lesion
65
What does a medial medulla lesion cause?
Contralateral loss of touch and vibratory Still has pain and touch
66
Lateral medullary syndrome presents how? Caused by what?
PICA lesion Spinal V lost - ipsilateral pain loss to face ALS lost - contra pain loss to body
67
What is the target of the spinal trigeminal pathway?
VPM of thalamus
68
What is the blood supply to the trigeminal strucutres in the medulla?
PICA
69
What are the division of the spinal V nucleus?
Pars caudalis Pars oralis Pars interpolaris
70
where is the pars caudalis located?
Spinal cord C2, C3 to obex
71
Where is the pars oralis?
Pons to superior medulla
72
What is pars interpolaris?
From superior medulla to obex
73
What happens if the spinal trigeminal tract is lesioned... Caudally? Rostrally?
Onion peel sensory loss Caudal lesion - mouth okay Rostral lesion - sensory loss at mouth and back of head
74
What is the indirect pathway for Trigeminal pathway? What does this facilitate?
Pain fibers to RF bilaterally as Trigeminoreticular fibers Helps ascending RAS system in arousal and alertness
75
What does a unilateral lesion of trigeminal n. Cause?
Loss of jaw jerk reflex Atrophy of Ms. of ma stication Anesthesia in trigeminal dermatomes Loss of ipsilateral and consensual corneal reflex
76
What could cause alternating analgesia?
Brainstem lesion in upper medulla | Damaging spinal V tract before it crosses
77
What causes alternating trigeminal hemiplegia?
Unilateral destruction of trigeminal n. And CST in PONS
78
What would a lesion to the trigeminal n. Or central nuclei cause?
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
How does the corneal reflex work?
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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