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NS-1 > 10.1 Somatosensory Tracts 1 (Dennis) > Flashcards

10.1 Somatosensory Tracts 1 (Dennis) Flashcards

1
Q

What type of information is carried by the PCML pathway?

A

Two point touch

Deep Pressure

Vibration

Propriception

Crude touch

Thermal sensation

Nociception

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2
Q

Where are the cell bodies for first order sensory neurons?

What type of nerves are these?

From what layer are these nerves derived?

A

Dorsal root ganglion.

Pseudounipolar nerves.

Neuroectoderm.

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3
Q

Where do the afferent first order fibers of the PCML system enter the spinal cord?

A

At the medial division of the posterior root.

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4
Q

Where is the switch over from fibers coming together to form the fasciculus gracilis to becoming the fasciculus cuneatus?

A

T6

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5
Q

In the fasciculae gracilis and cuneatus, are the fibers from the upper extremity more lateral or more medial to the fibers from the lower extremity?

A

Upper extremity fibers are more lateral in the PCML system.

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6
Q

Where do we find the nuclei gracilis and cuneatus?

A

In the posterior medulla.

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7
Q

What is the specialization of the outer shell and inner core of the nuclei gracilis and cuneatus?

A

The outer shell of the nuclei gracilis and cuneatus specializes in proprioception.

The inner core specializes in sensation.

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8
Q

What do we call the decussation of the PCML secondary fibers immediately after the synapse of the nucleus gracile/cuneatus?

A

Anterior arcuate fibers.

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9
Q

At the level of the pons, are fibers from the nucleus gracilis medial or lateral to the fibers of the nucleus cuneatus?

A

Fibers from the nucleus gracilis are lateral in the pons.

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10
Q

What nucleus in the thalamus does the PCML pathway synapse onto?

A

The ventral posteriolateral nucleus of the thalamus.

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11
Q

Where do the third order neurons of the PCML system travel?

What important structure do they pass through?

What is the name of the pathway?

A

The fibers from the ventral posterolateral nucleus runs through the thalamocortical pathway, through the posterior limb of the internal capsule, and to the somatosensory cortex.

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12
Q

What artery supplies the PCML in the spinal cord?

What artery supplies the PCML in the medulla (and up from there)?

A

Spinal cord = posterior spinal artery

Medulla and up = anterior spinal artery

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13
Q

What artery supplies the ventral posterolateral nucleus?

What would happen if these were occluded?

A

The thalamogeniculate branches of the posterior cerebral artery.

Complete loss of discriminative touch, pressure sensation, and proprioception to the contralateral body.

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14
Q

Where would lesions to the middle cerebral artery cause loss of sensation?

Where would lesions to the anterior cerebral artery cause loss of sensation?

A

The anterior cerebral artery damage would eradicate sensation from the lower extremity.

Middle cerebral artery damage would eradicate damage from the upper extremity and face.

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15
Q

What symptom is associated with damage to the secondary somatosensory area?

A

Agnosia – the loss of ability to recognize a limb as part of the body.

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16
Q

What are the functions of the sensory nuclei of the trigeminal nerve?

A

Main sensory nucleus (msT)

  • Touch and pressure.

Spinal nucleus

  • Touch
  • Pressure
  • Proprioceptin
  • Pain
  • Temperature

Mesencephalic nucleus (mes)

  • Proprioception for chewing.
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17
Q

What are the two divisions of the main sensory nucleus of the trigeminal nerve?

A

The main sensory nucleus has two divisions:

  • Dorsomedial division
    • Afferents just from the oral cavity.
  • Ventrolateral division
    • Afferents from V1, V2, and V3
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18
Q

What is the purpose of the mesencephalic nucleus?

A

Primarily relays proprioceptive information related to chewing.

19
Q

What are the three parts of the spinal nucleus of the trigeminal nerve?

A

Pars caudalis,

Pars oralis,

Pars interpolaris

20
Q

What are the targets of primary afferent nerves?

A

laminae I, II, and V of posterior horn

21
Q

What is the other name for Lissauer’s tract?

A

posterolateral fasciculus

where afferents of ALS travel

ascending branches go up to brain

some descending branches terminate on interneurons in SC gray matter for reflexes

22
Q

where are 3rd order neurons of the direct spinothalamic path located?

A

VPL

23
Q

What are spinoreticular fibers?

A

branches from ALS that terminate in reticular formation of brainstem

third order neurons then project to medial thalamic nuclei

24
Q

What are spinobulbar fibers?

A

info from sC that ascends to various brainstem nuclei

25
Q

What are spinomesnecephalic fibers?

A

from ALS –> terminate in midbrain reticular formation or transition to form spinotectal fibers –> superior colliculus and anterior pretectum

26
Q

What is the somatotopic relationship of the ALS?

A

axons from lower levels = lateral

axons from upper extremity = medial

27
Q

What is the blood supply to the ALS?

A

vasa corona and sulcal branches of the anterior spinal A

28
Q

What would occlusion of the arterial vasocorona and sulcal branches of Ant spinal A cause?

A

patchy loss of pain and thermal senses over contra side of body

29
Q

What does hemisection of the SC cause?

A

contralateral loss of pain and thermal sensations about 2 segments below lesion

ipsi loss of tactile and vibratory sense

30
Q

Where are medullary ALS fibers?

A

near anterolateral surface

anterior to spinal trigeminal nucleus

spearated from PCMLS

31
Q

What artery supplies the ALS fibers in the medulla?

What happens if a lesion occurs here?

A

PICA

contra loss of discriminative touch and vibratory sense, but pain/thermal sense is WNL (one modality absent, but not the other)

32
Q

How does the spinal trigeminal nucleus run?

A

afferents enter pons –> descend in spinal trigeminal tract, lateral to spinal nucleus –> becomes continuous w/ Lissauers tract in upper cervical cord

both nucleus and tract extend caudally to about 3rd cervical segment

33
Q

What are the parts of the spinal trigeminal tract and nucleus?

A

pars caudalis: moust caudal, from C2, C3 to obes

pars oralis: most rostral, from main sensory nucleus to pontomedullary jxn

pars interpolaris: in btw, in rostral medulla

34
Q

How are the spinal trigeminal tract and nucleus oriented in regard to dermatomes on face?

A

opposite: on face V1 = superior

in tract: V1 is inferior, V2 middle, V3 superior

35
Q

How are fibers arranged in the pars caudalis?

A

oral fibers (most superior on face) = most superior

caudal and lateral fibers = most caudal

36
Q

What is the pattern of sensory loss from a spinal trigeminal tract lesion?

A

onion-peel sensory loss

more caudal lesion –> larger the area surrounding the mouth that is spared from sensory loss

more reostral –> sensory loss starts and back of head and converges on mouth

37
Q

Where do neurons decussate in the Trigeminal tract?

A

second order axons from spinal trigeminal nucleus –> decussate –> ascend in contra anterior trigeminothalamic tract

38
Q

Where do nerves of the trigeminal system go once they are in the anterior trigeminothalamic tract?

A

(this is the medulla) –> ascend to trimeminal lemniscus in midbrain –> synapse is contra VPM of thalamus –> tertiary axons to posterior limb of internal capsule –> SI

39
Q

What are trigeminoreticular fibers?

A

pain fibers project bilaterally to reticular formation

facilitates ascending reticular activating system (ARAS) = arousal and alertness

40
Q

What happens in a unilateral lesion of the trigeminal N?

A

ipsi anesthesia

loss of jaw-jerk reflex

atrophy of muscles of mastication

loss of ipsi and consensual corneal reflex

41
Q

What is alternating analgesia?

A

brainstem lesions in upper medulla may destroy primary fibers in spinal trigeminal tract and secondary fibers in spinal lemniscus

ipsi hemianalgesia of face and contra hemeanalgesia of the body

42
Q

What is alternating trigeminal hemiplegia?

A

unilateral destruction of trigeminal n and CST in the pons

ipsi trigeminal anesthesia and paralysis

contra spastic hemiplegia

43
Q

What nerves does the corneal reflex go through?

A

afferent through V –> trigeminal ganglion –> motor to VII

NS-1 (50 decks)

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