Somatosensory Pathway 2

Question 1

Nondiscriminative touch, thermal, and nociceptive sensations are conveyed by the?

Answer 1

The Anterolateral System (ALS)

Question 2

The Anterolateral System (ALS) is relayed from?

Answer 2

• body –> thalamus –> somatosensory and limbic cortices

Question 3

Anterior trigeminothalamic pathway relays from?

Answer 3

face/head –> thalamus –> somatosensory and limbic cortices

Question 4

What symptoms does disruption of ALS cause?

Answer 4

Numbness, tingling, & prickling (paresthesia) → to

complete loss anesthesia

Question 5

Cutaneous Nociceptors and Primary Neurons:

• All are morphologically ?
• Fibers enter SC via the lateral division of ?

Answer 5

• free nerve endings

- posterior root entry zone

Question 6

Central Pathways from the Body:

• Travel in ?
• Central target of primary afferents includes laminae ? of posterior horn

Answer 6

• posterolateral fasciculus
  (Lissauer tract)
• I, II, and V

Question 7

Carries nondiscriminative tactile, innocuous thermal, and nociceptive
signals

Answer 7

Direct Spinothalamic Pathways

Question 8

Direct Spinothalamic Pathways:

• Ascending branches terminate on 2nd order neurons of the posterior
horn, which project to lateral region of the thalamus

• Axons cross midline via ?
• Ascend in the ?, few will ascend in ipsilateral ALS (not clinically relevant)

• Thalamic (3rd order) neurons are located in the VPL (VPI & posterior
group)

• ? terminate on interneurons within gray matter and contribute segmental spinal reflexes

Answer 8

• anterior white commissure
• contralateral ALS
• Descending branches

Question 9

Polysynaptic component that relays noxious and innocuous mechanical and thermal information to reticular formation

Answer 9

Indirect Spinothalamic Pathways

Question 10

Indirect Spinothalamic Pathways:

• Branches of these fibers ascend/descend in the posterolateral
fasciculus

• Synapse in laminae ? and ? will influence cells in laminae ? to ?
• Send axons that cross obliquely through AWC (over 1-3 segments) & to
  join contralateral ALS
• These ? terminate in reticular formation (brainstem)
• Third-order neurons in RF project to the ?

Answer 10

• II and III
• V to VIII
• spinoreticular fibers
• medial thalamic nuclei

Question 11

ALS fibers that ascends directly to ventral
posterolateral [VPL] and ventral posterior inferior [VPI] nuclei, and posterior
nuclear group (including VMpo)

Answer 11

Spinothalamic fibers

Question 12

info from SC that ascends to various brainstem nuclei

Answer 12

Spinobulbar fibers

Question 13

somatosensory info (including nociceptive)
from posterior horns that ascends directly to hypothalamus

Answer 13

Spinohypothalamic fibers

Question 14

may terminate in the midbrain reticular
formation

• May also transition to form ? targeting deep layers of superior colliculus & anterior pretectum

Answer 14

Spinomesencephalic fibers

• spinotectal fibers

Question 15

ALS

• Axons from lower levels
(coccygeal, sacral) of the body are found ?

• More rostral levels are added in an ?

Answer 15

• posterolaterally

- anteromedial sequence

Question 16

Lesions of ALS:

• Blood supply originates from ? & via ?

Answer 16

• arterial vasocorona

- sulcal branches of the anterior spinal artery

Question 17

Lesions of ALS:

• Occlusion results in patchy loss of nociceptive, thermal, & touch over the ? side of the body
- Begins about two spinal segments below the lesion

• What results in complete loss of these sensation?

Answer 17

• contralateral

- Anterolateral cordotomy

Question 18

What kind of loss do you get with Hemisection of the Spinal Cord?

Answer 18

• CONTRALATERAL loss of nociceptive & thermal sensations over body

• Begins about two segments below
  level of the lesion (ALS damage)

• IPSILATERAL loss of discriminative tactile, vibratory, and position sense over the body at and below the level of lesion (posterior column damage)

Question 19

Cystic cavitation of central regions of spinal

gray matter

Answer 19

Syringomyelia

Question 20

Syringomyelia:

• May impinge on ? (contains decussating
ALS fibers

• When located at the ? levels of the spinal cord

• Produces ? of
  nondiscriminative tactile, nociceptive, &
  thermal sensations
• Begins several segments below lesion
• Symptoms present in configuration of a
  cape draped over shoulders & down to
  nipple level

Answer 20

• AWC
• C4 to C5
• bilateral loss

Question 21

• Positioned near anterolateral surface,
anterior to spinal trigeminal nucleus

• Remain separated from the PCMLS

Answer 21

Medullary ALS Fibers

Question 22

Medullary ALS Fibers:

Vascular lesions/tumors in lower brainstem can affect?

Answer 22

discriminative

touch & nociception differentially

Question 23

contralateral loss of discriminative
touch & vibratory sense, but pain/thermal sensation is WNL (one
modality absent but not another)

Answer 23

Dissociated sensory loss

related to Medullary ALS Fibers

Question 24

Mixed nerve with sensory and motor
components
- Main sensory nerve for the head
- Innervates the muscles of mastication

Answer 24

Trigeminal Nerve

Question 25

Attaches to the brainstem as two adjacent roots (large sensory & smaller motor) on ventrolateral aspect of the pons

Answer 25

Trigeminal Nerve

Question 26

3 divisions of the Spinal Trigeminal Nucleus?

Answer 26

- pars caudalis, pars oralis, and pars interpolaris

Question 27

Spinal Trigeminal Nucleus: - Both nucleus & tract extend caudally to about ? segment

Answer 27

3rd cervical

Question 28

Spinal Trigeminal Tract & Nucleus: • In anatomic orientation, face is ? in spinal trigeminal tract & nucleus - Ophthalmic representation is located ? - Mandibular representation is located ?

Answer 28

- inverted - inferiorly - superiorly (opposite for clinical orientation)

Question 29

CN V Central Pathways: - most caudal part, extending from the spinal cord (C2, C3) to the obex

Answer 29

Pars caudalis

Question 30

CN V Central Pathways: -most rostral part, extending from the main sensory nucleus to pontomedullary junction

Answer 30

Pars oralis

Question 31

CN V Central Pathways: - located in between, in rostral medulla

Answer 31

Pars interpolaris

Question 32

Pars Caudalis: When spinal trigeminal tract is damaged have characteristic pattern of ?

Answer 32

onion-peel sensory | loss

Question 33

Pars Caudalis • spinal trigeminal tract is damaged: - More ? lesion → larger the area surrounding the mouth that is spared from sensory loss - More ? lesion (into brainstem) → sensory loss that starts at back of head & converges on mouth

Answer 33

- caudal | - rostral

Question 34

Trigeminal Pathway: - Second-order axons from caudal nucleus decussate & ascend in ? - Terminates in the ? VPM of thalamus (at periphery) - Tertiary axons extend in posterior limb of the ? → primary somatosensory cortex

Answer 34

- anterior trigeminothalamic tract - contralateral - internal capsule

Question 35

Trigeminal Pathway: - Blood supply to trigeminal structures in medulla are via ?

Answer 35

PICA & posterior spinal artery

Question 36

Pain fibers project bilaterally to the reticular formation as?

Answer 36

trigeminoreticular fibers

Question 37

- Trigeminal input into the RF facilitates the ascending reticular activating system (ARAS), & plays an important role in? - RF is a set of connected nuclei responsible for regulating?

Answer 37

- arousal & alertness | - wakefulness and sleep-wake transitions

Question 38

Extends from the level of entry (pons) to superior medulla - Receives tactile information from the central region of the face

Answer 38

Pars oralis

Question 39

Extends from superior medulla to obex | - Receives information from the peripheral region of the face

Answer 39

Pars interpolaris

Question 40

Heavily involved in functions homologous to somatic functions of the spinal cord - Project fibers to the cerebellum (through the inferior cerebellar peduncle) - Carry tactile information project to the contralateral VPM

Answer 40

Pars Oralis and Pars Interpolaris

Question 41

What does Unilateral lesion of the Trigeminal Nerve cause?

Answer 41

* Anesthesia and loss of general sensations in the trigeminal dermatomes * Loss of jaw-jerk reflex * Atrophy of the muscles of mastication * Loss of ipsilateral and consensual corneal reflex

Question 42

What does alternating analgesia of the Trigeminal Nerve cause?

Answer 42

``` • Brainstem lesions in the upper medulla may destroy the primary fibers in the spinal trigeminal tract (descending tract of V), & secondary fibers in the spinal lemniscus ``` • Patients demonstrate ipsilateral hemianalgesia of the face & contralateral hemianalgesia of the bod

Question 43

What does Alternating trigeminal hemiplegia of the Trigeminal Nerve cause?

Answer 43

* Unilateral destruction of the trigeminal nerve and CST in the pons * Ipsilateral trigeminal anesthesia and paralysis, and contralateral spastic hemiplegia

Question 44

What supplies the territory of anterolateral system AND spinal trigeminal nucleus/tract?

Answer 44

Posterior inferior cerebellar | artery (medulla)

Question 45

Vascular lesions involving Posterior inferior cerebellar artery (medulla) produces what syndrome?

Answer 45

lateral medullary (Wallenberg) syndrome (posterior inferior cerebellar artery syndrome)

Question 46

What occurs in patients with Lateral Medullary Syndrome?

Answer 46

• Contralateral loss of pain (hemianalgesia) and temperature (hemithermoanesthesia) over the body WITH • Ipsilateral loss of these modalities over the face

Question 47

In response to a stimulus that touches the cornea, the eyes blink

Answer 47

Corneal Reflex

Question 48

Corneal Reflex: • Afferent limb of originates from ? receptors in the cornea • Fibers travel on ? & have cell bodies in the trigeminal ganglion → terminate in ? spinal trigeminal nucleus • ? fibers send collaterals ? into the facial motor nucleus (efferent limb) of this reflex

Answer 48

- pain/touch - V1 - ipsilateral - Trigeminothalamic - bilaterally