Somatosensory II

Question 1

what information is carried by the anterolateral system (ALS)

Answer 1

nondiscriminative touch

thermal and nociceptive sensation

Question 2

what are sxs of lesion to the ALS

Answer 2

numbness, tingling, paresthia, anesthesia

Question 3

where is sensory information within the ALS relayed

Answer 3

body => thalamus => somatosensory and limbic cortices

Question 4

where is sensory information within the anterior trigeminothalamic pathway relayed

Answer 4

face/head => thalamus => sensory and limbic cortices

Question 5

where do cutaneous nociceptor fibers enter the SC

Answer 5

lateral division of the posterior root entry zone

Question 6

which laminae are central targets of the primary afferents of the ALS

Answer 6

laminae I, II, and V of the posterior horn

Question 7

where do fibers of the ALS travel within the spinal cord?

Answer 7

the posterolateral fasciculus (lissauer tract)

Question 8

where do axons of the 2nd order neurons of the direct spinothalamic pathway cross midline

Answer 8

the anterior white comissure, then ascent in the contralateral ALS

Question 9

where do descending branches of fibers of the direct spinothalamic pathway terminate

Answer 9

on interneurons within the grey mater

Question 10

what is the function of indirect spinothalamic pathways

Answer 10

relays noxious and innouous mechanical and thermal information

Question 11

where do branches of the indirect spinothalamic pathway synapse?

Answer 11

laminae II and III

Question 12

do axons of the indirect pathways join the contralateral ALS

Answer 12

YES

Question 13

what is the blood supple to the ALS

Answer 13

arterial vasocorona

sulcal branches of the anterior spinal a

Question 14

how does occlusion of the arterial vasocorona/sulcal branches of the anterior spinal artery present clinically?

Answer 14

patchy loss of nociceptive, thermal and touch sensation over the contralateral side 2 segments below the lesion

Question 15

what lesion would be indicated in a patient with ipsilateral loss of discriminative tactile, vibratory and position sense at and below the lesion

Answer 15

posterior column damage

Question 16

what is syringomyelia

Answer 16

cystic cavitation of the central regions of spinal grey matter

Question 17

what important structure may be impinged by syringomyelia

Answer 17

anterior white commissure

Question 18

how might syringomyelia cause bilateral loss of nondiscriminative tactile, nociceptive and thermal sensation

Answer 18

lesion of the AWC which contains ALS fibers from both sides

Question 19

how does a patient with impingment of the ALS by syringomyelia present

Answer 19

bilateral loss of nondiscriminative tactile, nociceptive and thermal sensation several segments below the lesion in UEs to nipple

Question 20

where are medullary ALS fibers positioned

Answer 20

near anterolateral surface, anterior to trigeminal nucleus

Question 21

what is dissociated sensory loss?

Answer 21

contralateral loss of either discriminative touch and vibratory sense OR pain and thermal sensation

Question 22

lesions to what area can cause dissociated sensory loss

Answer 22

vascular lesions or tumors of the lower brainstem

Question 23

in the upper cervical spinal cord, what does the spinal trigeminal tract become

Answer 23

Lissauer’s tract

Question 24

what are the three parts of the trigeminal tract

Answer 24

pars caudalis
pars oralis
pars interpolaris

Question 25

which part of the trigeminal tract extends from C2/C3 to the obex (4th ventricle)

Answer 25

pars caudalis

Question 26

which part of the trigeminal tract is in the superior medulla

Answer 26

pars interpolaris

Question 27

which part of the trigeminal tract extends from the main sensory nucleus to the pontomedullary jxn

Answer 27

pars oralis

Question 28

what is onion-peel sensory loss

Answer 28

a characteristic pattern of sensory loss depending on how rostral/caudal a lesion to the spinal trigeminal tract is

Question 29

what provides the blood supply to trigeminal structures in the medulla

Answer 29

PICA and posterior spinal artery

Question 30

where do secondary axons from pars caudalis terminate

Answer 30

contralateral VPM (ventral posteromedial nucleus) of the thalamus

Question 31

between what structures do tertiary axons of pars caudalis extend

Answer 31

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

Question 32

what is the reticular formation

Answer 32

a set of connected nuclei responsible for regulating wakefulness and sleep-wake transitions

Question 33

which part of the reticular formation does trigeminal input facilitate

Answer 33

ARAS (ascending reticular activating system)

Question 34

from what region does pars oralis receive tactile information

Answer 34

central face

Question 35

from what region does pars interpolaris receive tactile information

Answer 35

periphery of the face

Question 36

what lesion of the trigeminal nerve would be indicated in a pt with loss of jaw-jerk reflex, anesthesia in trigeminal dermatomes, atrophy of muscle of mastication, and loss of ipsilateral corneal reflex

Answer 36

unilateral

Question 37

what is alternating analgesia

Answer 37

ipsilateral hemianalgesia of the face | contralateral hemianalgesia of the body

Question 38

what kind of lesion would cause alternating analgesia

Answer 38

brainstem lesions in the upper medulla => destruction of primary trigeminal n fibers in the spinal trigeminal tract AND secondary fibers in the medial lemniscus

Question 39

what causes alternating trigeminal hemiplegia

Answer 39

unilateral destruction of the trigeminal nerve and corticospinal tract in the pons

Question 40

what is alternating trigeminal hemiplegia

Answer 40

IPSILATERAL trigeminal anesthesia and paralysis | CONTRALATERAL spastic hemiplegia

Question 41

what artery supplies both the ALS and spinal trigeminal tract?

Answer 41

posterior inferior cerebellar a

Question 42

what is the result of vascular lesion to the posterior inferior cerebellar a

Answer 42

lateral medullary syndrome (AKA wallenberg syndrome)

Question 43

what are the sxs of lateral medullary syndrome

Answer 43

contralateral loss of pain and temperature sensation in the body AND ipsilateral loss of pain and temperature in the face

Question 44

when testing the corneal reflex, where do trigeminothalamic fibers information to initiate blinking

Answer 44

bilateral collateral fibers to the facial motor nucleus