11. Somatosensory Pathways 2

Question 1

WHat is the difference between fine/crude and discriminating and nondiscriminating touch?

Answer 1

Fine/discriminating means you are being touched and know where exactly you are being touched
Crude/nondiscriminating meand you are being tocuhed but cannot localize it

Question 2

The anterolateral system (ALS) is associated with what sensations? 3

Answer 2

nondiscriminative touch, thermal, and nociceptive

Question 3

Disruption of the ALS system would cause numbness, tingling and what else? 2

Answer 3

prickling (paresthesia) to complete loss = anethesia

Question 4

Cutaneous nociceptors are distributed in skin and deep tissues and are all morphologically ?

Answer 4

free nerve endings which lack specialized receptor cells/encapsulations

Question 5

Fibers enter the spinal cord for nociceptor information via the lateral division of ?

Answer 5

posterior root entry zone

Question 6

Entry from the posterior root entry zone and travel in posterolateral fasciculus which is also known as?

Answer 6

Lissauer tract

Question 7

The posterolateral fasiculus bifurcates into ascending and descending branches which a central target of the primary afferents being?

Answer 7

Laminae 1, 2, 5 of the posterior horn

Question 8

The direct spinothalamic pathways carry nondiscrim touch, thermal and nociceptive signals to postero lateral fasciculus and bifurcates, leading to ascending and descending. What happens?

Answer 8

Ascending terminate on 2nd order neurons of posterior horn, cross midline via anterior white commissure, and ASCEND in contralateral ALS, 3rd order in VPL
Descending terminate on interneurons within gray matter and help with reflexes

Question 9

The indirect spinothalamic pathways relay noxious and innocuous mechanical and thermal info to reticular formation (RAS). Which ascend into?

Answer 9

posterolateral fasciculus

Question 10

the indirect spinothalamic once in the posterolateral fasciculus synapse in laminae II and III and send axons cross through AWC to contralateral ALS where?

Answer 10

the spinoreticular fibers terminate in the reticular formation in brainstem (3rd order) project to medial thalamic nuclei

Question 11

Within the anterolateral system ALS, where are the aons for lower levels and upper levels found?

Answer 11

lower levels (coccygeal/sacral) posterolateral to LE to throacic to UE anteromedial

Question 12

If there was an intramedullary or extramedullary tumor growing, it would affect the lateral or medial parts first as it grows. What blood supply could cause spotty damage to nociceptive, thermal and touch on the contralateral side, starting two spinal segments below, if occluded?

Answer 12

vasocorona A and via sulcal branchs of anterior spinal A

Question 13

What occurs in anterolateral cordotomy?

Answer 13

complete loss of ALS sensations (touch/pain/thermal)

Question 14

If there was hemisection of the spinal cord, what would be seen? (2)

Answer 14

contralateral loss of nociceptive/thermal sensations (below 2 segments and down)
ipsilateral loss of touch/vibration/proprioception (at and below)

Question 15

Syringomyelia is cystic cavitation of central regions of spinal gray matter and sometimes MAY impinge what fibers?

Answer 15

anterior white commisure (decussating ALS fibers - crossing)

Question 16

If a syringomyelia in the SC impinged the anterior white commisure located at C4 to C5 levels, what would be seen?

Answer 16

Bilateral loss of tocuh/pain/thermal begining 2 levels below (cape drapped over should to nipple)

Question 17

In the medulla, ALS fibers and PCMLS fibers remain separated, What does this mean for a lesion in the area?

Answer 17

Dissociated Sensory loss: contralateral loss of discriminative touch/vibratory sense but thermal sensation normal (vice versa depending)

Question 18

For pain/thermal to trigeminal, afferents enter pons and descends in what?

Answer 18

the spinal trigeminal nucleus tract lateral to spinal nucleus

Question 19

The spinal trigeminal nucleus tract becomes continuous with lissauer’s tract in the upper cervical cord. What are the 3 divisions of the spinal trigmenial nucleus?

Answer 19

pars caudalis
pars oralis
pars interpolaris

Question 20

What is the most important division of the spinal trigeminal nucleus?

Answer 20

par caudalis is where most pain and thermal for face and head from trigeminal go

Question 21

In anatomical orientation, the face is inverted in spinal trigeminal tract and nucleus. meaning opthalmic and mandibular representation is where?

Answer 21

located inferiorly and superiorly respetively

Question 22

What extends from the spinal cord (C2/3) to the obex concerning CN V?

Answer 22

pars caudalis

Question 23

What is the most rostral part of CN V pathways, extending from main sensory nucleus to pontomedullary junction?

Answer 23

pars oralis

Question 24

what regarding the CN V pathways is located in between in the rostral medulla?

Answer 24

pars interpolaris

Question 25

Pars caudalis fibers ending in the cervical cord overlap spinal fibers that represent adjacent areas of skin, when spinal trigeminal tract is damaged, what is seen?

Answer 25

onion peel sensory loss: more caudal the lesion = larger area surround the mouth is spared
more rostral = sensory loss from back head to mouth

Question 26

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

Answer 26

posterior inferior cerebral A

posterior spinal A

Question 27

Trigeminal for pain/temp:

1. primary afferents enter trigeminal ganglion and descend via spinal trigeminal tract to spinal trigeminal nucleus = pars caudalis
2. 2nd order axons cross and ascend via the anterior trigeminthalamic tract
3. Ascend more to contralateral VPM of thalamus
4. ?

Answer 27

4. From VPM (face/head pain/thermal info) tertiary axons extend to posterior limb of internal capsule to primary somatosensory cortex

Question 28

trigemino-reticulo-thalamic pathways: pain fibers project bilaterally to reticular formation as trigeminorecticular fibers. Input into RF facilitates ascending reticular activating system (RAS) which plays an important role in?

Answer 28

wakefullness and sleep-wake transitions

Question 29

Pars oralis receives tactile info from central region of face and pars interpolaris receives info from?

Answer 29

peripheral region of the face

Question 30

What is important to know about which fibers us VPM and VPL?

Answer 30

Ventral posteromedial nucleus: head and neck and face via trigeminal synapases here
ventral posterolateral nucleus: used by UE and LE

Question 31

If there was a unilateral lesion of the trigeminal nerve, what could be expected? (4)

Answer 31

anesthesia and loss of sensation to trigem dermatomes
loss jaw jerk refelx
atrophy of muscles mastication
loss of ipsilateral consensual corneal reflex

Question 32

Alternating analgesia are brainstem lesions in the upper medulla and may destroy the primary gibers in the spinal trigeminal tract and secondary fibers in spinal lemniscus. What can be seen?

Answer 32

ipsilateral hemianalgesia of face and contralateral hemianalgesia of body

Question 33

What occurs due to unilateral destruction of trigeminal N and CST in the pons, and presents with ipsilateral trigeminal anesthesia and paralysis and contralateral spastic hemiplegia?

Answer 33

alternating trigeminal hemiplegia

Question 34

What artery supplies the anterolateral system and spinal trigeminal tract/nucleus in medulla?

Answer 34

posterior inferior cerebellar A

Question 35

Occlusions of the posterior inferior cerebellar A produces lateral medullary (wallenberg) syndrome which presents with? 2

Answer 35

contralteral loss of pain (hemianalgesia) and temperature over body WITH ipsilateral loss of same modalities over face

Question 36

Afferent limb originates from pain/touch receptors in cornea. Fibers travel on V1 and have cell bodies in the trigeminal ganglion which terminate in ipsilateral spinal trigeminal nucleus. What is the end of the refelx?

Answer 36

trigeminthalamic fibers send collaterals bilaterally into the facial motor nucleus, cause facial motor to orbicularis oculi to close eye