Somatosensory Tracts 2

Question 1

Describe the anterolateral system

Answer 1

Comprises a set of fibers relaying pain, temperature and non-discriminative touch
Divided into several different tracts with the largest being the spinothalamic tract
Other smaller tracts terminate in the brainstem and diencephalon where they modulate pain and initiate responses to pain sensation

Question 2

Describe the ALS pathway

Answer 2

Free nerve endings distributed in skin as well as muscles, joints, blood vessels and viscera
Afferent fibers enter SC via the lateral division of posterior root entry zone
Ascend/descend 1-2 levels in the posterolateral (Lissauer) tract
Target 2nd order neurons in posterior horn in superficial laminae I, II and in the nucleus proprius (laminae III, IV)
2nd order neurons cross midline of SC to go to the ALS

Question 3

Describe the spinothalamic pathway

Answer 3

Carries non-discriminative tactile, innocuous thermal and nociceptive signals
Afferents enter posterolateral fasciculus and bifurcate
Ascending fibers synapse on 2nd order neurons on posterior horn -> cross midline via anterior white commissure
Descending fibers synapse on interneurons and moderate spinal reflexes

Question 4

Axons from lower levels (coccygeal, sacral) of the body are found where in the ALS?

Answer 4

Posterolaterally

Question 5

More rostral levels of the body (cervical) are added in what type of sequence in the ALS?

Answer 5

Anteromedial

Question 6

Deficits seen in pts with certain types of SC lesions reflect what?

Answer 6

Somatotopic pattern

Ex. Tumor on the medial ALS

Question 7

Describe the ascending STT pathway

Answer 7

Afferents enter the posterolateral fasciculus -> 2nd order neurons (posterior horn)
2nd order neurons cross midline (AWC), ascend in the contralateral ALS -> synapse on VPL of thalamus
3rd order neurons target somatosensory cortex (somatotopic)

Question 8

What type of sensation do spinoreticular fibers relay?

Answer 8

Noxious and innnocous mechanical and thermal information

Contributes to perception of dull pain and moderates behavior and motivational changes associated with pain

Question 9

Describe the indirect spinothalamic (spinoreticular) pathway

Answer 9

Afferents (posterolateral fasciculus) -> 2nd order neurons (laminae II/III) join contralateral ALS -> 3rd order neurons in reticular formation (RF) -> thalamus (intralaminar and posterior group nuclei)

Question 10

What provides blood supply to the ALS?

Answer 10

Arterial vasocorona and via sulcal branch’s of the anterior spinal artery

Question 11

Occlusions of the blood supply to the ALS result in what?

Answer 11

Patchy loss of nociceptive, thermal and touch over the contralateral side of the body, begins about 2 spinal segments below the lesion

Question 12

Complete spinal cord injuries produce what?

Answer 12

Bilateral, total loss of all motor and sensory function at/below the level of injury

Question 13

What is an incomplete SCI and what are some examples?

Answer 13

Some function remains below the primary level of injury

Ex: anterior cord syndrome, central cord syndrome, injuries to a specific nerve root and spinal contusions

Question 14

What is anterior cord syndrome?

Answer 14

Injury to the motor and pain/temperature pathways in the anterior SC
Pts still have proprioception and sensation (bc posterior cord isnt damaged)

Question 15

What is central cord syndrome?

Answer 15

Damage to the central of the cord/AWC

Causes loss of pain/temp pathways with deficits relative to the size of the lesion

Question 16

Describe injuries to a specific nerve root

Answer 16

May have motor and sensory deficits due to roots containing both types of nerves and location of deficits depends on distribution of nerve root involved

Question 17

What are spinal contusions?

Answer 17

Transient, generally resolving within 1-2 days

Produce neurological Sx including numbness, tingling, electric shock like sensations and burning in the extremities

Question 18

What is brown-sequard syndrome?

Answer 18

Combination of sensory and motor deficits due to damage to the ALS, PCML and CST pathways
Includes contralateral and ipsilateral deficits
Can also be referred to as a hemisection

Question 19

What are some contralateral deficits seen with brown-sequard syndrome?

Answer 19

Loss of nociceptive, thermal sensations (ALS), approximately two segments below level of lesion

Question 20

What are some ipsilateral deficits seen in brown-sequard syndrome?

Answer 20

Loss of discriminative tactile, vibratory and position sense (PCML), at/below the level of lesion
Paralysis of the trunk and extremity (CST), dependent on level of lesion

Question 21

Describe syringomyelia

Answer 21

A syrinx is a cystic cavitation of central regions of the SC which typically develops anywhere between C3-T2
Syrinx enlarges due to fluid accumulation -> surrounded neural tissue is destroyed
Initial damage to ALS fibers in AWC
Usually progresses to anterior horn causing motor deficits

Question 22

What are the distinct deficits seen with syringomyelia?

Answer 22

Present in a cape like pattern
Loss of pain and temperature bilaterally over the arms and shoulders
Weakness, atrophy and fasciculations of muscles of the hands

Question 23

Lesions of the ALS in the medulla cause what syndrome?

Answer 23

Lateral medullary syndrome (aka PICA syndrome or Wallenberg syndrome)

Question 24

What are the deficits seen with lateral medullary syndrome?

Answer 24

Contralateral loss of pain and thermal sensation on body (ALS)
Ipsilateral loss of pain and thermal sense on face and in the oral cavity (spinal trigeminal tract/nucleus)

Question 25

What vascular events can cause lateral medullary syndrome?

Answer 25

Occlusion of posterior inferior cerebellar A (PICA) and/or its branches Occlusion of vertebral artery at the origin of the PICA blocking PICA flow

Question 26

Lesions of the ALS in the pons cause what syndrome?

Answer 26

Lateral pontine syndrome

Question 27

What deficits are seen with lateral pontine syndrome?

Answer 27

Deficits vary depending on whether the lesion is located caudal or rostrally in the lateral pons Contralateral loss of pain and thermal sense from UE, trunk and LE (ALS) Ipsilateral loss of pain and thermal sense from face (spinal trigeminal tract and nucleus)

Question 28

What vascular events can cause lateral pontine syndrome?

Answer 28

Occlusion of long circumferential branches of basilar artery and/or branches of anterior inferior cerebellar artery or superior cerebellar artery

Question 29

Describe the spinal trigeminal nucleus

Answer 29

Obex -> C2/3 Pain, temperature and nondiscriminative touch Three divisions: pars caudualis*, pars oralis, pars interpolaris

Question 30

Describe the spinal trigeminal tract

Answer 30

Second order neurons are housed in spinal nucleus (caudal brainstem) but CN V enters at midpons level Primary trigeminal afferents must descend in the spinal trigeminal tract Tract extends caudally to about 3rd cervical segment and becomes continuous with Lissauer’s tract in the upper cervical cord

Question 31

Describe the anterior trigeminothalamic tract

Answer 31

Primary afferents descend via spinal trigeminal tract -> 2nd order neurons of spinal trigeminal nucleus cross midline, ascend as anterior trigeminothalamic tract -> 3rd order neurons of contralateral VPM (thalamus) target somatosensory cortex

Question 32

What are the two planes in which the spinal trigeminal nucleus (STN) is organized somatotopically?

Answer 32

Anterior -> posterior | Rostral -> caudal

Question 33

Describe the face in anatomical orientation

Answer 33

Face is inverted in spinal trigeminal tract and nucleus Opthalamic dermatome = anterior (inferior) Mandibular dermatome = posterior (superior)

Question 34

In regards to somatotopy of the STN, fibers from the circumoral/intraoral zones terminate where?

Answer 34

Rostrally near the obex

Question 35

In regards to somatotopy of the STN, fibers of mid cheek region target what?

Answer 35

Middle segments of STN

Question 36

In regards to somatotopy of the STN, fibers of lateral edges of the face target what?

Answer 36

Caudal regions down to C2/3

Question 37

Damage to the spinal trigeminal tract results in what?

Answer 37

Onion peel sensory loss

Question 38

A more caudal lesion of the spinal trigeminal tract leads to what?

Answer 38

Spares oral region, but affects posterior and lateral boundaries of the face (Onion peel)

Question 39

A more rostral lesion (into brainstem) of the spinal trigeminal tract leads to what?

Answer 39

Sensory loss that is increasingly anterior and converges on the mouth (Onion peel)

Question 40

Describe onion peel sensory loss

Answer 40

Trigeminal fibers ending in the cervical cord overlap spinal fibers that innervate C1-2 dermatomes Allows for a smooth transition of cutaneous info from posterior head (spinal) with cutaneous anterior face/head (brainstem)

Question 41

Describe clinical orientation

Answer 41

Relevant to evaluating neuroimaging and identifying lesions Opthalamic is superior and mandibular is inferior Posterior structures are down on the page and anterior structures are up

Question 42

Describe unilateral lesions of the trigeminal nerve/nuclei

Answer 42

Anesthesia and loss of general sensations in the trigeminal dermatomes Paralysis of the muscles of mastication Loss of ipsilateral afferent limb of corneal reflex

Question 43

Describe alternating trigeminal hemiplegia

Answer 43

Unilateral destruction of the trigeminal nerve and CST in the pons Ipsilateral trigeminal anesthesia and paralysis Contralateral spastic hemiplegia