Somatosensory Tracts: Pain, Temperature, Touch

Question 1

What information does the anterolateral system relay?

Answer 1

Pain, temperature, itching, non-discriminative touch from body and face

Question 2

What are the two ALS pathways?

Answer 2

Direct (specific feedback) and indirect (general feedback, awareness of pain)

Question 3

What fibers comprise the ALS?

Answer 3

Spinothalamic (direct)
Spinoreticular (indirect)
Spinomesencephalic
Spinobulbar
Spinohypothalamic

Question 4

Where do primary afferent fibers enter the spinal cord for the ALS?

Answer 4

Through the lateral division of the posterior root entry zone

Question 5

Where are the cell bodies of the primary afferent fibers in the ALS?

Answer 5

In the DRG

Question 6

What do primary afferent fibers of the ALS do when they enter the spinal cord?

Answer 6

They either stay at the level or travel up/down a couple of levels through Lissauer’s tract. Synapses occur in laminae 1, 2, or 5 of the posterior horn of the spinal cord.

Question 7

Where are the cell bodies of second order neurons in the ALS?

Answer 7

In laminae 1, 2, or 5 of the posterior horn

Question 8

What do second order neurons do in the ALS (direct pathway)?

Answer 8

After synapse, immediately cross through anterior white commissure to contralateral side and travel up the ALS to the VPL of the thalamus

Question 9

What do third order neurons do in the ALS (direct pathway)?

Answer 9

Synapse in the VPL with second order neurons before traveling to the somatosensory cortex

Question 10

How does the indirect pathway of the ALS work?

Answer 10

1- cell bodies located in DRG enter lateral division of posterior root entry zone to synapse in laminae 2, 3, 5-8
2- cell bodies located in laminae, travel in posterolateral fasciculus to reticular formation
3- cell bodies located in RF, project to intralaminar nuclei and posterior group nuclei (to cingulate, frontal, and limbic cortices)

Question 11

What is the organization of the ALS like somatotopically?

Answer 11

Lateral = sacral/lumbar
Medial = upper cervical

Question 12

What is the blood supply to the ALS?

Answer 12

Arterial vasocorona and sulcal branches of ASA

Question 13

Where is the trigeminal ganglion located?

Answer 13

Ventrolateral pons

Question 14

Where is the trigeminal nucleus located?

Answer 14

Pons down through medulla

Question 15

What is the pathway for the spinal trigeminal tract?

Answer 15

Primary fibers have cell bodies located in trigeminal ganglion, enter pons and go down to synapse at spinal nucleus which is at C2/C3 level of SC. Merge with fibers in Lissauer’s tract and ducussate to ascend in anterior trigeminothalamic tract to go to VPM. Third order neurons synapse here and travel via posterior limb of internal capsule to face section of somatosensory cortex

Question 16

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

Answer 16

PICA and PSA

Question 17

What are the divisions of the spinal trigeminal nucleus?

Answer 17

Pars oralis (pons down to superior medulla)
Pars interpolaris (superior medulla down to obex)
Pars caudalis (obex down to SC)

Question 18

What is the trigemino-reticulo-thalamic pathway?

Answer 18

General awareness of sensation via ascending reticular activating system (ARAS)

Question 19

What happens if blood supply is lost to the ALS?

Answer 19

Patchy loss of pain, temp, and touch over contralateral side of body (two spinal segments BELOW the lesion)

Question 20

What is Brown-Sequard syndrome?

Answer 20

Hemisection of spinal cord = contralateral loss of ALS beginning two segments below lesion (pain/temp) and ipsilateral loss of PCMLS at level of lesion (discriminitive touch/proprioception)
Also some motor loss

Question 21

What is syringomyelia?

Answer 21

Cystic cavitation of central regions of spinal gray matter that impinge on the anterior white commissure (both sides of ALS cross here = bilateral loss of pain/temp sensation at levels of cyst)

Question 22

What is medullary syndrome?

Answer 22

When a vascular lesion or tumor affects either ALS (laterally) or PCMLS (at ML medially) (depending on location)

Question 23

What is lateral medullary syndrome?

Answer 23

When a vascular lesion to PICA affects the ALS (contralateral loss pain/temp body) or spinal trigeminal tract (ipsilateral loss pain/temp face)

Question 24

What happens with a unilateral lesion of the trigeminal nerve?

Answer 24

Anesthesia in trigeminal dermatomes, loss of jaw-jerk reflex, atrophy of muscles of mastication, ipsilateral loss of corneal reflex

Question 25

What happens with alternating analgesia?

Answer 25

Lesion in upper medulla destroy fibers of spinal trigeminal tract and second order fibers of spinal lemniscus (from body). Causes ipsilateral hemianalgesia to face and contralateral hemianalgesia to body

Question 26

What happens with alternating trigeminal hemiplegia?

Answer 26

Unilateral destruction of trigeminal n in pons = ipsilateral trigeminal anesthesia/paralysis and contralateral spastic hemiplegia