Somatosensory Tracts: Pain, Temperature, Touch Flashcards
What information does the anterolateral system relay?
Pain, temperature, itching, non-discriminative touch from body and face
What are the two ALS pathways?
Direct (specific feedback) and indirect (general feedback, awareness of pain)
What fibers comprise the ALS?
Spinothalamic (direct) Spinoreticular (indirect) Spinomesencephalic Spinobulbar Spinohypothalamic
Where do primary afferent fibers enter the spinal cord for the ALS?
Through the lateral division of the posterior root entry zone
Where are the cell bodies of the primary afferent fibers in the ALS?
In the DRG
What do primary afferent fibers of the ALS do when they enter the spinal cord?
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.
Where are the cell bodies of second order neurons in the ALS?
In laminae 1, 2, or 5 of the posterior horn
What do second order neurons do in the ALS (direct pathway)?
After synapse, immediately cross through anterior white commissure to contralateral side and travel up the ALS to the VPL of the thalamus
What do third order neurons do in the ALS (direct pathway)?
Synapse in the VPL with second order neurons before traveling to the somatosensory cortex
How does the indirect pathway of the ALS work?
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)
What is the organization of the ALS like somatotopically?
Lateral = sacral/lumbar Medial = upper cervical
What is the blood supply to the ALS?
Arterial vasocorona and sulcal branches of ASA
Where is the trigeminal ganglion located?
Ventrolateral pons
Where is the trigeminal nucleus located?
Pons down through medulla
What is the pathway for the spinal trigeminal tract?
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
What is the blood supply to trigeminal structures in the medulla?
PICA and PSA
What are the divisions of the spinal trigeminal nucleus?
Pars oralis (pons down to superior medulla) Pars interpolaris (superior medulla down to obex) Pars caudalis (obex down to SC)
What is the trigemino-reticulo-thalamic pathway?
General awareness of sensation via ascending reticular activating system (ARAS)
What happens if blood supply is lost to the ALS?
Patchy loss of pain, temp, and touch over contralateral side of body (two spinal segments BELOW the lesion)
What is Brown-Sequard syndrome?
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
What is syringomyelia?
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)
What is medullary syndrome?
When a vascular lesion or tumor affects either ALS (laterally) or PCMLS (at ML medially) (depending on location)
What is lateral medullary syndrome?
When a vascular lesion to PICA affects the ALS (contralateral loss pain/temp body) or spinal trigeminal tract (ipsilateral loss pain/temp face)
What happens with a unilateral lesion of the trigeminal nerve?
Anesthesia in trigeminal dermatomes, loss of jaw-jerk reflex, atrophy of muscles of mastication, ipsilateral loss of corneal reflex
What happens with alternating analgesia?
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
What happens with alternating trigeminal hemiplegia?
Unilateral destruction of trigeminal n in pons = ipsilateral trigeminal anesthesia/paralysis and contralateral spastic hemiplegia
