10. Somatosensory pathways pt. 2 Flashcards
What types of information is carried in the anterolateral system (ALS)?
non-discriminative touch, thermal, and nociceptive sensations
how is information relayed in the ALS?
relayed from body–> thalamus–> somatosensory and limbic cortices
anterior trigeminothalamic pathway relays from face/head–> thalamus–> somatosensory and limbic cortices
*limbic- to recognize pain that is unwanted
What does disruption of the ALS produce?
numbness, tingling, and prickling (paresthesia)–> complete loss anesthesia
What are cutaneous nociceptors and primary neurons? Where are they distributed?
receptors distributed in skin, deep tissues, including muscles joints, BVs, and viscera
all are morphologically free nerve endings
lack specialized receptor cells or encapulations as innervate skin
Whats the difference between the posterior columns fibers and the anterolateral systems fibers as they enter the SC?
Posterior column: comes in through medial division of SC
ALS: crosses immediately in spinal cord and tract followed is in different position (more antero-laterally positioned in white matter of SC)
How do ALS fibers enter SC? what do they travel in the central pathway?
entry via lateral division of POSTERIOR ROOT ENTRY ZONE
travel in the posterolateral fasciculus/ LISSAUER TRACT** (bifurcates into asc/desc branches)
some collaterals terminate on interneurons in SC grey matter for reflexes (i.e. flexor withdrawal)
What are the central targets of primary afferents in the ALS central pathway?
laminae 1, 2, and 5 of posterior horn
What does the direct spinothalamic pathway carry?
carries nondiscriminative tactile, innocuous thermal, and nociceptive signals
Where are 3rd order thalamic neurons of the direct spinothalamic pathway located?
in the VPL nucleus
Where do descending branches of the direct spinothalamic pathway terminate? What do they contribute?
on interneurons within gray matter
contribute segmental spinal reflexes
What is the path of the Direct Spinothalamic pathway?
enters into posterolateral fasciculus and bifurcates
ascending branches terminate on 2nd order neurons of posterior horn
project to lateral region of thalamus
axons cross midline via anterior white commissure
ascend in the contralateral ALS mostly–> thalamus
end on interneurons within gray matter
What does the indirect spinothalamic pathway relay?
polysnaptic component- relays noxious and innocuous mechanical and thermal information to reticular formation (goes to reticular system)
What is the path of the Indirect Spinothalamic Pathway?
branches of fibers ascend/descend in the posterolateral fasciculus
synapse in laminae 2 and 3–> influences cells in laminae 5 to 8
sends axons that CROSS obliquely through AWC (over 1-3 segments) and to join contralateral ALS
SPINORETICULAR fibers terminate in reticular formation
Where are 3rd order neurons of the indirect spinothalamic pathway projecting to?
3rd order neurons in reticular formation project to the medial thalamic nuclei
How is the ALS somatotopically organized?
Rostral: upper extremity and thoracic regions are more MEDIALLY positioned (anteromedial)
Lower: LE and lower thoracic regions are more LATERALLY positioned (posterolateral)
What is the blood supply to the ALS? What might damage do?
sulcal branches of anterior spinal A. and arterial vasocorona
damage= spotty lesion deficits; patchy loss of nociceptive, thermal, and touch over CONTRALATERAL side of the body (begins about 2 spinal segments below lesion)
What are spinothalamic fibers?
the main ones we’ve been mentioning!
primary/peripheral afferents–> through spinal cord–> thalamus; ascends directly to VPL and VPI nuclei + posterior nuclear group
What are other ALS fibers and what info is by each?
Spinobulbar fibers- info from SC that ascends to various brain stem nuclei
Spinohypothalamic fibers- somatosensory info (nociceptive too) from posterior horns that ascends directly to hypothalamus; pain associated with memory!!
Spinomesencephalic fibers- may terminate in midbrain reticular formation (or transition to form spinotectal fibers targeting deep layers of superior colliculus and anterior pretectum)
its a mix of fibers to appropriately register pain with different regions!!
What happens with lesions or slow-growing tumors on the ALS?
lesions of all of ALS: will have major pain and temperature deficits
slow growing tumor: can start to impinge either Lower or Upper regions and it can grow in either direction
What does an anterolateral cordotomy result in?
true transection results in complete loss of these sensations (anesthesia)
What loss occurs after a true hemisection of the spinal cord?
CONTRALATERAL loss of nociceptive and thermal sensations over body (begins 2 segments below lesion)
IPSILATERAL loss of discriminative tactile, vibratory, and position sense over body at and below level of lesion (posterior column damage)
What is Syringomyelia?
when have a cystic cavitation of central regions of spinal gray matter (near central canal) and impacts the anterior white commissure (AWC)
may impinge on AWC (with decussating ALS fibers)
What happens when Syringomyelia is located at C4-C5 levels of spinal cord, what happens? Sx?
BILATERAL loss of nondiscriminative tactile, nociceptive, and thermal sensations
several segments below lesion starts
Sx: present in configuration of a cape draped over shoulders and down to nipple
Where are medullary ALS fibers positioned?
near anterolateral surface, anterior to spinal trigeminal nucleus
