Ascending Systems Flashcards
What function do most axons in the posterior column-medial lemniscus pathway have?
Touch, proprioception, vibratory sense, from various mechanoreceptors
Describe the pathway for primary order fibers in the posterior column-medial leminscus
Mechanoreceptors -> dorsal root ganglion -> fascillicus gracilis (LL) and fascillicus cuneatusn (UL) -> synapse in nucleus gracilis and cuneatus
Describe the pathway for second and third order fibers in the posterior column - medial lemniscus
Nucleus gracilis and nucleus cuneatus -> cross midline at caudal medulla forming medial lemniscus -> synapse with 3rd order fibers in thalamus (VPL) -> primary somatosensory cortex (postcentral gyrus)
In the PC-ML the most medial axons correspond to the __________ while the lateral axons correspond to the ______________.
Sacral levels (LL); cervical levels (UL)
What would an injury to the posterior column-medial lemniscus lead to?
Impaired proprioception and discriminative touch
T/F: In the event of a PC-ML injury, total loss of function will always follow?
FALSE.
In time other pathways will over compensate
What its the major function of the spinothalamic tract/anterolateral pathway?
Convey pain and temperature info
Where do many STT axons synapse with the receptor fibers?
Substantia gelatinosa
Do STT fibers cross the midline?
Yes. After the synapse in the substantia gelatinosa, 2nd order fibers cross the midline on their way up and collect to form anterolateral pathway
What is the somatotopic organization of the anterolateral pathway?
The most lateral fibers are LL and the medial are UL.
Makes sense because fibers add to the pathway in the medial after they cross midline
Describe the path 2nd order fibers in the AP/STT.
Cross midline to join AP medially -> pathway migrates from anterolateral to posterolateral in the rostral pons -> fibers have multiple origins including VPL of thalamus
What are some major destinations for fibers in the anterolateral pathway?
Reticular formation: attention to pain
Mesencephalic (midbrain): pain control
Hypothalamus: autonomic response
What would an injury to the STT/AP cause?
Loss of pain, temp, itch and tickle.
Would a unilateral injury cause a deficit in bowel and bladder pressure or sexual sensation?
No because fibers ascend bilaterally
In a cordotomy where would the surgeon cut?
Lateral funiculus rostral to highest dermatome level pain level
