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Flashcards in Anatomy - ALS Deck (20)
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what senses are conveyed by ALS

nondiscriminative touch
nociceptive sensations


what is unique about the neurons of the ALS system

they are lightly myelinated free nerve endings that lack specialized receptor cells


what tract does the ALS run in

Lassauer's tract


where do ALS fibers enter the spinal cord

lateral division of posterior horn in laminae I, II, and V


after entering the spinal cord, what do most ALS fibers do in the direct pathway

cross the anterior white commissure and ascend in contralateral antero-lateral portion of spinal cord


where do ascending ALS fibers synapse in the thalamus

the VPL


where do descending ALS fibers in the direct pathway terminate

on interneurons within the grey matter to contribute to spinal reflexes


describe the indirect pathway of the spinothalamic tract

synapse in laminae II and III in posterior horn --> cross anterior white commissure to join contralateral ALS --> these spinoreticular fibers terminate in reticular formation --> third order neurons in the reticular formation project info to the thalamus


function of the indirect pathway of spinothalamic tract

relays noxious and non-noxious mechanical and thermal info


where do the fibers terminate in the indirect pathway of the spinothalamic tract

in the reticular formation before third order neurons project to the thalamus


describe the spinothalamic fibers of the ALS system

they ascend directly to VPL and VPI (the main fibers of the tract)


describe the spinobulbar fibers of the ALS system

fibers take info from spinal cord and ascend to various brainstem nuclei


describe the spinohypothalamic fibers of the ALS system

fibers take somatosensory info from posterior horns --> hypothalamus
(recognition of pain associated with memory)


describe the spinomesencephalic fibers of the ALS system

fibers that terminate in the midbrain reticular formation


describe the somatotopic organization of the ALS

axons from lower levels (coccyx, sacral): posterolateral
axons from upper levels: anteromedial


blood supply of the ALS

arterial vasocorona via the sulcal branches of the anterior spinal artery


sx of a hemisected spinal cord

contralateral loss of nociceptive and thermal sensations over body two levels below lesion (ALS damage)

ipsilateral loss of discriminative sense at or below lesion (PCML damage)


what is dissociated sensory loss

contralateral loss of discriminative touch and vibratory sense but pain/thermal sensation is normal (or vice versa)


how does likelihood of dissociated sensory loss change along the spinal cord for ALS fibers

the likelihood decreases as you ascend the spinal cord because as you get higher in the spinal cord the ALS system gets closer to the medial leminiscus


if you have a lesion in the brainstem and the ALS system has been affected and the PCML has not, or vice versa, what can you assume

that you are lower in the brainstem (where the ALS and the medial leminiscus are farther apart)