Anatomy - ALS Flashcards
what senses are conveyed by ALS
nondiscriminative touch
thermal
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)
