Anatomy - ALS

Question 1

what senses are conveyed by ALS

Answer 1

nondiscriminative touch
thermal
nociceptive sensations

Question 2

what is unique about the neurons of the ALS system

Answer 2

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

Question 3

what tract does the ALS run in

Answer 3

Lassauer’s tract

Question 4

where do ALS fibers enter the spinal cord

Answer 4

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

Question 5

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

Answer 5

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

Question 6

where do ascending ALS fibers synapse in the thalamus

Answer 6

the VPL

Question 7

where do descending ALS fibers in the direct pathway terminate

Answer 7

on interneurons within the grey matter to contribute to spinal reflexes

Question 8

describe the indirect pathway of the spinothalamic tract

Answer 8

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

Question 9

function of the indirect pathway of spinothalamic tract

Answer 9

relays noxious and non-noxious mechanical and thermal info

Question 10

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

Answer 10

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

Question 11

describe the spinothalamic fibers of the ALS system

Answer 11

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

Question 12

describe the spinobulbar fibers of the ALS system

Answer 12

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

Question 13

describe the spinohypothalamic fibers of the ALS system

Answer 13

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

Question 14

describe the spinomesencephalic fibers of the ALS system

Answer 14

fibers that terminate in the midbrain reticular formation

Question 15

describe the somatotopic organization of the ALS

Answer 15

axons from lower levels (coccyx, sacral): posterolateral

axons from upper levels: anteromedial

Question 16

blood supply of the ALS

Answer 16

arterial vasocorona via the sulcal branches of the anterior spinal artery

Question 17

sx of a hemisected spinal cord

Answer 17

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)

Question 18

what is dissociated sensory loss

Answer 18

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

Question 19

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

Answer 19

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

Question 20

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

Answer 20

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