Anterolateral System (ALS) & Spinal Trigem. Nuclei Flashcards
What does the Anterolateral System communicate?
Pain, temperature and non-discriminative touch
What are the main tracts of the ALS?
Spinothalamic and Spinoreticular
The spinothalamic pathway is a ____ pathway
Direct
The spinoreticular pathway is a ______ pathway
Indirect
Where do the afferent fibers of the ALS pathway enter the spinal cord?
Lateral division of the posterior root
Once the afferent fibers of the ALS enter the posterior root, then where do they go?
They either ascend or descend 1-2 levels in the posterolateral tract/fasciculus and then synapse
Another name for the posterolateral tract/fasciculus?
Lissauer’s tract
Where are the 2nd order neurons located for the ALS?
Posterior horn lamina
What lamina layers do the afferent fibers synapse to in the posterior horn?
1,2,3,4
What are laminas 3 and 4 called?
Nucleus proprius
Where do the 2nd order neurons go for the ALS pathway?
Across the midline using the anterior white commissure to the contralateral ALS
Where is the ALS?
Anterior and lateral within the spinal cord
As the 2nd order neurons ascend within the ALS, where do they synapse?
VPL of thalamus to 3rd order neurons
Where do the 3rd order neurons of the ALS go?
Somatosensory cortex
Is the ALS somatotopy the same as the PCML?
NO; they are exact opposites
Describe the ALS somatotopy
The medial side of the ALS = upper arm/neck fibers
The lateral side of the ALS = lower extremity fibers
What lamina levels do the spinoreticular fibers synapse on to 2nd order neurons at?
2 and 3
What is the extra step in the spinoreticular tract?
2nd order neurons synapse at the Reticular Formation (RF)
Once the spinoreticular 2nd order neurons have synapsed at the RF, where do the 3rd order neurons go?
To the thalamus and resume normal pathway
What is the benefit of the spinoreticular tract?
It adds higher order neural processing of the sensory information = more specific information about the stimulus
Blood supply to the ALS?
Arterial Vasocorona and anterior spinal A.
What will a lesion of the blood supply to the ALS cause?
Patchy loss of nociception, thermal and touch on the contralateral side of body starting 1-2 segments below where the lesion is
Bilateral loss of sensory and motor function at/below site of injury
complete spinal cord injury
Some function at or below site of injury
Incomplete spinal cord injury
If a patient has sensation and proprioception, but has loss of motor and pain/temp sensation, what syndrome?
Anterior cord syndrome - anterior half (anterior horn and ALS pathways) have been injured but PCML still in tact
If a patient has loss of pain and temperature pathways, what is the likely syndrome?
Central cord - damage to anterior white commissure
Transient symptoms like numbness, tingling, burning that resolve in 1-2 days
spinal contusion
Damage to 1/2 of the spinal cord
Brown-sequard syndrome (hemisection)
What is damaged with brown-sequard syndrome?
PCML, ALS, CST pathways
Describe the unique sensation result from a brown-sequard syndrome
Loss of touch/pressure/proprioception from the ipsilateral side (PCML)
Loss of pain and temperature from the contralateral side 1-2 segments below injury (ALS)
Loss of motor function from ipsilateral side (CST)
What happens with syringomyelia?
Cyst cavitation in central regions of the spinal cord
What is initially damaged with syringomyelia?
Anterior white commissure of ALS
As the cyst in syringomyelia accumulates fluid and grows, what region will then be damaged?
Anterior horn of the spinal cord
What is the result of syringomyelia?
Bilateral cape pain/temp lost = both arms and shoulders; eventually UE muscle weakness
What is the blood supply to the medullary ALS?
PICA - posterior inferior cerebellar A.
What is the blood supply to the pons ALS?
Basilar or anterior inferior cerebellar or superior cerebellar
What is the result of both medullary ALS lesion and pons ALS lesion?
Contralateral loss of pain/temp.
What does the spinal trigeminal nucleus communicate?
Pain, temperature and non-discriminative touch
Where does the spinal trigeminal nucleus span?
Obex -> C2,C3
What is the main division within the spinal trigeminal nucleus?
Pars caudalis
The afferent signals from the trigeminal enter at the level of the midpons, how do the reach the spinal nucleus?
They must descend to synapse to their 2nd order neurons in this nucleus
What do the afferent signals descend down to reach the spinal trigeminal nucleus?
Spinal trigeminal tract
Once synapsed at their 2nd order neurons in the spinal trigeminal nucleus, what do the 2nd order neurons travel?
Ascend the anterior trigeminothalamic tract
Where do the 2nd order neurons travel to once they are in the anterior trigeminothalamic tract?
VPM of thalamus
What 2 planes is the spinal trigeminal nucleus somatotopy in?
Anterior -> posterior
Rostal -> caudal
Describe the anterior to posterior mapping for the spinal trigeminal nucleus
Anteriorly = V1 Posteriorly = V3
Describe the rostral to caudal mapping for the spinal trigeminal nucleus
Rostal (near obex) = mouth
Middle = midcheek
Caudal (near C2,C3) = lateral edges of face near ears
Lesions that affect the rostal to caudal ends of the spinal nucleus is referred to as what type of sensory loss?
Onion-peel sensory loss
Sensory loss in layers from mouth back to the ears when going from rostral to caudal in the nucleus
Lateral medullary and lateral pontine lesions affect the spinal trigeminal nucleus how?
IPSILATERAL loss of pain and temperature sensation
