Somatosensory II Flashcards
what information is carried by the anterolateral system (ALS)
nondiscriminative touch
thermal and nociceptive sensation
what are sxs of lesion to the ALS
numbness, tingling, paresthia, anesthesia
where is sensory information within the ALS relayed
body => thalamus => somatosensory and limbic cortices
where is sensory information within the anterior trigeminothalamic pathway relayed
face/head => thalamus => sensory and limbic cortices
where do cutaneous nociceptor fibers enter the SC
lateral division of the posterior root entry zone
which laminae are central targets of the primary afferents of the ALS
laminae I, II, and V of the posterior horn
where do fibers of the ALS travel within the spinal cord?
the posterolateral fasciculus (lissauer tract)
where do axons of the 2nd order neurons of the direct spinothalamic pathway cross midline
the anterior white comissure, then ascent in the contralateral ALS
where do descending branches of fibers of the direct spinothalamic pathway terminate
on interneurons within the grey mater
what is the function of indirect spinothalamic pathways
relays noxious and innouous mechanical and thermal information
where do branches of the indirect spinothalamic pathway synapse?
laminae II and III
do axons of the indirect pathways join the contralateral ALS
YES
what is the blood supple to the ALS
arterial vasocorona
sulcal branches of the anterior spinal a
how does occlusion of the arterial vasocorona/sulcal branches of the anterior spinal artery present clinically?
patchy loss of nociceptive, thermal and touch sensation over the contralateral side 2 segments below the lesion
what lesion would be indicated in a patient with ipsilateral loss of discriminative tactile, vibratory and position sense at and below the lesion
posterior column damage
what is syringomyelia
cystic cavitation of the central regions of spinal grey matter
what important structure may be impinged by syringomyelia
anterior white commissure
how might syringomyelia cause bilateral loss of nondiscriminative tactile, nociceptive and thermal sensation
lesion of the AWC which contains ALS fibers from both sides
how does a patient with impingment of the ALS by syringomyelia present
bilateral loss of nondiscriminative tactile, nociceptive and thermal sensation several segments below the lesion in UEs to nipple
where are medullary ALS fibers positioned
near anterolateral surface, anterior to trigeminal nucleus
what is dissociated sensory loss?
contralateral loss of either discriminative touch and vibratory sense OR pain and thermal sensation
lesions to what area can cause dissociated sensory loss
vascular lesions or tumors of the lower brainstem
in the upper cervical spinal cord, what does the spinal trigeminal tract become
Lissauer’s tract
what are the three parts of the trigeminal tract
pars caudalis
pars oralis
pars interpolaris
which part of the trigeminal tract extends from C2/C3 to the obex (4th ventricle)
pars caudalis
which part of the trigeminal tract is in the superior medulla
pars interpolaris
which part of the trigeminal tract extends from the main sensory nucleus to the pontomedullary jxn
pars oralis
what is onion-peel sensory loss
a characteristic pattern of sensory loss depending on how rostral/caudal a lesion to the spinal trigeminal tract is
what provides the blood supply to trigeminal structures in the medulla
PICA and posterior spinal artery
where do secondary axons from pars caudalis terminate
contralateral VPM (ventral posteromedial nucleus) of the thalamus
between what structures do tertiary axons of pars caudalis extend
in the posterior limb of the internal capsule to the primary somatosensory cortex
what is the reticular formation
a set of connected nuclei responsible for regulating wakefulness and sleep-wake transitions
which part of the reticular formation does trigeminal input facilitate
ARAS (ascending reticular activating system)
from what region does pars oralis receive tactile information
central face
from what region does pars interpolaris receive tactile information
periphery of the face
what lesion of the trigeminal nerve would be indicated in a pt with loss of jaw-jerk reflex, anesthesia in trigeminal dermatomes, atrophy of muscle of mastication, and loss of ipsilateral corneal reflex
unilateral
what is alternating analgesia
ipsilateral hemianalgesia of the face
contralateral hemianalgesia of the body
what kind of lesion would cause alternating analgesia
brainstem lesions in the upper medulla => destruction of primary trigeminal n fibers in the spinal trigeminal tract AND secondary fibers in the medial lemniscus
what causes alternating trigeminal hemiplegia
unilateral destruction of the trigeminal nerve and corticospinal tract in the pons
what is alternating trigeminal hemiplegia
IPSILATERAL trigeminal anesthesia and paralysis
CONTRALATERAL spastic hemiplegia
what artery supplies both the ALS and spinal trigeminal tract?
posterior inferior cerebellar a
what is the result of vascular lesion to the posterior inferior cerebellar a
lateral medullary syndrome (AKA wallenberg syndrome)
what are the sxs of lateral medullary syndrome
contralateral loss of pain and temperature sensation in the body AND
ipsilateral loss of pain and temperature in the face
when testing the corneal reflex, where do trigeminothalamic fibers information to initiate blinking
bilateral collateral fibers to the facial motor nucleus
