10.2 Somatosensory Tracts 2 (Dennis) Flashcards
What types of sensation are carried in the anterolateral system?
Crude touch
Thermal sensation
Nociception
Itching
What is the direct pathway of the ALS from primary neuron to thalamus?
Primary neurons (may travel up or down 3 vertebral levels) then synapse in lamina I.
They then decusate (forming the anterior white commisure) and travel up the anterolateral system.
They synapse again at the ventral posterolateral nucleus of the thalamus
then travels thru the posterior limb of the internal capsule on its way to S1
What is the indirect pathway of the ALS from primary neuron to thalamus?
Primary neurons (may travel up or down 3 vertebral levels) then synapse in lamina II or III.
They then decusate (forming the anterior white commisure) and travel up the anterolateral system.
They then synapse on the “reticular system of the spinal cord / brain stem reticular formation”.
Neurons in the reticular formation then project to the medial thalamic nuclei.
third order neurons in RF will project to intralaminar nuclei and posterior group nuclei
How are the fibers in the ALS somatotopically arranged?
Opposite to the PCML pathway. The lower levels are posterolateral, and the upper levels get added anteromedially.
(Upper levels are medial, lower levels are lateral)
What are Aδ nerve fibers responsible for?
What are C fibers responsible for?
Aδ nerve fibers are responsible for acute “sharp” pain.
C fibers are for dull chronic pain.
What is the function of the spinohypothalamic fibers?
Nocioceptive and somatosensory issues that associates with the hypothalamus for memory formation and interpretation of pain.
Describe the central pathway from the body of cutaneous nociceptors and primary neurons
free nerve endings all over the body come into contact with a stimulus and via signal from ligand gated ion channels, GPCR, etc.
nerve ending axons enter spinal cord through lateral division of the posterior root entry zone
target primary afferent lamina of I, II and V of the posterior horn
then they move within the posterolatral fasciulus (Lissaur’s tract)
decussate and ascend or descend the spinal cord
can also initate reflexes if interacting with interneurons
What is dissociated sensory loss, and what might cause it?
Dissociated sensory loss is where one afferent tract (say PCML, for example) is compressed, but another one (say, ALS) is not. This leads to damage to one modality, but not the other.
What is Brown-Sequard?
Contralateral: loss of pain and thermal sensation over body two segments below lesion (ALS damage)
Ipsilateral: loss of discriminative, vibrator and position sense at level of lesion (PCMLS damage) and motor loss with paralysis of extremities depending on level
What is the blood supply to the spinal trigeminal nucleus and tract within the medulla?
PICA and PSA
Pathway of facial sensory input
pain/temp–>trigeminal ganglion–>nucleus of spinal tract of trigeminal–>project down to C3, lateral to nucleus ->Lissaur’s tract to target the VPM of the thalamus
What is the pars caudalis?
it’s a division of the spinal trigeminal nucleus
it is basically the inversion of the anatomic distribution of the facial nerve with the V1 division being the most inferior and the V3 division being most superior
most caudally located from spinal cord C2-3 to obex
What are the sx of a lesion of the Pars Caudalis?
onion peel sensory loss
more caudal lesion: larger area surrounding mouth that is SPARED from sensory loss
more rostral lesion (into brain stem): sensory loss that starts at back of head and goes toward mouth
what is the pars oralis?
extends from level of entry (pons) to superior medulla
receives tactile info from central face
What is the pars interpolaris?
extends from superior medulla to obex
receives info from peripheral face and projects via inferior cerebellar peduncle
relays tactile info the contralateral VPM
What sx will you see in an occulusion of the arterial vasocorona (branch of sulcal branches from ASA)
what sx will you see with an anterolateral cordotomy?
patchy loss of nociceptive, thermal, and touch over contralateral side of body 2 segments below lesion
complete loss of the above sensations
What is syringomyelia?
what sx will you see with this?
cystic cavitation of central regions of spinal gray matter, may impinge on anterior white commissure containing Decussating ALS fibers
bilateral loss of crude touch, pain, and thermal senses several segments below lesion
cape-like distribution over shoulders to nips
What sx will you see with herpes zoster infection?
(you better know this by now, it comes back in every block)
shingles
viral, known for dermatomal distribution
causes dimished sensation/postherpetic neuralgia
What is medullary syndrome?
Waht sx will you see?
vascular lesions or tumors in brain stem/medial portion of pons
contralateral loss of discriminative touch and vibratory sense
pain and thermal sensation intact
dissociated sensory loss
Describe lateral medullary Syndrome AKA Wallenberg Syndrome
vascular lesion to PICA
contralateral loss of pain and temp over body with ipsilateral loss of pain and temp over face
What sx will you see with unilateral lesion of the trigeminal nerve?
loss of sensation over dermatomes
loss of jaw-jerk reflex (may not if only one side is injured)
atrophy of MoM
loss of ipsilateral and consensual corneal reflex
What causes alternating analgesia of trigeminal nerve
what sx will you seE?
brainstem lesions in upper medulla that destory spinal tract
ipsilateral hemianalgesia of face and contralateral hemianalgesia of body
What sx will you see with alteranting trigeminal hemiplegia?
What causes it ?
ipsilateral trigeminal anasthesia and paralysis
contralateral spastic hemiplegia
unilateral destruction of trigeminal nerve and CST of pons
What are teh sx of a lesion of the central nuclei of the trigeminal nerve?
ipsilateral loss of pain, thermal and tactile sensation on face, scalp, mouth, teeth
ipsilateral paralysis of MoM
possible ipsilateral loss of the corneal reflex (afferent limb) –>touching corneal on other side will ilicit blink in both eyes
may not cause loss of jaw jerk reflex if only one of the trigeminal nerves is damaged
