10. Somatosensory: Nociception, Thermal Sense & Touch Flashcards
what is the purpose of the anterolateal system (ALS)
somatosensory system to notify us about tissue damage
-nociception, thermal sensation, nondiscriminative touch, itching to body
what is the basic path for direct ALS pathway
sp cord –> lateral thalamus –> somatosensory cortices
what is the basic path for indirect ALS pathway
sp. cord –> reticular formation –> medial thalamus –> cingulate, frontal & limbic cortices
what fibers make up the ALS
spino—
- —thalamic (direct path)
- —mesencephalic
- —reticular (indirect path)
- —bulbar
- —hypothalamic
what is the basic path of the spinothalamic fibers
spine –> thalamus (VPL & VPI nuclei)
what is the basic path for spinomesencephalic fibers
spine –> reticular formation & periaqueductal gray
what is the basic path of the spinobulbar fibers
spine –> various nuclei of brain
what is the basic path of spinohypthalamic fibers
spine —> hypothalamus & other nuclei
what is the basic path of the spinoreticular fibers
spine –> medulla, pons, midbrain (reticular formation)
=indirect path
what are characteristics of free nerve endings
found all over the body
density varies on body part: more receptors in hands, face
=generic
where do free nerve ending fibers enter the spinal cord
lateral division of post root entry zone
–> stay, ascend, descend 2ish segments at laminae 1, 2, 5
where do free nerve ending fibers fo after they enter the spinal cord
move w/i post.lat. fasciculus (Lissauer Tract)
-ascend/descend after bifurcating
or stay in same level and end on interneuron to stimulate reflex
what are the steps of the direct spinothalamic pathways
nondiscrim tactile, thermal, nociceptive signal –>
enter lat root entry –>
enter post.lat. fasciculus & bifurcate –>
ascending/descending branches end on 2nd order neuron on post horn –>
cross midline via ant commissure –>
move up in contralateral ALS (few ipsi)–>
end on VPL/VPI of thamalus (3rd order)
–> 3rd order neuron to S1
how is the indirect path different than the direct path
terminate on the reticular formation, instead of going up to cortex
-some to VPM and then cortices
=indirect, general feedback from body ==> makes you aware of signal
what are the steps of the indirect spinothalamic pathway
fibers into post horn - ascend/descend & synapse at laminae 2 and 3
–> send axons cross and join the contralat ALS
–> project to reticular formation
–> 3rd order neurons project to intalaminar nuclei & post group nuclei
what is the ALS somatotopic organization
sacral/coccyx - post.lat
most rostral are added in ant.medially (lower cervical & Upper cervical)
what happens when you hace a tumor compresing the cord from lateral to medial at the ALS region
affect lumbar/sacral regions first
what happens if you have an intermedullary tumor damaging the cord from medial to lateral at the ALS region
affect upper cervical first
what is the path for facial sensation
direct/indirect via trigeminal N
primary afferent from trigeminal ganglion –>
attach to sensory/motor roots at ventrolat. pons –>
project down in spinal trigeminal tract to C3 –>
join Lissauer’s (post.lat) tract
–> target VPM
–> 3rd order to part of homunculus that represents face
what is the basic path of the anterior trigminothalamic pathway
face –> spinal cord to 2nd order axon from causal nucleus
–> up as anteriro trigeminothalamic tract
–> contralat VPM
–> posterior limb of internal capsule
–> somatosensory (& limbic cortices)
what is the BS to trigeminal structures in the medulla
PICA
Post. spinal A
what is the anatomical orientation of the face on the spinal trigeminal nucleus
inverterd
V1 inferior & V3 superior
what is the pars caudalis
most caudal part of spinal trigeminal nucleus
from C2/C3 to Obex
-somatotopic head to toe representation –> circumoral/intraoral fibers terminate near obex
–> caudal/lateral fibers terminate in caudal regions of cerival cord
what is pars oralis
spinal trigreminal nucleus part that extends from pons to superior medulla
-tactile info from central face
what is the pars interpolaris
spinal trigeminal nucleus part that goes from superior medulla to obex
- get info from peripheral face
- projects to cerebellum via inf cerebellar peduncle
- relay tactile info to contralat VPM
explain “onion-peel sensory loss”
caudal leasion –> large area around mouth spared from sensory loss
rostral region –> sensory loss stars at back of head & converges at eyes
*rmr trigeminal fibers overlap spinal fibers of adjacent areas of skin*
what is the trigemino-reticulo-thalamic-path
pain fibers - bilateral to reticular formation(RF) as terigeminoreticular fibers
-input fasciliate ascending reticular activating system (in aroudal & alertnes)
*RF responsible for regulating wakefulness & sleep-wake transition*
what occurs if sulcal branches of ant. spinal A are occluded
patchy loss of nociceptive, thermal & touch over contralateral side (about 2 segments below lesion)
what occurs in an ant.lat cordotomy
complete loss of nociceptive, thermal and touch
What happens with hemisection of sp. cord (Brown-sequad)?
contralat: loss of nociceptive & thermal sensation over body (start 2 segments below lesion)
ipsi: loss of discriminative tactile, vibtation and proprioception over the body at and below lesion –> could have motor loss/paralysis depending on level
- affecting both ALS and post column
what is syringomyelia
cystic cavitation of central regions of spinal grey matter
-impinge ant comminssure (contains both sided ALS fibers that cross)
if at C4-C5 -> bilateral loss of nondiscriminative tactile nociception and thermal (several segments below)
“Cape-like” loss = over shoulders and down to nipple level
what happens in herpes zosters infxn
viral, dermatomal distribution
latent in NS –> reactivate with stress & travel to that dermatome –> skin irritation, loss of sensibilty & postherpetic neuralgia (severe pain(=)
what is medullary syndrome ?
what if lesion medial medulla?
vascular lesion/tumor br.st affect discriminative touch & nociceptin differently
lesion medial medulla —> contralat loss of discriminative touch & vibration (but pain and thermal intact)
what occurs in lateral medullary (wallenburg) syndrome
vascular lesion to PICA -
contralat loss of pain and temp over body (ALS)
& ipsilat loss of pain/temp over face (spinal trigeminal tract)
PICA supplies ALS and spinal trigeminal nucleus/tract
what occurs in an unliteral lesion of the trigeminal N
- Anesthesia and loss of general sensations in the trigeminal dermatomes
– Loss of jaw-jerk reflex
– Atrophy of the muscles of mastication
– Loss of ipsilateral and consensual corneal reflex
what is alternating analgesia of the trigeminal n
Br.st lesions in upper medulla may destroy primary fibers in spinal
trigeminal tract (descending tract of V), & secondary fibers in spinal lemniscus
= ipsilateral hemianalgesia of the face & contralateral hemianalgesia of the body
what is alternating trigeminal hemiplegia
Unilat destruction of the trigeminal nerve & CST in the pons
– Ipsilateral trigeminal anesthesia & paralysis, & contralateral spastic hemiplegia
what are the primary defects in lesions of trigeminal N or its central nuclei
Ipsilateral loss of pain, thermal, and tactile sensations of face & scalp
– Ipsilateral loss of the same sensations in the oral cavity & teeth
– Ipsilateral paralysis of masticatory muscles
-possible ipsilat loss of afferent limb of corneal reflex (but still get blinking on both sides bc contralat side intact)
