SS Tracts: Nociception, Thermal Sense, and Touch (Dennis) Flashcards
1
Q
What are the different tracts of the ALS, what is their target and function?
A
- spinothalamic (largest): target is VPL, posterior nucleus, and intralaminar nuclei in thalamus > function is awareness and gating of info to cortex
- spinomesencephalic: target is periaqueductal gray (PAG) gray matter of midbrain > function is pain modulation by releasing NT’s
- spinoreticular (also sends fibers to spinothalamic): target is reticular formation in brainstem > function is widespread cerebral cortex response to pain and activation of monaminergic systems
- spinobulbar: target is brainstem nuclei > function is adaptive responses through brainstem nuclei
- spinohypothalamic: target is hypothalamus > function is autonomic response to pain
2
Q
What is the somaticsensory function of the ALS?
A
- fibers that relay pain, temperature, and nondiscriminative touch, mostly from the spinothalamic tract
- other smaller tracts that terminate in brainstem and diencephalon modulate pain and initiate responses to pain sensation
3
Q
Where are the 1st and 2nd order neurons located in the ALS and what is the route of their axons?
A
- ALS starts w/ free nerve endings distributed in skin, muscles, joints, blood vessels, and viscera
- peripheral processes from the nerve endings synapse at the pseudounipolar neurons (1st order neurons) in the dorsal root ganglion
- central processes project afferent fibers enter SC via the lateral division of the posterior root entry zone (posterior gray horn)
- fibers ascend/descend 1-2 spinal levels in posterolateral Lissauer’s tract
- fibers then synapse on 2nd order neurons located in the posterior horn in superficial laminae I (marginal zone), II (substantia gelatinosa), and nucleus proprius (laminae III and IV)
4
Q
What signals does the spinothalamic pathway carry?
A
- nondiscriminative tactile
- innocuous thermal (temp)
- nociceptive (pain)
5
Q
Where does the spinothalamic tract enter the SC and what are the two possible routes it can take once entering?
A
- afferent fibers enter posterolateral fasiculus (Lissauer’s tract)
two routes:
- ascending fibers synapse on 2nd order neurons of posterior horn > fibers cross midline via anterior white commissure
- descending fibers synapse on interneurons and moderate spinal reflexes
6
Q
What is the somatotopic organization of the ALS?
A
- axons from lower levels (coccygeal, sacral) of the body are found posterolaterally
- more rostral levels are added in an anteromedial sequence
in general:
lower body > upper body
posterolateral > anteromedial
*ALS map is opposite of the posterior column’s*
7
Q
What is the general path of the ascending spinothalamic tract?
A
- fibers synapse on pseudounipolar neurons (1st order) in the DRG
- afferents enter the posterolateral fasiculus > 2nd degree neurons in posterior horn
- 2nd degree neurons cross midline at the anterior white commissure and ascend in the contralateral ALS > VPL of thalamus (few ascend in ipsilateral ALS, not clinically relevant)
- 3rd order neurons in VPL target somatosensory cortex (somatotopic)
8
Q
What is the general pathway of the ALS STT?
A
- axons enter spinal cord from spinal ganglia (1st order neurons), ascend/descend 1-2 segments in Lissauer’s tract, and then synapse in the posterior horn (2nd order neurons)
- axons of secondary neurons cross midline in the anterior white commissure and ascend as the anterolateral tract in the spinal cord
- anterolateral tract travels through caudal medulla
- in rostral medulla, anterolateral tract lies between inferior olivary nucleus and the nucleus of the spinal tract of the trigeminal nerve
- in the pons and midbrain, the anterolateral tract lies lateral to the medial lemniscus
- anterolateral tract terminates in the VPL of the thalamus (3rd order neurons); from the thalamus, fibers project through the IC and corona radiata to terminate in the primary somatosensory cortex (postcentral gyrus)
9
Q
- most of these fibers are C fibers (hot temp, dull pain), with a small amount being Aδ fibers (pin-prick pain, cold temp)
- relay noxious and innocuous mechanical and thermal info
- contributes to perception of dull pain and moderates behavioral and motivational changes a/w pain
- type of pain that will keep you up at night (arthritis) because the associated dull, aching pain is relayed through the reticular formation, which alerts a large portion of the cerebral cortex of the pain
A
spinoreticular fibers
10
Q
What is the general route of the spinoreticular tract?
A
- 1st order afferents enter SC through posterolateral fasiculus
- 2nd order neurons located in the posterior gray horn in the laminae II and III join contralateral ALS by crossing over AWC
- 3rd order neurons are located in reticular formation
- fibers relayed to thalamus (intralaminar and posterior group nuclei)
11
Q
What is the blood supply to the ALS and what would lesions of these vessels result in?
A
- blood supply originates from arterial vasocorona via sulcal branches of the anterior spinal artery
- occlusion/lesions result in patchy loss of nociceptive, thermal, and touch over the contralateral side of the body, about two spinal segments below the lesion
12
Q
- SCI that produces bilateral, total loss of all motor and sensory function at/below the level of injury
A
complete SCI
13
Q
- SCI injury to the motor and pain/temp pathways in the anterior SC
- patients still have propriception and sensation
A
anterior cord syndrome
14
Q
- SCI to the center of the cord or anterior white commissure
- causes loss of pain/temp pathways w/ deficits relative to the size of the lesion
A
*central cord syndrome*
15
Q
- SCI where individuals may have motor and sensory deficits due to roots containing both types of nerves
- location of deficits depends on distribution of nerve root involved
A
injuries to spinal nerve root
17
Q
- combination of sensory and motor deficits due to damage to ALS, PCMLS, and CST pathways
- contralateral deficits involve ALS and are approx 2 segments below lesion
- ipsilateral deficits involve PCML at/below level of lesion and CST dependent on level of lesion
A
Brown-Séquard syndrome
18
Q
What are the contralateral deficits of Brown-Séquard syndrome?
A
- loss of nociceptive and thermal sensations a/w ALS
- occurs approx 2 segments below level of lesion
19
Q
What are the ipsilateral deficits associated with Brown-Séquard syndrome?
A
- loss of discriminative tactile vibratory, and position sense (PCMLS), at/below the level of lesion
- paralysis of the trunk and extremity (CST), dependent on level of lesion
20
Q
- condition involving cystic cavitation of central regions of SC, typically develops between C3-T2
- syrinx enlarges due to fluid accumulation > surrounding neural tissue destroyed
- initial damage is to ALS fibers in AWC, usually progresses to anterior horn causing motor deficits
- deficits present in distinct cape-like pattern: loss of pain and temp bilat over arms/shoulders; weakness, atrophy, and fasciculations of muscles of hands
A
syringomyelia
21
Q
- lesion location: lateral medulla
- syndrome:
- deficits:
- vascular territory:
A
- lesion location: lateral medulla
- syndrome: lateral medullary syndrome (aka PICA syndrome or Wallenburg syndrome)
- deficits: contralateral loss of pain and thermal sensation (body)
- vascular territory: occlusion of posterior inferior cerebellar A.; occlusion of vertebral artery at the origin of the PICA, blocking the PICA flow
22
Q
- lesion location: lateral pons
- syndrome:
- deficits:
- vascular territory:
A
- lesion location: lateral pons
- syndrome: lateral pontine syndrome
- deficits: contralateral loss of pain and thermal sensation (body)
- vascular territory: occlusion of long circumferential branches of basilar A. and branches of anterior inferior cerebellar A. or superior cerebellar A.
23
Q
What is the nucleus of the trigeminal nerve that is involved in pain, temp, and nondiscriminative touch?
A
spinal trigeminal nucleus
(3 parts: pars caudalis, pars oralis, and pars interpolaris)
24
Q
What is the general path of the spinal trigeminal tract?
A
(SGN runs from obex in pons > C2/C3)
- pain/temp signals relayed to 1st order neurons located in the trigeminal nucleus
- primary trigeminal afferents descend to 2nd order neurons located in the spinal trigeminal nucleus (caudal brainstem)
- tract extends caudally to about 3rd cervical segment and becomes continuous w/ Lissauer’s tract in the upper cervical cord
- 2nd order neurons cross midline and ascend as anterior trigeminothalamic tract
- 3rd order neurons of contralateral VPM (thalamus) target somatosensory cortex
25
Q
What is the purpose of SGN descending to the 3rd cervical segment when the primary afferents enter around the midpons area?
A
This allows the SGN fibers to meet and mix w/ C2/C3 fibers which provide somatosensory innervation to regions of the posterior head.
This prevents gapping in innervation from C2/C3 and the trigeminal N.
26
Q
What is the somatotopic organization of the spinal trigeminal nucleus?
A
STN organized in two planes:
-
anterior > posterior
- face is inverted, opthalmic (V1) dermatome is anterior in the STN and mandibular (V3) dermatome is posterior - rostral > caudal
- fibers from circumoral/intraoral zones terminate rostrally, near obex; fibers of midcheek region target middle segments of STN; fibers of lateral edges of face target caudal regions down to C2/C3
27
Q
- damage to spinal trigeminal tract leads to this type of sensory loss
- more caudal lesion > spares oral region, but affects posterior and lateral boundaries of face
- more rostral lesion (into brainstem) > sensory loss that is increasingly anterior and converges on mouth
- trigeminal fibers ending in cervical cord overlap spinal fibers that innervate C1 and C2 dermatomes, allows for smooth transition of cutaneous info from posterior head (spinal) w/ cutaneous anterior face/head (brainstem)
A
onion-peel sensory loss
28
Q
What is the difference between anatomical vs. clinical orientation?
A
- anatomical: based on anatomical images; ophthalmic is inferior, mandibular is superior; posterior structures are up on the page and anterior structures are down
- clinical: relevant to evaluating neuroimaging and identifying lesions; opthalmic is superior, mandibular is inferior; posterior structures are down and anterior structures are up
31
Q
What deficits arise from lateral medullary syndrome?
(LMS: occlusion of posterior inferior cerebellar artery (PICA) or branches of PICA)
A
- Contralateral loss of pain and thermal sense on body (ALS)
- Ipsilateral loss of pain and thermal sense on face and in the oral cavity (Spinal trigeminal tract/nucleus)
- Dysphagia, soft palate paralysis, hoarseness, diminished gag reflex (Nucleus ambiguus, roots CNIX/X)
- Ipsilateral Horner syndrome (miosis, ptosis, anhidrosis, flushing of face) (Hypothalamospinal fibers)
- Nausea, diplopia, tendency to fall to ipsilateral side, nystagmus, vertigo (vestibular nuclei)
- Ataxia to the ipsilateral side (restiform body, spinocerebellar fibers)
33
Q
- medulla: vascular territories of spinal trigeminal nucleus and spinal trigeminal tract
A
34
Q
- pons: vascular territories of mesencephalic and principal sensory nuclei
A
35
Q
- midbrain: vascular territories of mesencephalic and principal sensory nuclei
A
