Somatosensory Tracts 2 Flashcards
Describe the anterolateral system
Comprises a set of fibers relaying pain, temperature and non-discriminative touch
Divided into several different tracts with the largest being the spinothalamic tract
Other smaller tracts terminate in the brainstem and diencephalon where they modulate pain and initiate responses to pain sensation
Describe the ALS pathway
Free nerve endings distributed in skin as well as muscles, joints, blood vessels and viscera
Afferent fibers enter SC via the lateral division of posterior root entry zone
Ascend/descend 1-2 levels in the posterolateral (Lissauer) tract
Target 2nd order neurons in posterior horn in superficial laminae I, II and in the nucleus proprius (laminae III, IV)
2nd order neurons cross midline of SC to go to the ALS
Describe the spinothalamic pathway
Carries non-discriminative tactile, innocuous thermal and nociceptive signals
Afferents enter posterolateral fasciculus and bifurcate
Ascending fibers synapse on 2nd order neurons on posterior horn -> cross midline via anterior white commissure
Descending fibers synapse on interneurons and moderate spinal reflexes
Axons from lower levels (coccygeal, sacral) of the body are found where in the ALS?
Posterolaterally
More rostral levels of the body (cervical) are added in what type of sequence in the ALS?
Anteromedial
Deficits seen in pts with certain types of SC lesions reflect what?
Somatotopic pattern
Ex. Tumor on the medial ALS
Describe the ascending STT pathway
Afferents enter the posterolateral fasciculus -> 2nd order neurons (posterior horn)
2nd order neurons cross midline (AWC), ascend in the contralateral ALS -> synapse on VPL of thalamus
3rd order neurons target somatosensory cortex (somatotopic)
What type of sensation do spinoreticular fibers relay?
Noxious and innnocous mechanical and thermal information
Contributes to perception of dull pain and moderates behavior and motivational changes associated with pain
Describe the indirect spinothalamic (spinoreticular) pathway
Afferents (posterolateral fasciculus) -> 2nd order neurons (laminae II/III) join contralateral ALS -> 3rd order neurons in reticular formation (RF) -> thalamus (intralaminar and posterior group nuclei)
What provides blood supply to the ALS?
Arterial vasocorona and via sulcal branch’s of the anterior spinal artery
Occlusions of the blood supply to the ALS result in what?
Patchy loss of nociceptive, thermal and touch over the contralateral side of the body, begins about 2 spinal segments below the lesion
Complete spinal cord injuries produce what?
Bilateral, total loss of all motor and sensory function at/below the level of injury
What is an incomplete SCI and what are some examples?
Some function remains below the primary level of injury
Ex: anterior cord syndrome, central cord syndrome, injuries to a specific nerve root and spinal contusions
What is anterior cord syndrome?
Injury to the motor and pain/temperature pathways in the anterior SC
Pts still have proprioception and sensation (bc posterior cord isnt damaged)
What is central cord syndrome?
Damage to the central of the cord/AWC
Causes loss of pain/temp pathways with deficits relative to the size of the lesion
Describe injuries to a specific nerve root
May have motor and sensory deficits due to roots containing both types of nerves and location of deficits depends on distribution of nerve root involved
What are spinal contusions?
Transient, generally resolving within 1-2 days
Produce neurological Sx including numbness, tingling, electric shock like sensations and burning in the extremities
What is brown-sequard syndrome?
Combination of sensory and motor deficits due to damage to the ALS, PCML and CST pathways
Includes contralateral and ipsilateral deficits
Can also be referred to as a hemisection
What are some contralateral deficits seen with brown-sequard syndrome?
Loss of nociceptive, thermal sensations (ALS), approximately two segments below level of lesion
What are some ipsilateral deficits seen in brown-sequard syndrome?
Loss of discriminative tactile, vibratory and position sense (PCML), at/below the level of lesion
Paralysis of the trunk and extremity (CST), dependent on level of lesion
Describe syringomyelia
A syrinx is a cystic cavitation of central regions of the SC which typically develops anywhere between C3-T2
Syrinx enlarges due to fluid accumulation -> surrounded neural tissue is destroyed
Initial damage to ALS fibers in AWC
Usually progresses to anterior horn causing motor deficits
What are the distinct deficits seen with syringomyelia?
Present in a cape like pattern
Loss of pain and temperature bilaterally over the arms and shoulders
Weakness, atrophy and fasciculations of muscles of the hands
Lesions of the ALS in the medulla cause what syndrome?
Lateral medullary syndrome (aka PICA syndrome or Wallenberg syndrome)
What are the deficits seen with lateral medullary syndrome?
Contralateral loss of pain and thermal sensation on body (ALS)
Ipsilateral loss of pain and thermal sense on face and in the oral cavity (spinal trigeminal tract/nucleus)
What vascular events can cause lateral medullary syndrome?
Occlusion of posterior inferior cerebellar A (PICA) and/or its branches
Occlusion of vertebral artery at the origin of the PICA blocking PICA flow
Lesions of the ALS in the pons cause what syndrome?
Lateral pontine syndrome
What deficits are seen with lateral pontine syndrome?
Deficits vary depending on whether the lesion is located caudal or rostrally in the lateral pons
Contralateral loss of pain and thermal sense from UE, trunk and LE (ALS)
Ipsilateral loss of pain and thermal sense from face (spinal trigeminal tract and nucleus)
What vascular events can cause lateral pontine syndrome?
Occlusion of long circumferential branches of basilar artery and/or branches of anterior inferior cerebellar artery or superior cerebellar artery
Describe the spinal trigeminal nucleus
Obex -> C2/3
Pain, temperature and nondiscriminative touch
Three divisions: pars caudualis*, pars oralis, pars interpolaris
Describe the spinal trigeminal tract
Second order neurons are housed in spinal nucleus (caudal brainstem) but CN V enters at midpons level
Primary trigeminal afferents must descend in the spinal trigeminal tract
Tract extends caudally to about 3rd cervical segment and becomes continuous with Lissauer’s tract in the upper cervical cord
Describe the anterior trigeminothalamic tract
Primary afferents descend via spinal trigeminal tract -> 2nd order neurons of spinal trigeminal nucleus cross midline, ascend as anterior trigeminothalamic tract -> 3rd order neurons of contralateral VPM (thalamus) target somatosensory cortex
What are the two planes in which the spinal trigeminal nucleus (STN) is organized somatotopically?
Anterior -> posterior
Rostral -> caudal
Describe the face in anatomical orientation
Face is inverted in spinal trigeminal tract and nucleus
Opthalamic dermatome = anterior (inferior)
Mandibular dermatome = posterior (superior)
In regards to somatotopy of the STN, fibers from the circumoral/intraoral zones terminate where?
Rostrally near the obex
In regards to somatotopy of the STN, fibers of mid cheek region target what?
Middle segments of STN
In regards to somatotopy of the STN, fibers of lateral edges of the face target what?
Caudal regions down to C2/3
Damage to the spinal trigeminal tract results in what?
Onion peel sensory loss
A more caudal lesion of the spinal trigeminal tract leads to what?
Spares oral region, but affects posterior and lateral boundaries of the face
(Onion peel)
A more rostral lesion (into brainstem) of the spinal trigeminal tract leads to what?
Sensory loss that is increasingly anterior and converges on the mouth
(Onion peel)
Describe onion peel sensory loss
Trigeminal fibers ending in the cervical cord overlap spinal fibers that innervate C1-2 dermatomes
Allows for a smooth transition of cutaneous info from posterior head (spinal) with cutaneous anterior face/head (brainstem)
Describe clinical orientation
Relevant to evaluating neuroimaging and identifying lesions
Opthalamic is superior and mandibular is inferior
Posterior structures are down on the page and anterior structures are up
Describe unilateral lesions of the trigeminal nerve/nuclei
Anesthesia and loss of general sensations in the trigeminal dermatomes
Paralysis of the muscles of mastication
Loss of ipsilateral afferent limb of corneal reflex
Describe alternating trigeminal hemiplegia
Unilateral destruction of the trigeminal nerve and CST in the pons
Ipsilateral trigeminal anesthesia and paralysis
Contralateral spastic hemiplegia
