Somatosensory Pathway 2 Flashcards
Nondiscriminative touch, thermal, and nociceptive sensations are conveyed by the?
The Anterolateral System (ALS)
The Anterolateral System (ALS) is relayed from?
- body –> thalamus –> somatosensory and limbic cortices
Anterior trigeminothalamic pathway relays from?
face/head –> thalamus –> somatosensory and limbic cortices
What symptoms does disruption of ALS cause?
Numbness, tingling, & prickling (paresthesia) → to
complete loss anesthesia
Cutaneous Nociceptors and Primary Neurons:
- All are morphologically ?
- Fibers enter SC via the lateral division of ?
- free nerve endings
- posterior root entry zone
Central Pathways from the Body:
- Travel in ?
- Central target of primary afferents includes laminae ? of posterior horn
- posterolateral fasciculus
(Lissauer tract) - I, II, and V
Carries nondiscriminative tactile, innocuous thermal, and nociceptive
signals
Direct Spinothalamic Pathways
Direct Spinothalamic Pathways:
• Ascending branches terminate on 2nd order neurons of the posterior
horn, which project to lateral region of the thalamus
- Axons cross midline via ?
- Ascend in the ?, few will ascend in ipsilateral ALS (not clinically relevant)
• Thalamic (3rd order) neurons are located in the VPL (VPI & posterior
group)
• ? terminate on interneurons within gray matter and contribute segmental spinal reflexes
- anterior white commissure
- contralateral ALS
- Descending branches
Polysynaptic component that relays noxious and innocuous mechanical and thermal information to reticular formation
Indirect Spinothalamic Pathways
Indirect Spinothalamic Pathways:
• Branches of these fibers ascend/descend in the posterolateral
fasciculus
- Synapse in laminae ? and ? will influence cells in laminae ? to ?
- Send axons that cross obliquely through AWC (over 1-3 segments) & to
join contralateral ALS - These ? terminate in reticular formation (brainstem)
- Third-order neurons in RF project to the ?
- II and III
- V to VIII
- spinoreticular fibers
- medial thalamic nuclei
ALS fibers that ascends directly to ventral
posterolateral [VPL] and ventral posterior inferior [VPI] nuclei, and posterior
nuclear group (including VMpo)
Spinothalamic fibers
info from SC that ascends to various brainstem nuclei
Spinobulbar fibers
somatosensory info (including nociceptive) from posterior horns that ascends directly to hypothalamus
Spinohypothalamic fibers
may terminate in the midbrain reticular
formation
- May also transition to form ? targeting deep layers of superior colliculus & anterior pretectum
Spinomesencephalic fibers
- spinotectal fibers
ALS
• Axons from lower levels
(coccygeal, sacral) of the body are found ?
• More rostral levels are added in an ?
- posterolaterally
- anteromedial sequence
Lesions of ALS:
• Blood supply originates from ? & via ?
- arterial vasocorona
- sulcal branches of the anterior spinal artery
Lesions of ALS:
• Occlusion results in patchy loss of nociceptive, thermal, & touch over the ? side of the body
- Begins about two spinal segments below the lesion
• What results in complete loss of these sensation?
- contralateral
- Anterolateral cordotomy
What kind of loss do you get with Hemisection of the Spinal Cord?
• CONTRALATERAL loss of nociceptive & thermal sensations over body
- Begins about two segments below
level of the lesion (ALS damage)
• IPSILATERAL loss of discriminative tactile, vibratory, and position sense over the body at and below the level of lesion (posterior column damage)
Cystic cavitation of central regions of spinal
gray matter
Syringomyelia
Syringomyelia:
• May impinge on ? (contains decussating
ALS fibers
• When located at the ? levels of the spinal cord
- Produces ? of
nondiscriminative tactile, nociceptive, &
thermal sensations - Begins several segments below lesion
- Symptoms present in configuration of a
cape draped over shoulders & down to
nipple level
- AWC
- C4 to C5
- bilateral loss
• Positioned near anterolateral surface,
anterior to spinal trigeminal nucleus
• Remain separated from the PCMLS
Medullary ALS Fibers
Medullary ALS Fibers:
Vascular lesions/tumors in lower brainstem can affect?
discriminative
touch & nociception differentially
contralateral loss of discriminative
touch & vibratory sense, but pain/thermal sensation is WNL (one
modality absent but not another)
Dissociated sensory loss
related to Medullary ALS Fibers
Mixed nerve with sensory and motor
components
- Main sensory nerve for the head
- Innervates the muscles of mastication
Trigeminal Nerve
Attaches to the brainstem as two adjacent roots (large sensory &
smaller motor) on ventrolateral aspect
of the pons
Trigeminal Nerve
3 divisions of the Spinal Trigeminal Nucleus?
- pars caudalis, pars oralis, and pars interpolaris
Spinal Trigeminal Nucleus:
- Both nucleus & tract extend caudally to about ? segment
3rd cervical
Spinal Trigeminal Tract & Nucleus:
• In anatomic orientation, face is ? in spinal trigeminal tract
& nucleus
- Ophthalmic representation is
located ?
- Mandibular representation is
located ?
- inverted
- inferiorly
- superiorly
(opposite for clinical orientation)
CN V Central Pathways:
- most caudal part, extending from the spinal
cord (C2, C3) to the obex
Pars caudalis
CN V Central Pathways:
-most rostral part, extending from the main sensory
nucleus to pontomedullary junction
Pars oralis
CN V Central Pathways:
- located in between, in rostral medulla
Pars interpolaris
Pars Caudalis:
When spinal trigeminal tract is damaged have
characteristic pattern of ?
onion-peel sensory
loss
Pars Caudalis
• spinal trigeminal tract is damaged:
- More ? lesion → larger the area surrounding
the mouth that is spared from sensory loss - More ? lesion (into brainstem) → sensory
loss that starts at back of head & converges on
mouth
- caudal
- rostral
Trigeminal Pathway:
- Second-order axons from caudal nucleus decussate & ascend in ?
- Terminates in the ? VPM of thalamus (at periphery)
- Tertiary axons extend in posterior limb of the ? → primary somatosensory cortex
- anterior trigeminothalamic tract
- contralateral
- internal capsule
Trigeminal Pathway:
- Blood supply to trigeminal structures in medulla are via ?
PICA & posterior spinal artery
Pain fibers project bilaterally to the reticular formation as?
trigeminoreticular fibers
- Trigeminal input into the RF facilitates the ascending reticular activating system (ARAS), & plays an important role in?
- RF is a set of connected nuclei responsible for regulating?
- arousal & alertness
- wakefulness and sleep-wake transitions
Extends from the level of entry (pons) to superior
medulla
- Receives tactile information from the central region of the face
Pars oralis
Extends from superior medulla to obex
- Receives information from the peripheral region of the face
Pars interpolaris
Heavily involved in functions homologous to somatic functions of the spinal cord
- Project fibers to the cerebellum (through the inferior cerebellar
peduncle) - Carry tactile information project to the contralateral VPM
Pars Oralis and Pars Interpolaris
What does Unilateral lesion of the Trigeminal Nerve cause?
- 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 does alternating analgesia of the Trigeminal Nerve cause?
• Brainstem lesions in the upper medulla may destroy the primary fibers in the spinal trigeminal tract (descending tract of V), & secondary fibers in the spinal lemniscus
• Patients demonstrate ipsilateral hemianalgesia of the face & contralateral
hemianalgesia of the bod
What does Alternating trigeminal hemiplegia of the Trigeminal Nerve cause?
- Unilateral destruction of the trigeminal nerve and CST in the pons
- Ipsilateral trigeminal anesthesia and paralysis, and contralateral spastic hemiplegia
What supplies the
territory of anterolateral
system AND spinal trigeminal nucleus/tract?
Posterior inferior cerebellar
artery (medulla)
Vascular lesions involving Posterior inferior cerebellar artery (medulla) produces what syndrome?
lateral
medullary (Wallenberg)
syndrome (posterior inferior cerebellar artery syndrome)
What occurs in patients with Lateral Medullary Syndrome?
• Contralateral loss of pain (hemianalgesia) and temperature
(hemithermoanesthesia) over the body WITH
• Ipsilateral loss of these modalities over the face
In response to a stimulus that touches the cornea, the eyes blink
Corneal Reflex
Corneal Reflex:
• Afferent limb of originates from ? receptors in the cornea
• Fibers travel on ? & have cell bodies in the trigeminal ganglion →
terminate in ? spinal
trigeminal nucleus
• ? fibers send collaterals ? into the facial motor nucleus (efferent limb) of this reflex
- pain/touch
- V1
- ipsilateral
- Trigeminothalamic
- bilaterally
