Nociception, Thermal Sense, and Touch Flashcards
What does the anterolateral system do?
Supplies information to the brain about signals your experiencing in the body, especially those that can cause tissue damage; includes nociception, thermal sensations, nondiscriminative touch from body and face, and itching sensations
What is the direct pathway of the anterolateral system? Indirect pathway?
Direct: spinal cord -> lateral thalamus -> somatosensory cortices
Indirect: spinal cord -> reticular formation -> medial thalamus -> cingulate, frontal, and limbic cortices
What fibers make up the anterolateral system?
Spinothalamic, spinomesencephalic, spinoreticular, spinobulbar, and spinohypothalamic
Where do spinothalamic fibers travel?
Spine -> thalamus -> ventral posterolateral nuclei and/or ventral posterior inferior nuclei
Where do spinomesencephalic fibers travel?
Spine -> midbrain reticular formation and/or periaqueductal gray
Where do spinobulbar fibers travel?
Spine -> various nuclei of the brain
Where do spinohypothalamic fibers travel?
Spine -> hypothalamus and other nuclei
Where do spinoreticular fibers travel?
Spine -> medulla, pons, and midbrain (reticular formation)
What are cutaneous nociceptors and primary neurons? Where are they found?
First structures that pick up sensation being transmitted; free nerve endings; deep tissue, muscle, joints, blood vessels, internal organs
What mechanisms do cutaneous nociceptors and primary neurons use?
Ligand-gated ion channels, glutamate receptors, g-protein coupled receptors
Where do these free nerve ending fibers enter the spinal cord?
Lateral division of posterior root entry zone
Where are the central target of the primary afferents in the anterolateral system?
Laminae I, II, and V of posterior horn
What do the fibers of the ALS do once in the spinal cord?
Move within posterolateral fasciculus (Lissauer Tract); most cross the spinal cord and ascend/descend after bifurcating; can also stay at the same level in the spinal cord and terminate on the interneurons for reflexes
Where are axons from lower levels (coccygeal and sacral) found in the spinal cord? What about more rostral levels?
Lower levels are found posterolaterally; more rostral levels are added in anteromedial sequence
What does the face use in the anterolateral system?
Direct and indirect pathways from the body; sensory and motor information is transmitted via CN V
Where do nerves of the trigeminal nerve transmitting sensory information (primary afferents) come from?
Cell body of trigeminal ganglion and attaches to brainstem as adjacent motor and sensory roots at ventrolateral pons (large sensory and smaller motor)
What is the pathway of the anterior trigeminothalamic pathway?
Face -> thalamus -> somatosensory and limbic cortices
What is the course of facial sensory distribution?
2nd-order axons from caudal nucleus decussate and ascend in anterior trigeminothalamic tract and terminates in contralateral VPM of thalamus (at periphery); tertiary axons extend in posterior limb of the internal capsule -> primary somatosensory cortex
What supplies blood to the trigeminal structures in medulla?
PICA and posterior spinal artery
What are the divisions of the spinal trigeminal nucleus?
Pars caudalis, pars oralis, and pars interpolaris
In anatomic orientation, how is the face oriented in the spinal trigeminal tract and nucleus?
Face is inverted; opthalmic representation is located inferiorly, mandibular representation is located superiorly
What is anatomic vs clinical orientation? Which one do we use when considering patients?
In terms of CN V, anatomic is the orientation of the nerves on the face (opthalmic is superior, mandibular is inferior); clinical is the orientation of the representation of the face in the tract and nucleus (opthalmic is inferior, mandibular is superior); we use clinical orientation
What is the pars caudalis?
Most caudal part extending from spinal cord (C2-3) to the obex; has somatotopic arrangement with rostral-caudal distribution
Where do circumoral and intraoral fibers terminate?
Near obex
Where do caudal and lateral fibers terminate?
Terminate in caudal regions of cervical spinal cord
What happens when spinal trigeminal tract is damaged?
Get characteristic onion-peel sensory loss; a more caudal lesion -> larger the area surrounding the mouth that is spared from sensory loss; more rostral lesion (into brainstem) -> sensory loss that starts at back of head and converges on 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 projets to cerebellum via inferior cerebellar peduncle; relays tactile info to contralateral VPM
What is the trigemino-reticulo-thalamic pathway?
Pain fibers that project bilaterally to reticular formation as trigeminoreticular fibers and this input facilitates the ascending reticular activating system (ARAS) in arousal and alertness
What is the reticular formation and the ARAS?
RF: set of connected nuclei responsible for regulating wakefulness and sleep-wake transitions
ARAS: part of RF and is mostly composed of various nuclei in the thalamus
Where does blood supply to the ALS originate from? What do occlusions result in?
Arterial vasocorona and via sulcal branches of the anterior spinal artery; occlusion results in patchy loss of nociceptive, thermal, and touch over contralateral side of the body beginning about 2 spinal segments below the lesion
What does generalized disruptions of the ALS produce?
Numbness, tingling, prickling, paresthesia, or even total anesthesia
What does an anterolateral cordotomy result in?
Complete loss of nociceptive, thermal, and touch sensations
What does Brown-Sequard syndrome cause contralaterally? Ipsilaterally?
Contra: loss of nociceptive and thermal sensations over body beginning about 2 segments below level of lesion (ALS damage)
Ipsil: loss of discriminative tactile, vibratory, and position sense over the body at and below the level of the lesion (posterior column damage); motor loss with paralysis of extremities (depending on level)
What is syringomyelia?
Cystic cavitation of central regions of spinal gray matter; may impinge on anterior white commissure that contains decussating ALS fibers
What happens when syringomyelia occurs at C4-5?
Bilateral loss of nondiscriminative tactile, nociceptive, and thermal sensations; starts below lesion (several segements); “cape-like” distribution of loss over the shoulders and down to the nipple level
What is a Herpes Zoster infection (shingles)?
Viral infection that reactivates when under stress; virions travel down peripheral processes of the neurons to produce skin irritation in the dermatome; leads to diminished sensibility (hypesthesia) over affected dermatomes with poorly understood pain (postherpetic neuralgia)
What is medullary syndrome?
In medulla, ALS fibers are near anterolateral surface but remain separate from PCMLS through medulla and pons; vascular lesions or tumors in brainstem can affect discriminative touch and nociception differentially
What would a lesion at the medial portion of medulla cause?
Contralateral loss of discriminative touch and vibratory sense; pain and thermal sensation remain intact; also have dissociated sensory loss
What is lateral medullary (wallenberg) syndrome?
Vascular lesion to PICA, which supplies territory of ALS and spinal trigeminal nucleus/tract; results in contralateral loss of pain and temp over body with ipsilateral loss of pain and temp over face
What does a unilateral lesion of the trigeminal nerve cause?
Anesthesia and loss of general sensations in trigeminal dermatomes; loss of jaw-jerk reflex; atrophy of muscles of mastication; loss of ipsilateral and consensual corneal reflex
What is alternating analgesia of trigeminal nerve?
Brainstem lesions in upper medulla destroy primary fibers in spinal trigeminal tract (descending tract of V) and secondary fibers in spinal lemniscus; patients demonstrate ipsilateral hemianalgesia of face and contralateral hemianalgesia of body
What is alternating trigeminal hemiplegia?
Unilateral destruction of trigeminal nerve and CST(?) in pons; ipsilateral trigeminal anesthesia and paralysis; contralateral spastic hemiplegia
What do primary deficits in lesions (trigeminal nerve or central nuclei) cause?
Ipsilateral loss of pain, thermal, and tactile sensations of face and scalp; ipsilateral loss of same sensations in oral cavity and teeth; ipsilateral paralysis of masticatory muscles
Something about corneal reflex on slide 49
Review it
Where do afferent limbs of the corneal reflex originate from?
Pain/touch receptors in cornea
Where do fibers of corneal reflex travel?
On V1 and have cell bodies in trigeminal ganglion -> terminate in ipsilateral spinal trigeminal nucleus; trigeminothalamic fibers send contralaterals bilaterally inito facial motor nucleus (efferent limb) of this reflex
