Nociception, Thermal Sense, and Touch

Question 1

What does the anterolateral system do?

Answer 1

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

Question 2

What is the direct pathway of the anterolateral system? Indirect pathway?

Answer 2

Direct: spinal cord -> lateral thalamus -> somatosensory cortices

Indirect: spinal cord -> reticular formation -> medial thalamus -> cingulate, frontal, and limbic cortices

Question 3

What fibers make up the anterolateral system?

Answer 3

Spinothalamic, spinomesencephalic, spinoreticular, spinobulbar, and spinohypothalamic

Question 4

Where do spinothalamic fibers travel?

Answer 4

Spine -> thalamus -> ventral posterolateral nuclei and/or ventral posterior inferior nuclei

Question 5

Where do spinomesencephalic fibers travel?

Answer 5

Spine -> midbrain reticular formation and/or periaqueductal gray

Question 6

Where do spinobulbar fibers travel?

Answer 6

Spine -> various nuclei of the brain

Question 7

Where do spinohypothalamic fibers travel?

Answer 7

Spine -> hypothalamus and other nuclei

Question 8

Where do spinoreticular fibers travel?

Answer 8

Spine -> medulla, pons, and midbrain (reticular formation)

Question 9

What are cutaneous nociceptors and primary neurons? Where are they found?

Answer 9

First structures that pick up sensation being transmitted; free nerve endings; deep tissue, muscle, joints, blood vessels, internal organs

Question 10

What mechanisms do cutaneous nociceptors and primary neurons use?

Answer 10

Ligand-gated ion channels, glutamate receptors, g-protein coupled receptors

Question 11

Where do these free nerve ending fibers enter the spinal cord?

Answer 11

Lateral division of posterior root entry zone

Question 12

Where are the central target of the primary afferents in the anterolateral system?

Answer 12

Laminae I, II, and V of posterior horn

Question 13

What do the fibers of the ALS do once in the spinal cord?

Answer 13

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

Question 14

Where are axons from lower levels (coccygeal and sacral) found in the spinal cord? What about more rostral levels?

Answer 14

Lower levels are found posterolaterally; more rostral levels are added in anteromedial sequence

Question 15

What does the face use in the anterolateral system?

Answer 15

Direct and indirect pathways from the body; sensory and motor information is transmitted via CN V

Question 16

Where do nerves of the trigeminal nerve transmitting sensory information (primary afferents) come from?

Answer 16

Cell body of trigeminal ganglion and attaches to brainstem as adjacent motor and sensory roots at ventrolateral pons (large sensory and smaller motor)

Question 17

What is the pathway of the anterior trigeminothalamic pathway?

Answer 17

Face -> thalamus -> somatosensory and limbic cortices

Question 18

What is the course of facial sensory distribution?

Answer 18

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

Question 19

What supplies blood to the trigeminal structures in medulla?

Answer 19

PICA and posterior spinal artery

Question 20

What are the divisions of the spinal trigeminal nucleus?

Answer 20

Pars caudalis, pars oralis, and pars interpolaris

Question 21

In anatomic orientation, how is the face oriented in the spinal trigeminal tract and nucleus?

Answer 21

Face is inverted; opthalmic representation is located inferiorly, mandibular representation is located superiorly

Question 22

What is anatomic vs clinical orientation? Which one do we use when considering patients?

Answer 22

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

Question 23

What is the pars caudalis?

Answer 23

Most caudal part extending from spinal cord (C2-3) to the obex; has somatotopic arrangement with rostral-caudal distribution

Question 24

Where do circumoral and intraoral fibers terminate?

Answer 24

Near obex

Question 25

Where do caudal and lateral fibers terminate?

Answer 25

Terminate in caudal regions of cervical spinal cord

Question 26

What happens when spinal trigeminal tract is damaged?

Answer 26

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

Question 27

What is the pars oralis?

Answer 27

Extends from level of entry (pons) to superior medulla; receives tactile info from central face

Question 28

What is the pars interpolaris?

Answer 28

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

Question 29

What is the trigemino-reticulo-thalamic pathway?

Answer 29

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

Question 30

What is the reticular formation and the ARAS?

Answer 30

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

Question 31

Where does blood supply to the ALS originate from? What do occlusions result in?

Answer 31

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

Question 32

What does generalized disruptions of the ALS produce?

Answer 32

Numbness, tingling, prickling, paresthesia, or even total anesthesia

Question 33

What does an anterolateral cordotomy result in?

Answer 33

Complete loss of nociceptive, thermal, and touch sensations

Question 34

What does Brown-Sequard syndrome cause contralaterally? Ipsilaterally?

Answer 34

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)

Question 35

What is syringomyelia?

Answer 35

Cystic cavitation of central regions of spinal gray matter; may impinge on anterior white commissure that contains decussating ALS fibers

Question 36

What happens when syringomyelia occurs at C4-5?

Answer 36

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

Question 37

What is a Herpes Zoster infection (shingles)?

Answer 37

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)

Question 38

What is medullary syndrome?

Answer 38

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

Question 39

What would a lesion at the medial portion of medulla cause?

Answer 39

Contralateral loss of discriminative touch and vibratory sense; pain and thermal sensation remain intact; also have dissociated sensory loss

Question 40

What is lateral medullary (wallenberg) syndrome?

Answer 40

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

Question 41

What does a unilateral lesion of the trigeminal nerve cause?

Answer 41

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

Question 42

What is alternating analgesia of trigeminal nerve?

Answer 42

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

Question 43

What is alternating trigeminal hemiplegia?

Answer 43

Unilateral destruction of trigeminal nerve and CST(?) in pons; ipsilateral trigeminal anesthesia and paralysis; contralateral spastic hemiplegia

Question 44

What do primary deficits in lesions (trigeminal nerve or central nuclei) cause?

Answer 44

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

Question 45

Something about corneal reflex on slide 49

Answer 45

Review it

Question 46

Where do afferent limbs of the corneal reflex originate from?

Answer 46

Pain/touch receptors in cornea

Question 47

Where do fibers of corneal reflex travel?

Answer 47

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