Somatosensory Tracts: Nociception, thermal sense, Touch

Question 1

What modalities are carried in the Anterolateral System

Answer 1

Nociception (pain)

Thermal sensations

Nondiscriminative touch

Itching sensation

Question 2

What are the 5 tracts that travel in the Anterolateral system

Answer 2

Spinothalamic
Spinomesencephalic
Spinoreticular
Spinobulbar
Spinohypothalamic

Question 3

where does the spinothalamic tract go

Answer 3

spine to the thalamus

Ventral Posterolateral Nuclei

Ventral posterior Inferior Nuclei

Question 4

Where does the spinomesencephalic tract go

Answer 4

spine to the Midbrain Reticular formation
and
Periaqueductal Gray

Question 5

Where does the spinobulbar tract go

Answer 5

spine to Various Nuclei of the Brain

Question 6

Where does the spinohypothalamic tract go

Answer 6

spine to the Hypothalamus and other nuclei

Question 7

What are some examples of the primary afferent neurons

Answer 7

Free nerve endings: Ligand gated ion channels, glutamate receptors, G protein coupled receptors

• C fiber axons
• Alpha fiber axons

Question 8

where do the free nerve endings travel to enter the spinal cord, and what do they synapse on

Answer 8

Lateral division of the posterior root entry zone

synapse on the laminae I, II, V

however once the fibers are in the spinal cord they are going to ascend in the posterolateral fasciculus (lissauers tract) usually only two segments and then synapse

some will stay at the same level and terminate on the interneurons to function as a reflex arc

Question 9

What is the Direct pathway of the ALS

Answer 9

Nondiscrimitive tactile, temperature, and pain enters the posterolateral fasciculus and bifurcates

ascending branch (2 segments) will then terminate on the 2nd order neurons of the posterior horn

axons will then cross the midline via the anterior white commissure and ascend in the Anterolateral system (some will ascend ipsilaterally but this isnt clinically relevant)

These second order neurons will then synapse on the third order neurons in the thalamus specifically the Ventral posterolateral nucleus. then this will be conveyed up to the cortex in the posterior limb of the internal capsule to the primary somatosensory cortex

the other segment of the bifurcation from earlier will serve as part of the reflex and synapse on the interneurons

Question 10

What is the indirect pathway of the ALS

Answer 10

instead of projecting all the way up to the cortex like the direct pathway, it will synapse on the reticular formation to provide indirect feedback and awareness of pain to the body. (send signals to other parts of the body like the intralaminar nuclei and the posterior group nuclei)

the fibers that do this are called the spinoreticular fibers which will terminate in the reticular formation (on the nuclei)

relay the noxious and innocuous mechanical and thermal information

synapse on the spinal cord at lamina II, and II and influence lamina V-VIII

Question 11

the somatotopic organization of the ALS

Answer 11

axons from lower levels of the body are found more posterolaterally and the areas that are from the rostral part of the body are more anteromedial

Question 12

Pathway of the facial sensory input via the nucleus of the spinal tract of the trigemina

Answer 12

Pain and temperature information are going to come from a primary afferent via the trigeminal ganglion and will descend and synapse on the nucleus of the spinal tract of the trigeminal

-this occurs around C3 location

then the 2nd order neurons will decussate and ascend in the anterior trigeminothalamic tract and terminate on the contralateral Ventral posteromedial nucleus of the thalamus

the teritary neurons will then extend in the posterior limb of the internal capsule and end up in the primary somatosensory cortex

Question 13

What is the blood supply of the trigeminal structures in the medulla

Answer 13

the Posterior inferior cerebellar artery and the posterior spinal artery

Question 14

What is the clinical orientation of the in the spinal trigeminal tract and nucleus?

Answer 14

the face is inverted

the ophthalamic representation is located inferiorly where as the mandibuar representation is located superiorly

Question 15

What are the divisions of the spinal trigeminal nucleus and what are their modalities

Answer 15

Pars Caudalis: nociceptive input
caudal region of the nucleus - extends from C2,C3 to Obex

Pars oralis: tactile info from central face
extends level of pons to superior medulla

Pars Interpolaris: tactile info
extends obex to the superior medulla
relay info to cerebellum via cerebellar peduncle

Question 16

Onion peel sensory loss

Answer 16

since the spinal trigeminal nerce characteristic pattern has some of the cervical innervation on the head and very little on the chin
(mouth is the center of the innervation or the most rostral region innervates the mouth)

caudal lesion = larger the area surrounding the mouth that is spared from sensory loss

rostral lesion: = sensory loss that starts at the back of the head and converges on the mouth

Question 17

Trigemino-reticulo-thalamic Pathway

Answer 17

pain fibers project bilateraly to reticular formation as trigeminoreticular fibers

input facilitates the ascending reticular activating system in arousal and alertness

Reticular formation is a set of connected nuclei that is responsible for regulating wakefulness and sleep wake transitions

Ascending reticular activating system is part of the Reticular formation

Question 18

Vascular lesions of what leads to patch loss of nociceptive, thermal and touch of the contralateral side

Answer 18

arterial vasocorona via the sucal branches of the anterior spinal artery

this will occur about two spinal segments below the lesion due to the fact that the primary neurons ascend 2 segments before they synapse and deccusate

anterolateral cordotomy would be complete loss of these sensations

Question 19

Brown-sequard, deficits?

Answer 19

hemisection of the spinal cord

Contralateral:
-loss of nociceptive and thermal sensations over the body that begin 2 segments below the lesion of damage

Ipsilateral:
loss of discriminitive tactile, vibratory, and proprioception over the body at and below the level of damage
-motor loss with paralysis of extremities

Question 20

Syringomyelia

Answer 20

cystic cavitation of central regions of spinal gray matter

impinge on anterior white commissure that contains the decussating ALS fibers
(bilateral loss of that segment)

When this occurs at the C4-C5

• bilateral loss of nondiscriminitive tactile, nociceptive, temperature
• starts below the legion
• cape like distribution loss
• over the shoulders and down the nipple
• patient will unknowingly will burn their hands

Question 21

Herpes zoster infection

Answer 21

shingles

appear due to stress and makes home in your nervous system

will move down your peripheral processes of the neurons and provide a skin irritation in the dermatome

hypesthesia

postherpetic neuralgia (poorly understood pain)

Question 22

medial Medullary syndrome

Answer 22

lesion at the medial portion of the medulla lead to contralateral loss of discriminitive touch, vibration, and proprioception due to the fact that the medial leminiscus is right there

pain and temperature is still in tact

Question 23

Lateral medullary syndrome (wallenberg)

Answer 23

Vascular lesion to the posterior inferior cerebellar artery

supplies the ALS system and the spinal trigeminal nucleus and tract

contralateral loss of pain and temp over the body
ipsilateral loss of pain and temp over the face

Question 24

Lesions of the Trigeminal nerve: unilateral

Answer 24

• 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 consencual corneal reflex

Question 25

Lesions of the Trigeminal nerve: Alternating analgesia

Answer 25

cant feel pain

• brainstem lesions in the upper medulla may destroy the primary fibers in the spinal trigeminal tract and secondary fibers in the spinal tract
• paitents have ipsilateral hemianalgesia of the face and contralateral analgesia of the body

Question 26

Lesions of the Trigeminal nerve: Alternating trigeminal hemiplegia

Answer 26

Unilateral destruction of the trigeminal nerve and the Cortical spinal tract in the pons

Ipsilateral trigemenial anesthesia and paralysis
contralateral spastic hemiplegia

Question 27

Corneal reflux

Answer 27

Afferent limb of orginates from pain/touch receptors in the cornea

fibers travel on V1 and have cell bodies in the trigeminal ganglion: terminate in ipsilateral spinal trigeminal nucleus

Trigeminothalamic fibrs send collaterals bilaterally into the facial motor nucleus of the reflux

In resposne to a stimulus that touches the cornea the eyes blink