Somatosensory Tracts: Nociception, Thermal Sense, and Touch

Question 1

The Anterolateral System is responsible for the perception of nociception (pain), temperature, and non-discriminatory touch (crude touch). VEry generally it’s divided into direct and indirect pathways that travel different routes and convey different types of pain. What are the general routes taken by the direct and indirect pathway?

Answer 1

Direct Pathway

Spinal cord > Lateral THalamus > Somatosensory Cortex

Indirect Pathway

Spinal Cord > Reticularformation > Medial Thalamus > Cingulate, Frontal, and Limbic Cortcies

Question 2

The Anterolateral System is comprised of fiber bundles that split off to travel to different targets. These fibers are either direct or indirect. Listed below are these fibers, for the bolded fibers indicate whether they are dirrect or indirect.

Spinothalamic

Spinomesencephalic

Spinoreticular

Spinobulbar

Spinohypothalamic

Answer 2

Spinothalamic: Direct

Spinomesencephalic: Indirect

Spinoreticular: Indirect

Question 3

Where do the direct fibers of the Spinothalmic tract go?

Answer 3

Spine > Thalmus > Ventral Posterlateral Nuclei& VEntral Posterior Inferior Nuclei

Question 4

Where do the indirect fibers of the Spinomesencephalic fibers go?

Answer 4

Spine > Midbrain Reticular Formation & Periaqueductal Gray

Question 5

Which of the following ALS fibers fo to the medulla, pons and midbrain?

A. Spinohypothalmic

B. Spinobulbar

C. Spinoreticular

D. Spinothalamic

Answer 5

Spinoreticular

Question 6

T/F: Free nerve endings don’t have specialized receptor cells, so sensation is transmitted through ligand-gated ion channels, glutamate receptors, and G-protein coupled receptors

Answer 6

True

Question 7

In the central pathway of the ALS, free nerve fibers enter the spinal cord through what location?

Answer 7

Lateral Division of the Posterior Root

Question 8

The Central Target of the primary afferents specifically decussate in what 3 laminae?

Answer 8

1, 2, 5

Question 9

In the central pathway, once the fibers reach the spinal cord, they move within what structure and can cross ascend and descend?

Answer 9

Lissauers Tract (Posterolateral Fasciculus)

Question 10

In the central pathway, most fibers cross across the spinal cord and ascend/descend after bifurcating. Other fibers can also stay at the same spinal level and terminate on interneurons. What action do these fibers relate to?

Answer 10

Reflexes

Question 11

What type of sensory does the Direct Spinothalmic Pathway provide?

Answer 11

Non-discriminitive touch

Thermal (harmful temperatures)

Nociceptive Signals

Question 12

Where do the descending branches of the Direct Spinothalmic Pathway terminate?

What actions do they contribute to?

Answer 12

Interneurons in the gray matter

Spinal reflexes

Question 13

Ascending 2nd order neurons in the direct spinothalamic pathway cross the midline via the anterior white commissure and synapse on the 3rd order neurons in what location?

Answer 13

Venteral Posterolateral region of the thalamus

Question 14

Instead of projecting to the somatosensory cortex, the indirect pathway targets what structure?

What type of sensation does it provide?

Answer 14

REticular Formation

Awareness of pain

Essentially the indirect spinothalamic pathways provide signals that your body is aware of but not as directly

Question 15

Fibers of the indirect spinothalmic pathway ascend and descend in what fasciculus?

The fibers synapse in what laminae?

Answer 15

Posterolateral Fasciculus

Laminae 2, 3, and 5-8

Question 16

Fibers of the indirect spinothalmic pathway ascend _______ which is is hwy its hard to specify the pain

Answer 16

Fibers of the indirect spinothalmic pathway ascend bilaterallywhich is is hwy its hard to specify the pain

Question 17

The ALS is somatotopic. Axons from the lower levels (coccygeal, sacral of the body are found more ________, while more rostral levels are added in an _________ sequence.

Answer 17

The ALS is somatotopic. Axons from the lower levels (coccygeal, sacral of the body are found more posterolateral, while more rostral levels are added in an anteromedial sequence.

Question 18

An extramedullary tumor is found compressing the spinal cordfrom the lateral to medial direction. Which of the following areas would you most likely begin to see issues?

A. Cervical

B. Thoracic

C. Lumbar

D. Sacral and Coccygeal

Answer 18

Sacral and Coccygeal

Question 19

Nerves transmitting sensory information (primary afferents) come from the cell body of what ganglion?

Answer 19

Trigeminal Ganglion

Question 20

Sensation goes to the face carried by CN V, and once it gets to the trigeminal ganlgion it will _________ into the brainstem and merfe with the ______ trigeminal tract in C3, lateral to teh nucleus. The information then projects down to join the ___________.

Answer 20

Sensation goes to the face carried by CN V, and once it gets to the trigeminal ganlgion it will DESCEND into the brainstem and merfe with the SPINAL trigeminal tract in C3, lateral to teh nucleus. The information then projects down to join the LISSAUER’S TRACT.

Question 21

Second order axons from the caudal nucleus decussate and ascend in what tract for facial sensory distribution?

Where does the second-order axon terminate?

Answer 21

Anterior Trigeminothalmic Tract

Contralateral VPM of Thalamus

Question 22

T/F: The anatomic orientation of the trigeminal nerve branches is inverted in the spinal trigeminal tract and nucleus

Answer 22

True

Question 23

Blood supply to trigeminal structures in the medulla come from what two arteries?

Answer 23

Posterior Inferior Cerebellar A

Posterior Spinal A.

Question 24

Which of the following extends from the level of entry (pons) to the superior medulla. It also recieves tactile info from central face.

A. Pars Caudalis

B. Pars Oralis

C. Pars Interpolaris

D. None of the above

Answer 24

Pars Oralis

Question 25

Which of the following extends from the superior medulla to obex, and receieves tactile information from the peripheral face? A. Pars Caudalis B. Pars Oralis C. Pars Interpolaris D. None of the above

Answer 25

Pars Interpolaris

Question 26

Hemisection of the spinal cord results in Brown-Sequard Syndrome. What are the general affects of this syndrome

Answer 26

**ALS damage**: Controlateral loss of nociception and thermal sensation over body (can start two segments below) **Medial Lemniscal Damage:** Ipsilateral **l**oss of Tactile, vibratory, and proprioception (can cause flaccid paralysis) Motor Deficits: Ipsilateral paralysis of extremities (can lead to spastic paralysis)

Question 27

Syringomyelia is cystic cavitation of the central regions of the grey matter may impinge on the Anterior White Commissure that contains the decussating ALS fibers. What happens when syringomyelia happens at C4-C5?

Answer 27

Bilateral loss of nondiscriminitive tactile, nocieptive, and thermal censations

Question 28

What is postherpetic neuralgia?

Answer 28

"worst pain of your life" experienced as a result of Herpes Zoster Infection

Question 29

In the medulla, ALS fibers are near the anterolateral surface, so a lesion at the medial portion of the medulla can cause what presentation of Medullary Syndrome?

Answer 29

Contrlateral loss of discriminitive touch and vibratory sense, but pain and thermal sensation remain intact "dissociative sensory loss"

Question 30

Lateral Medullary Syndrome aka Wallenberg syndrome is a vascular lesion to what artery that supplies the anterolateral system and the spinal trigeminal nucleus/tract? What deficits will you see in the Wallenberg Syndrome?

Answer 30

Posterior Inferior Cerebellar A. Contralateral loss of pain and temperature over body Ipsilateral loss of pain and temperature over the face

Question 31

Answer 31

Nice