Lecture 10: Somatosensory Pathways Part 2

Question 1

What is anterior white commissure?

Answer 1

The name of the fibers in the ALS tract that have decussated and continuing upwards toward thalamus

Question 2

What are symptoms of Lateral Medullary/Wallenberg Syndrome?

Answer 2

Contralateral loss of pain/temp over body and ipsilateral loss of pain/temp over face

Question 3

What are signs of a syringomyelia?

Answer 3

Bilateral loss of pain/temp sensation

C4/C5: cape like distribution

Question 4

What happens to fibers that stay at the same level?

Answer 4

Terminate on interneurons for reflexes

Question 5

What happens to most fibers that enter the lateral spinal cord?

Answer 5

Will ascend or descend (mostly ascend) 1-2 levels in Lissauer’s Tract

Question 6

What supplies the trigeminal structures in the medulla?

Answer 6

Posterior Inferior Cerebellar Artery

Posterior Spinal Artery

Question 7

What is the indirect pathway of the ALS?

Answer 7

Spinal Cord –> Reticular System –> Medial Thalamus –> Cingulate, Frontal, and Limbic Cortices

Question 8

Where do primary afferents for the ALS tract come from?

Answer 8

Trigeminal Ganglion

Question 9

What are the divisions of the spinal trigeminal nucleus?

Answer 9

Pars Caudalis
Pars Oralis
Pars Interpolaris

Question 10

What picks up pain/temperature sensation?

Answer 10

Free nerve endings found all over the body

Question 11

What artery can be damaged in Lateral Medullary/Wallenberg Syndrome?

Answer 11

PICA

Question 12

What are symptoms of [Medial] Medullary Syndrome?

Answer 12

Contralateral loss of discriminative touch and vibratory sense but intact pain/temp sensation

Question 13

What supplies the ALS tract in the spinal cord?

Answer 13

Sulcal Branches of Anterior Spinal Artery - symptoms start two levels below lesion

Question 14

What happens if there is a rostral lesion in pars caudalis?

Answer 14

Sensory loss starts back of head and converges on mouth

Question 15

Where do spinoreticular fibers terminate?

Answer 15

Terminates in reticular formation (upper pons)

Question 16

In the spinal trigeminal tract, how are the branches of the trigeminal nerve oriented?

Answer 16

Ophthalmic is inferior

Mandibular is superior

Question 17

In the ALS tract, where are axons from the lower and upper extremities found?

Answer 17

Lower: Posterolaterally
Upper: Anteromedially

Question 18

What are signs of a Brown-Sequard Syndrome?

Answer 18

Contralateral: loss of pain/temp sensation over body two segments below lesion
Ipsilateral: Loss of general sensory info at or below lesion and motor loss with paralysis of extremities

Question 19

For the spinoreticular fibers that does continue upward, where does it terminate?

Answer 19

Medial Thalamus

Question 20

In the direct pathway what happens after the fibers ascend?

Answer 20

1. They synapse at a cell body in the dorsal horn of gray matter
2. They decussate (cross over) at the same level and continue upwards, contralaterally

Question 21

What happens if there is a caudal lesion in pars caudalis?

Answer 21

Area around mouth more likely to be spared from sensory loss

Question 22

Where do the primary afferent fibers for the ALS tract synapse?

Answer 22

Spinal Trigeminal Nucleus

Question 23

Where do second order axons terminate at?

Answer 23

They decussate and ascend contralaterally to the VPM where they terminate

Question 24

Where is pars interpolaris?

What does it do?

Answer 24

Superior medulla to obex

Receives info from peripheral face and projects info to cerebellum

Question 25

What are symptoms of shingles?

Answer 25

Diminished sensibility over affected dermatomes and severe pain

Question 26

Where is pars oralis?

What does it do?

Answer 26

Superior medulla to lower ons

Receives tactile info from central face

Question 27

What is the function of the trigemino-reticulo-thalamic pathway?

Answer 27

Facilitates Reticular Activating System in arousal and alertness

Question 28

Why do the primary afferent fibers descend to join Lissauer’s Tract?

Answer 28

The blending allows cross over of sensation in the upper cervical area

Question 29

What is syringomyelia?

Answer 29

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

Question 30

What laminae are targeted by primary afferents of the ALS tract?

Answer 30

Laminae I, II, and V

Question 31

In the direct pathway, where do fibers go after synapsing at the VPL?

Answer 31

Somatosensory cortex via posterior limb of internal capsule

Question 32

In the indirect tract, what laminae do the fibers synapse in?

Answer 32

Laminae II and III and influences Laminae V-VIII

Question 33

In the direct pathway where does the anterior white commissure synapse?

Answer 33

Synapses at Ventral Posterolateral Nucleus of thalamus (VPL)

Question 34

What does the Spinothalamic/ALS system do?

Answer 34

Relays information about pain, temperature, and crude touch from the body to the brain

Question 35

Where is pars caudalis?

Answer 35

Starts around C2/C3 and extends to obex of medulla

Question 36

What is the direct pathway of the ALS?

Answer 36

Spinal Cord –> Lateral Thalamus –> Somatosensory Cortices

Question 37

Where does nerve fibers from the free nerve endings travel to?

Answer 37

Lateral division of the posterior root of the spinal cord

Question 38

Where do fibers go from the VPM?

Answer 38

Primary Somatosensory cortex via posterior limb of internal capsule

Question 39

What does the indirect pathways of the ALS tract do?

Answer 39

Relay awareness of pain rather than specific sensation