6 - Somatosensory Systems Review

Question 1

What is the function of the DC/ML system? Where does this pathway travel in the caudal medulla, rostral medulla, and pons?

Answer 1

Fine touch from the body.

Medial lemniscus stays medial.

Question 2

Describe the medial lemniscus? What is the somatotopy of the DC/ML system?

Answer 2

Like a ribbon that twists as it moves upwards through the CNS.

Fallen over drunk person with feet towards center from spinal cord through the caudal medulla.

Rostral medulla though the pons they try to stand up with hands and arms in the center.

At the thalamus they hall over with their head towards the center.

Then they drunkenly flip over so their feet are in the center of the cortex.

Question 3

What is the function of the anterolateral system?

Answer 3

Pain and temperature from the body

Question 4

What are the functions of the trigeminal sensory system?

Answer 4

Fine touch from the face

Pain and temp from the face

Question 5

Describe the anterolateral systems path in comparison to the DC/ML system?

Answer 5

It ascends rostrally and LATERAL in the causal medulla, pons, and midbrian.

This differs from the DC/ML which is MEDIAL.

Question 6

Where do the nerves of the trigeminal system that bring fine touch sensation to the face enter brainstem? Where do they synapse?

Answer 6

They don’t come in until the pons level to synapse almost immediately at the chief nucleus.

Question 7

Where do the nerves of the trigeminal system that bring pain and temp from the face enter the brainstem? Where do they synapse?

Answer 7

At the level of the pons and dive down into the trigeminal tract of five where they synapse along the spinal nucleus of five.

Question 8

Where is the tract located in the DC system? What about in the anterolateral system?

Answer 8

DC: posterior funiculus - middle part of the dorsal spinal cord

Anterolateral: anterior lateral funiculus - ventral lateral spinal cord on either side

Question 9

Between the DC/ML system and anterolateral system, how do the crossing points differ?

Answer 9

DC: fibers cross to opposite side in one place in the medulla (sensory decussation)

Anterolateral: cross to opposite side in spinal cord and cross all along spinal cord at levels near where afferents enter.

Anterolateral crosses first.

Question 10

What are the three major pathways of the anterolateral system?

Answer 10

Spinothalamic: thalamus

Spinoreticular: reticular formation in medulla and pons

Spinomesencephalic: midbrain PAG, superior colliculus.

Question 11

Where does the major pathway of the DC system go?

Answer 11

One major pathway to the thalamus.

Question 12

What results from damage to the spinal cord in the dorsal column?

Answer 12

IPSI loss of tactile, vibration, and joint position just below the lesion.

Question 13

What results from damage to the spinal cord in the anterolateral system?

Answer 13

CONTRA loss of pain and temp by 2-3 segments below the lesion.

Question 14

By the level of the thalamus, what has happened in both the DC and anterolateral systems?

Answer 14

All information has crossed to the opposite side (decussation).

Question 15

What results from lesions to the thalamus and cortex?

Answer 15

Contralateral deficits in ALL sensation (fine touch and pain/temp).

Question 16

What results from a lesion on one side of the spinal cord that wipes out an entire side (hemisection)?

Answer 16

ISPI loss of fine touch discrimination, joint position, and vibration immediately below the lesion.

CONTRA loss of pain and temp complete by 2-3 segments below the lesion (some crude touch lost also)

TOTAL loss of all sensation at level of lesion b/c nothing can enter at that dorsal root.

Also IPSI paralysis and muscle weakness because motor pathways also cut.

Question 17

What is a Rhizotomy? What does it cause?

Answer 17

Surgical cutting of the dorsal root for pain relief. Usually cut levels above and below as well because of mixing fibers.

IPSI loss of fine touch discrimination, joint position, vibration, and pain/temp to that dermatome.

Pain often comes back.

Question 18

What is a cordotomy? What happens if one side is cut vs both sides?

Answer 18

Surgical cutting of anterolateral fiber tracts in the spinal cord for pain relief in terminally ill.
-Cut at 2-3 spinal segments above the dermatome where pain begins to get all the fibers after they have crossed.

One side: contra loss of pain and temp

Both sides: bilateral loss of pain and temp

Question 19

What is glove and stocking sensory loss? What is it typically caused by?

Answer 19

Lack of fine touch, pain, and temperature ONLY.

In PART of a limb of PARTS of limbs.

Indicates metabolic disorder such as diabetic neuropathy.

Question 20

What would result from complete transection of the spinal cord?

Answer 20

Bilateral loss of tactile, pain/temp below lesion.

Also complete loss of motor control and voluntary muscle contraction below the lesion.

Question 21

What can cause anterior cord syndrome? What is the associated deficit?

Answer 21

A contusion of the cord or an infarct (loss of blood supply).

Bilarteral loss of pain and temp below the lesion and also weakness.

Usually spares DC so fine discrimination, vibration, and joint position are OK.

Question 22

What deficit is associated with posterior cord syndrome?

Answer 22

Affects dorsal columns.

Bilateral loss of fine discrimination, vibration, and joint position below the lesion.

Pain and temp are OK.

Question 23

What does central cord syndrome cause? What can cause this condition?

Answer 23

Syringomyelia: tube-like enlargement of the central canal from excess fluid.

Hyperextension of the cervical spine can damage the center of the cord.

Question 24

What deficits are associated with central cord syndrome? What is usually spared with a small lesion?

Answer 24

Cutting of the 2nd order anterolateral fibers that cross in the spinal cord.

Results in bilateral loss of pain and temp in the dermatomes of spinal levels with the lesion.

Small lesions usually spare dorsal columns and tactile sense; also spares anterolateral tracts and pain/temp below the lesion.

Question 25

What can a large lesion of central cord syndrome affect?

Answer 25

Dorsal columns, bilateral loss of fine discrimination, joint position below lesion.

Motor neurons in ventral horn - loss of motor control.

Can affect anterolateral tracts causing bilateral loss of pain and temp with sacral sparing.

Question 26

What deficits can result from a Unilateral lesion of the VPL of the thalamus?

Answer 26

CONTRA loss of fine touch AND pain/temp from the BODY.

This is because the anterolateral and DC/ML pathways go through the VPL. Face not impacted because those go through VPM.

Question 27

What deficits result from a unilateral lesion in the VPM of the thalamus?

Answer 27

CONTRA loss of fine touch and pain/temp to the FACE.

This is because the trigeminal sensory pathways and the trigeminothalamic tract go through the VPM.

Question 28

What can a superior focal lesion of the cortex result in?

Answer 28

CONTRA loss of fine touch and pain/temp sensation to the HAND region.

Envision the homunculus of he cortex.

Question 29

What can a lateral focal lesion of the cortex result in?

Answer 29

CONTRA loss of fine touch and pain/temp sensation to the FACE.

This is because the face and mouth are located laterally on the cortex homunculus.

Question 30

What deficits would result from a lateral lesion of the pons or medulla?

Answer 30

CONTRA loss of pain and temp sensation from the BODY (anterolateral pathway)

IPSI loss of pain and temp sensation from the FACE (spinal trigeminal nucleus and tract).