Anterolateral System N21

Question 1

Anterolateral System is made up of what tracts?

Answer 1

Spinothalamic Tract (STT), Spinoreticulothalamic tract (SRTT), Spinotectal tract (SpTT)

Question 2

Spinothalamic tract function

Answer 2

epicritic, sharp, fast, primary pain, slow, burning second pain

Question 3

Direct spinothalamic tract

Answer 3

direct conscious appreciation of pain

Question 4

Peripheral receptors associated with STT tract

Answer 4

Nociceptors (A-delta, III fibers, lightly myelinated) thermal receptors, thermal nociceptors (A-delta and C fibers for slow, burning second pain)

Question 5

Primary neuron in STT

Answer 5

pseudounipolar, DRG –> Lissauer’s tract (lateral entry zone) –> substantia gelatinosa

Question 6

Secondary neuron in STT

Answer 6

cell body in substantia gelatinosa –> decussate at the anterior white commissure 1-2 segments rostral –> ventrolateral STT –> VPL of the thalamus

Question 7

Decussation of STT

Answer 7

Anterior white commissure 1-2 segments rostral to entry

Question 8

Somatotopy of STT

Answer 8

Inferior segments are located laterally in the STT and cervical segments medially

Question 9

Third order neuron of STT

Answer 9

Located in the VPL of the thalamus –>posterior limb of internal capsule –> primary somatosensory cortex (3,1,2)

Question 10

Spinoreticulothalamic Tract (SRTT) function

Answer 10

Protopathic, slow, dull aching pain and crude touch

Question 11

Indirect spinothalamic tract

Answer 11

SRTT for affective and arousal impact of pain

Question 12

Peripheral receptors for SRTT

Answer 12

Nociceptors (slow, burning pain), Thermal receptors, tactile receptors (crude touch)

Question 13

All receptors of SRTT are associated with what type of fibers?

Answer 13

C fibers with slow conduction velocity

Question 14

Primary neuron in SRTT

Answer 14

Periphery –> DRG –> Lissauer’s Tract (medial entry zone)

Question 15

Second neuron in SRTT

Answer 15

Substantia Gelatinosa (II or V) –> decussate at anterior white commissure (1-2 above)–> joins STT through spinal cord–> leaves ALS in brainstem to synapse on reticular formation

Question 16

Third neuron in SRTT

Answer 16

Reticular formation –> intralaminar nuclei of the thalamus

Question 17

Fourth neuron in SRTT

Answer 17

Intralaminar nuclei of thalamus –> widespread area of cerebral cortex (not just SI)

Question 18

Spinotectal Tract (SpTT) Function

Answer 18

Slow, burning pain, temperature, crude touch, UNCONSCIOUS FEEDBACK (reflexes and inhibition of STT and SRTT)

Question 19

Receptors associated with the SpTT

Answer 19

Nociceptors, thermal receptors, tactile receptors

Question 20

Fibers associated with the SpTT receptors

Answer 20

ALL unmyelinated C-fibers (slow)

Question 21

1 neuron in SpTT

Answer 21

periphery –> Lissauer’s Tract –> substantia gelatinosa

Question 22

2 neuron in SpTT

Answer 22

Substantia Gelatinosa –> anterior white commissure (1-2 segments above) –> ALS –> exits ALS at MIDBRAIN –> Periaqueductal gray (PAG) and Superior Colliculus

Question 23

3 neuron in SpTT

Answer 23

Periaqueductal gray and superior colliculus –> S.C. contributes to the tectospinal descending tract for cervical reflexes from noxious stimuli and PAG descend to alter STT and SRTT incoming sensory information

Question 24

Fate of PAG neurons of SRTT

Answer 24

descend to synapse on the primary neurons of STT and SRTT to inhibit pain transmission

Question 25

mechanism of inhibition of pain by PAG on STT and SRTT

Answer 25

synapse and release ENKEPHALINS which inhibit release of Substance P from

Question 26

Fate of Superior Colliculus neurons of SRTT

Answer 26

descends as the tectospinal tract and goves reflexes to the cervical region (head, neck, eye) towards noxious stimuli

Question 27

When would STT and SRTT be suppressed by descending pathways

Answer 27

Times of emotional stress

Question 28

Descending pathways that modify activity of ascending pathways include

Answer 28

corticospinal, reticulospinal, raphespinal