anterolateral system

Question 1

What is pain

Answer 1

an unpleasant sensory and emotional experience associated with actual or potential tissue damage:
2 people can experience pain stimulus differently (due to a different genetic background or sociology or psychology

It is complex, cognitive perception of a noxious stimulus

Question 2

Anesthesia, analgesia, athermia, hypoalgesia, hypersthesia, paresthesia, pruritus, allodynia

Answer 2

Anesthesia: lack of all sensation
Analgesia: lack of pain
Athermia: lack of thermal sensation
Hypoalgesia: decreased sensitivity to pain
hyperalgesia: increased sensitivity to any stimulus (sunburn slap)
Paresthesia: pins and needles
Pruritis: itching
Allodynia: pain from normally non-painful stimulus example (sunburn touch)

Question 3

Acute vs chronic pain

Answer 3

Acute pain: critical protective function, warning that injury should be avoided. acute pain is critical for daily protection and survival

Chronic pain: pain that doesn’t go away or adapt. no useful purpose (neuropathic or

Question 4

Nociceptive pain

Answer 4

soft tissue damage, inflammation of soft tissue causes activation of nociceptor terminals in skin

inflammatory chemicals released from blood stream, immune cells, chemicals activate receptors on free nerve endings of C fibers

Sensitize nociceptors-> lower threshold respond more

NSAIDs reduce inflammatory pain

Question 5

Neuropathic pain

Answer 5

nerves are directly damaged in PNS or CNS

Allodynia to light touch common

Resistant to NSAIDs or opioid drugs

Question 6

Pain pathway

Answer 6

The anterolateral system, a combination of several ascending tracts

Convey info about pain and temperature to cortex

Question 7

input to the anterolateral system

Answer 7

noxious mechanical, thermal, chemical stimulation
Activate Ad or C fibers in skin

Ad fibers: sharp first pain
C fibers: dull second pain

Question 8

Spinal Cord

Answer 8

Central process of nociceptors enter lateral dorsal horn via dorsal lateral tract of Lissauer

Synapse on sp cd neurons on Lamina 1/5 or 2

The synapse nociceptors release glutamate and substance P which activate receptors on sp neurons

Question 9

2nd order sp neurons

Answer 9

send axons to contralateral side of sp cd within 2-3 segments rostral and ascend in anterolateral tract

lesion sp cd get loss of pain and temp below lesion on contralateral side, loss is complete by 2-3 segments

Question 10

lesions of sp cd that causes loss of pain and temperature

Answer 10

Anterolateral tract lesion: 1 side lose pain and temp on contralateral side, 2 side loss on bilateral

if dorsal columns are spared fine touch, joint position intact

Question 11

lesions of sp cd

Answer 11

central cord syndrome: hole in the center of the sp cd, syringomyelia: cavity or cyst in center of sp cd, can extend several segments
Lesion cuts crossing axons of the 2nd order neurons that go into anterolateral tract, bilateral loss of pain and temp but vibration, light touch, joint pos intact

Question 12

Termination of higher brain centers

Answer 12

3 major anterolateral paths: all begin in sp cd, ascend next to each other terminate in different places rostrally

1. spinothalamic tract (end in thalamus)
2. Spinoreticular tract (terminates in reticular formation, long column of gray matter in pons and medulla)
3. Spinomesencephalic tract (terminates in mesencephalon, midbrain, PAG

Sp Thalamic (discrimination), Sp Rf (attention arousal Affect), Sp Mes (pain relief)

Question 13

Spinothalamic tract

Answer 13

MAJORITY OF 2ND ORDER NEURONS END IN THALAMUS
mediates desciminative aspects pf pain and temperature sense, location, intensity, duration of noxious stimulus

In thalamus axons terminate in VPL, central lateral nucleus

VPL recieves pain information from body and projects to S1 (areas 3b, 1, 2) to discriminate pain, somatotopy (legs are lateral, arms are medial)

Central lateral nucleus: part of intralaminar nuclei, 3rd order axons from CL project to many areas of cortex, limbic cortex, involved in emotional suffering during chronic pain

Question 14

Spinoreticular tract

Answer 14

anterolateral axons terminate in reticular formation, reticular formation processing changes in level of attention to painful stimuli, involved in emotional arousal , attention and affective response to noxious stimuli

Question 15

spinomesencephalic tract

Answer 15

anterolateral axons that terminate in midbrain in the superior colliculus and periaquaductal gray (PAG)
Other neurons in PAG send axons back down to sp cd, and control the pain signals

Question 16

Cortex

Answer 16

projections from thalamus to cortex
1. Thalamic neurons from VPL project to: S1 areas 3b, 1, 2, and subsequently S2 cortex which helps localize painful stimulus

2. Cingulate gyrus: part of limbic system, processes emotional component of pain: fear anxiety depression anger and attention
3. Insular cortex: processes info on internal, autonomic state of body, and integrates discriminative affective emotional and cognitive components of pain: Asymbolia for pain (it hurts but i dont care)

Question 17

Central control of pain, Descending pathway

Answer 17

inhibit pain: activation by spinomesencephalic tract, exogenous opioids

Neurons with cell bodies in PAG send axons to Raphe nuclei (medulla), and locus ceruleus (pons)
2. These neurons send axons to sp cd (synapse on inhibitory interneurons or spinothalamic tract neurons (inhibit)
Supresses transmission of ascending noxious info to thalamus and cortex