03 Anterolateral system

Question 1

% of american that suffer from chronic pain

Answer 1

50%

Question 2

anesthesia

Answer 2

lack of all sensation

Question 3

analgesia

Answer 3

lack of pain sensation

Question 4

athermia

Answer 4

lack of temperature sensation

Question 5

hypoalgesia

Answer 5

lowered sensitivity to pain sensation

Question 6

hyperesthesia

Answer 6

increased sensitivity to all sensations

Question 7

paresthesia

Answer 7

abnormal tingling sensations (eg pins and needles)

Question 8

pruritus

Answer 8

itchiness

Question 9

hyperalgesia

Answer 9

increased senstivity to pain

Question 10

allodynia

Answer 10

Sensation of pain from non-pain stimulus

Question 11

2 physiologic types of pain (not acute vs chronic)

• physiology
• pain treatment

Answer 11

1. Nociceptive pain
   - activation of nociceptors in skin by inflammatory chemicals
   - NSAIDs reduce inflammatory pain, opioids also effective
2. Neuropathic pain
   - nerves directly damaged
   - resistant to NSAIDs and opioids

Question 12

Types of myelinated fibers in anterolateral system

Answer 12

1. A delta (thinly myelinated) for fast pain

2. C fibers (no myelination) for slow pain

Question 13

Nociceptors release what neurotransmitters when synapsing onto spinal neurons?

Answer 13

• glutamate

- substance P

Question 14

• Where in spinal cord to nociceptors enter?

- where synapse on spinal neurons?

Answer 14

• nociceptor axons enter via Lissauer’s tract of dorsal horn

- synapse in superficial dorsal horn (lamina I/II or V)

Question 15

Central cord syndrome: why does it affect anterolateral system?

Answer 15

Because the spinal neurons decussate close to the central canal of the spinal cord.

Question 16

Major anterolateral pathways (3)

Answer 16

1. spinothalamic-to VPL and Central lateral nucleus in thalamus
2. spinoreticular-to reticular formation in medulla and pons
3. spinomesencephalic-to midbrain

Question 17

VPL

Answer 17

Ventral posterior lateral nuclei of thalamus. Both anterolateral and PCML system synapse here, but different neurons. Thalamic neurons project to 3,1,2 of SS cortex.

Question 18

Central lateral nucleus

Answer 18

In addition to VPL, anterolateral system synpases here in the thalamus. These neurons project to limbic cortex for emotional suffering.

Question 19

Spinoreticular tract

Answer 19

• 4 neurons total, not 3
• 2nd order neurons go to medullary-pontine reticular formation. Some terminate here, others–3rd order neurons go to thalamus.
• mediates changes in attention level to stimuli
• involved in emotional/attention response to pain

Question 20

Spinomesencephalic tract

Answer 20

• 2nd order neurons go in midbrain in the superior colliculus and PAG (periaqueductal gray)
• Descending Control Pathways: neurons from PAG go back down spinal cord to INHIBIT pain signals coming up.

Question 21

Thalamic neurons (of spinothalamic pathway) project to which parts of cortex?

Answer 21

1. SI cortex (then neurons there project to SII cortex)
2. Cingulate gyrus of limbic system (emotion part of pain)
3. Insular cortex–processes info on internal, autonomic state of body (heart races, breathing rapid, etc), also integrates emotional and sensory components of pain

Question 22

Pain Asymbolia

-what is it, what causes it

Answer 22

• aka Pain dissociation
• patients perceive pain but don’t suffer. emotional response is inappropriate.
• Lesion in Insular Cortex (thalamic neurons project there)

Question 23

Descending Pathways that inhibit pain:

-which neurons, where do they synapse

Answer 23

1. PAG neurons send axons to Raphe nuclei in medulla or to Locus ceruleus in pons
2. These neurons send axons to spinal cord, synapse on inhibitory interneurons or directly on spinothalamic tract neurons (direct inhibitory effect).

Question 24

Why does referred pain occur?

Answer 24

Visceral and somatic nociceptors both synapse on the SAME spinothalamic neurons in dorsal horn of spinal cord.