Module D-04

Question 1

What are the 2 major classes of pain?

Answer 1

1) Nociceptive pain

2) Neuropathic pain

Question 2

What causes nociceptive pain?

Answer 2

Physiological, activation of nociceptors by stimuli that may cause tissue damage

Question 3

What causes neuropathic pain?

Answer 3

Pathological, caused by aberrant processing in the CNS or PNS

Question 4

2 types of Nociceptive pain

Answer 4

1)First Pain is recognized as a sharp, pricking sensation
2)Second Pain is recognized as a burning sensation that
has a slower onset

Question 5

What type of Nociceptors are activated in First pain?

Answer 5

thermal or mechanical nociceptors

Question 6

What type of fibers conduct the signal for First pain?

Answer 6

myelinated A-delta fibers (conduction velocities

between 4 and 46 m/sec)

Question 7

What type of Nociceptors are activated in Second pain?

Answer 7

Polymodal Nociceptors

Question 8

What type of fibers conduct the signal for Second pain?

Answer 8

unmyelinated C fibers (conduction velocities between 0.4 and 2 m/sec)

Question 9

Where are no nociceptors found?

Answer 9

in the brain

Question 10

Why do we still get headache if there are no brain nociceptors?

Answer 10

Because of the nociceptors in the meninges, periosteum and blood vessels

Question 11

Through which fibers are Visceral or deep pain sensations conducted?

Answer 11

unmyelinated C fibers ( that is why visceral pain is felt as aching, burning pain)

Question 12

Why is pain from Viscera felt as referred pain?

Answer 12

• Afferent fibers of visceral nociceptors enter the spinal cord through the dorsal roots, using the same route of entry as the nociceptors innervating the body’s surface
• neurons in the grey matter of the spinal cord receive convergent inputs from visceral and somatic afferent neurons and send ascending projections into the anterolateral system (ALS)

Question 13

Describe the 3 neuron pathway for Pain

Answer 13

1) First order neurons (somatosensory receptor neuron): afferent fibers in peripheral nerve
2) Second order neurons: fibers crossing the midline and terminating in thalamus
3) Third order neurons: fibers running in posterior limb of internal capsule and ending in S1 (primary somatosensory cortex)

Question 14

Where do the primary afferent fibers of spinal pain pathway synapse in the spinal cord?

Answer 14

dorsal horn of the grey matter of the spinal cord, in a region
called substantia gelatinosa

Question 15

Where does cross over occur in the anterolateral system

Answer 15

immediately in the spinal cord

Question 16

Where do the pain 2nd order neurons synapse

Answer 16

VPL of thalamus

Question 17

Where do pain 3rd order fibers synapse

Answer 17

through the internal capsule=> corona radiata=> primary somatosensory cortex

Question 18

Describe the trigeminal pathway for pain

Answer 18

1) Primary afferent fibers enter the brainstem at the pons and the fibers descend (!) ipsilaterally in the spinal trigeminal tract, to synapse in the lower third of the spinal nucleus of CN V, located in the lower medulla.
2) second order neurons immediately cross the body’s midline in the lower medulla and then ascend in the ventral trigeminothalamic tract until they reach the ventral posterior medial nucleus of the thalamus.
3) Axons of the third order neurons ascend through the posterior limb, close to the genu of the internal capsule, run through the corona radiata, and synapse in the primary somatosensory cortex (S1)

Question 19

Ascending and descending fibers can be seen on both sides of the brain stem, the ascending fiber is the one ________ to the input and the descending fiber is _________

Answer 19

contralateral; ipsilateral

Question 20

How are chemosensitive nociceptors activated ?

Answer 20

by chemical substances released due to tissue damage:
• Potassium from damaged cells
• Bradykinin from blood
• Histamine from mast cells

Question 21

What is Hyperalgesia?

Answer 21

• an enhanced sensitivity and responsivity to stimulation of the area around the damaged tissue.
• Stimuli that are already painful under normal circumstances cause a more intense pain sensation

Question 22

Why does hyperalgesia occur?

Answer 22

due to sensitization of nociceptors by chemicals released from damaged cells

Question 23

What chemical substances released cause sensitization of nociceptors?

Answer 23

• Prostaglandins from damaged cells
• Leukotrienes from damaged cells
• Substance P from primary afferents

Question 24

What is allodynia?

Answer 24

When a previously painless stimulus becomes painful

An effect of sensitization of nociceptors

Question 25

2 neuronal mechanisms for pain control

Answer 25

1) Afferent Regulation of pain - gate control circuitry

2) Descending regulation of pain

Question 26

Describe the gate control circuitry

Answer 26

large myelinated fibers carrying touch sensations activate
inhibitory interneurons within the dorsal horn of the spinal
cord, which then reduce the flow of nociceptive information through the “gate” between nociceptors (first order neurons of the pain pathway) and their second order neurons by hyperpolarizing it

Question 27

What neurotransmitter do the interneurons release?

Answer 27

Enkephalin (opioid peptide)

Question 28

Where are the opioid receptors found in the gate control circuitry?

Answer 28

• on the cell bodies of the primary afferent neurons,
• on their presynaptic ending,
• also on the postsynaptic membrane of the second order neurons (projection neurons)

Question 29

Where are nuclei of descending pain located?

Answer 29

In the brainstem:
-midbrain = periaqueductal grey, (serotonergic)
-Medulla = nucleus raphe magnus (serotonergic)
-Pons = locus ceruleus (noradrenergic)
spinomesencephalic fibers) and the reticular
formation of pons and medulla (spinoreticular fibers)

Question 30

Describe the descending pain regulation.

Answer 30

• nuclei where the descending pain control fibers originate, receive input from ascending ALS fibers carrying nociceptive information
• descending monoaminergic fibers run in the lateral and anterior funiculi of the spinal cord and terminate on the
  opioidergic interneurons in the dorsal horn, where they
  control the transmission of pain

Question 31

What is the effect of Aspirin?

Answer 31

inhibit the enzyme cyclooxygenase thereby inhibiting synthesis of prostaglandins, agents which sensitize
sensory afferent fibers.

Question 32

Example of an opioid

Answer 32

morphine

Question 33

What type of pain is phantom limb pain?

Answer 33

Neuropathic (deafferentation) pain