SS25 Pain Pathways (Exam 2)

Question 1

Differentiate the sensory-discriminative & motivational-affective aspects of pain.

Answer 1

• Sensory-discriminative - Ascending pathways via spinothalamic & trigemino-thalamic tracts and cerebral cortex → perception of pain (location, intensity, sensation, etc.)
• Motivational-affective - responses to painful stimuli (Ex. Attention/ Arousal, Somatic/ Autonomic reflexes, Endocrine responses, and Emotional changes)

Question 2

What is nociception?

Answer 2

• The experience of pain through a series of complex neurophysiologic processes.
• Medications target causes of pain by actions on transduction, transmission, interpretation, & modulation in both PNS and CNS

Question 3

What are the four stages of pain perception?

Answer 3

1. Transduction (tissue level)
2. Transmission (via nerve impulses)
3. Modulation (via spinal cord)
4. Perception (CNS)

Question 4

Where does the modulation of pain impulses occur?
- What drugs work here?

Answer 4

• Dorsal horn of the spinal cord and produces reflex reactions
• Afferent fibers project signals to brain
• LAs, opioids, ketamine, A-2 agonist

Question 5

What drugs are used to affect the transduction of pain?
What specifically is being affected by these drugs?

Answer 5

• Local anesthetics & NSAIDs
• Peripheral nociceptors - mechanical, thermal, and chemical stimuli

Question 6

What drugs are used to affect the transmission of pain?
What specifically is being affected by these drugs?

Answer 6

• Local anesthetics
• Αδ and C fibers

Question 7

What drugs are used to affect the perception of pain?
What specifically is being affected by these drugs?

Answer 7

• General anesthetics, opioids, α2 agonists
• Brain

Question 8

Where are nociceptors located?

Answer 8

• Skin
• Muscles
• Joints
• Viscera
• Vasculature

Question 9

What characterizes afferent C-fibers?

Answer 9

• Unmyelinated
• Burning pain from heat
• Sustained pressure
• Slow (less than 2 m/s)

Question 10

What characterizes Alpha fibers?

Answer 10

• Myelinated
• Type I: Aβ & Aδ (heat,mechanical, chemical)
• Type II: Aδ (heat)
• Fast (>2 m/s)

Question 11

What chemical mediators of pain are targeted with spinal anesthetics?

Answer 11

Peptides

• Substance P
• Calcitonin
• Bradykinin
• CGRP

Question 12

Which chemical mediator is released first in response to injury?

Answer 12

• Bradykinin

Question 13

What chemical mediators of pain are inhibited by NSAIDs?

Answer 13

• Lipids (Prostaglandins &Thromboxanes)

Question 14

What chemical mediators of pain are inhibited by cannabis?

Answer 14

• Lipids (Endocannabinoids)

Question 15

What is sensitization?

Answer 15

• Decreased pain threshold (likely due to upregulation of receptors)

Question 16

Differentiate hyperalgesia and allodynia.

Answer 16

• Hyperalgesia - ↑ pain sensations to normally painful stimuli.
• Allodynia - perception of pain to things that aren’t normally painful.

Question 17

What characterizes primary hyperalgesia?

Answer 17

Hyperalgesia at original site of injury.

• Lower pain threshold
• Spontaneous pain
• Expansion of receptive field (upregulation of receptors)

Question 18

What characterizes secondary hyperalgesia?

Answer 18

• Sensitization of CNS → hyperalgesia from uninjured skin surrounding injury.

Question 19

What area of the brain accounts for the perception (location & intensity) of pain?

Answer 19

• Somatosensory Cortex I & II (SI & SII)

Question 20

What is the relay center for nociceptive and sensory activity?
How does sensory activity travel from this area to the cerebrum?

Answer 20

• Spinal Dorsal Horn
• Ascending pathways

Question 21

What areas of the brain may depress or facilitate the integration of painful information in the spinal dorsal horn?

Answer 21

• PAG - Peraqueductal Gray Matter
• RVM - Rostral Ventral Medulla

Question 22

Where are afferent C-fibers located in the spinal column?

Answer 22

• Dorsal horn: Lamina I (marginal layer) & Lamina II (Substantia Gelantinosa)

Question 23

What is another name for Lamina II?
What drugs work here?

Answer 23

• Substantia gelatinosa
• Opioids act on chronic pain here (afferent C-fibers)

Question 24

What nerve fibers are associated with an “open-gate” for pain?
What nerve fibers can shut this gate?

Answer 24

• Aδ & C-fibers = open
• Aβ fibers = closed (numbs, pressure)

Question 25

What receptors does ketamine target for pain modulation?

Answer 25

- NMDA

Question 26

The excision of what structure would result in the complete loss of perception of pain?

Answer 26

Amygdala *Bonus points if you just said the whole brain you degenerate*.

Question 27

What neurotransmitters propagate excitatory transmissions in the spinal column?

Answer 27

- Glutamate - Calcitonin - Neuropeptide Y - Aspartate - Substance P

Question 28

What neurotransmitters propagate inhibitory transmissions in the spinal column?

Answer 28

- GABA_A - Glycine - Enkephalins - NE - Dopamine

Question 29

What are the four ascending pain pathways?

Answer 29

- Spinothalamic - Spinomedullary - Spinobulbar - Spinohypothalamic

Question 30

What information is carried by the spinothalamic pathway? What laminae are used?

Answer 30

- Pain, Temp, & Itch - Laminae I, VII, and VIII

Question 31

What information is carried by the spinobulbar pathway? What laminae are used?

Answer 31

- Behavior towards pain - Laminae I, V, and VII

Question 32

What information is carried by the spinohypothalamic pathway? What laminae are used?

Answer 32

- Autonomic, neuroendocrine & emotional aspects of pain - Laminae I, V, VII, & X.

Question 33

What part of the suprapinal pathway differentiates where pain is coming from?

Answer 33

S1 & S2 (Somatosensory cortex 1 & 2)

Question 34

What supraspinal areas deal with the emotional/motivational aspects of pain?

Answer 34

- Anterior cingulate cortex (ACC) - Insular Cortex (IC) - Amygdala

Question 35

Where do the descending inhibitory tracts originate? Where do they then synapse at?

Answer 35

- PAG (periaqeueductal gray matter) - Synapse at dorsal horn

Question 36

What neurotransmitters are increased with exercise?

Answer 36

- Endorphins - Enkephalins - Serotonin

Question 37

How do inhibitory tracts inhibit the propagation of painful stimuli?

Answer 37

**Hyperpolarizing Aδ & C fibers** - ↓ release of substance P - Open K channels and inhibit Ca channels

Question 38

Where does the pain inhibiting impulse originate from in the descending inhibitory tracts?

Answer 38

PAG-RVM areas

Question 39

When is pain considered chronic rather than acute?

Answer 39

- If pain persists beyond tissue healing > 3 - 6 months

Question 40

Who is at increased risk of neuropathic chronic pain?

Answer 40

- Cancer patients - Diabetics

Question 41

What is the treatment for chronic neuropathic pain?

Answer 41

- Opioids - Gabapentin - Amitriptyline - Cannabis *All situation dependent*

Question 42

How is visceral pain characterized? What examples were given in lecture?

Answer 42

- Diffuse and poorly localized; referred to somatic sites (muscles/skin) - Examples: ischemia, stretching of ligamentous attachment, spams, organ distention, pancreatic cancer

Question 43

What is complex regional pain syndrome?

Answer 43

- Variety of painful conditions **following injury** (sponateous pain, hyperalgesia, edema, allodynia, autonomic abnormalities, etc.)

Question 44

When can babies begin to perceive pain?

Answer 44

23 weeks

Question 45

How does pain affect the GI/GU system?

Answer 45

- ↑ Sympathetic tone = ↑ sphincter tone and ↓ peristalsis = **ileus, urinary retention** - Hypersecretion of acid = Stress ulcers, AA - **N/V** - Abdominal distention

Question 46

How can the effects of pain in the cardiovascular system be summarized?

Answer 46

- ↑ SNS: ↑ BP, tachycardia, ↑SVR, myocardial irritability - Compromised LV:↓ CO, MI

Question 47

What hormones experience a decrease in response to chronic pain?

Answer 47

**Anabolic Hormones** - Insulin - Testosterone

Question 48

What are the pulmonary effects of chronic pain?

Answer 48

- ↑ total O2 consumptiom/CO2 production - ↑ RR & WOB, splinting - ↓ chest wall mvmt → **atelectasis, intrapulmonary shunting and impaired cough** increased infxn risk)