Exam #6: Sensory Physiology of Pain

Question 1

Why is chronic pain important?

Answer 1

• 30% US population experiences chronic pain
• Leading neurological disorder & high cost to society
• Leading cause of disability & suffering

Question 2

What is the difference between nociception & pain?

Answer 2

Nociception= sensory response to a noxious stimulus

Pain= perception of nociceptive sensory information

Question 3

What are the two components of pain?

Answer 3

1) Sensory-discrimination= perception of external or internal noxious stimuli & the localization to the site of the stimulus
2) Motivation-affective= emotional & sympathetic responses associated with behavior

Question 4

What brain regions are associated with sensory discrimination?

Answer 4

Primary & secondary somatosensory cortices

Question 5

What brain regions are associated with the motivational-affective component of pain?

Answer 5

Frontal cortex
Limbic system
Brainstem

Question 6

What type of sensory information associated with the sensory-discriminative component of pain?

Answer 6

Location
Intensity
Modality (e.g. stab vs. burn)

Question 7

What type of information is conveyed by the emotional component of pain?

Answer 7

• Negative impact on mood

- Depression associated with chronic pain

Question 8

What is acute pain? What are the functions of acute pain?

Answer 8

• Body’s warning signal that is critical for survival
• Pain felt within 0.1 sec of stimulus i.e. VERY FAST
• Very adaptive i.e. tissue heals and pain abates

Question 9

What fibers conduct acute pain?

Answer 9

A-delta

Question 10

What is pathologic or chronic pain?

Answer 10

• Pain that begins >1 sec after stimulus and then progressively worsens
• Can become MALADAPTIVE i.e. persists even if there is no more tissue damage

Question 11

What fibers conduct pathologic pain?

Answer 11

Persistent and SLOW conducting C-fibers

• small
• unmyelianted

Question 12

What are the qualities of acute pain?

Answer 12

Sharp
Prickling
Electric
Cutting

Question 13

What are the qualities of chronic pain?

Answer 13

Dull
Throbbing
Aching
Nauseous

Question 14

What is nocicpetive pain?

Answer 14

Physiologic pain that serves as a warning to the body

Question 15

What is inflammatory pain?

Answer 15

Pain that is associated with healing

Question 16

What is dysfunctional pain?

Answer 16

Pain without an underlying lesion or that is disproportionate to tissue injury

• IBS
• Fibromyalgia

Question 17

What is neuropathic pain?

Answer 17

Pain from damage to the CNS or PNS that is disproportionate to intensity of nociceptor activation

Question 18

What is the difference between somatic and visceral pain?

Answer 18

Somatic= superficial or deep pain originating from the body

Visceral= pain originating from internal organs

Question 19

What is the difference between the fibers that mediate somatic and visceral pain?

Answer 19

Somatic= A-delta 
Visceral= C

Question 20

What are the four general steps from external injury to perception of pain?

Answer 20

1) Transduction
2) Transmission
3) Modulation
4) Perception

Question 21

What is peripheral transduction?

Answer 21

Conversion of injury to electrical stimulus

Question 22

What type of receptors are nociceptors?

Answer 22

Free-nerve endings

Question 23

Where are the soma of nociceptions in the body vs. the face?

Answer 23

Body= DRG 
Face= Trigeminal ganglia

Question 24

What are the important functional characteristics of nociceptors?

Answer 24

• High threshold

- Slowly adapting

Question 25

What stimuli can activate nociceptors?

Answer 25

- Mechanical (of high intensity) - Thermal - Chemical

Question 26

What are the different types of thermal nociceptors?

Answer 26

``` CMR-1= cold VRL-1= noxious heat VR-1= noxisous heat/ capsaicin ```

Question 27

What is "inflammatory soup?"

Answer 27

Tissue injury resulting in the release of a number of inflammatory mediators *****These inflammatory mediators stimulate nociceptors & lead to indirect sensitization or LOWERED THRESHOLD

Question 28

What is peripheral sensitization?

Answer 28

1) Lowered threshold of activation for nociceptors in response to injury - Increased sensitivity of neurons directly involved - Increased sensitivity of a wider area of tissue 2) Activation of silent nocicpetors

Question 29

What NT plays the largest role in peripheral sensitization?

Answer 29

Substance P

Question 30

What is allodynia?

Answer 30

Pain resulting from non-noxious stimuli

Question 31

What is hyperalgesia?

Answer 31

Increased response to a stimulus that is normally painful

Question 32

What is axon reflex?

Answer 32

Coupling of sensory system to the SNS in response to inflammatory mediators

Question 33

What is the triple response of Lewis?

Answer 33

Redness Edema Wheal

Question 34

What is the difference between A-delta & C fibers?

Answer 34

A-delta= myelinated--faster - localized - sharp - "first" pain C= unmyelinated--slower - poorly localized/ diffuse - polymodal - "second" pain

Question 35

What types of fibers are associated with the cutaneous tissue?

Answer 35

A-delta & C

Question 36

How do joints and muscles differ from cutaneous tissue in regards to fiber types?

Answer 36

2x as many C fibers compared to A-delta

Question 37

What fiber types are present in the viscera?

Answer 37

Predominantly C-fibers

Question 38

What happens in the dorsal horn of the spinal cord in the transmission of pain?

Answer 38

Synapse from 1st order neuron to dorsal horn 2nd order neuron

Question 39

What tracts carry nociceptive information in the spinal cord?

Answer 39

Spinothalamic tracts

Question 40

What lamina are associated with A-delta fibers vs. C?

Answer 40

``` A-delta= Lamina I C= Lamina II & III ```

Question 41

What are WDRs?

Answer 41

Polymodal second order neurons that can respond to noxious stimuli and other stimuli

Question 42

What NT is being release at the synapse between first & second order neurons in the spinal cord? What receptors are on the second order dendrite?

Answer 42

Glutamate= - NMDA - AMPA

Question 43

Recall, what kind of threshold do A-delta & C fibers have?

Answer 43

High-threshold

Question 44

What is central sensitization?

Answer 44

Amplification of pain signaling in the spinal cord

Question 45

What is secondary hyperalgesia?

Answer 45

Prolonged & increased activation of nocicpetors in the periphery & projection pathways in the spinal cord - Recruitment of adjacent areas - Increased release of NT

Question 46

What NT & receptor type underlies secondary hyperalgesia?

Answer 46

Glutamate & NMDA-R

Question 47

What is neuronal plasticity?

Answer 47

Modulation of intracellular signaling & changes in gene expression

Question 48

What does neuronal plasticity underlie in respect of pain?

Answer 48

Memories of pain & the lasting effects of chronic pain

Question 49

What sensations are carried by the DC/ML?

Answer 49

Discriminative Touch | Proprioception

Question 50

What sensations are carried by the AL system?

Answer 50

Temp. Pain Crude touch

Question 51

What is the neospinothalamic tract?

Answer 51

- Pathway of pain from A-delta fibers | - Lamina I, IV, V

Question 52

What information is carried by the neospinothalamic tract?

Answer 52

Sensory-discriminative

Question 53

What is the paleospinothalamic tract?

Answer 53

- Slow type C fibers | - Lamina II, III, V

Question 54

What information is carried by the paleospinothalamic tract?

Answer 54

Emotional/ affective

Question 55

What is the function of the spinoreticular tract in pain?

Answer 55

Motor response to pain i.e. descending pain control

Question 56

What is the function of the spinomesencephallic tract in pain?

Answer 56

Descending pain control, particularly eye movements and regulation of gaze to site of injury via the superior colliculus

Question 57

Where in the brain does the perception of pain occur?

Answer 57

Sensory= somatosensory association cortex Emotional= insular cortex & anterior cingulate cortex Cognitive= prefrotnal cortex

Question 58

What does the anterior cingulate cortex (ACC) contribute in terms of pain?

Answer 58

Attention to pain *****Conscious activation of the ACC can dampen pain signaling

Question 59

When is the ACC most active?

Answer 59

1) Perception of pain 2) Imagining pain 3) Observation of pain in others

Question 60

What is the Gate Control Theory?

Answer 60

Generally, this is distraction | - A-beta (mechanoreceptor/ proprioceptor) activation inhibits C-fiber transmission

Question 61

What is descending pain control?

Answer 61

Endogenous mechanism in the body to regulate pain