lecture 21

Question 1

define somatosensation

Answer 1

mechanosensation + pain/temp sensation

Question 2

what is thermoreception?

Answer 2

sensation of temperature in environment/body

Question 3

what is nociception?

Answer 3

sensation of pain

Question 4

what are nociceptors?

Answer 4

specialized sensory neurons that responf to noxious stimuli by sending signals to the brain

Question 5

define “noxious”

Answer 5

damaging to tissue

Question 6

describe the relationship between stimulus intensity and pain intensity

Answer 6

slow build to steep curve then plateau

increases but I dont think proportionally..

Question 7

what are the 4 major types of pain?

Answer 7

• nociceptive (noxious stimuli - high threshold) (normal)
• inflammatory (lower threshold) (normal)
• neuropathic (nerve pain - lower threshold) (abnormal)
• dysfunctional (no obvious cause) (abnormal)

Question 8

define pain

Answer 8

unpleasent discriminative and emotional (affective) sensation assoicated with tissue damage

Question 9

explain TRP receptors

Answer 9

• nerve endings have channels with receptors that open in response to temperature change, depolarizing the nerve
• certain plants can bind teh receptor and open the associated channel (hot peppers - capsaicin)

Question 10

explain nociceptors

Answer 10

open due to deformation or inflammation, but can detect higher temperatures as well, cause pain

Question 11

what is first pain?

Answer 11

relatively fast conducting A(gamma) fibers mediate fast, sharp and localized pain

Question 12

what is second pain?

Answer 12

relatively slow conducting C fibers mediate a delayed, diffuse and longer-lasting pain

Question 13

describe the difference between fast and slow conducting fibers

Answer 13

slow conducting fibers are typically unmyelinated and more narrow in diameter

Question 14

how are action potentials more easily blocked along A fibers?

Answer 14

by crushing the nerve

Question 15

how are action potentials more easily blocked along C fibers?

Answer 15

by Na+ channel antagonists

Question 16

describe inflammatory pain (generally)

Answer 16

pain that occurs over the long term (mins-days) due to inflammation - which promotes constant traffic along second pain pathways (mainly C fibers)

Question 17

describe the inflammatory pain that results after damage

Answer 17

• substances, such as K, serotonin, histamine, etc., are released into damaged tissues
• these make nociceptors more sensitive
• thus, non-painful stimuli can become painful, leading to hyperalgesia and sensitization

Question 18

where is affective pain perceived?

Answer 18

percieved by neocortex that is not primary somatosensory cortex

Question 19

affective pain is mainly carried by ___ fibers?

Answer 19

C

Question 20

describe the sensation of affective pain

Answer 20

dull, throbbing, porrly localized, may be unremitting

Question 21

provide an example of affective pain

Answer 21

psycological pain of serious depression

Question 22

what is gate theory of second pain?

Answer 22

• there is interaction btwn pain reception and mechanoreception
• helps to rub toe after stub it
• essentially, nonpainful stimuli stops (closes gates for) painful stimuli
• due to inhibitory local circut neuron

Question 23

where do the first pain signals ascend to?

Answer 23

primary somatosensory cortex

Question 24

where do the second pain signals ascend to?

Answer 24

cingulate cortex and insular cortex

Question 25

summary - describe the anterolateral system pathways

Answer 25

sensory (discriminative):
spinothalamic tract –> ventral posterior nucleus –> somatosensory cortex (S1, S2)

affective (motivational):
spinothalamic tract –> midline thalamic nuceli –> anterior cingulate cortex/insular cortex
OR
spinothalamic tract –> amygdala, hypothalamus, periaquaductal gray, superior colliculus, reticular formation

Question 26

define hyperalgesia

Answer 26

heightened sense of pain to noxious stimuli

Question 27

define allodnyia

Answer 27

pain resulting from normally painless stimuli

Question 28

what does allodnyia result from?

Answer 28

(hypothesized to be) the development of altered central pathways being activated by the surviving afferent nerves

Question 29

what does neuropathic pain result from?

Answer 29

complete or partial nerve transection or compression

Question 30

phantom limb is an example of which type of pain?

Answer 30

neuropathic

Question 31

explain how phantom limb arises

Answer 31

when arm or leg has been removed bc of illness/injury, but the brain still gets pain messages from the pathway that origionally carried impulses from the missing limb
-i.e., altered proprioceptiv/pain pathways and cortical reorganization are the cause

Question 32

what are some common causes of neuropathic pain?

Answer 32

diabetes, injury or trauma to PNS/CNS, MS, HIV infection, chemotherapy

Question 33

patients with congenital limb deficiency may also experince phantom limb sensations, what does this suggest?

Answer 33

there is an innate central representation of the limbs in the primary sensory cortex

Question 34

what is reffered pain?

Answer 34

pain perceived on the body’s surface at a site distant from the actual site of injury/inflammation

Question 35

pain from viscera is commonly reffered where? explain why.

Answer 35

• to the surface of the body
• dorsal horn neurons receive input from primary afferent neurons from both the surface and viscera
• by some unclear mechanism, the visceral input is transferred to the somatic pathway

Question 36

describe some remedies for pain relief

Answer 36

• drugs
• rhizotomy (snip dorsal root)
• chordotomy (snip spinal tracts for pain)
• cingulotomy (remove anterior cingulate cortex)
• spinal cord stimulation

Question 37

recap - axon input from pain goes where?

Answer 37

spinothalamic tract to periaquaductal gray (PAG) and reticular formation (RF)

Question 38

describe central regulation of ascending pain

Answer 38

descending pathways from the cortex, hypothalamus and amygdala send relays through PAG and raphne nuclei in the RF - which dampens ascending pain activity in the spinothalamic tract

Question 39

describe the role of endogenous opiods in the central regulation of pain

Answer 39

• endogenous opiods (codeine, morphine, heroin)
• bind g-coupled protein receptors (opiod receptors) to releive pain
• involved in gating

Question 40

is the placebo affect a real physiological procces? why or why not?

Answer 40

yes - placebo pills can reduce pain and can be blocked by naloxone (comp. agonist of opiod receptors)

Question 41

how is the right prefrontal cortex involved in placebo?

Answer 41

• RPRC is associated with the inhibition of affective thought and behaviour
• placebo increases RPRC response to pain, & improves symptoms

Question 42

how is the anterior cingulate cortex involved in placebo?

Answer 42

• associated with sensing affective pain

- placebo decreases ACC reactivity to pain, & improves symptoms

Question 43

describe the relationship btwn the right prefrontal cortex and the anterior cingulate gyrus with respect to the placebo effect

Answer 43

negatively correlated (one increases, other decreases)

Question 44

summarize the placebo pathway

Answer 44

• cortical beleif caused by placebo activates right prefrontal cortex
• rpfc is though to inhibit anterior cingulate cortex
• reduced acc means increased descending control of ascending pain
• results in symptom improvement

Question 45

explain reflexology

Answer 45

• whole body is mapped to feet

- pressure is applied to feet to releive pain

Question 46

explain magnet therapy

Answer 46

magnets applied to body to reset the magnetic field

Question 47

explain homeopathy

Answer 47

tiny amounts of natural substances (herbs, etc.) or drugs are used to promote healing