05b: Somatosensation and Pain

Question 1

List various sensory receptor types, from deep to superficial

Answer 1

1. Pacinian corpuscles
2. Ruffini’s corpuscles
3. Merkel’s disks
4. Meissner’s corpuscles
5. Free nerve endings

Question 2

T/F: All classes of cutaneous sensation are represented among the free nerve endings.

Answer 2

True

Question 3

Two-point discrimination smaller on (fingertips/back)

Answer 3

Fingertips

Question 4

Central neurons, (like/unlike) receptors, use (X) mechanism for transmitting info about a stimulus intensity.

Answer 4

Like;

X = frequency coding

Question 5

(Primary afferent fibers/central neurons) have complex receptive fields. Explain.

Answer 5

Central neurons;

Lateral inhibition (sharpens transmission of sensory messages)

Question 6

Detailed topographical representation of (ipsi/contra)-lateral body forms within thalamus.

Answer 6

Contralateral

Question 7

Cutaneous afferents are found within (X) regions of thalamus.

Answer 7

X = posterior

Question 8

T/F: Pain is always subjective.

Answer 8

True

Question 9

T/F: Pain is always unpleasant.

Answer 9

True

Question 10

T/F:Pain is activity induced in nociceptor/nociceptive pathway by noxious stimulus.

Answer 10

False - pain is psych state

Question 11

T/F: Noxious stimulus is defined as one that produces tissue damage.

Answer 11

True

Question 12

List 3 classes of nociceptors.

Answer 12

1. Mechanical
2. Thermal
3. Polymodal

Question 13

Mechanical nociceptors respond to (X) stimuli and have (small/large) receptive fields.

Answer 13

X = crushing P

Large

Question 14

Thermal nociceptors respond to (X) stimuli and have (small/large) receptive fields.

Answer 14

X = temperatures above 45C or below 15C

Large

Question 15

Polymodal nociceptors respond to (X) stimuli and have (small/large) receptive fields.

Answer 15

X = both high threshold mechanical and thermal stimulation;

Large

Question 16

(X) caused by (Y) provide(s) the principal stimulus for nociceptor activation.

Answer 16

X = chemicals;
Y = release from damaged tissue (into extracellular fluid)

Question 17

List some “pain related molecules”. Star those that sensitize all classes of nociceptors.

Answer 17

1. Bradykinin
2. Substance P
3. Histamine
4. K+
5. Prostaglandins*

Question 18

A noxious stimulus evokes release of (X) from (Y). Be specific.

Answer 18

X = Bradykinin
Y = damaged tissue

Question 19

List effect(s) of bradykinin.

Answer 19

1. Excites nociceptor
2. Increases prostaglandin production
3. Dilates blood vessels

Question 20

You step on a nail. In response to (excitatory/inhibitory) actions of (Y), the nociceptor terminal releases (X).

Answer 20

Excitatory;
X = bradykinin and prostaglandins;
Y = substance P

Question 21

You step on a nail. Effect of Substance P, when released from (X).

Answer 21

X = nociceptor terminal

1. Further sensitizes nerve terminal
2. Increases blood vessel dilation
3. Increases inflammatory response

Question 22

T/F: Similar to other receptors, nociceptors adapt with frequent stimulation.

Answer 22

False - sensitize with frequent stimulation

Question 23

Pain is subserved primarily by which peripheral nerve fiber types?

Answer 23

1. A-delta

2. C

Question 24

In terms of conduction velocity, A-delta are the most rapid of (X) fibers, but the slowest of the (Y) fibers.

Answer 24

X = pain;
Y = A

Question 25

A-delta fibers are distributed in (X) parts of body and carry information about (Y) stimuli.

Answer 25

``` X = skin and mucous membranes Y = mechanical and thermal ```

Question 26

C fibers are distributed in (X) parts of body and carry information about (Y) stimuli.

Answer 26

``` X = deep tissues and skin Y = polymodal ```

Question 27

T/F: C fibers outnumber A-delta fibers in the skin.

Answer 27

True

Question 28

Sharp, stinging painful sensation carried by which type of pain fibers?

Answer 28

A-delta

Question 29

Burning, unpleasant painful sensation carried by which type of pain fibers?

Answer 29

C fibers

Question 30

A-delta fibers synapse in (X), on the dendrites of neurons with somata in Rexed's Laminae (Y). This gives rise to (Z) tract.

Answer 30

``` X = substantia gelatinosa Y = 1 and 5 Z = neospinothalamic ```

Question 31

Neospinothalamic tract terminates in (X). Then signal goes to (Y) cortex.

Answer 31

``` X = VPL thalamus; Y = somatosensory cortex ```

Question 32

C fibers synapse in (X), on the dendrites of (Y), which send info to cells in Rexed's Laminae (Z).

Answer 32

``` X = substantia gelatinosa Y = small, excitatory interneurons Z = 5-8 ```

Question 33

C-fibers use (X) as the NT at their synapse in substantia gelatinosa.

Answer 33

X = Substance P

Question 34

Rexed Laminae (X) give rise to paleospinothalamic tract.

Answer 34

X = 6-8

Question 35

Rexed Lamina 5 neurons, receiving input from (A-delta/C) pain fibers, contribute primarily to (X) tract.

Answer 35

C-fibers; | X = spinomesencephalic

Question 36

T/F: Both neo and paleospinoathalmic tracts are somatotopically organized.

Answer 36

False - paleo is not

Question 37

Paleospinothalamic tract terminates in (X). Then signal goes to (Y) cortex.

Answer 37

``` X = intralaminal nucleus of thalamus; Y = cingulate ```

Question 38

Collaterals from (neo/paleo)spinothalamic tracts contribute to which ascending brainstem tracts?

Answer 38

Both; 1. Spinomesencephalic 2. Spinoreticular tract

Question 39

Spinomesencephalic tract arises from neurons in lamina (X) and projects to (Y).

Answer 39

``` X = 1 and 5 Y = PAG ```

Question 40

Spinoreticular tract arises from neurons in lamina (X) and projects to (Y) via (Z).

Answer 40

``` X = 6-8 Y = thalamus Z = reticular formation ```

Question 41

WDR, aka (X), neurons are in lamina (Y). They're termed this because of which characteristic?

Answer 41

``` X = wide dynamic range; Y = 5 ``` Excited by multimodal/diverse inputs from A-beta, A-gamma, and C fibers

Question 42

WDR neurons activate (X) via (Y) tract.

Answer 42

``` X = PAG; Y = spinomesencephalic ```

Question 43

In addition to receiving pain info from WDR neurons, the (X) receives input from (Y), conveying info on emotional/physio responses to pain.

Answer 43

``` X = PAG Y = amygdala, hypothalamus, neocortical areas ```

Question 44

PAG neurons normally (stimulate/inhibit) nucleus raphe magnus (NRM).

Answer 44

Inhibit

Question 45

Enkephalin, released by (X), has (stimulatory/inhibitory) effect on (Y), thus activating (Z).

Answer 45

X = PAG neurons Inhibitory; Y = other PAG neurons Z = NRM cells

Question 46

Descending serotonergic (PAG/NRM) inputs (excite/inhibit) (X) interneurons in (brainstem/SC).

Answer 46

NRM; Excite; X = enkephalinergic SC

Question 47

Release of enkephalin in SC has which effect(s)?

Answer 47

Inhibits: 1. Afferent pain fiber activity 2. WDR activity

Question 48

Ideal way to alleviate pain is to:

Answer 48

Treat underlying disease

Question 49

Pharmacological treatment of pain is possible via:

Answer 49

1. NSAIDS | 2. Opioids

Question 50

NSAIDS mechanism

Answer 50

Inhibit cyclooxygenase

Question 51

Cyclooxygenase involved in which reaction?

Answer 51

Conversion of arachidonic acid to prostaglandin

Question 52

Give examples of commonly used NSAIDS

Answer 52

1. Ibuprofin 2. Aspirin 3. Acetaminophen