23: Sensory Phys And Pain

Question 1

What determines how much a fiber contributes to a compound AP?

Answer 1

Conduction velocity

Question 2

Two types of skin (thick and thin)

Answer 2

Thick: glabrous
Thin: hairy

Question 3

Receptor adaptation

Answer 3

When a stimulus persists unchanged for a period of time, the neural response diminishes and sensation is lost

Question 4

Slowly vs rapidly adapting receptors

Answer 4

Slow: respond to prolonged and constant stimulus - you feel it the whole time
Rapid: respond only at the beginning or end of a stimulus

Question 5

Receptive field

Answer 5

Area of innervation where individual mechanoreceptors fibers convey info from a limited area of skin

Question 6

What does 2-point discrimination test?

Answer 6

Tactile acuity

Question 7

Where is tactile acuity highest?

Answer 7

Fingertips, lips (small receptive fields)

Question 8

What principle describes why phantom limb pain exists?

Answer 8

Law of Projection

Question 9

Law of Projections

Answer 9

No matter where along the afferent pathway a stimulation is applied, the perceived sensation arises from the origin of sensation

Question 10

Pain vs nociception

Answer 10

Pain: unpleasant sensory and emotional experience associated with actual or potential tissue damage
Nociception: neural process encoding noxious stimuli, without pain necessarily being implied

Question 11

Consequences of nociception

Answer 11

Can be autonomic (ex: elevate BP) or behavioral (ex: motor withdrawal reflex)

Question 12

Hypersensitivity

Answer 12

Increased responsiveness of nociceptive neurons to their normal input

Question 13

Hyperaesthesia

Answer 13

Increased sensitivity to stimulation, excluding special senses

Question 14

Hyperalgesia

Answer 14

Increased pain from a stimulus that normally provokes pain

Question 15

Allodynia

Answer 15

Pain due to stimulus that does not normally provoke pain (ex: laying on sheets while sunburnt)

Question 16

Myelination of C fibers vs A(delta) fibers

Answer 16

C fibers: unmyelinated

A(delta): myelinated

Question 17

Three types of pain characterization/nociceptor modalities

Answer 17

1. Mechanical
2. Chemical
3. Thermal

Question 18

Two reasons we have referred pain

Answer 18

1. Brain requires experience to localize pain - visceral pain is not typically experienced early in development to train the brain to localize it
2. Afferents converge in dorsal horn

Question 19

What does TRP stand for?

Answer 19

Transient receptor potential

Question 20

What type of receptors are TRPs?

Answer 20

Ligand gated non-selective cation channels (for Ca, Na, K)

Question 21

What happens when a TRP V1 is activated?

Answer 21

AP occurs + neuropeptides are released -> further signaling occurs -> vasodilation and immune cell recruitment -> inflammation

Question 22

Two fiber types in nociceptors

Answer 22

C fibers and A(delta) fibers

Question 23

What type of receptor is a nociceptor

Answer 23

Free nerve endings

Question 24

Two types of free nerve endings

Answer 24

Peptidergic: expresses neuropeptides

Non-peptidergic: does not express neuropeptides

Question 25

Two neuropeptides expressed by peptidergic free nerve endings

Answer 25

Substance P, CGRP

Question 26

Where are peptidergic free nerve endings found vs non-peptidergic?

Answer 26

Peptidergic: most visceral afferents + 1/2 of cutaneous afferents
Non-peptidergic: few visceral + 1/2 of cutaneous afferents

Question 27

Peptidergic free nerve endings are involved in what?

Answer 27

Chronic inflammation, visceral pain

Question 28

What are non-peptidergic free nerve endings involved in?

Answer 28

Somatic chronic pain states (ex: diabetic neuropathy)

Question 29

Neuropeptides released by C fibers and A(delta) fibers

Answer 29

A(delta): EAA

C fibers: EAA, SP/CGRP

Question 30

Two ways nociception is modulated

Answer 30

1. Local system: gate control theory

2. Descending inhibition: dampens on way up to cortex

Question 31

Most powerful form of inhibitory control of all primary afferent fibers

Answer 31

Pre-synaptic inhibition

Question 32

What happens in presynaptic inhibition?

Answer 32

1. GABAergic associated influx of Cl into axon
2. Hyperpolarization
3. Less Ca enters cytosol
   4 .less NT release

Question 33

Six steps of descending inhibition

Answer 33

1. PAG activated by opiates, EAA, and cannabinoids
2. Descending projections -> locus ceruleus + raphe nucleus
3. Serotonin and NE released into dorsal horn -> activate inhibitory interneurons
4. Local inhibitory interneurons release opiates
5. Opiates activate mu receptors on pre-synaptic terminals of C-fiber
6. Reduction of SP from C-fiber, reduces nociception

Question 34

Central vs peripheral sensitization

Answer 34

Central: post-injury hypersensitivity due to neuronal plasticity in the CNS
Peripheral: neuroplastic chnages in function, chemical profile, or structure of the PNS involving the receptors, ion-channels, and nt expression levels

Question 35

Central inflammation

Answer 35

Pro-inflammatory signals from glial cells that contribute to central sensitization

Question 36

What causes peripheral sensitization

Answer 36

Inflammatory soup due to injured tissues - sensitized nociceptors

Question 37

What factors of sensitization play a role in chronic pain

Answer 37

Both peripheral and central sensitization

Question 38

Insular cortex functions

Answer 38

1. Interpreting nociception
2. Processing info about internal state of body
3. Autonomic response to pain
4. Integrates all signals related to pain

Question 39

What does damage of insular cortex cause?

Answer 39

Asymbolia

Question 40

Asymbolia

Answer 40

Altered experience of pain

Question 41

What is the amygdala important for with pain?

Answer 41

Emotional component of pain