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Neuro Exam 2 > Sensory Physiology and Pain > Flashcards

Sensory Physiology and Pain Flashcards

1
Q

Peripheral Nerves are classified by two schemes

A
  1. Their contribution to a compund action potential (A, B, C waves) recorded from an entire mixed peripheral nerve
  2. Based on fiber diameter, myelin thickness, and conduction velocity (class 1, 2, 3, 4)
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2
Q

What are the sensory afferent fiber types?

A

A-alpha, A-beta, A-delta, C fibers

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3
Q

What sensory afferent fiber diameter is the largest?

What sensory afferent fiber diameter is the smallest?

A

Large = A-alpha

Small - C fiber

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4
Q

What sensory afferent fiber has the fastest conduction velocity and which sensory afferent fiber has the slowest conduction velocity?

A

A-alpha = fastest (80-120)

C fiber = slowest (.5-2)

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5
Q

What do A-alpha sensory afferent receptor supplied?

A

Primary muslce spindles and glogi tendon organ

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6
Q

What do A-beta sensory afferent receptor supplied?

A

Seconday muscle spindles, skin mechanoreceptors

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7
Q

What do A-delta sensory afferent receptor supplied?

A

skin mechanoreceptors, thermal receptors, and nociceptors

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8
Q

What do C-fibers sensory afferent receptor supplied?

A

Skin mechanoreceptors, thermal receptors, and nociceptors

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9
Q

what classification of afferent fibers is A-alpha, A-beta, A-delta, and C fibers?

A

A-alpha = 1a and 1b

A-beta= 2

A-Delta= 3

C fibers = 4

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10
Q

What are the motor efferent fiber types?

A

A-alpha, A-gamma, B, C

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11
Q

What is the motor efferent receptor supplied for A-alpha?

A

extrafusal skeletal muscle fibers

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12
Q

What is the motor efferent receptor supplied Agamma?

A

intrafusal muscle fibers

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13
Q

What is the motor efferent receptor supplied for B?

A

preganglionic autonomic fibers

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14
Q

What is the motor efferent receptor supplied for C?

A

postganglionic autonomic fibers

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15
Q

What are the two different types of skin?

A

Hairy skin - ie skin on the back of your hands

Glabrous (hairless) skin - ie the palms of the hand

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16
Q

What is receptor adaptation?

A

when a stimulus persits unchanged for several minutes without a change in position or amplitude, the neural response diminishes and sensation is lost overtime

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17
Q

Slowly adapting receptors are

A

slowly adapting receptors are receptors that respond to prolonged and constant stimulation

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18
Q

rapidly adapting receptors are

A

receptors that respond only at the beginning or end of a stimulus and are only active when stimulus intensity increases or decreases

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19
Q

Meissner corpuscle

A

low threshold, rapidly adapting

found in glaborous skin

sensation: touch and vibration less than 100 hz. fluttering and tapping

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20
Q

Pacinian corpuscle

A

low threshold, rapidly adapting

found in both hairy and glaborous skin

Sensation: Rapid indentation of the skin such as that during hgih frequency vibration (100-400 hz). Vibration.

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21
Q

Ruffini Corpuscle

A

low threshold, slowly adapting

found in both hairy and glaborous skin

Sensation: Magnitude and direction of stretch. Touch and pressure and proprioception

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22
Q

Merkel Cell

A

low threshold, slowly adapting

Found in glaborous skin

Pressure

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23
Q

Hair follicle receptor

A

rapidly and slow adapting

sensation - motion across the skin and directionality of that motion

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24
Q

Tactile free nerve ending

A

high threshold, slowly adapting

sensation- pain and temperature

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25
Q

What are receptive fields?

A

areas of innervation where individual mechanoreceptor fibers convey information from a limited area of skin

Receptive fields also vary in size

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26
Q

What is 2 point discrimination?

A

Allows for spatial resolution of detalied textures

tactile acuity is HIGHEST in fingertips and lips (smallest receptive fields)

tactile acuity is LOWEST in back and thigh and calf (large receptive fields

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27
Q

What does the sensory cortex include?

A

Senosry cortex includes primary, secondary, and associated areas

28
Q

Where is the primary somatosensory cortex (S1) located and what integration of information is involved with S1?

A

It is located in post central gyrus and it has brodmann area 3,1,2 and is somatopically organized

S1 is the first stop for most cutaneous senses and S1 is invovled in the integration of the information for position sense as well as size, shape discrimination

29
Q

where is the secondary somatosensory cortex (S2) located and what is S2 involved in the integration of information?

A

located in the wall of the sylvian fissure

receives input from S1 and has somatotopic organization but it is less organized

cognitive touch

Comparison between objects, different tactile sensations and determining whether something becomes memory

30
Q

What is the Parieto-temporal-occipital association cortex?

A

High level interpretation of sensory inputs

recieves input from multiple sensory areas

analyzes spatial coordinates of self in environment

names objects

no somatotopic organization

high level thinking - gets sensory input from all other areas

31
Q

What is phantom limb pain?

A

Phantom limb pain describes the pain in a body part that is no longer present, which occurs in many amputees

Law of projection

32
Q

What is the Law of projection?

A

Law of projections is that no matter where along the afferent pathway a stimulation is applied, the perceived sensation arises from the orgin of the sensation

33
Q

What is the definition of pain?

A

An unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage

34
Q

What is the definition of nociception?

A

The neural process of encoding noxious stimuli (a stimulus that is damaging or threatens damage to normal tissue

35
Q

What is the definition of hypersensitivity?

A

increased responsiveness of nociceptive neurons to their normal input, and or recruitment of a response to normally subthreshold inputs

36
Q

What is the definition of hyperaesthesia?

A

increased sensitivity to stimulation, excluding the special senses

doesn’t necessarily have to be nociception it can be any except for special senses

37
Q

What is hyperalgesia?

A

increased pain from a stimulus that normally provokes pain

38
Q

What is the definition of allodynia?

A

Pain due to a stimulus that does not normally provoke pain. Classic example is the lay of sheets on skin that has been sunburned

39
Q

What is the biphasic response to pain?

A

In phase 1 you have A-delta fibers so you have a big sharp peak and then you have C fibers which is a slow delated response which is dull.

Phase 1 would be described as sharp and Phase 2 would be decribed as throbbing/dull/etc

Ex. Together, this is why when you smash your thumb with a hammer, there is an initial sharp pain followed by a dull, throbbing pain that lasts quite a while

40
Q

Compare A-delta fibers to C-fibers in terms of:

diameter size

Mylination

Conduction velocity

Sensation modality

receptive field size

localization

A

A delta fibers C fibers

diameter size: 2-5 mm in diameter .4-1.2 mm

Mylination: myelinated unmyelinated

Conduction velocity fast conduction. slow conduction

Sensation modality primarily mechanical. high intens thermal and chemical (can be invovled in mechanical

receptive field size small larger

localization percise localization. imprecise localization

41
Q

Pain characterization: Nociceptor modality - Mechanical

A

response to mechanical forces ranging from moderate pressure with a blunt object to overtly tussue-damaging stimuli

42
Q

Pain characterization: nociceptor modality: Chemical

A

response to endogenous or exogenous chemical compounds, such as pro-inflammatory mediators, acids, or capsaicin, teh pungent ingredient in chili peppers

43
Q

Pain characterization: nociceptor modality: Thermal

A

response to noxious heat and cold will directly activate theremal receptors expessed by nociceptors

44
Q

What are the two reasons we have referred pain?

A
  1. Brain requires some experience to localize pain; visceral pain is not experienced often enough in early development to “train” the brain to localize it
  2. Afferents converge in dorsal horn

A delta fibers require training early in life to be able to develop percise localization and orgin of pain. we don’t get a lot of visceral pain early in life

45
Q

What are the three Transient receptor potential?

A
  • TRPV1
  • TRPA1
  • TRPM8

ligand gated non-selective cation channel permeable to Ca++, Na+, and/or K+

Upon activation you will have opening of cation channel that can allow Ca++, Na+, K+ to flow through it

46
Q

TRPV1

A

Many C fibers express transient receptor potenital vanilloid 1 (TRPV1) and are sensitive to Vanilloid compounds, ie - Capsaicin

in addition to Activation by exogenous compounds, they are activated by endogenous substances, ie - inflammatory mediator, bradykinin and. by heat greater than 43 degrees celcius

47
Q

What happens with activatin of TRPV1?

A

Activation of TRPV1 in peripheral sensory nerve fibers not only leads to AP firing but also release of neuropeptides

sustained TRPV1 activation leads to further signaling molecule release, which leads to vasodilation and immune cell recruitment of inflammation

TRPV1 is invovled with a wide variety of pain conditions including migraine, dental pain, cancer pain, inflammatory pain, neuropathic pain, visceral pain, osteoarthritis

48
Q

TRPA1

A

Active ingredient is allyl isothiocuanate: in mustard oil, wasabi, horseradish, cinammon

TRPA1 activity is also involved with a number of inflammatory pain states, including: allergic contact dermatitis, chronic itch, painful bladder syndrome, migraine, IBS, and pancreatitis

Anesthetics often have a paradoxal pro-nociceptive effects by acting through TRPA1

49
Q

TRPM8

A

TRPM8 can be activated by both innocuous cooling (26-15 degrees celcius) and noxious cold (15-8) temperatures, as well as by a number of cooling agents such as camphor or menthol, which are commonly used for their analgestic properties

ex. vicks vaporub, biofreeze, oral B orajel

50
Q

What are free nerve endings?

A

axons with peripheral terminals that are not associated with specifc structures or cell types

Free nerve endings lack specialized receptor cells or encapsulations

51
Q

Peptidergic Nocioceptors

A

Express neuropeptides: substance P and CGRP

Most visceral afferents and half of cutenaeous afferents

  • Chronic inflammation
  • Visceral Pain
  • Chronic inflammation upregulates neuropeptides
52
Q

Non-peptidergic Nocioceptors

A

Does not express CGPR or substance P

less common

invovled in somatic chronic pain states such as that of diabetic neuropathy

53
Q

EAA and SP/CGRP is for what fiber

A

C fiber

A-delta fiber only releases EAA

54
Q

Gate control theory

A

Gate is closed when there is no pain

In the absence of input from C fibers, tonicallt active inhibitory interneurons supress pain pathway

No pain is sensed because the inhibitory interneuron is blocking the nociceptive signal from continuing to move forward

55
Q

Gate control theory with pain

A

With strong pain, C fibers stops inhibition of the pathway, allowing a strong signal to be sent to the brain

56
Q

Gate control theory with pain and improving pain by rubbing or shaking finger

A

Activate an A-beta fiber by normal stimuli. the. central process of this fiber branches in the dorsal horn and synapses on an inhibitory interneuron upon which it releases EAA

the activated interneuron releases glycine and inhibits secondary sensory neuron of teh nociceptive pathway

rubbing an area of affected skin activates the A beta fiber and reduces sensation of pain

57
Q

Pre-synaptic inhibiton

A

more powerful form of inhibitory control in all promary affernet fibers

The inhibition is actually a diminished excitatory signal

  1. GABAergic assocaited influx of C1- into the axon
  2. Results in hyperpolarization
  3. less Ca2+ enters cytosol
  4. Leads to less NT release
58
Q

Descending Inhibition Pathway

A
  1. Periaqueductal gray matter (PAG) is activated by opiates, EAA, and cannabinoids
  2. Descending projections travel to: Locus Coeruleus (NE) and Raphe Nucleus (Serotonin)
  3. Serotonin and NE released into dorsal horn and acrivate inhibitory interneurons
  4. Local inhibitory interneurons release opiates (like enkephalin)
  5. Opiates activate Mu receptors on pre-synaptic (and post synaptic( terminals of C-fibers
  6. Results in a reduction of SP from teh C-fiber and reduces nociception
59
Q

Central Sensitization

A

Can be at the level of spinal cord, higher brain regions, or both

reduces threshold of involved neurons to noxious stimuli

invovles synaptic plasticity - persistent stimulation of EAA receptors and intracellular signaling

60
Q

Peripheral sensitization

A

inflammatory soup that develops in injured tissues sensitizes the nociceptor

can increase intensity and duration of pain

can come from nearby immune cells

61
Q

What does the insular cortex improtant in?

A

important in interpretation of nociception

processes info about interbal state of the body

contributes to autonmic response to pain

integrates all signals related to pain

damage causes asymbolia

62
Q

Amygdala and pain

A

is important to the emotional component to pain

63
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64
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65
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Neuro Exam 2 (3 decks)

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