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NE Exam 2 > Sensory Physiology > Flashcards

Sensory Physiology Flashcards

1
Q

Sensory (Afferent) Fiber Type: Aα
(1) Classification:
(2) Fiber Diameter:
(3) Conduction Velocity:
(4) Receptor Supplied:

A

(1) Ia and Ib
(2) Large
(3) 80-120 (fast)
(4) Primary muscle spindles, golgi tendon organs

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2
Q

Sensory (Afferent) Fiber Type: Aβ
(1) Classification:
(2) Fiber Diameter:
(3) Conduction Velocity:
(4) Receptor Supplied:

A

(1) II
(2) Medium-Large
(3) Medium-Fast
(4) Secondary muscle spindles, skin mechanoreceptors

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3
Q

Sensory (Afferent) Fiber Type: Aδ
(1) Classification:
(2) Fiber Diameter:
(3) Conduction Velocity:
(4) Receptor Supplied:

A

(1) III
(2) Medium-Small
(3) Medium-Slow
(4) Skin mechanoreceptors, thermal receptors, nociceptors

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4
Q

Sensory (Afferent) Fiber Type: C
(1) Classification:
(2) Fiber Diameter:
(3) Conduction Velocity:
(4) Receptor Supplied:

A

(1) IV
(2) Small
(3) 0.5-2 (slow)
(4) Skin mechanoreceptors, thermal receptors, nociceptors

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5
Q

Motor (Efferent) Fiber Type: Aα
(1) Fiber Diameter:
(2) Conduction Velocity:
(3) Receptor Supplied:

A

(1) Biggest
(2) Fastest
(3) Extrafusal skeletal muscle fibers

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6
Q

Motor (Efferent) Fiber Type: A
(1) Fiber Diameter:
(2) Conduction Velocity:
(3) Receptor Supplied:

A

(1) Medium-Big
(2) Medium-Fast
(3) Intrafusal muscle fibers

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7
Q

Motor (Efferent) Fiber Type: B
(1) Fiber Diameter:
(2) Conduction Velocity:
(3) Receptor Supplied:

A

(1) Medium-Small
(2) Medium-Slow
(3) Preganglionic autonomic fibers

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8
Q

Motor (Efferent) Fiber Type: C
(1) Fiber Diameter:
(2) Conduction Velocity:
(3) Receptor Supplied:

A

(1) Small
(2) Slow
(3) Posterganglionic autonomic fibers

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9
Q

Receptor Adaptation

A

When a stimulus persists unchanged for several minutes without a change in position or amplitude, the neural response diminishes and sensation is lost over time

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10
Q

Slowly Adapting Receptors

A

Receptors that respond to prolonged and constant stimulation; continues to fire APs thru entire duration of stimulus

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11
Q

Rapidly Adapting Receptors

A

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

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12
Q

Mechanoreceptors

A

Cutaneous and subcutaneous; involved in touch, pressure, vibration and pain

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13
Q

What are the 6 Mechanoreceptors?

A

(1) Meissner Corpuscle
(2) Pacinian Corpuscle
(3) Ruffini Corpuscle
(4) Merkel Cell
(5) Hair-follicle Receptor
(6) Tactile Free-Nerve Ending

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14
Q

Meissner Corpuscle
(1) Receptor Type:
(2) Location:
(3) Sensation:

A

(1) Low-threshold, rapidly adapting
(2) Glaborous skin
(3) Touch and vibration less than 100 Hz, flutter and tapping

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15
Q

Pacinian Corpuscle
(1) Receptor Type:
(2) Location:
(3) Sensation:

A

(1) Low-threshold, rapidly adapting
(2) Hairy and glabrous skin
(3) Rapid indentation of the skin such as that during high-frequency vibration (100-400Hz); vibration

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16
Q

Ruffini Corpuscle
(1) Receptor Type:
(2) Location:
(3) Sensation:

A

(1) Low-threshold, slowly adapting
(2) Hairy and Glabrous skin
(3) Magnitude and direction of stretch, touch and pressure and proprioception

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17
Q

Merkel Cell
(1) Receptor Type:
(2) Location:
(3) Sensation:

A

(1) Low-threshold, slowly adapting
(2) Glabrous skin
(3) Pressure

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18
Q

Hair-Follicle Receptor
(1) Receptor Type:
(2) Sensation:

A

(1) Rapidly and slowly adapting
(2) Motion across the skin and directionality of that motion

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19
Q

Tactile-Free Nerve Ending
(1) Receptor Type:
(2) Sensation:

A

(1) High threshold, slowly adapting
(2) Pain and temperature

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20
Q

Receptor Fields

A

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

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21
Q

2-Point Discrimination

A
  • Allows for spatial resolution of detailed textures
  • Tactile acuity is highest in fingertips and lips (smallest receptive fields)
  • Tactile acuity is lowest in calf, back and thigh (largest receptive fields)
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22
Q

S1 (Primary Somatosensory Cortex) is involved in:

A

Integration of the information for position sense as well as size, shape discrimination

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23
Q

S2 (Secondary Somatosensory Cortex)

A
  • Located in wall of the sylvian fissure
  • Receives input from S1
  • Somatotopic representation (less detailed)
  • Cognitive touch
  • Comparisons between objects, different tactile sensations and determining whether something becomes a memory
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24
Q

Parieto-Temporal-Occipital Association Cortex

A
  • High level interpretation of sensory inputs
  • Receives input from multiple sensory areas
  • Analyzes spatial coordinates of self in environment
  • Names objects
  • Many more functions…
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25
Q

Phantom Limb Pain

A
  • Pain in a body part that is no longer present, which occurs in many amputees
  • Pathophysiology not well known but believe it involves the Law of Projection
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26
Q

Law of Projection

A

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

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27
Q

Pain

A
  • Feeling
  • Unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage
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28
Q

Nociception

A
  • Signal
  • Neural process of encoding noxious stimuli (stimulus that is damaging or threatens damage to normal tissue)
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29
Q

Hypersensitivity

A

Increased responsiveness of nociceptive neurons to their normal input, and/or recruitment of a response to normally subthreshold inputs; signal is heightened above and beyond what it should be

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30
Q

Hyperaethesia

A

Increased sensitivity to stimulation, excluding the special senses

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31
Q

Hyperalgesia

A

Increased pain from a stimulus that normally provokes pain

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32
Q

Allodynia

A
  • Pain due to a stimulus that does not normally provoke pain
  • Ex. Lay of sheets on skin that has been sunburned
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33
Q

Phase One of Pain Response

A
  • Only Aδ fibers (first response to pain)
  • Pain described as sharp
34
Q

Phase Two of Pain Response

A
  • Only C-Fibers
  • Pain described as throbbing
35
Q

Biphasic Pain Response

A
  • Combination of C- and Aδ fibers
  • Reason why when you smash your finger with a hammer, there is an initial sharp pain followed by a dull, throbbing pain that lasts quite a while
36
Q

Nociceptors

A
  • Used to signal pain characteristics
  • A high threshold sensory receptor of the peripheral somatosensory nervous system that is capable of transducing and encoding noxious stimuli
37
Q

Nociceptor Modality: Mechanical

A

Response to mechanical forces ranging from moderate pressure with a blunt object to overtly tissue-damaging stimuli

38
Q

Nociceptor Modality: Chemical

A

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

39
Q

Nociceptor Modality: Thermal

A

Response to noxious heat and cold will directly activate thermal receptors expressed by nociceptors

40
Q

Stimuli Required to Activate Nocicpetors in Skin

A
  • Thermal: hot or cold
  • Mechanical: cutting, pinching, crushing)
  • Chemical: inflammatory and other mediators released from or synthesized by damaged skin, and exogenous chemical stimuli such as formalin, carrageenan, bee venom, capsaicin
41
Q

Stimuli Required to Activate Nocicpetors in Joints

A
  • Mechanical: rotation, torque beyond the joints normal ROM
  • Chemical: inflammatory and other mediators released into or injected into the joint capsule
42
Q

Stimuli Required to Activate Nocicpetors in Muscle

A
  • Mechanical: blunt force, stretching, crushing, overuse
  • Chemical: inflammatory and other mediators released from or injected into muscle
43
Q

Stimuli Required to Activate Nocicpetors in Viscera

A
  • Mechanical: distension, traction on the mesentery
  • Chemical: inflammatory and other mediators released from inflamed or ischemic organs, inhaled irritants
44
Q

2 Reasons why 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 onto common set of secondary neurons in the dorsal horn

45
Q

TRP Receptors

A
  • Transient Receptor Potential family of receptors
  • Sense noxious stimuli – located on nociceptors
  • Ligand-gated non-selective cation channel permeable to Ca++, Na+ and/or K+
46
Q

TRPV1

A
  • Expressed by many C fibers
  • Sensitive to vanilloid compounds (i.e capsaicin)
  • Also activated by endogenous substances, especially the inflammatory mediator, bradykinin and by heat greater than 43 C
  • Involved in many pain conditions likes migraine, dental pain, cancer pain, inflammatory pain, neuropathic pain, visceral pain, and OA
47
Q

Activation of TRPV1

A
  • Activation in peripheral sensory nerve fibers leads to AP firing and the release of neuropeptides
  • Sustained activation leads to further signaling molecule release, which leads to vasodilation and immune cell recruitment and inflammation
48
Q

TRPA1

A
  • Many modulators, regulators of function, and agonists, but some include mustard oil (allyl isothiocyanate), wasabi, horseradish
  • Involved in inflammatory pain states like allergic contact dermatitis, chronic itch, painful bladder syndrome, migraine, IBS, pancreatitis
49
Q

Anesthetics often have paradoxical pro-nociceptive effects by acting through:

A

TRPA1

(means the anesthetic actually produces pain instead or reducing it)

50
Q

TRPM8

A
  • Activated by both innocuous cooling (26-15 C) and noxious cold (15-8 C) temperatures as well as by “cooling agents” such as camphor or menthol which are commonly used for their analgesic properties (i.e VapoRub, Orajel, Biofreeze)
51
Q

Axons of nociceptors have ___ Fibers or ___ fibers that are not associated with specific structures or cell types —> Free Nerve Endings

A
  • C Fibers
    (slow conducting, unmyelinated)
  • Aδ Fibers
    (thinly myelinated, axons with peripheral terminals)
52
Q

Free Nerve Endings

A
  • Lack specialized receptor cells or encapsulations
  • Characterization can be broken down by molecular markers: Peptidergic vs Non-Peptidergic
53
Q

Free Nerve Endings: Peptidergic

A
  • Express Neuropeptides Substance P and CGRP
  • Most visceral afferents and half of cutaneous afferents
  • Involved in chronic inflammation, visceral pain
  • Chronic inflammation upregulates neuropeptides
54
Q

Free Nerve Endings: Non-Peptidergic

A
  • Does not express CGRP or SP neuropeptides
  • Very few visceral afferents are non-peptidergic
  • Half of cutaneous afferents are non-peptidergic
  • Involved in somatic chronic pain states such as that of diabetic neuropathy
55
Q

Gate Control Theory of Pain

A
  • Interrupt pain signals with another input
  • Ex. Rubbing the spot that hurts to ease the pain
56
Q

Descending Inhibition

A
  • Dampens input on its way up to the cortex
  • Pre-synaptic inhibition is a type of descending inhibition
57
Q

Central Sensitization
(1) Location:
(2) Part Affected:
(3) Mechanism:
(4) Result:

A

(1) CNS: Brain or spinal cord
(2) Synapses between neurons; ‘synaptic plasticity’
(3) Inflammation – central inflammation from microglia (Glial cells)
(4) Reduced threshold, increased sensitivity, elevated or chronic pain

58
Q

Peripheral Sensitization
(1) Location:
(2) Part Affected:
(3) Mechanism:
(4) Result:

A

(1) PNS
(2) Free nerve endings / nociceptor perohperal terminals; ‘neuroplasticity’
(3) Inflammation in the periphery from a variety of immune cells – inflammatory soup, bradykinin and prostaglandin E2 (PGE2)
(4) Reduced threshold, increased sensitivity, elevated or chronic pain

59
Q

Afferent C Fibers: NT

A

EAA and SP/CGRP

60
Q

Afferent Aδ Fibers: NT

A

EAA

61
Q

Central and Peripheral Sensitization lead to ___ pain

A

worsened

62
Q

Gate Control Theory of Pain and Descending Inhibition ___ pain

A

improve

63
Q

Nociceptors are modulated by:

A

Descending systems and interneurons in Dorsal Horn

64
Q

Gate Control Theory of Pain: Gate Closed

A

No pain sensed because inhibitory internueorn blocks nociceptive signal from continuing to move forward

65
Q

Gate Control Theory: 3 Steps

A

(1) Activate Aβ fiber w/ normal stimuli –> central process branches in dorsal horn and synapses on inhibitory interneuron –> EAA released
(2) Activated interneuron releases glycine –> inhibits secondary sensory neuron of nociceptive pathway
(3) Rubbing area of affected skin activates Aβ and reduces pain sensation

66
Q

Primary afferent NT is controlled by:

A

Pre- and Post-synaptic inhibitory mechanisms

67
Q

Presynaptic Inhibition

A

(1) GABAergic associated influx of Cl- into axon
(2) Hyperpolarization
(3) Less Ca++ enters cytosol
(4) Less NT release

68
Q

Descending Inhibition

A

(1) PAG activated
(2) Descending projections to Locus Coeruleus and Raphe Nucleus
(3) Serotonin and NE released into dorsal horn –> activate inhibitory interneurons
(4) Local inhibitory interneurons release opiates
(5) Opiates activated mu receptors on pre-synaptic terminals C-fiber
(6) Reduction SP from C-fiber –> reduced nociception

69
Q

What activates PAG?

A
  • Opiates
  • EAA
  • Cannabinoids
  • Higher brain regions
70
Q

Locus Coeruleus

A

NE

71
Q

Raphne Nucleus

A

Serotonin

72
Q

2 Roles of Descending Serotonergic and NE neurons:

A

(1) Activate local interneurons
(2) Supress spinothalamic projection neurons

73
Q

Which regions of the brain receive input from nociceptors and play a role in pain localization?

A

S1 and S2

74
Q

S1

A

Identify size and shape of object via touch

75
Q

S2

A
  • “Cognitive touch”
  • Compares objects by touch alone
76
Q

Insular Cortex

A
  • Important in interpretation of nociception
  • Processes information about internal state of body
  • Contributes to autonomic response to pain
  • Integrates all signals related to pain
77
Q

Damage of Insular Cortex causes:

A

Asymbolia
(inability to recognize the unpleasant or disagreeable component of a painful or threatening stimulus, with the result that little or no defense reaction is produced, although the noxious stimulus itself is perceived)

78
Q

Lesions in a single area of the ___ alters the experience of pain, but does not abolish it completely

A

Insula

79
Q

Amygdala

A

Important in the emotional part of pain

80
Q

Visceral input travels with ___ nerves to the ___ and the ____, integrating physiological changes associated with visceral pain

A
  • Autonomic
  • Hypothalamus
  • Medulla

NE Exam 2 (19 decks)

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