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Neurophysiology Final > Neurophysiology of Nociception: Sensory Transduction > Flashcards

Neurophysiology of Nociception: Sensory Transduction Flashcards

1
Q

The processing of nociceptive information is accomplished via?

A

electrochemical reactions that occur along specific nociceptive pathways

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2
Q

Can the perception of pain occur without nociception?

A

YES

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3
Q

What are the 4 distinct neurophysiological events of nociception?

A

Transduction
Transmission
Modulation
Perception

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4
Q

What is transduction?

A

converting noxious stimuli into electrochemical impulses

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5
Q

What is transmission?

A

transmitting electrochemical impulses along afferent fibers to various nervous system regions

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6
Q

What is modulation?

A

altering the perception of noxious stimuli by peripheral or central mechanisms

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7
Q

What is perception?

A

the conscious experience of pain created by the interpretation of nociceptive information by higher centers of the CNS

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8
Q

What is sensory transduction?

A

the process in which information from various forms of noxious stimuli (chemical, thermal and/or mechanical) is transformed into electrochemical energy by sensory nerve ending (nociceptors)

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9
Q

Nociceptors are free nerve endings of what?

A

specialized afferent fibers

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10
Q

Nociceptors respond to?

A

intense, noxious stimuli

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11
Q

The primary cell bodies of neurons carrying noxious info from the body are located where?

A

in dorsal root ganglia (DRG)

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12
Q

Primary cell bodies of neurons carry noxious info from the face are located where?

A

trigeminal ganglia

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13
Q

All nociceptive neurons utilize what as primary neurotransmitters?

A

glutamate and substance P

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14
Q

What are the properties of peripheral nociceptor fibers?

A

myelinated A delta and unmyelinated C fibers

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15
Q

Myelinated nociceptors (20%)

A
  • A delta fiber group
  • Large myelinated axons
  • conduct at ~20 m/s
  • Bimodal: respond to noxious mechanical & thermal stimuli
  • Small receptive fields (clusters of sensitive spots)
  • Project to lamina I of spinal cord grey
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16
Q

Unmyelinated nociceptors (80%)

A
  • C fiber group
  • Small axons in remak bundles
  • Conduct at ~2 m/s
  • Polymodal: respond to mechanical, thermal and chemical stimuli
  • Large receptive fields
  • Project to lamina II and III of spinal cord grey
17
Q

Myelinated bimodal nociceptors (A delta):

What is the adequate noxious stimuli for activation?

A

Mechanical: > 10 grams of pressure
Thermal: Heat (>45 C); Cold (11° C)

18
Q

Unmyelinated polymodal nociceptors (C fiber):

What is the adequate noxious stimuli for activation?

A

Mechanical: >10 grams of pressure
Thermal: Heat (>45 C); Cold (11° C)
Chemical: numerous substances

19
Q

What is the perception of first and second pain?

A

pain perception has been described:

- A first sharp pain and a more delayed diffuse and longer-lasting second pain

20
Q

What fiber will be activated when intensity of a stimulus initially reaches the threshold of nociception?

A

Fast-conducting A-delta fibers

- producing a sharp painful sensation (first pain)

21
Q

If a noxious stimulus persists which fibers are then activated? and what is there response?

A

Slowly adapting C-fibers will be activated

- producing a less well-localized pain of a dull quality

22
Q

How fast do A-delta and C-fibers deactivate?

A
  • A-delta fibers rapidly deactivate

- C-fibers deactivate slowly –> extending sensation of dull pain

23
Q

Somatosensory quality (modality) processing form?

A 
Receptor type (transduction)
- i.e. temp, pressure, pain
24
Q

Somatosensory intensity (magnitude) processing form?

A

Impulse (frequency)

- i.e. light or heavy pressure

25
Q

Somatosensory spatial (location) processing form?

A

Receptive field

- i.e. superficial or deep, on leg or arm

26
Q

After an injury to peripheral tissue, numerous chemical substances are released, what is the functional purpose of this?

A

Inflammatory response to protect the injured area (by inducing hyperalgesia and allodynia) and also to promote healing and guard against infection

27
Q

What else may also result with peripheral inflammation?

A

inflammatory and neuropathic pain

28
Q

What two mechanisms can inflammation enhance the perception of pain?

A
  1. Modifying the degree of nociceptor activation/excitation

2. Sensitization of nociceptors (peripheral sensitization)

29
Q

What does modifying the degree of nociceptor activation/excitation result in?

A

an increased transmission of nociceptive information and enhanced perception of pain

30
Q

What does sensitization of nociceptors (peripheral sensitization) result in?

A

Increased responsiveness (due to decreased threshold of excitation) to either thermal, mechanical, or chemical stimuli that may be translated to nociceptive information

31
Q

What is peripheral sensitization?

A

increased sensitivity of a peripheral nociceptor to nociceptive stimuli (lowered threshold) which results in subsequent hyperalgesia and allodynia

32
Q

What cellular mechanisms underly the sensitized state of peripheral nociceptors?

A
  • Increased expression of Na ion channels

- R/c up regulation along the afferent fibers

33
Q

When can peripheral sensitization occur?

A
  • Exposure to inflammatory mediators

- Repeated application of noxious stimulus

34
Q

K+ ion & histamine (origin and action)

A

O- escape from damaged cells

A- Activate polymodal nociceptors

35
Q

Prostaglandins (origin and action)

A

O- Synthesized by enzymes released from substrates created by tissue damage
A- Sensitize nociceptors

36
Q

Bradykinin, 5HT & ATP (origin and action)

A

O- Arrive following plasma effusion or lymphocyte migration

A- Activate and sensitize nociceptors

37
Q

Substance P, calcitonin gene-related peptide (CGRP) (origin and action)

A

O- Secreted by nociceptor activity

A- Contribute to inflammatory response by initiating release of other substances

Neurophysiology Final (10 decks)

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