Nociceptive Pathway

1
Nociceptive Pathway

• By
• Sitthichai Wanachantararak

2
Pain

• There are several aspects associated with pain
• Sensory-discriminative aspects location,
  intensity, duration of the pain
• Motivational-affective dimension unpleasant
  feeling associated with pain.
• Pain has an urgency.
• Pain can be modulated by behavioral experiences.
• There are neural mechanisms that can modulate
  pain transmission and the emotional reaction to
  pain.

3
Pain
The subjects conscious perception of modulated
nociceptive impulses that generate an unpleasant
sensory and emotional experience associated with
actual or potential tissue damage, or described
in terms of such damage (IASP definition, 1994)

• The subjects conscious perception of modulated
  nociceptive impulses that generate an unpleasant
  sensory and emotional experience associated with
  actual or potential tissue damage, or described
  in terms of such damage
• (IASP definition, 1994)

The subjects conscious perception of modulated
nociceptive impulses that generate an unpleasant
sensory and emotional experience associated with
actual or potential tissue damage, or described
in terms of such damage (IASP definition, 1994)
The subjects conscious perception of modulated
nociceptive impulses that generate an unpleasant
sensory and emotional experience associated with
actual or potential tissue damage, or described
in terms of such damage (IASP definition, 1994)
4
4 processes of pain sensation

• Transduction receptors
• Transmission
• Primary afferent neuron (first order)
• Secondary order neuron
• Interaction of neuron netween the thalamus,
  cortex and limbic system
• Modulation
• Perception

5
Sensory Receptors

• Exteroceptor surface of skin and mucosa
• Merkels corpuscle, Meissners corpuscle, Kruses
  corpuscle or end bulbs, Free nerve ending
• Proprioceptors skeletal muscle for control
  movement
• Muscle spindle, golgi tendon organ, pacinian
  corpuscle, periodontal mechanoreceptors, free
  nerve ending
• Interoceptors viscera

6
(No Transcript)
7
Structure of peripheral nociceptors and primary
afferents

• What is a nociceptor?
• The peripheral sense organs or receptors, that
  respond to noxious stimuli are called
  nociceptors.
• Definition of a noxious stimulus?
• A stimulus (e.g., chemical, thermal, mechanical)
  that can potentially produce tissue damage.
• What do nociceptors look like?
• Free-nerve endings
• Nociceptors are widely distributed.

8
Pain vs Nociception

• Pain is the perception of the aversive or
  unpleasant sensation that is thought to arise in
  a specific region of the body.
• Nociception refers to the reception of action
  potentials in the CNS evoked by the activation of
  specialized sensory receptors (called
  nociceptors) that provide information about
  tissue damage.

9
Pain vs Nociception

• Not all noxious stimuli that activate these
  nociceptors and produce action potentials that
  travel towards the CNS, necessarily produce the
  experience of pain.
• The nociceptive impulses can be gated out and
  prevented from accessing higher centers of the
  brain.

10
Functions of nociceptors

• Provide information about the location, intensity
  and duration of a noxious stimulus to the body
• Nociceptors are connected to primary afferent
  nerve fibers.
• Nociceptors fire action potentials because they
  are responding to changes in their chemical
  environment.

11
First Order Neuron

• Attached to receptor
• diameter of axon conduction velocity
• A fiber
• alpha (a) 13-20 mm, 70-120 m/s
• beta (ß) 6-13 mm, 40-70 m/s
• gamma (?) 3-8 mm, 15-40 m/s
• delta(?) 1-5 mm, 5-15 m/s
• C fiber 0.5-1 mm, 0.5-2 m/s

12
Generation ofactionpotential
13
Impulse Propagation
14
The Erlanger/Gasser classification of peripheral
nerve fibres (1939)
15
Characteristics of pulpal sensory fibres
(Trowbridge and Kim, 1991)
16
Pain

• Superficial Pain
• Sharp, pricking sensation,
• brief duration(ltmin.)
• 1st pain or initial pain
• Deep pain
• Dull, aching, burning, diffuse,
• long duration (min., hrs., days)
• second pain

17
Nociceptive first order neuron

• Mechanothermal afferents
• A delta fibers c.v. 12-18 m/s response to heat
  and mechanical stimuli
• Polymodal afferents
• C fiber c.v. 0.5 m/s response to mechanical, heat
  and chemical stimuli
• High-threshold mechanoreceptive afferents
• mostly A delta response to mechanical, noxious
  thermal and chemical stimuli

18
Synapse
19
Synapses at Cell Body
20
Second Order Neuron

• Low threshold mechanoreceptive neuron (LTM)
• tactile, pressure and proprioception
• Nociceptive specific neuron (NS)
• Pain and noxious stimuli
• Wide dynamic range neuron (WDR)
• non noxious to noxious stimuli

21
(No Transcript)
22
Substantia gelatinosa
23
(No Transcript)
24
Brain Stem and Brain

• Brain stem medulla oblongata, pons,
  mesencephalon (midbrain) diencephalon
• reticular formation of medulla oblongata can
  modulate sensory impulses
• Thalamus relay station for almost all signal
• hypothalamus --gt produce hormone and interact
  with sympathetic --gt nociceptive impulse

25
(No Transcript)
26
Cerebrum

• Cerebral cortex
• thinking process, memory, skill
• area 3, 1, 2
• Basal ganglion
• caudate nu, putamen, globus pellidus
• control gross movement of skeletal
• Limbic system
• emotion and behavior

27
(No Transcript)
28
Trigeminal Sensory Pathway
Primary Neurons

• Nociceptor
• Trigeminal nu.
• Tactile
• Motor nu. of V
• Proprioceptive
• Mesencephalic nu.

29
Second Order Neuron of V

• Low threshold mechanoreceptive neuron (LTM)
• tactile, pressure and proprioception
• Nociceptive specific neuron (NS)
• Pain and noxious stimuli
• Wide dynamic range neuron (WDR)
• non noxious to noxious stimuli

30
TMJ Sensory Pathway

• Proprioceptive
• Golgi tendon organ Muscle spidle
• Proprioceptive receptor in periodontium
• Mesencephalic nucleus of V
• Pain Trigeminal ganglion

31
(No Transcript)
32
(No Transcript)
33
(No Transcript)
34
(No Transcript)
35
References

• Textbook of Physiology
• Textbook of Pain by Wall, P and Melzack, R 4th
  edition Churchill and Livingstone 1999.
• Disorders and Orofacial Pain. by Klineberg, I
  Craniomandibular Wright, Oxford. 1991.
• Basic Neuroscience for Health Professions. by
  Littell, EH SLACK corporation, New Jersey. 1990.

36
Thank You