PAIN 1 (1)111111111111111111111111111111

metodologia

1. PAIN
Pathophysiology and routes

2. Definition
“An unpleasant sensory and emotional experience associated with actual or
potential tissue damage”. International Association for the Study of Pain
Difficult to measure : subjectivity / physical and emotional overtones
Mistreatment
Vital protective sensory phenomenon essential for survival
Alerts and permits avoidance of the offending pathogen or stimulus.
Lee G, Neumaister M. Pain: pathways and physiology. Clin Plastic Surg -(2019)

3. Definition
Balance between nociception and antinociception, under the influence of a set
of neurobiochemical, inflammatory, metabolic, genetic, therapeutic,
psychological and socio-affective factors
Mild: local inflammatory response.
Severe: systemic inflammatory response syndrome
Max. expression
of the lesion =
Max.expression of
pain
Cruz E, , Zúñiga V & Serratos M. Tratamiento del dolor en pacientes con quemaduras severas. Revista mexicana de anestesiología, 2021,44(1), 55-62.

4. Definition
Pain:the conscious, subjective experience or perception of a feeling or
sensation
Nociception: physiologic activation of neural pathways by stimuli (noxious,
thermal, mechanical, or chemical) that are potentially or currently damaging.
Proprioception:the awareness of oneself or one’s body part relative to their
environment
Lee G, Neumaister M. Pain: pathways and physiology. Clin Plastic Surg -(2019)

5. Definition
Lee G, Neumaister M. Pain: pathways and physiology. Clin Plastic Surg -(2019)

6. Definition
Lee G, Neumaister M. Pain: pathways and physiology. Clin Plastic Surg -(2019)

7. Definition
Somatic = receptors located in musculoskeletal tissue. Well located, stinging
and radiates following the nervous path.
Visceral = receptors in the viscera, runs through sympathetic and
parasympathetic fibers →less specific location.
Lee G, Neumaister M. Pain: pathways and physiology. Clin Plastic Surg -(2019)

8. Classification
Lee G, Neumaister M. Pain: pathways and physiology. Clin Plastic Surg -(2019)

9. Physiology
1.Afferent sensory nerves send
information
2.Create an electrical impulse or
action potential within the sensory
nerve.
3.Transduced to the nerve cell body
within the dorsal root ganglion of
the spinal cord: Spinothalamic and
spinoparabrachial tracts
4.Brain network: parabrachial medulla
oblongata, thalamus, amygdala and
limbic system, and somatosensory
cortex.Lee G, Neumaister M. Pain: pathways and physiology. Clin Plastic Surg -(2019)

10. Physiology
Three noxious stimuli: mechanical, thermal,
chemical.
Mechanical stimuli deform the receptor to augment
receptor ion permeability.
Bradykinin, serotonin, histamine, potassium ions,
acids, acetylcholine, and proteolytic enzymes →bind
directly to receptors to influence membrane
permeability
Pain receptors are unencapsulated free nerve
endings.
Lee G, Neumaister M. Pain: pathways and physiology. Clin Plastic Surg -(2019)

11. Intense, sharp,
tingling sensation.
“The first pain”
Dull prolonged
burning sensation.
“the second pain”
Lee G, Neumaister M. Pain: pathways and physiology. Clin Plastic Surg -(2019)

12. Sensory neuron cell bodies are located in
the dorsal root ganglia →first order neuron
One process extends into the peripheral
nerve and the other process extends
centrally, transmitting information through
the dorsal root into the spinal cord.
The most common neurotransmitter that is
synthesized by DRG cells is glutamate
Bourne S, Machado A, Nagel S. Basic anatomy and physiology of pain pathways. Neurosurg Clin N Am -(2014)

13. Second-order neurons then cross to the opposite
side, in the ventral decussation of the central
canal of the spinal cord.
The Lissauer tractcontains both unmyelinated C
fibers and myelinated A-delta fibers.
Rexed lamina I,or the marginal layer, is
composed of two main types of cells, nociceptive-
specific neurons, and wide dynamic range
neurons
Lamina II (substantia gelatinous) may play a role
modulating spinothalamic and spinobulbar
projection neurons via its numerous inhibitory
interneurons that primarily release GABA.
Bourne S, Machado A, Nagel S. Basic anatomy and physiology of pain pathways. Neurosurg Clin N Am -(2014)

14. Spinothalamic pathways
One dorsolateral, carrying axons from the superficial lamina, and the other ventrolateral, carrying
axons from deeper lamina.
The paleospinothalamic tract projects to brain-stem reticular formation, hypothalamus, and
thalamic nuclei
These neurons include both wide range neurons and nociceptive-specific neurons
Involved in motivational-affectivecomponent of pain.
Bourne S, Machado A, Nagel S. Basic anatomy and physiology of pain pathways. Neurosurg Clin N Am -(2014)

15. The spinomesencephalictract originates in laminae I and IV-V
It projects to areas including periaqueductal gray, pretectal
nuclei, red nucleus, Edinger-Westphal nucleus, and interstitial
nucleus of Cajal.
Neurons in this tract are nociceptive.
They are involved in aversive behavior and orientation
responses, and may activate descending antinociceptive
systems.
Spinothalamic pathways
Bourne S, Machado A, Nagel S. Basic anatomy and physiology of pain pathways. Neurosurg Clin N Am -(2014)

16. Descending systems
Originating in the brain regulate incoming signals
from noxious stimuli
The rostral ventromedial medulla,the dorso-
lateral pontomesencephalic tegmentum, and the
PAG region
Dysfunction = chronic pain conditions
Activation of opioid receptors in the brain,
specifically the mu receptor, blocks pain
transmission centrally in the brain but also will
activate descending systems.
Bourne S, Machado A, Nagel S. Basic anatomy and physiology of pain pathways. Neurosurg Clin N Am -(2014)

17. Modulation of pain
Endogenous mechanism that dissociates and modulates (enhances or
diminishes) the transmission of pain
Segmental inhibition:“gate theory” infers that the synapses between
noxious stimuli (Ad and C fibers) can be blocked.
When large myelinated nerve fibers (Ab) that sense touch (non-noxious
stimuli), stimulate the inhibitory nerve →inhibits the transmission by
suppressing transmission in small unmyelinated C fiber afferents.
Rubbing an injury reduces the sensation of pain.
Lee G, Neumaister M. Pain: pathways and physiology. Clin Plastic Surg -(2019)

18. Modulation of pain
The endogenous opioid systemarose when receptors
to opium derivatives were found in the central nervous
system (PAG, ventral medulla) and spinal cord (lamina I
and II)
Enkephalins, endorphins, and dynorphins →bind to the
opioid receptors in the pain pathway and modulate the
pain signal
Lee G, Neumaister M. Pain: pathways and physiology. Clin Plastic Surg -(2019)

19. Modulation of pain
The descending inhibitory nerve systemcontrols the transmission
of noxious signaling by using the neurotransmitters serotonin and
norepinephrine.
They are released to dampen the pain signal in the dorsal horn
(1) direct inhibition of the dorsal horn cells transmitting pain
(2) inhibition of excitatory dorsal horn neurons that work to
enhance/exacerbate the transmission of pain
(3) excitation of inhibitor neurons in the dorsal horn.
Lee G, Neumaister M. Pain: pathways and physiology. Clin Plastic Surg -(2019)

20. Next class
Homework
Pain routes