physiology 7-pain
TRANSCRIPT
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Physiology of pain
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Pain • unpleasant sensory & emotional
feeling, connected with true or potential damage of tissue or organ, which is described in the terms of such a damage.
International expert commiteeJ. “Pain” 6, 248-252, 1979
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Pain • Doesn’t give any info about the external
environment;• Adequate stimulus – any suprathreshold
stimulus damaging the tissue or causing the danger of damage:
MechanicalThermal (burn or frostbite)Chemical (metabolism disorders)
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pain• Danger signal that occurs at the damage
or the threat of damage of:SkinPeritoneumMeninxPericardithis.
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Nociception • Nociception - sensor modality in
animals which causes pain feeling in man.
• Nociceptors - pain receptors
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Types of painPain
Somatic Visceral
superficial deep
Early or primaryepicritical
Delayed or secondaryprotopatic
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Superficial pain localization - skin
Early or primary – strictly localized,
Dissapears with the dissapearence of the stimulus
(pinch, hit, pin)
Latent period – sec
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Superficial pain localization - skin
Delayed or secondary- Not localized, dyes out
slowly.Dull, diffuse
Latent period – 0,5-1,0 sec
diffuse
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Deep painLocalization - connective tissue, muscles, bones, joints, teethTypes – muscle cramps, headache, toothache. Characteristics - dull, non-localized,irradiating Latent period 1-3 minAcute, sub-active, chronic
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Visceral pain
Diffuse pain Pain with irradiation
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Visceral pain• Localization – internal organs• Types - kidney, liver, intestinal cramps,
gastric ulcer pains, appendicitis, cardiac pain • Characteristics - dull, non-localized,
irradiating to other organs & tissue. May be acute but diffuse.
• Reasons – quick & excessive stretching of hollow organs, cramps, spastic contractions, ischemia
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Pain duration• Acute pain – localized in the damaged area, its
intensity depends on the stimulus intensity, has signaling function, quickly dissapears.
• Chronic pain – lasts up till half a year, has stable & recurrent forms. No connections between pain intensity & level of organic damage.
• May become a separate syndrome
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Other types of pain• Psycogenic – no peripheral organic
reason – neurosis.• Itching – caused by the increased
concentration of hystamine in skin
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COMPONENTS OF PAIN
1. SENSORY DISCRIMINATIVE2. AFFECTIVE (EMOTIONAL)3. VEGETATIVE4. LOCOMOTOR5. COGNITIVE (intensity evaluation)
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SENSORY DISCRIMINATIVE• Is enabled by thalamus & cortex.• When the hand is deepened into the water with
t0>450С skin receptors are excited, they send info to the cortex about the localization of hot stimulus, its intensity, the starting point & the end point of its action.
• Sensation is formed• This component prevails in superficial pain
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Affective or emotional• Is enabled by limbic system• Negative emotions are formed• Is the prevailing component in chronic pain
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vegetative• Is enabled by ANS• BP elevation, HR increase, pupil dilation,
changed rhythm of respiration • Sympatho-adrenal system is activated,
vasopressin (АDH) is produced.• Is the strongest in visceral pain
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locomotor
• Is enabled by motor zones of cortex• Is displayed in flexor reflexes (defence
reflex), abdominal muscles tension, pscycomotor behavioral reactions
• Accompanies all types of pains
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cognitive• Present pain is evaluated in comparison to
previous pains.• This evaluation depends on many factors:Social statusBringing up in the familyEthnic originCircumstances at which the pain occured
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Pain neurophysiology
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Pain theories
1. Theory of specificity – M.Frey – end of XIX century
2. Theory of intensity – Goldshteiner - end of XIX century
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Theory of specificity
• Pain is an independent feeling with specialized nervous apparatus of receptors, conducting pathways & centres
• Prof – the correlation between skin pain dots and the dots of pressure & temperature is 9:1
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Pressure & pain dots on the skin
Pressure dot
Pain dots
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Intensity theory
• Pain may be caused by suprathreshold stimuli of different modality.
• Not proved to be true.
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NociceptorsFree nervous endings of 2 types:• Non-myelinized fibres of C type – the velocity
of impulse conduction is up to 1 m/sec – are present everywhere (skin, joints, internal organs)
• Myelinized fibres of Аδ type – the velocity of impulse conduction is up to 20
m/sec– only in skin
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Nociceptors Аδ • High threshold receptors;• May be sencibilized ;• Have small receptive fields.• 3 types:Mechano-Тhermo-Mechano-thermo-
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Nociceptors of С type fibres
• High threshold, may cause sencibilization, have big receptive fields (17mm2).
• Polymodal
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Nociceptors blocking
• Local anaestetics in low concentration block С type fibres
• Pressure – blocks just Аδ fibres. This activates С fibres
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Algogenic substanses• Substances from damaged cells – potassium,,
АТP. • From plasma – bradikinins, Н+
• From must cells – hystamine• From platelets – serotonin• From nervous afferent fibres – substance Р• SNS mediators – adrenalin,noradrenalin
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Nociceptive system
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Receptive fields
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Spinal cordЖелатинозная субстанция
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skin
Internal org.
Аδ
Аδ
С
С
С
n. Vagus 70%
VPLThalamus
SI-SII
Thalamusn.medialis
5 –Associative cortex.(temporal & frontal)RF
3
45
12
1 –Tr. Neospino-thalamicus2 – tr. Paleospinothalamicus3 – Hypothalamus4 – Limbic cortex
Asparaginic acid
Sub. Р
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Conducting pathways• Tr. Neospino-thalamicus – in the anterior
funiculus, has somatotypical organization. Enables primary pain conduction.
• Tr. paleospinothalamicus – non-specific system (RF) – has many synapses on one level in the spinal cord, makes diffuse connections in cortex. Enables emotional component of pain – secondary pain
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First danger (bacterial infection, inflamation, mechanical influence)
Cortex- feeling of pain
Afferent fibres
Spinal cord
Supraspinal centers
Impulse conduction
Transduction & transformation
Nociceptors
Algogenic substanses formation
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Refered pains
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Pain irradiation
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Pain progection in the cortex (due to lateral spino-thalamicus tract)
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Antinociceptive systemGigantic-cell nucleus RF
Spinal cord neurons secreting endoopiates
Inhibition of afferent nociceptive neurons & neurons of posterior horn ІІ & Y plates
serotonin
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Antinociceptive systemCentral grey matter
Ruph nucleiNoradrenalin, alpha-2 adrenoreceptors
serotonin
Spinal cord neurons releasing endoopiates
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OPIOID ANALGESICS• Relieve pain as a symptom• Perception of pain & reaction to it are both
altered• Opioid receptor activation reduces intracellular
c-AMP formation,opens K-channels or suppresses voltage-gated Ca- channels, hyperpolarization of a neuron, decreased neurotransmitter release by CNS & myenteric neurons
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MECHANISM OF OPIOID ACTION