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Anatomy 2 > Understanding Basic Principles of Nociception and Pain > Flashcards

Understanding Basic Principles of Nociception and Pain Flashcards

1
Q

What is Pain

A

The unpleasant sensory and emotional experience associated with tissue damage

Pain is a variable experience and requires cortical involvement to be able to experience it

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2
Q

What is Nociception

A

The neuronal process of encoding and process noxious stimuli

Noxious stimuli is the insult causing the tissue damage

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3
Q

Five Steps of Nociception

A
  • Transduction
  • Transmission
  • Modulation
  • Projection
  • Perception
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4
Q

Transduction

A
  • The process of turning a noxious stimulus to an electrical signal
  • Nociceptors are free nerve endings with no capsule
  • Variable types of nociceptors that respond to specific stimuli
  • RECEPTORS ARE CALLED NOCICEPTORS
  • Nociceptors are found throughout most of the body
  • NOT FOUND IN THE BRAIN (but are found in the meninges)
  • Activation requires an adequate stimuli to cause a receptor potential
  • Nociceptors are NON-ADAPTING
  • They will not adapt to a persistent stimulus
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5
Q

Types Of Nociceptors

A

Mechano-sensitive
Mechano-thermal
Chemical
Polymodal
Silent

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6
Q

Mechano-Sensitive Nociceptor

A

Respond to intense pressure, stretch or strain (A-delta fiber)

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7
Q

Mechano-Thermal Nociceptor

A

Respond to extreme temperature: < 5 C / 41 F ; >45 C / 113 F)
(A-delta fiber)

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8
Q

Chemical Nociceptor

A

Respond to chemicals released from tissue
damage (i.e: bradykinin, prostaglandin, substance P,
histamine) or from external chemicals (i.e.: topical
capsaicin) (C-fiber)

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9
Q

Polymodal Nociceptor

A

Sensitive to combinations of mechanical,
thermal, and chemical (C-fiber)

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10
Q

Silent Nociceptor

A

Silent nociceptors must be first activated or “awakened” by tissue inflammation
before responding to a mechanical, thermal, or chemical stimulus. Most visceral
nociceptors are silent nociceptors

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11
Q

Transmission

A
  • Process of sending signal from receptor to CNS
  • Transmission is carried via TWO different afferent fibers ( A-delta and C fibers)
  • Travel via nerve to dorsal root to synapse in the dorsal horn
  • Sensory fibers synapse on different lamina in the dorsal horn gray matter
  • Do not need to know which lamina
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12
Q

Two primary afferent fibers : Transmission

A
  • (A-delta) Fibers
    • myelinated: associated with thermal and
      mechanosensitive nociceptors
    • Fast pain, easy to localize location
  • C fibers
    • unmyelinated: associated with chemical,
      polymodal, silent receptors
    • Slow pain, difficult to localize specific location
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13
Q

Clinical Note” Referred Pain

A
  • Signals from nociceptors in the viscera can be felt as pain ELSEWHERE in the body
  • A heart attack leads to referred pain in the chest and left arm
    • The convergence of visceral and somatic afferent fibers is suspected as the underlying cause
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14
Q

Clinical Note: Wind Up Pain

A
  • Also called central sensitization
  • Chronic pain -> chronic enhancement of the central pain-processing circuits
  • The synapse becomes MORE EFFICIENT at relaying noxious information;
    synaptic activity may persist after healing
    • Phantom limb pain
    • Chronic pain syndromes
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15
Q

Projection

A
  • The processing of
    sending information via
    ascending pathways to
    the higher brain centers
  • AKA – ”projecting it up
    to the brain”
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16
Q

HOW NOCICEPTIVE SIGNALS TRAVELS UP THE CORD

A
  • Travels predominantly via the Spinothalamic
    Pathway
  • The majority cross the midline of the spinal cord at
    the spinal cord segment they originate from and
    travel in the lateral funiculus to the thalamus.
  • These pathways do travel up both sides of the cord
  • Contralateral predominates
17
Q

Perception

A
  • Involves many cortical areas whose
    activity is widely influenced critically
    by the context in which the noxious
    stimulus is presented
  • Also altered by an individual’s prior
    experience
  • Nociception is interpreted as pain by
    the CONTRALATERAL cortex.
  • Relay nuclei in the thalamus receive the signal
    from the spinal cord
  • Relay nuclei send projections to limbic structures,
    hypothalamus, and amygdala
  • Allows for an emotional response with pain
  • Other areas of brain stimulated in humans
  • VERY COMPLICATED PROCESS!
18
Q

Modulation

A
  • This neuronal process reduces the activity of
    pain transmission system – OCCURS AT THE
    LEVEL OF THE SPINAL CORD
  • Involves DESCENDING signals from portions of
    the brain
  • Two Primary Systems:
  • Endogenous Opioids
  • Gate Control Theory
19
Q

MODULATION: ENDOGENOUS ANALGESIA SYSTEM

A
  • Collection of neurons that function to reduce
    the activity of nociceptive neurons
  • These neurons are located in:
  • Periaqueductal gray matter (PAG)
  • Pons/Medulla
  • Dorsal Horn (inhibitory interneurons)
  • Activation of the endogenous analgesia system stimulates inhibitory
    interneurons in the dorsal horn gray matter via opioid receptors
  • Decreases in synaptic activity between peripheral neuron (C-Fiber) and the spinal cord
    tract
  • Leads to inhibition of local excitatory neurotransmitters
20
Q

Gate-Control Theory

A
  • Mechanical stimulation of the A-Beta (Aβ) fiber reduces the activation of the
    relay in the dorsal horn by increasing inhibitory interneuron activity
  • Examples:
  • Transcutaneous Electrical Nerve Stimulation (TENS)
  • Rubbing/ Massage of area close to injury
  • Ice/Warm packing of site
21
Q

Pain Pathway Summary

A
  • Pain is a PERSONAL EXPERIENCE
  • Individuals will experience pain differently
  • It is is the cortical awareness and response to
    nociception
  • Nociception:
  • A noxious stimuli damages tissue leading to transduction at the nociceptors
  • Transmission of the signal occurs from the nociceptors to the spinal cord via
    specific fibers
  • The signal is projected (sent) to the brain in a process known as Projection.
  • That signal undergoes Modulation at the level of the spinal cord via
    descending pathways
  • Finally, Perception occurs within the cortex and emotional reactions and
    sensations are experienced by organism
22
Q

Clinical Applications of Pain

A

Dysesthesia

Parasthesia

Allodynia

Hyperesthesia

23
Q

Dysesthesia

A

Unpleasant abnormal sensations – itching, burning,
tingling

24
Q

Parasthesia

A

Spontaneous or evoked abnormal sensation

25
Q

Allodynia

A

Pain response to non-noxious stimulus of normal skin

26
Q

Hyperesthesia

A

Increased sensitivity (exaggerated response) to a normally noxious stimulus

27
Q

Pain Assessment in Animals

A
  • Assessing pain in animals is focused on evaluating behavior and response to stimuli
  • Glasgow Pain Scale
28
Q

Glasgow Pain Scale

A
  • Behavioral assessment
  • Can be subjective between observers
29
Q

Pain on Neurological Exam

A
  • Evaluate posture!
  • Firm palpation of neck
    • I personally do NOT ventroflex the neck on every case
      • Small dogs with atlantoaxial instability can become worse
    • May use food and see how the voluntarily follow food
  • Firm palpation along back
    • Two fingers – lightly at first!!

Anatomy 2 (16 decks)

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