Exam #6: Sensory Physiology of Pain Flashcards
Why is chronic pain important?
- 30% US population experiences chronic pain
- Leading neurological disorder & high cost to society
- Leading cause of disability & suffering
What is the difference between nociception & pain?
Nociception= sensory response to a noxious stimulus
Pain= perception of nociceptive sensory information
What are the two components of pain?
1) Sensory-discrimination= perception of external or internal noxious stimuli & the localization to the site of the stimulus
2) Motivation-affective= emotional & sympathetic responses associated with behavior
What brain regions are associated with sensory discrimination?
Primary & secondary somatosensory cortices
What brain regions are associated with the motivational-affective component of pain?
Frontal cortex
Limbic system
Brainstem
What type of sensory information associated with the sensory-discriminative component of pain?
Location
Intensity
Modality (e.g. stab vs. burn)
What type of information is conveyed by the emotional component of pain?
- Negative impact on mood
- Depression associated with chronic pain
What is acute pain? What are the functions of acute pain?
- Body’s warning signal that is critical for survival
- Pain felt within 0.1 sec of stimulus i.e. VERY FAST
- Very adaptive i.e. tissue heals and pain abates
What fibers conduct acute pain?
A-delta
What is pathologic or chronic pain?
- Pain that begins >1 sec after stimulus and then progressively worsens
- Can become MALADAPTIVE i.e. persists even if there is no more tissue damage
What fibers conduct pathologic pain?
Persistent and SLOW conducting C-fibers
- small
- unmyelianted
What are the qualities of acute pain?
Sharp
Prickling
Electric
Cutting
What are the qualities of chronic pain?
Dull
Throbbing
Aching
Nauseous
What is nocicpetive pain?
Physiologic pain that serves as a warning to the body
What is inflammatory pain?
Pain that is associated with healing
What is dysfunctional pain?
Pain without an underlying lesion or that is disproportionate to tissue injury
- IBS
- Fibromyalgia
What is neuropathic pain?
Pain from damage to the CNS or PNS that is disproportionate to intensity of nociceptor activation
What is the difference between somatic and visceral pain?
Somatic= superficial or deep pain originating from the body
Visceral= pain originating from internal organs
What is the difference between the fibers that mediate somatic and visceral pain?
Somatic= A-delta Visceral= C
What are the four general steps from external injury to perception of pain?
1) Transduction
2) Transmission
3) Modulation
4) Perception
What is peripheral transduction?
Conversion of injury to electrical stimulus
What type of receptors are nociceptors?
Free-nerve endings
Where are the soma of nociceptions in the body vs. the face?
Body= DRG Face= Trigeminal ganglia
What are the important functional characteristics of nociceptors?
- High threshold
- Slowly adapting
What stimuli can activate nociceptors?
- Mechanical (of high intensity)
- Thermal
- Chemical
What are the different types of thermal nociceptors?
CMR-1= cold VRL-1= noxious heat VR-1= noxisous heat/ capsaicin
What is “inflammatory soup?”
Tissue injury resulting in the release of a number of inflammatory mediators
*****These inflammatory mediators stimulate nociceptors & lead to indirect sensitization or LOWERED THRESHOLD
What is peripheral sensitization?
1) Lowered threshold of activation for nociceptors in response to injury
- Increased sensitivity of neurons directly involved
- Increased sensitivity of a wider area of tissue
2) Activation of silent nocicpetors
What NT plays the largest role in peripheral sensitization?
Substance P
What is allodynia?
Pain resulting from non-noxious stimuli
What is hyperalgesia?
Increased response to a stimulus that is normally painful
What is axon reflex?
Coupling of sensory system to the SNS in response to inflammatory mediators
What is the triple response of Lewis?
Redness
Edema
Wheal
What is the difference between A-delta & C fibers?
A-delta= myelinated–faster
- localized
- sharp
- “first” pain
C= unmyelinated–slower
- poorly localized/ diffuse
- polymodal
- “second” pain
What types of fibers are associated with the cutaneous tissue?
A-delta & C
How do joints and muscles differ from cutaneous tissue in regards to fiber types?
2x as many C fibers compared to A-delta
What fiber types are present in the viscera?
Predominantly C-fibers
What happens in the dorsal horn of the spinal cord in the transmission of pain?
Synapse from 1st order neuron to dorsal horn 2nd order neuron
What tracts carry nociceptive information in the spinal cord?
Spinothalamic tracts
What lamina are associated with A-delta fibers vs. C?
A-delta= Lamina I C= Lamina II & III
What are WDRs?
Polymodal second order neurons that can respond to noxious stimuli and other stimuli
What NT is being release at the synapse between first & second order neurons in the spinal cord? What receptors are on the second order dendrite?
Glutamate=
- NMDA
- AMPA
Recall, what kind of threshold do A-delta & C fibers have?
High-threshold
What is central sensitization?
Amplification of pain signaling in the spinal cord
What is secondary hyperalgesia?
Prolonged & increased activation of nocicpetors in the periphery & projection pathways in the spinal cord
- Recruitment of adjacent areas
- Increased release of NT
What NT & receptor type underlies secondary hyperalgesia?
Glutamate & NMDA-R
What is neuronal plasticity?
Modulation of intracellular signaling & changes in gene expression
What does neuronal plasticity underlie in respect of pain?
Memories of pain & the lasting effects of chronic pain
What sensations are carried by the DC/ML?
Discriminative Touch
Proprioception
What sensations are carried by the AL system?
Temp.
Pain
Crude touch
What is the neospinothalamic tract?
- Pathway of pain from A-delta fibers
- Lamina I, IV, V
What information is carried by the neospinothalamic tract?
Sensory-discriminative
What is the paleospinothalamic tract?
- Slow type C fibers
- Lamina II, III, V
What information is carried by the paleospinothalamic tract?
Emotional/ affective
What is the function of the spinoreticular tract in pain?
Motor response to pain i.e. descending pain control
What is the function of the spinomesencephallic tract in pain?
Descending pain control, particularly eye movements and regulation of gaze to site of injury via the superior colliculus
Where in the brain does the perception of pain occur?
Sensory= somatosensory association cortex
Emotional= insular cortex & anterior cingulate cortex
Cognitive= prefrotnal cortex
What does the anterior cingulate cortex (ACC) contribute in terms of pain?
Attention to pain
*****Conscious activation of the ACC can dampen pain signaling
When is the ACC most active?
1) Perception of pain
2) Imagining pain
3) Observation of pain in others
What is the Gate Control Theory?
Generally, this is distraction
- A-beta (mechanoreceptor/ proprioceptor) activation inhibits C-fiber transmission
What is descending pain control?
Endogenous mechanism in the body to regulate pain
