Pain/Nociception (6.1)

Nociception definition:

Neural signaling related to actual or potential tissue damage

• can occur with conscious pain

Pain definition:

Conscious, interpreted experience

• includes sensory, emotional cognitive, autonomic, and behavioral

• Can occur when tissue damage isn’t present

Nociceptors are:

sensory receptors specialized for detecting actual or potential tissue threat

Most nociceptors are…

• Free nerve endings

• found in skin, muscle, joints, and many other tissues

• Activated by intense mechanical, thermal, or chemical stimuli

Some nociceptors are polymodal, meaning…

they respond to more than one type of threat

Nociceptor to Dorsal horn route:

Nociceptor > Peripheral nerve > Dorsal root ganglion > Dorsal root > Dorsal horn

What happens when a signal reaches the dorsal horn?

It is processed as information

Spinothalamic tract pathway:

Supports sensory-discriminative aspects of pain

• Location and intensity

• Where and When the pain is!

Divergent nociceptive pathways:

info can spread to multiple CNS targets

• Contribute to arousal, attention, autonomic responses, emotion, guarding, avoidance, protective behavior

Spinoreticular pathway:

Transmits slow, dull pain and helps maintain alertness and arousal in response to harmful stimuli

Spinomesencephalic pathway

Processes pain and temperature signals and helps control pain

Spinolimbic pathway

carries slow, emotional, and affective pain information from the body to the brain

• unpleasant emotional response associated with pain

What does divergent pain processing help explain?

Pain can effect arousal, attention, autonomic responses, emotion, guarding, avoidance, protective behavior

Pain modulation

Nociceptive input can be increased, decreased, filtered, amplified or inhibited

• Due to: inflammation, previous experience, stress, fear, contest

Bottom-up processing:

Nociceptors detect actual sgignals

Top-Down processing:

Brain evaluates the context

• this can amplify the signal using things like expectations, past experience, and emotions

Peripheral sensitization

Increased responsiveness of nociceptors, often near injured/inflamed tissue

• Lower threshold at receptor level

Peripheral sensitization example

• Sunburn pain

• Inflammed joint pain

Central sensitization:

Increased responsiveness in CNS pathways

• spread beyond original injury area (crawling up)

• Amplified processing in brain/spinal cord

Central sensitization examples:

• Phantom limb pain

• Widespread chronic pain

• Pain starting central and crawling up

What type of sensitization is this? 3 days after an ankle sprain, injured area is sensitive to pressure

Peripheral sensitization

What type of sensitization is this? Months after original injury, pain sensitivity persisted and spread

Central sensitization

Types of amplified pain processing

• Hyperalgesia

• Allodynia

• Temporal summation

• Secondary hyperglesia

Hyperalgesia

increased pain from a painful stimulus

Allodynia

pain from a normally non-painful stimulus

Temporal summation

Repeated or sustained stimulation feels increasingly painful

Secondary hyperglesia

Increased sensitivity spreads to adjacent, non-injured tissue

A client reports that light touch from clothing feels painful after a burn. What term describes this?

Allodynia - because the touch is typically non-painful

Is pain processing modifiable?

Yes, pain can be modulated.

Descending modulation examples:

• Pain may feel less intense during an emergency

• Pain may feel worse when a person is fearful, exhausted, or expecting harm

Acute pain

Shorter duration

• usually resolves as tissue or injury heals

Chronic pain

Lasts or recurs longer than 3 months

• can significantly affect function, sleep, mood, movement, and participation

Biopsychosocial model of pain:

Biological factors, Psychological factors, and Social/Contextual factors all interact with each other

Biological factors:

Tissue state, nervous system sensitivity, fatigue, inflammation

Psychological factors:

Attention, fear, family roles, culture, social support, access to care

Social/contextual factors

Work demands, family roles, culture, social support, occupational demands