Senses - Pain

Pain

unpleasant sensory and emotional experience associated with actual or potential tissue damage (IASP)

Nociception

the reception of sensations carried by nociceptors (free nerve endings) in response to tissue damage

located in periphery

carry signals from noxious stimuli

A-delta Group

group of myelinated axons conduct 5-30 m/s speed

C Group

unmyelinated axons conduct less than 2 m/s speed

First Pain

sharp

carried by A-delta fibers

Second Pain 

dull/burning

carried by C fibers 

Pain Perception - Process

1. inflammation

2. dorsal horn

3. medulla

4. descending connections

5. pain signals in the brain

Pain Perception - Inflammation (1)

injury sets a release of various chemicals that alert the nerve impulses that are processed as pain

histamine released to site to cause swelling

Pain Perception - Dorsal Horn (2)

on to the opposite side of the spinal cord

pain signal enters dorsal horn of the spinal cord

Pain Perception - Medulla (3)

pain signals pass through the medulla which in turn activates the ANS to increase BP, HR, RR

Pain Perception - Descending Connections (4)

fibers descending from pain regions of the cortex intercept ascending pain information and modify signals

chemicals in brainstem can released to decrease pain felt 

Pain Perception - Pain Signals (5)

signals are transmitted to the various areas of the cerebral cortex which then interprets signals 

Pain Pathways

nociceptor → spinal cord (decussates) → brain stem → thalamus → cerebral cortex

Brown Sequard

pattern of disassociated sensory loss after a spinal cord hemi section

• motor weakness on same side as lesion

• decreased pain and temp on opposite side of lesion 

Stages of Pain (4)

1. transduction

2. transmission

3. perception

4. modulation

Pain Stages - Transduction (1)

when free endings of nociceptors in the periphery become stimulated

Pain Stages - Transmission (2)

conduction of pain signals along different pathways in the periphery to the spinal cord and brain 

A-delta fibers and C fibers involved

Pain Stages - Perception (3)

how the cortex attaches meaning to or interrupts pain signals

involves threshold and pain tolerance 

Pain Stages - Modulation

modification of pain signals by different CNS and PNC centers along the pain pathway

pain can be modified at the level of the peripheral nociceptor, the SC, the brainstem, and the cortex 

Peripheral Nociceptive

injury to musculoskeletal tissues

mediated by inflammatory response

Peripheral Neurogenic

injury within the PNS

mediated by inflammatory response

Not Mediated by Inflammatory Response (2)

1. central pain lesion / CNS dysfunction

2. presence of abnormal pain states 

Shingles

infection of dorsal root ganglion or cranial nerve ganglion with varicella-zoster virus

affects one dermatome usually

virus irritates and inflames nerve, causing pain

skin lesions around affected area

Shingles - Treatment

antiviral drugs

NSADIS

neuropathic pain meds

alternative treatments

Pain Threshold

amount of pain stimulation required before pain is received 

Pain Tolerance

the amount of pain a person can tolerate before seeking healthcare intervention

Somatic Pain

occurs from the body (skin, muscle, bones) can be divided into superficial or deep pain

Visceral Pain

pain from the viscera (internal organs, glands, smooth muscles) and is not localized

Referred Pain - Definition/Examples

pain that is perceived to originate from one body region, but truly originates from another 

• HA

• gallbladder

Referred Pain - Causes

dermatomal distribution could have the same level representation for dermatome 

OR

dorsal root neurons have 2 peripheral axons: 1 for innervating skin and skeletal muscle, and 1 for innervating the viscera

Acute Pain

less than 30 days

resolves quickly

Chronic Pain

last longer than expected length of recovery

longer then 3-6 months

Sharp Pain

localized

short lasting

carried by A-delta fibers

Dull Pain

diffusive

longer lasting

carried by C fibers

Gate Theory of Pain

there is a “gate” that controls the transmission of pain stimuli 

the brain sends inhibitory or stimulatory signals to that gate 

Pronociception

biologic amplification of nociception

Descending Connections

thalamus and pituitary glands releasing natural opioids (endorphins) that are transmitted during stress and pain

Opiates

block nociceptor signals without affecting other sensations