Pain

less

pain is ___ discrete than other tactile senses

threshold

first pain

tolerance

maximum intensity of pain a person is capable of enduring

second pain

longer lasting, diffuse pain after "first pain" subsides

hyperalgesia

increased response to noxious stimuli

primary hyperalgesia

increased sensitivity at the site of injury

secondary hyperalgesia

Increased sensitivity outside the site of injury

allodynia

painful response to a non-noxious stimulus

acute pain

associated with actual/potential tissue damage
- severity of injury not necessarily related to intensity of pain
protective mechanism

chemical, mechanical, and thermal

what types of nociceptors are activated by noxious stimuli in acute pain?

protective mechanism of acute pain

withdrawal from harm to prevent further damage
healing behaviors (not weight bearing after hurting ankle)

A delta and C

what fiber types transmit pain?

A delta fibers

tissue damage- mechanical stimulus
- may also respond to chemical
cooling temperature
coarse touch (perceive touch but can't localize)

C fibers

tissue damage: mechanical, chemical, and thermal
heating temperature
itch
tickle

cutaneous pain

discriminative pain
usually sharp
rarely refers to other areas

muscle pain

diffuse
dull/aching/cramping
often refers to superficial structures

neuropathic pain

damage to nerves themselves
burning/shooting/tingling

visceral pain

from visceral organs
diffuse
dull/stabbing/cramping
often refers!!!

amygdala and hypothalamus

what two structures involve an emotional aspect of pain?

periaqueductal gray

the ____ ____ is involved in descending pain inhibition

reticular formation

the ____ ____ is why pain can interfere with sleep?

DCML

visceral pain is carried through the ____ pathway

wide dynamic range neurons

in lamina V
receive non-noxious and noxious information
also receive visceral sensory info
likely a mechanism for referred pain (may fire spontaneously)

peripheral sensitization

triggered by inflammatory response to tissue damage
- nociceptor threshold is lower
- firing rate of pain neurons is increased
- dorsal horn of SC: increased excitatory NTs (glutamate, aspartate, and substance P)

Pain signal is larger compared to before tissue damage!!

central sensitization

hyper-excitability of CNS neurons associated with pain perception
can occur in the absence of tissue injury

happens when there is prolonged peripheral sensitization

peripheral sensitization nociceptors

release substance P, calcitonin gene-related peptide, and ATP
facilitate inflammatory response
- vasodilation
- edema
- release of histamine from mast cells

histamine

non-neural cells like mast cells, macrophages, and neutrophils release bradykinin, ____, serotonin, prostaglandins, and cytokines

increase the response of nociceptors

glutamate; increased

peripheral sensitization the amount of ___ released by the presynaptic neuron in the dorsal horn is _____, causing a greater pain signal transmitted by the post-synaptic neuron

silent nociceptors

not normally responsive to mechanical stimuli but become responsive under inflammatory conditions (peripheral sensitization)

chronic pain

pain that is present beyond the normal time frame of healing
- not associated with tissue damage
non-protective: no adaptive purpose
"faulty" neuroplasticity
pain response is greater than what would be expected based on clinical exam

3

chronic pain is characterized as pain that lasts ___ months or longer

characteristics of chronic pain

1. increase receptive field size
2. increased response to noxious stimuli (hyperalgesia)
3. increased response to non-noxious stimuli (allodynia)
4. increase in spontaneous neuronal firing (flares of pain w/o sensory input)
5. decrease in activation threshold of spinal neurons

hyper-excitable

CNS pain-related neurons/structures are _____ in central sensitization of chronic pain

injury/damage

chronic pain can occurs with or without actual tissue ____/____

wind-up

happens with highly sensitized nervous system
firing of APs after a stimulus stops

spinal; supraspinal

descending pain inhibition is influenced by ____ and _____ influences

NE; serotonin

neurotransmitters involved in descending pain inhibition are opioids, _____, and _____

PAG

in the midbrain
pain suppression signal
- antinociception via activation of pons/medulla
- enkephalins, endorphins, dynorphins (opioids)

NE

in the pons, the locus coeruleus releases the NT ____

serotonin

in the medulla the NT that is released is ____

level I

inflammatory mediators
- NSAIDs, RICE principle
- minimize sensitization, directly target inflammation

level II

spinal cord level in dorsal horn
- gate control theory
- enkephalins at lamina II suppress impulses in spinothalamic tract

level III

brainstem level
- conditioned pain modulation

level IV

pituitary level
- pain causes release of endorphins into blood stream
- "runner's high"

level V

cortical
- motivation, placebo, expectations, distractions, stress

gate-control theory

activation of large diameter sensory fibers inhibits pain signal from small diameter sensory fibers
- rubbing something that hurts causes some suppression of the signal

inhibitory

in the gate control theory, large diameter sensory neurons activate _____ interneurons found in lamina II of the dorsal horn

segmental inhibition

occurs in the gate control theory
happens at a specific spinal cord level where the sensory neurons are activated to produce pain signals

conditioned pain modulation

pain inhibits pain
reduced in patients with chronic pain (may still be intact but pain may/ may not decrease)
- ice water bath and finger pressure pain

threshold; tolerance

to measure conditioned pain modulation, the pressure pain ____ and pain ____ are used

gate control theory

threshold; less

in CPM, the descending inputs make it harder for the 2nd order neuron to reach ____ and also inhibit the 1st order neuron to release ____ NT

opioids

in the PAG the NTs that are secreted are enkephalins, endorphins, and dynorphins, also known as ____

dynorphins

in the RVM and dorsal horn the NTs that are released are enkephalins and ____

decreases

in the dorsal horn, the endogenous opioids are released on the presynaptic sensory neuron which ____ the amount of NT released

inflammatory

opioids receptors are more likely to bind in _____ states

hyperpolarize

endogenous opioids decrease the amount of NT released and ____ the postsynaptic neuron

endorphins

released into blood stream by pituitary gland
released into PAG by hypothalamic neurons

locations of EO

peripheral terminals of small diameter nociceptic afferents
spinal cord (upregulated in inflammatory states)
RVM
PAG
Pons
Amygdala
Bowel muscles and anal sphincter
Brainstem

constipation

a side effect of EOs is ____ because EOs slow down gut motility

suppress

since EOs are found in the brainstem they can ____ CV and respiratory systems to an extreme

placebo effect

the phenomenon in which the expectations of the participants in a study can influence their behavior

limbic system

the placebo effect likely activates the EO system in cortical and subcortical areas like the ____ _____ which is why emotion is involved

narcan

the placebo effect can be blocked by the administration of ____ because it blocks endogenous opioids

catastrophizing

psychological aspect of pain
pain response is increased by patient thinking the pain will be significant/disabling/intractable
"spiraling"
heightened pain perception

kinesiophobia

fear of movement
believe moving will make pain worse

phantom limb

cortical reorganization is a possible mechanism
peripheral neurons another possible mechanism (turns on sensory nerves)
- can use cortical mechanisms as treatment

different

every person experiences ___ phantom limb pain
- no two people are the same

a box with a mirror inside is a common treatment for phantom limb pain
- the mirror allows the brain to ____ perceive the phantom limb is not clenched/cramped etc.

brain

pain is always an output of the ____, 100% of the time

damage

pain does not equal the amount of tissue ____

stress

pain is influenced by multiple factors such as thoughts, activity, sleep, mood, and ____
- influenced by emotions

injury

acute pain serves a useful protection function to warn of danger or ____

hypersensitive

chronic pain results from a ____ nervous system and usually no longer warns of danger

pain

many treatments can help "turn down" a hypersensitive nervous system, reduce ____, and improve quality of life