5070: Pain

is pain subjective or objective?

subjective

what type of pain affects all aspects of quality of life?

unremitting pain

what type of pain is protective?

acute

what type of pain is maladaptive and harmful, and not protective?

chronic

what type of pain usually appears in distress?

acute

what type of pain extends beyond the expected time course of painful syndrome?

chronic

what does the primary somatosensory cortex do with regard to pain? x 2 things

receives sensory/proprioceptive info from body

then LOCALIZES pain

what does localizes pain mean?

input from specific areas of the body signal specific areas of the primary somatosensory cortex

what does the somatosensory association cortex do? x 2 things

interprets/understands pain

where are the 2 somatosensory cortexes located in relation to one another

primary somatosensory cortex anterior to somatosensory association cortex

what is a dermatome?

an area of skin innervated by sensory fibers from a single spinal nerve

why can pain be localized?

because nociceptor pathways are kept in a specific anatomical order in the spinal cord and somatosensory cortex

what is the function of the dorsal horn of the spinal cord, and what is it made of?

grey matter

receives sensory information

what is the anatomical function of afferent neurons?

they are sensory neurons which transmit impulses from skin/internal organs TO the CNS

what is the primary afferent neuron?

the first neuron in the somatosensory pathway

what is the dorsal root ganglion?

what is located inside it?

enlarged area of the dorsal root where the cell bodies of afferent neurons are located

what are interneurons?

what are some types of these able to do?

connector neurons between sensory and motor neurons

inhibit transmission of the pain signal at the level of the dorsal horn

what are nociceptors?

what do they do?

specialized sensory receptors in body

selectively respond to noxious or potentially tissue-damaging stimuli

what are the 3 types of stimuli that nociceptors could respond to?

thermal, mechanical, chemical

what is an example of a thermal stimuli?

what about mechanical stimuli?

extremes of temp

pressure

what is an example of a chemical stimuli?

irritants like capsaicin, K+ or H+ ions

some nociceptors are normally _____, but can be recruited to send ______.

this can be especially true after what event?

silent, pain signals

esp. after inflammatory molecules are released

what might silent nociceptors play a role in?

perpetuating chronic pain

what is an anatomical description of nociceptors?

free (non-encapsulated) nerve endings of primary afferent nerve fibers (axons) in peripheral tissues

what can cause nociceptors to become sensitized? x 2 things

result of tissue damage and inflammation

What are 2 results of nociceptor sensitization?

reduction in response threshold to noxious stimulus

increase in magnitude of response, including increased rate of Action Potential generation

what does nociceptive pain result from?

tissue damage or potential tissue damaging stimuli

what are the 2 types of nociceptive pain?

somatic pain

visceral pain

somatic pain has what quality of localization?

well-localized

originates from receptors in skin, muscles, joints, or bones

visceral pain has what quality of localization?

what does this occur from?

poorly localized

internal organs swelling, stretching, becoming damaged

what is nociception conceptually?

is this proportionate to pain?

how tissue damage is conveyed to the central nervous system

yes, more tissue damage → more pain

what are the 4 basic processes of nociception?

transduction, transmission, perception, modulation

what is transduction?

nociceptors do what 2 things during this?

conversion of painful stimuli to neuronal action potentials

transduce and are sensitized

what do the release of chemical mediators K+, H+, 5ht, bradykinins, etc do with regard to transduction? x 2 things

alter the membrane potential of nociceptor

lead to increased sensitivity of nociceptor to noxious stimuli

what occurs during transmission?

stimulated nociceptors transmit impulses to the CNS through specialized sensory fibers

what are the 2 types of primary pain sensory fibers?

A-delta and C fibers

what are 5 characteristics of A-delta fibers?

large, myelinated, fast transmission of sharp and highly localized pain

what are 5 characteristics of C fibers?

small, unmyelinated

slow transmission of dull, poorly localized pain

how do sensory afferent pain fibers enter the spinal cord?

through the posterior nerve roots

where are cell bodies of pain neurons located?

dorsal root ganglion of spine

how do pain signals transmitted by afferent fibers move through the spinal cord? x 6 steps

1. enter spinal cord through dorsal horn

2. synapse w 2nd order neurons

3. decussate (cross the cord)

4. project centrally in anterolateral tract

5. NTs that bind NMDA, AMPA receptors in SC are released

6. signal ends in thalamus, which relays to cortical regions

the ascending sensory pathway involves how many neurons that communicate?

what are these called?

3 nuerons

1st, 2nd, 3rd order neurons

what is the first-order neuron known as?

what does it synapse with and where?

primary afferent neuron

synapses with 2nd order neuron at dorsal horn

what does the 2nd order neuron do, how does it travel?

what does it synapse with?

originates at dorsal horn

decussates and travels through anterolateral tract to thalamus

synapses with 3rd order neuron

what does the 3rd order neuron do?

relays pain signal to somatosensory cortex

what is substance P?

what is one source of this?

peptide neurotransmitter

nociceptors themselves

what does substance P contribute to ? x 2 things

nociceptor excitation and sensitization

contributes to inflammatory pain by inducing release of histamine from mast cells

what are 3 NTs/NPs that are involved with synaptic transmission at spinal cord level?

substance P, glutamate

calcitonin gene-related peptide (CGRP)

without (what molecule), pain signals wouldn’t be transmitted to CNS

sodium

what is a pain threshold?

level of pain stimulation required to be perceived

what is pain tolerance?

how does this change between individuals?

degree of pain an individual is willing to bear before seeking relief

varies among individuals

where does modulation take place in the body?

in the descending pathway from the brain to the dorsal horn of the spine

what is perception of pain?

impulse of pain becomes a conscious perception of pain

what is modulation?

mechanism of synaptic transmission of pain signals changing, could be inhibited or amplified

what are 4 things that can inhibit pain signals?

endogenous opioids (endorphins)

5-HT, NE, GABA

what is the difference between 5HT and NE in the ascending and descending pathways?

in descending they can reduce pain

in ascending they can increase signal

what do endogenous opioids do with regard to pain signals in the modulation pathway?

blocks release of NT like glutamate and substance P

What does rubbing your arm when injured do?

activates non-nociceptive A-beta fibers

what do non-nociceptive A-beta fibers do?

what is this also called?

inhibit the transmission of nociceptive information

the “Gate control theory of pain”

what is the general gist of the Gate Control Theory?

non-painful stimulus can block or weaken transmission of a painful stimulus

what is the normal function of A-beta fibers?

to carry information about touch, vibration, or pressure

NOT PAIN

what are inhibitory interneurons?

where are these typically located?

neurons that normally inhibit 2nd order neurons that transmit pain

in the dorsal horn

which fibers normally inhibit inhibitory interneurons?

what does this allow pain signal to do?

c-fibers

pain signal can continue its journey

during a pain stimulus, what could A-beta fibers do to the signal?

what is the overall result in this

stimulate interneurons → inhibit 2nd order pain-transmitting neurons

non-painful mechanical stimuli decreases pain transmission

Gate Control Theory is the basis of what therapies?

TENS units

transduction definition

noxious stimuli converted to impulses, action potential generated

transmission definition

movement of impulses ascending from the periphery to the spine and then to the brain

perception definition

recognizing, defining, and responding to the pain

modulation definition

descending pathways inhibit or amplify pain transmission

analgesia definition

reduced perception of pain stimuli

anesthesia definition

reduced perception of all sensation

paresthesia definition

what are some examples of this?

abnormal sensation; usually not unpleasant

tingling, numbness, sensation of coolness

dysesthesia definition

examples of this?

abnormal sensation, not pleasant

burning, stabbing, electric shock-like, stinging

what are the two types of sensations that don’t have to have external stimulus and/or noxious input that causes the sensation?

paresthesia

dysesthesia

allodynia definition

how does this begin?

pain response to normally non-painful stimuli.

it is provoked

hyperalgesia definition

overly extreme pain response to painful stimuli

secondary hyperalgesia definition

spread of sensitivity to non-injured areas

how is inflammatory pain an adaptive mechanism?

it facilitates the healing of injured tissues

low contact with injured tissue until repair is complete

how does inflammatory pain usually go away?

abates and resolves with healing

what happens when inflammatory pain occurs?

what is an example of this?

increases sensitivity to stimuli in affected area

sunburned skin

under conditions of inflammation, silent nociceptors do what?

become responsive to noxious stimuli

inflammatory pain plays a role in these 2 types of sensitizations

peripheral and central

where does peripheral sensitization occur?

in the periphery where the nociceptors are located

where does central sensitization occur?

in the CNS (spinal cord and brain)

what can prolonged peripheral sensitization lead to?

central sensitization

what 7 things are included in “inflammatory soup”?

substance P, CGRP,

5-HT, NE,

histamines, prostaglandins, H+ ions

in peripheral sensitization, tissue injury leads to what directly being released?

inflammatory soup being released

what is the effect of peripheral sensitization?

lower the threshold for neuronal activation and increase rate of firing (which generate action potentials)

peripheral sensitization is usually (protective/not protective), but may become chronic and (protective/not protective).

usually protective

not protective

what is a basic definition of central sensitization ?

increased excitability of neurons within the CNS

what is central sensitization triggered by?

a burst of activity in nociceptors (after injury) that alters the strength of synaptic connections between nociceptor and neurons of the spinal cord

what is “wind up”?

what is this caused by

gradual increase in dorsal horn neuron firing, progressively more action potentials per stimulus

ongoing nociceptive input from periphery

prolonging ongoing input from periphery causes what?

what is this caused by, and what can this lead to?

longer-lasting dorsal horn excitability

changes in expression of genes via activation of transcription factors

chronic pain

what type of receptors increase in # in the dorsal horn during a “wind-up”?

how do they influence pain during this?

NMDA (glutamate’s receptors)

switch a low level of pain perception to a high level, perpetuate the pain state

how long can the incr in receptor # last during central sensitization?

long after peripheral stimulus has ceased

during central sensitization, pain feels like it originates in periphery, but where is it manifesting from?

manifesting from abnormal sensory processing in CNS

central sensitization manifests in these 4 ways….

1. hyperalgesia

2. allodynia (recruitment of A-beta touch fibers to signal pain)

3. persistent pain

   1. referred pain

central sensitization may result from

inadequately-treated acute pain

what are 2 characterizations/descriptions for neuropathic pain?

maladaptive

non-protective

where does neuropathic pain originate from?

what does this result in?

direct injury or irritation of nerves

results in disturbance in function or pathologic change