Lecture 10 Pain Systems

pain is a ___ feeling often caused by ___

distressing

intense or damaging stimuli

pain motivates you to

withdraw from a damaging situation

what are the two types of pain?

somatic and visceral

somatic pain is pleasant/unpleasant?

both

visceral pain is pleasant/unpleasant?

unpleasant

somatic pain is caused by

touch

temperature

cutting

ischemia

inflammation

visceral pain is caused by

ischemia

inflammation

distension/stretching

cramping

visceral pain is not elicited by ___, ___, or ___

squeezing

burning

cutting

free nerve ending is a(n) ___, ___ ___ ___ that sends its signal to a ___ ___

unspecified

afferent nerve fiber

sensory neuron

free nerve endings are also called

cutaneous nociceptors

most abundant type of nerve endings

free nerve endings

nociceptors are ___ receptors

pain

nociceptors are found in

any area of the body that can sense noxious stimuli either externally or internally

nausea, vomiting is what type of pain?

visceral

cutaneous means

related to skin

four major processes of pain

1. transduction/conduction

2. transmission

3. modulation

4. perception

transduction/conduction

tissue damaging stimuli activate nerve endings

stimuli that can activate pain include

mechanical (pressure, pinch)

heat

chemical

transmission

relay of message from site of injury to brain regions involved with perception

modulation

the brain can reduce or increase activity in the transmission system

why do we shake our hand when we jam our finger?

increasing peripheral sensory input inhibits the pain gate

perception

subjective awareness produced by sensory signals

neuroanatomical reasons why people's perception of pain differs lies in what process of pain?

modulation

pain pathway in CNS is unique because it has

both ascending and descending pathways

the cell bodies of the primary afferent pain neurons from the ___, ___, and ___ are located in the ___ and ___ respectively

dorsal root ganglia (DRG)

trigeminal nerve (CN V)

free nerve endings arise from ___ and ___, which are scattered together

A delta fibers

unmyelinated C fibers

A delta neurons are what group

III

C neurons are what group

IV

A delta neurons carry ___ or ___ and are ___myelinated

sharp pain

cool/cold info

thinly

C neurons carry ___, are the ___ axons and are ___myelinate

dull pain, deep pain, crude touch, or warm/hot info

smallest different

un(myelinated)

3 major types of pain

nociceptive

neuropathic

nociplastic "other"

nociceptive pain involves

- damage to body tissues

- radicular (back and hip), somatic, visceral

most common type of pain

nocicpetive

neuropathic pain involves

- damage to nerves that transfer info b/t brain and spinal cord

- burning sensaiton, sensitive, numbness

- cancer, surgery, viral infections

nociplastic pain involves

- altered process of pain-related pathways

- "unknown"

- chronic pain

sharp, stinging pain sensation carried fast by A delta fibers. pain is precisely located and of short duration "fast pain"

pricking pain

pricking pain is mainly

nociceptive

caused by inflammation, burned skin, etc. Carries by C fibers (slowly conducted). diffuse, slower to onset, and longer in duration

burning (soreness) pain

burning (soreness) pain is mainly

nociceptive

arises mainly from viscera and somatic deep structures. not distinctly localized and carries by C fibers

aching pain

aching pain is mostly

neuropathic, nociplastic

decussate means

cross over

spinothalamic tract (1-3rd order neuron pathway)

- 1st order comes from body, comes in via afferent fiber to dorsal horn

- synapses with 2nd order in dorsal horn

- 2nd order decussates at level of spinal cord and out through ventral horn

- synapses with 3rd order at thalamus

- 3rd order terminates at somatosensory cortex

spinoreticular/spinomesencephalic tract (1-3rd order neuron pathway)

- 1st order comes from body, comes in via afferent fiber to dorsal horn

- synapses with 2nd order in dorsal horn

- 2nd order decussates at level of spinal cord and out through ventral horn

- 2nd order terminates at brainstem/reticular formation

which tract is involved with burning, throbbing, long-lasting pain?

spinoreticular/spinomesencephalic tract

ascending pain pathways = ___ system

anterolateral

what three tracts make up the anterolateral system?

spinothalamic

spinoreticular

spinomesencephalic

which tract conveys pain, temperature, and crude touch

spinothalamic

some aspects of touch are carried by both the ___ and the ___

dorsal column

spinothalamic tract

which tract is involved with fast, localizing pain?

spinothalamic

reticular formation is a set of

interconnected nuclei located throughout the brainstem

what tract is involved with "deep" pain and pain modulation

spinoreticular

reticular formation serves as a

major integration and relay center for many brain functions

reticular formation is involved with

arousal, consciousness, pain

spinoreticular tract axons terminate in

(brainstem) medulla and pons

third order neurons of spinoreticular tract project to the

thalamus

spinomesencephalic tract terminates in the

periaqueductal gray (PAG)

periaqueductal function

release of endorphins or other natural analgesics that can suppress pain signals at level of spinal cord

descending inhibition refers to the ability of

activation in various brain areas to attenuate spinal (or trigeminal) dorsal horn neuronal responses to peripheral stimuli, most commonly applied with noxious stimuli

___ and ___ contain high concentrations of opioid receptors and endogenous opioids

midbrain

rostral medulla

descending pathways project to the ___ and ___ pain transmission

dorsal horn

inhibit

descending inhibition lower the ___ and changes how your ___ responds to pain

number of pain signals your body sends to your brain

brain

gate control theory of pain: activation of nerves that...

do not transmit pain interfere with large pain fibers

activation of nerves in gate control theory excites the ___ neurons which ___ the transmission of pain info via ___ or ___

inhibitory

diminishes

mechanical stimulation

release of natural opioids

gate control takes place in

substantia gelatinosa region of dorsal horn

when first order neurons are excited, they excite the ___ and inhibit the ___

2nd order neuron

inhibitory interneuron

non-painful signals are transduced via

A-beta fibers

A-beta fibers are activated by

non-painful signals such as skin rubbing, hot/cold packs

activation of A-beta fibers leads to

reactivation of inhibitory interneuron

endorphins released from the brain reduce transmission of pain by

1. preventing release of neurotransmitter pre-synaptically (1st order neuron)

2. inhibiting action potentials post-synaptically (2nd order neuron)

referred pain occurs due to the

convergence of different afferents onto the same dorsal horn neurons in the spinal cord

physiological processes that enhance and lead to chronic pain

sensitization (repeated stimuli leads to thresholds decreasing)

hyperactivity of the sympathetic nervous system

acute vs chronic pain

acute pain

- activation of nociceptors for limited time

- not associated with significant tissue damage

chronic pain

- prolonged pain lasting for months or longer

- arises from tissue injury, inflammation, nerve damage, tumor growth, lesion, or occlusion of blood vessels

phantom pain

the experience of pain w/o any signals from nociceptors

phantom pain typically relates to

a limb or an organ that is not physically part of the body

characteristics of phantom pain

- remaining cut ends of nerves grow nodules called neuromas

- overactive spinal neurons

- abnormal somatosensory cortex activation

- burst firing thalamus neurons