Mechanisms of Pain Flashcards
According to the International Association for the Study of Pain what is pain?
“An unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.”
3 treatment goals in regards to pain
1) Resolve underlying pathology
2) Modify patient’s perception of discomfort
3) Maximize function whether or not the source of pain can be modified
Pain is categorized by _____ or ____.
Duration
Source
Two types of pain categorized by duration
1) Acute
2) Chronic
Two types of pain categorized by source
1) Referred
2) Radiating
Acute vs. Chronic Pain
Acute pain lasts less than 6 months whereas chronic pain persists past the normal time for tissue healing (>6 months)
The major difference between chronic and acute pain is what??
Acute pain is a reaction to a noxious stimulus and will last as long as this stimulus exists.
Chronic pain persists after the noxious stimuli is gone
Referred vs. Radiating Pain
Referred pain is experienced in an area other than the location of the actual tissue damage, whereas radiating pain is caused by irritation of nerves and nerve roots
When treating referred pain what is important to keep in mind?
Always treat the joint above and below
Are there common referral patterns from internal organs?
Yes, there are common sites of referred pain for specific internal organs
5 red flags for referred pain
1) Pain that is not relieved by rest
2) Pain that is not relieved by change of position
3) Pain/symptoms that do not fit an expected mechanical or neuromuscular pattern
4) Pain that increases at night
5) When pain cannot be reproduced, aggravated, or altered in any way
Pain is a response to stimulation of _____ _____.structures.
peripheral nociceptive
Afferent vs. Effernet nerve fibers
- Afferent nerve fibers transmit impulses from the sensory receptors toward the brain
- Efferent nerve fibers such as motor neurons transmit impulses from the brain toward the periphery
What are nociceptors?
free, non-corpuscular peripheral nerve endings
2 types of nociceptors
1) C fibers (aka Group IV afferents)
2) A-delta fibers (aka Group III afferents)
Describe C fibers
- Small, slow, unmyelinated (1 – 2.5 meters/second)
- Transmit pain sensations that are often described as dull, throbbing, aching, burning, tingling or tapping
- Slow onset, long lasting
- Accompanied by nausea, sweating, incr. BP or HR
- Can be blocked by opioids (morphine, oxycodone, hydrocodone)
Describe A-delta fibers
- Small, faster, myelinated (30 meters/second)
- Most sensitive to high intensity mechanical stimulation
- Described as sharp, stabbing, or picking
- Quick onset, last a short time
- Generally not blocked by opioids
Pain-transmitting neurons originating in the spinal cord ascend to the thalamus via what tracts?
spinothalamic (ST) tracts
In the hypothalamus what tracts relay sharp pain?
Lateral spinothalamic tract (LST)
In the hypothalamus what tracts relay prolonged, aching pain?
Anterospinothalamic tract (AST)
What type of cell increases muscle spasms?
T-cells
How does the Sympathetic Nervous System influence pain?
- SNS involved in producing effects that prepare the body for “fight or flight”
- These hyperactive responses from the SNS can increase the severity of pain and cause symptoms of sympathetic activity
What is Complex Regional Pain Syndrome (CRPS)?
an abnormal sympathetic activation caused by a hyperactive response of the sympathetic nervous system to an acute injury, or a failure of the sympathetic response to subside after an acute injury, which can increase pain severity and exaggerate s/s of sympathetic activity
3 Pain Theories
- Specificity Theory
- Pattern Theory
- Gate Control
What does Von Frey’s Specificity Theory state?
The body has a separate sensory system for perceiving pain and the quality of sensation is dependent upon the nerve’s properties
What are Pacinian corpuscles?
pressure receptors, responsible for detecting vibration from steady pressure (quick)
What are Merkel’s disks?
touch receptors, responsible for discriminative touch (slow)
What are Ruffini endings?
receptors that detect heavy and continuous touch sensations (slow)
What are Meissner’s corpuscles
receptors detect light touch and determine the texture of an object (quick)
What does Goldschneider’s pattern theory state?
That there is no separate system for perceiving pain, rather the pattern of stimulation is determined whether the brain would interpret the stimulus as pain
Many physical agents are thought to work via the what theory? (Ex. TENS)
Gate Theory
What does the gate control theory state?
Severity of pain is determined by the balance of excitatory and inhibitory inputs to T cells in the substantia gelatinosa of the spinal cord
T cells receive excitatory input from what types of receptors?
C and A-delta nociceptive afferents
T cells receive excitatory input from what types of receptors and what other sources?
- A-beta non-nociceptive sensory afferents
- descending neurons from the limbic system, the raphe nucleus and the reticular systems
Increased activity of the non-nociceptive sensory afferents cause what 3 things?
- Presynaptic inhibition of T cells
- Effectively closes the spinal gate to the cerebral cortex
- Decreases the sensation of pain
Input of large A fibers excited the inhibitory interneuron, thus “____ the gate” and inhibiting ascending nociceptive stimuli
closing
Input from small C fibers stimulated the excitatory interneurons tending to “____ the gate” and allowing ascending nociceptive stimuli
open
What are Opiopeptins also known as?
Endorphins
How do Opiopeptins work?
They control pain by binding to specific opioid receptors in the nervous system.
Opiopeptins cause presynaptic inhibition by suppressing the inward flux of _____ ions.
Calcium
Opiopeptins cause postsynaptic inhibition by promoting the outward flux of ______ ions
potassium
What are the advantages and disadvantages of physical agents when compared to pharmacological agents?
Advantages: Fewer side effects and Long term
Disadvantages: Takes longer, Last for a short period of time, and Requires work
