Clin Med - Pain Mgmt Flashcards
Define pain
An unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.
Biologists recognize that those stimuli or illnesses that cause pain are likely to damage tissue.
How is pain subjective?
each individual learns the meaning of the word “pain” through experiences related to injury in early life.
Implications of pain for clinical practice
- there is no physiological, imaging, or laboratory test that can identify or measure pain.
- pain is what the patient says it is.
- clinician must accept the patient’s report of pain.
Define nociception
- the process by which information about a noxious stimulus is conveyed to the brain.
- the total sum of neural activity that occurs prior to the cognitive processes that enable humans to identify a sensation as pain.
Nociception vs. pain
Pain is a conscious experience that results from brain activity in response to a noxious stimulus and engages the sensory, emotional and cognitive processes of the brain.
What are the 2 dimensions/components of pain?
- sensory-discriminative
2. affective-emotional
Goal of pain therapies
to relieve pain whenever possible: from nociception to the conscious experience as well as to decrease the emotional response to the unpleasant experience
Reduction of symptoms = improved quality of life
Physiology pain pathway
-4 steps
- Transduction
- Transmission via Ascending pain pathway: Spinothalamic Tract
- Perception
- Modulation via Descending pain pathway: Corticospinal Tract
Define transduction
phys process where a noxious mechanical, chemical, or thermal stimulus is converted (transduced) via specialized receptors on primary afferents into an electrical impulse (action potential)
Where does transduction occur?
nociceptors
What are nociceptors?
a subpopulation of primary sensory neurons that are activated by intense stimuli such as pressure, heat, mechanical insults (a surgical incision) or irritant chemicals (including those which are released by damaged cells)
What are some of the irritating chemicals released by cells?
bradykinin, cholecystokinin and prostaglandins, activate or sensitize nearby nociceptors.
Examples of interventions that reduce transduction
ice or NSAIDs
*recall that NSAIDs inhibit the synthesis of prostaglandins - normally produced and released at the site of injury, and which in turn make neighboring nociceptors more responsive to noxious and innocuous stimuli.
How are action potentials conducted to the CNS?
via two types of primary afferent neurons:
- thinly myelinated, faster conducting A delta fibers and
- unmyelinated, slowly conducting C fibers, both termed primary afferents.
Action potentials result from activation of specific sodium channels
Nociceptive impulses travel along…
travel along these peripheral nerve fibers (peripheral transmission) to the dorsal horn of the spinal cord where they synapse with the second order neurons (synaptic transmission)
Where is the impulse transmitted after it reaches the dorsal horn of the spinal cord and synapses with second order neurons?
the impulse is further transmitted via neurons which cross the spinal cord and ascend to the thalamus and branches to the brainstem nuclei (central transmission)
Nociceptive impulses are then relayed…
to multiple areas of the brain including the:
- somatosensory cortex
- the insula
- frontal lobes
- limbic system
Intervention action
- local anesthetics
- some epileptic drugs
Local anesthetics and some antiepileptic drugs block sodium channels and inhibit the production of action potentials along the nociceptive afferents
Intervention action
-opioids
Opioids bind to presynaptic receptors in the dorsal horn and decrease release of neurotransmitters such as glutamate
Intervention action
-peripheral and spinal nerve blocks
interfere with propagation of action potentials and pain transmission into the CNS (at the nociceptors, along the nerve, at the dorsal root ganglion and along the spinothalamic tracts)
Intervention action
- epidural
- intrathecal
may provide presynaptic and postsynaptic inhibition of receptors at the level of dorsal horn neurons and affect the transmission of nociceptive impulses
Define perception
the process by which a noxious event is recognized as pain by a conscious person
What parts of the brain are involved in perception?
- multiple areas of the brain are involved.
- there is no one location where perception occurs, although major defining components of pain are attributed to processes that take place in specific areas of the brain
What does the limbic system mediate?
the affective-emotional response to the noxious stimulus is mediated by the limbic system
Descending input from the brainstem influences…
central nociceptive transmission in the spinal cord
How does descending modulation occur?
specific brainstem nuclei send projections to the dorsal horn of the spinal cord and, when activated by ascending nociceptive impulses and other influences from the brain, result in descending modulation
Modulation results in descending inhibition of nociception through which neurotransmitters?
release of neurotransmitters such as serotonin, norepinephrine, and endogenous opioids
How is descending facilitation increased?
modulatory processes can also increase descending facilitation of nociception and consequently pain