The Physiology of Pain Flashcards
What are the two way of characterizing pain?
Fast pain: generally associate w/ the immediate injury
Slow pain: often characterized as dull or achy, often occurs after the injury
What are the sensors of the nociceptive system.
the nociceptors
bare nerve ending
Two types of fibers:
Alphadelta-small, spasely myelinated. Fast, sharp pain
C fibers- unmyelinated fiber associated with dull pain (slow pain)
What are the types of nociceptors?
sensitive to both thermal and mechanical stimuli
sensitive only to thermal stimuli
sensitive only to mechanical
silent/sleeping
What type of receptor do mixed modality express?
TRP family of receptors along with a mechansensitive Na+ channel
mutations in this channel lead to an absence of pain sensation or produces a paroxysmal pain syndrome
How do nociceptors alter the sensitivity to input?
nociceptors express a number of ligand-gated receptors ( in addition to the stimulus-gated channels)
including receptors for:
Substance P, The Kinins, ATP and H+
What happens to nociceptors when ligands (ATP, H+, Kinins, Substance P) bind to them?
they change their sensitivity of the receptor (usually increasing) and activate the silent nociceptors
What neurotransmitters are released by the axons of the nociceptors?
EAA (from alpha-delta neurons) acting primarily on non-NMDA receptors.
Substance P and EAA are released from C fibers
What do C fiber do before ascending to the reticular formation.
nociceptor that travel wit the spinoreticulothalamic pathway synapse on an interneuron in the spinal cord before ascending
The interneuron synapse of C fiber allows for ________.
modulation (of spinal cord function)
local (gate theory)
descending (opioid pathways)
T/F nociceptive input is distributed widely in the cortex?
True
The _____ _____ is particularly important in the interpretation of nociceptive inputs
insular cortex
Function: process info. about the internal state of the body, contributes to the autonomic response to the pains, integrates all signals related to the pain
Lesion in any one area _____ abolish the ability to experience pain, although the experience is changed
does not
Where do many nociceptive input go?
To the amygdala
important for activating/producing the emotional components inherent in the sensation of pain
Visceral nociceptors, traveling with the autonomic nerve, have additional synapses within the ________ and ________.
hypothalamus and medulla
theses synapse form the basis of the physiological changes associated w/ visceral pain, including diaphoresis and altered blood pressure
What are the 2 ways to physiological modification of painful inputs?
- Peripheral mechanisms
2. descending Mechanisms
What is the basis for peripheral mechanism of modifying painful inputs?
observation that other somatic input can alleviate pain (rubbing the area)
What is the 3 steps involved in the peripheral mechanism of modifying pain?
activate an alpha-delta fiber by the normal stimuli. The alpha-delta fiber has a branch that travels via dorsal columns, but it also branches within the spinal cord
Step 2. The alpha-delta fiber releases EAA and actives an inhibitory interneuron in the spinal cord
Step 3. The inhibitory neuron releases glycine to inhibit the activity of the second order neuron in the pain pathway
Result: Rubbing the area of skin activated by the alpha-delta fiber will reduce the sensation of pain
What is the basis for the descending mechanisms of modifying painful inputs?
use presynaptic inhibition to reduce activation of the second-order nociceptive neuron in the spinal cord
What are the steps in the descending mechanism of modifying painful inputs?
Step 1. neurons in the periaqueductal gray are activated by numerous inputs, including opiate, EAA and the cannabinoids
Step 2. axons from the PAG neurons travels to the midline Raphe nuclei and release enkephalins, which activate the raphe neurons
Step 3. axons from the raphe neuron travel to the spinal cord and release serotoin, which activate inhibitory interneurons, causing them to release opiates
Step 4. The opiates release by the interneuorn activate mu receptors on the presynaptic terminal of the C fibers
Step 5. This produces pre-synaptic inhibition that reduces the release of substance P from the nociceptor and reduces pain transmission
What qualities are associated with deep pain?
associated w/ periosteum, ligaments
usually dull, achy
few A delta fibers and many C fibers
associated with muscles spasm
Why do people experience muscles pain?
claudication, in which blood flow to the muscles in her legs is impeded during exercise. This creates ischemia and local acidosis, which will activate the pain fibers embedded in her muscles
What qualities are associated with muscle pain?
both Group II and IV fibers present
get both fast and slow pain associated with muscles
Describe visceral pain.
poorly localized
few receptors (almost all Group IV)
Stretch receptors (distension)
often referred
