The Physiology of Pain

Question 1

What are the two way of characterizing pain?

Answer 1

Fast pain: generally associate w/ the immediate injury

Slow pain: often characterized as dull or achy, often occurs after the injury

Question 2

What are the sensors of the nociceptive system.

Answer 2

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)

Question 3

What are the types of nociceptors?

Answer 3

sensitive to both thermal and mechanical stimuli
sensitive only to thermal stimuli
sensitive only to mechanical
silent/sleeping

Question 4

What type of receptor do mixed modality express?

Answer 4

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

Question 5

How do nociceptors alter the sensitivity to input?

Answer 5

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+

Question 6

What happens to nociceptors when ligands (ATP, H+, Kinins, Substance P) bind to them?

Answer 6

they change their sensitivity of the receptor (usually increasing) and activate the silent nociceptors

Question 7

What neurotransmitters are released by the axons of the nociceptors?

Answer 7

EAA (from alpha-delta neurons) acting primarily on non-NMDA receptors.

Substance P and EAA are released from C fibers

Question 8

What do C fiber do before ascending to the reticular formation.

Answer 8

nociceptor that travel wit the spinoreticulothalamic pathway synapse on an interneuron in the spinal cord before ascending

Question 9

The interneuron synapse of C fiber allows for ________.

Answer 9

modulation (of spinal cord function)

local (gate theory)
descending (opioid pathways)

Question 10

T/F nociceptive input is distributed widely in the cortex?

Answer 10

True

Question 11

The _____ _____ is particularly important in the interpretation of nociceptive inputs

Answer 11

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

Question 12

Lesion in any one area _____ abolish the ability to experience pain, although the experience is changed

Answer 12

does not

Question 13

Where do many nociceptive input go?

Answer 13

To the amygdala

important for activating/producing the emotional components inherent in the sensation of pain

Question 14

Visceral nociceptors, traveling with the autonomic nerve, have additional synapses within the ________ and ________.

Answer 14

hypothalamus and medulla

theses synapse form the basis of the physiological changes associated w/ visceral pain, including diaphoresis and altered blood pressure

Question 15

What are the 2 ways to physiological modification of painful inputs?

Answer 15

1. Peripheral mechanisms

2. descending Mechanisms

Question 16

What is the basis for peripheral mechanism of modifying painful inputs?

Answer 16

observation that other somatic input can alleviate pain (rubbing the area)

Question 17

What is the 3 steps involved in the peripheral mechanism of modifying pain?

Answer 17

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

Question 18

What is the basis for the descending mechanisms of modifying painful inputs?

Answer 18

use presynaptic inhibition to reduce activation of the second-order nociceptive neuron in the spinal cord

Question 19

What are the steps in the descending mechanism of modifying painful inputs?

Answer 19

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

Question 20

What qualities are associated with deep pain?

Answer 20

associated w/ periosteum, ligaments
usually dull, achy
few A delta fibers and many C fibers
associated with muscles spasm

Question 21

Why do people experience muscles pain?

Answer 21

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

Question 22

What qualities are associated with muscle pain?

Answer 22

both Group II and IV fibers present

get both fast and slow pain associated with muscles

Question 23

Describe visceral pain.

Answer 23

poorly localized
few receptors (almost all Group IV)
Stretch receptors (distension)
often referred