Peripheral Mechanisms of Pain

Question 1

What is pain?

Answer 1

Unpleasant sensory and emotional experience associated with tissue damage

Question 2

What class of receptor are all nocicpetors?

Answer 2

free nerve endings

Question 3

What are A-delta mechanosensitive nociceptors?

Answer 3

Activated by noxious mechanical stimulation

Question 4

Whare are A-delta mechanothermal nociceptors?

Answer 4

Activated by both noxious mechanical and thermal stimulation

Question 5

What are C fibers?

Answer 5

Activated by a variety of chemical stimuli in addition to noxious mechanical and thermal stimulation

When they respond to all three, they are also called polymodal nociceptors

Question 6

What is the difference between an activator and a sensitizer?

Answer 6

Activators are capable of directly activating nociceptors

Sensitizers are capable of lowering the threshold for nociceptor activation

Question 7

What are four activators of nociceptors?

Answer 7

Potassium

Serotonin

Bradykinin

Histamine

Question 8

What are four sensitizers of nociceptors?

Answer 8

Prostaglandins

Leukotrienes

Substance P

Calcitonin gene-related peptide (CGRP)

Question 9

What does the response of a nociceptor depend on?

Answer 9

The type of receptor proteins contained in their peripheral endings

Question 10

What is the axon reflex?

Answer 10

Activation of one nociceptor ending initiates action potentials that propagate antidromically to invade nociceptor endings which were not activated by the noxious stimulus

Question 11

What do axon terminals of nociceptors release?

Answer 11

Glutamate

Many also co-release either Substance P or CGRP

Question 12

What is hyperalgesia?

Answer 12

Increase in pain response to normally painful stimulation

Question 13

What is primary hyperalgesia caused by?

Answer 13

Occurs in tissue surrounding the site of injury

Caused by peripheral release of chemical activators and sensitizers during the axon reflex

Question 14

What is secondary hyperalgesia caused by?

Answer 14

Occurs in the area surrounding the area of primary hyperalgesia

Mediated centrally in spinal cord and brain through multiple processes

Question 15

What is spontaneous pain?

Answer 15

Pain in the absence of any apparent stimulation

Question 16

What is allodynia?

Answer 16

Sensation of pain resulting from stimuli which are not normally capable of evoking pain

Question 17

What is acute pain?

Answer 17

Short duration and resolves with healing of damaged tissue

Question 18

What is chronic pain?

Answer 18

Pain that lasts longer than the time required for normal healing

Clinical definitions are given as fixed times

Question 19

What is neuropathic pain?

Answer 19

Caused by damage or dysfunction in any part of the peripheral or central nervous system

Question 20

What is caused by trauma to a peripheral nerve?

Answer 20

A traumatic neuroma is formed by proliferating Schwann cells and axon sprouts attempting to regrow

Question 21

What are ectopic discharges?

Answer 21

Action potentials generated at an abnormal location

Can be generated by axons in a neuroma

Question 22

What channel changes occur due to peripheral nerve injury?

Answer 22

Abnormally increased expression of voltage-gated sodium channels in the neuroma and cell body - contribute to ectopic discharges

Increased TRP channel expression in nociceptors

Question 23

What are Cyclo-oxygenase inhibitors?

Answer 23

Inhibit the formation of prostaglandins, reducing the production of painful chemical stimuli

Question 24

How do corticosteriods relieve pain?

Answer 24

Reducing inflammation, thereby reducing the amount of activators and sensitizers produced

Question 25

How do local anesthetics relieve pain?

Answer 25

Use-dependent block (binding to open channels) of voltage-gated sodium channels

Question 26

How does capsaicin relieve pain?

Answer 26

Long-term desensitization to painful stimuli