Feb 5th

Question 1

two types of sensitization

Answer 1

peripheral and central

Question 2

central sensitization

Answer 2

occurs in the central nervous system, and happens in either the DRG or the spinal cord

Question 3

peripheral sensitization

Answer 3

neurochemical

Question 4

Skin-nerve preparation

Answer 4

take a piece of skin from an animal while it’s still alive, and you tease out a nerve fibre that would have been running from the skin to the DRG and spinal cord and put it in a bath to keep it alive and record from it

Question 5

what do you look at for skin-nerve preparation

Answer 5

number of action potentials per second that the nociceptor has fired

Question 6

With more bradykinin

Answer 6

more action potentials are firing at lower temperatures, including non-noxious temperatures.

Question 7

Clifford Woolf

Answer 7

discovered central sensitization in a sole-authored study published in 1983 in a paper called Nature in which he applied a heat stimulus to rats to measure the lowest amount of mechanical stimulus in grams it would take for the rat to try to withdraw from it

Question 8

what did Woolf measure his experiment

Answer 8

using WDR (second-order) neurons in the spinal cord.

Question 9

Woolf experiment

Answer 9

After the injury, the rats were extremely allodynic for about 5 hours. Before the burn injury, they fire, but it stops really quickly. After the injury, they fire more, and the fire lasts for longer.

Question 10

what was a surprise in Woolfs experiment

Answer 10

the neurons were firing on the contralateral side

Question 11

only way to explain the transfer of pain from one side to the other was if

Answer 11

the WDR neurons themselves had changed such that a stimulus that would normally not be painful before the injury but after the injury, the WDR neurons have changed their properties such that normal stimulation of intact, non-injured skin on the other side of the body is now making them fire as well

Question 12

Electrophysiological recording can distinguish between

Answer 12

peripheral and central sensitization

Question 13

injuries can cause

Answer 13

peripheral and central sensitization

Question 14

how can you differentiate central and peripheral sensitization

Answer 14

Suppose there’s only peripheral sensitization, regardless of where you’re recording from. In that case, you will see a certain amount of firing from before the injury and more firing after the injury, and you will see the same thing in the CNS. If there’s only central sensitization, you wouldn’t see any change in the periphery, but there will be more firing in the spinal cord.

Question 15

in central sensitization its the __ that has changed

Answer 15

the spinal cord neuron

Question 16

in peripheral sensitization

Answer 16

the nociceptor will be activated more

Question 17

temporal summation or ‘the wind up effect’

Answer 17

when you give a pain stimulus in one-second intervals (for example), as the more times you give the stimulus, the more times the neurons will fire.

Question 18

If stimuli are far enough apart, they will

Answer 18

not produce temporal summation and it will simply be a stimulus.

Question 19

if the stimuli are close enough to summate with each other, the pain ratings will

Answer 19

get higher and higher the more you give the stimulus

Question 20

Temporal summation is the evidence that

Answer 20

central sensitization has occurred

Question 21

Sensitization produces

Answer 21

hyperalgesia or allodynia

Question 22

primary vs secondary hyperalgesia

Answer 22

Primary hyperalgesia is the thing that happens close to or at the site of the injury. Secondary hyperalgesia is mechanically specific; it doesn’t work with heat stimuli.

Question 23

two types of secondary hyperalgesia

Answer 23

bc two types of mechanical stimuli - poking (punctuate and static) vs brushing (stroking and dynamic)

Question 24

By using stroking stimuli, the area of secondary hyperalgesia

Answer 24

doesn’t go as far, but it will go further if a punctate stimulus is used.

Question 25

Some evidence of this is 'mirror pain'

Answer 25

where if the injury is on one side of the body, you can see hyperalgesia and allodynia on the other side of the body - and you can apply compounds that either cause analgesia or complete desensitization of the area which gets rid of primary pain, but doesn't do anything to secondary hyperalgesia.

Question 26

secondary hyperalgesia is

Answer 26

mechanically specific; it doesnt work with heat stimuli

Question 27

diagram on L3S54

Answer 27

there's the external stimulus, which is either nothing, an innocuous stimulus (in blue), or a noxious stimulus (in red). The blue is A-beta, and the red is A-delta or a C. The halo symbolizes that the nociceptor is sensitized. The halo is peripheral sensitization. The neurons, or afferents, lead to boxes called the central sensory pathways, which are either the brain or the spinal cord. The box can be blue for normal or red for centrally sensitized.

Question 28

first gray box

Answer 28

if either an innocuous or a noxious stimulus impinges on a nociceptor that is sensitized, even if it is impinging on a normal non-sensitized spinal cord, that will be enough to produce allodynia - in the case of the innocuous stimulus- or hyperalgesia - in the case of the noxious stimulus. However, they will be primary allodynia or hyperalgesia, so you will only find it at the site where the injury is

Question 28

second gray box

Answer 28

there is central sensitization. So, the innocuous stimulus will make a touch fibre fire, and because the spinal cord neuron is sensitized, it will produce allodynia in the secondary area. For hyperalgesia, the same thing occurs, except the stimulus is noxious.

Question 29

third gray box

Answer 29

there is no stimulus at all; this is spontaneous pain caused by the afferents firing by themselves. It is called ectopic firing when afferents fire by themselves, with no peripheral input. If a nociceptor fires ectopic activity, that is spontaneous pain. If a low-threshold neuron or a touch fibre fires ectopic activity, that is paraesthesia. If an A-beta fires ectopic activity and you already have central sensitization, then in addition to spontaneous pain, you will also get dysesthesia.

Question 30

injury produces lots of

Answer 30

plasticity

Question 31

functional plasticity

Answer 31

when whatever is there changes its function to produce sensitization

Question 32

what changes occur in functional plasticity

Answer 32

molecular, synaptic, cellular, and network

Question 33

structural plasticity

Answer 33

when new things are being made or taken away; some physical change has occurred

Question 34

what changes in structural plasticity

Answer 34

can change the number of synaptic spines, the connectivity of the axons (denervation or hypotrophy), and number of cells you have

Question 35

immune cells or glial cells are

Answer 35

very important to the study of pain

Question 36

neuroimmunology happens

Answer 36

both the periphery and spinal cord

Question 37

easy ways to measure pain include

Answer 37

a thermode (a device that you place on the skin that can be heated up), the cold presser test (someone places their hand or arm in cold water), or a pressure algometer (you put it on a particular body part and press down harder and harder until the patient says they feel pain)

Question 38

pain threshold

Answer 38

how much of a specific stimulus (heat, cold, pressure) someone can take until it becomes pain

Question 39

pain tolerance

Answer 39

how much pain stimulus you can take until it becomes too much.

Question 40

problem with pain threshold

Answer 40

it's hard to figure out the exact second that something goes from not being painful to being painful

Question 41

problem with pain tolerance

Answer 41

as a measure is that it can be affected by all sorts of things (someone forcing themselves to hold on for longer than they normally would because of the fact that it's a study, etc.)

Question 42

NRS

Answer 42

numeric rating scale is an 11 point scale, from 0-10