Neural Basis of Pain

Question 1

What is pain?

Answer 1

Unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage

Question 2

What is a nociceptor?

Answer 2

Free dendritic nerve ending which detects pain stimuli

Question 3

Name the 3 types of nociceptor

Answer 3

Chemical
Thermal
Mechanical

Question 4

Which channel is most important in detecting noxious stimuli?

Answer 4

TRPV1 receptor

Question 5

What is the TRPV1 receptor activated by?

Answer 5

Protons (pH<6.0)

Temperature (>43 Celcius)

Question 6

Which ascending tract do pain neurones travel in?

Answer 6

Spinothalamic tract

Question 7

Where do pain fibres decussate the midline?

Answer 7

At their spinal level

Question 8

Name the system which pain fibres from the face enter

Answer 8

Trigeminothalamic system

Question 9

Name the 2 fibres that nociceptors normally associate with

Answer 9

C-fibres

A-delta fibres

Question 10

Describe pain C-fibres

Answer 10

Small, unmyelinated, slow conduction velocity, dull, aching pain, polymodal

Question 11

Describe A-delta pain fibres

Answer 11

Larger, myelinated, faster conduction, sharp pain, only activated by mechanical stress and heat

Question 12

Where abouts in the dorsal horn do the pain ascending tracts lie?

Answer 12

Lamina I and V

Question 13

Where can the substantia gelatinosa be found?

Answer 13

Lamina II

Question 14

What is the substantia gelatinosa?

Answer 14

Inhibitory interneurons which run to lamina I and V to inhibit transmission between 1st order and 2nd order neurons

Question 15

Describe the process of descending inhibition of pain

Answer 15

Neurones from the peri-aquaductal grey have an analgesic effect
The descending fibres synapse on the substantia gelatinosa and cause more inhibition to the connecting 1st and 2nd order neurons

Question 16

Why can rubbing an area of pain cause pain relief?

Answer 16

A-beta mechanoreceptors are activated which synapse on the substantia gelatinosa. This increases inhibition of the 1st order afferent neuron which relieves pain

Question 17

Name the nucleus in the medulla of the descending inhibition pathway

Answer 17

Nucleus raphe magnus

Question 18

Explain how peripheral sensitisation can occur

Answer 18

When cells are damaged, their contents are released and there is an inflammatory response. The ECF is filled with histamine, 5 HT, substance P, bradykinin and prostaglandins.
These can activate nociceptive receptors to cause pain or can sensitise the receptors like TRPV1 so they are activated more readily. More pain is felt

Question 19

What is wind up?

Answer 19

Receptive field expansion at the peripheries

Question 20

Describe acute pain

Answer 20

Short term pain, >3 months

Question 21

Describe chronic pain

Answer 21

Long term, >3 months

Question 22

What is hyperalgesia?

Answer 22

Increased pain at normal stimulation

Question 23

What is allodynia?

Answer 23

Pain from a stimuli that is not normally painful

Question 24

What is referred pain?

Answer 24

Pain in a different area to where the tissue damage is located

Question 25

What is neuropathic pain?

Answer 25

Pain of neuronal origin. Cannot be explained by a single disease process or specific location

Question 26

What is phantom limb pain?

Answer 26

Patients who have lost limbs sometimes complain of feeling pain in the limb which is no longer present
The pain does not respond to morphine suggesting the pain arises centrally

Question 27

Describe some symptoms of Complex Regional Pain Syndrome

Answer 27

Severe, continuous burning pain 
Hyperalgesia
Allodynia
Temperature asymmetry
Oedema
Sweating 
Motor dysfunction

Question 28

What can cause Complex Regional Pain Syndrome?

Answer 28

Minor trauma
Bone fractures
Surgery 
Stroke
MI