Pathophysiology of pain

Question 1

Describe step 1 in the pain pathway

Answer 1

Periphery - detection, transmission to spinal cord

Question 2

Describe step 2 in the pain pathway

Answer 2

Spinal Cord - procession, transmission to the brain

Question 3

Describe step 3 in the pain pathway

Answer 3

Brain - perception, learning, response

Question 4

Describe step 4 in the pain pathway

Answer 4

Modulation -descending tracts

Question 5

What fibres are involved in noceception?

Answer 5

A-delta and C fibres

Question 6

What do nociceptors respond to?

Answer 6

Thermal, chemical, mechanical noxious stimuli

Question 7

Where do nociceptive fibres synapse?

Answer 7

DRG in spinal cord

Question 8

What is the function of the thalamus?

Answer 8

To act as a second relay station

Question 9

Name a function of the descending pathways

Answer 9

To decrease the pain signal

Question 10

Where do descending pathways arise from?

Answer 10

The dorsal horn

Question 11

Describe the affect allodynia has on the nociceptor?

Answer 11

central pain sensitisation following non-painful, repetitive stimulation resulting in pain response from a stimulus which usually does not cause pain

Question 12

Describe the affect that hyperalgesia has on the nociceptor?

Answer 12

Exaggerated response to normal and supranormal stimuli

Question 13

Describe central sensitisation

Answer 13

condition of the nervous system that is associated with the development and maintenance of chronic pain. Occurs at level of spinal cord and is the response of second order neurons in CNS to both noxious and non-noxious stimuli

Question 14

Describe wind up

Answer 14

A pathological change that lowers the threshold for pain signals to be transmitted. Caused by repeated stimulation of C fibres

Question 15

Descrbe classical central sensitisation

Answer 15

Involves opening of new synapses in dorsal horn which recieve input and record nociception. Signal has to be intense enough to elicit a response. Response is immediate and might outlast duration of stimulus

Question 16

Describe long term potentiation

Answer 16

Persistent strengthening of synapses based on recent patterns of activity resulting in long lasting transmission signal increase between two neurones. Only occurs in active neurones and for very intense stimuli

Question 17

Describe the characteristics of acute pain?

Answer 17

Usually obvious tissue damage, increased nervous system activity, pain resolves upon healing, serves as a protective function

Question 18

Describe the characteristics of chronic pain?

Answer 18

> 3-6 months, pain beyond expected period of healing, usually has no protective function, degrades health and function

Question 19

What is nociceptive pain?

Answer 19

A sensory experience that occurs when specific peripheral sensory neurones respond to noxious stimuli

Question 20

Describe features of nociceptive pain?

Answer 20

Pain region is typically localised at site of injury, usually time limited and resolves when damaged tissue heals, can also be chronic, tends to respond to conventional analgesics

Question 21

What is neuropathic pain?

Answer 21

pain initiated or caused by a primary lesion or dysfunction in the somato-sensoty nervous system

Question 22

What are features of neuropathic pain?

Answer 22

The painful region may not necessarily be the same as the site of injury- pain occurs in the neurological territory of the affected structure, almost always in a chronic condition, responds poorly to conventional analgesics

Question 23

What may cure pain from the transduction pathway?

Answer 23

NSAIDs, Ice, Rest, LA block

Question 24

What may cure pain from the transmission pathway?

Answer 24

Nerve blocks, Drugs, Surgery

Question 25

What may cure pain from the perception pathway?

Answer 25

Education, CBT, Distraction, Relaxation, Graded Motor Imagery, Mirror Box Therapy

Question 26

What may cure pain from the descending modulation pathway?

Answer 26

Placebos, Drugs, Surgery

Question 27

What are primary afferents?

Answer 27

Cell body is in DRG, they synapse at spinal cord

Question 28

Where does pain perception occur?

Answer 28

The somatosensory cortex

Question 29

Describe the ascending pain pathway

Answer 29

Prostaglandins is released in response to inflammation and sensory nerves respond to this by projecting to the dorsal horn of spinal cord.

1st order neurons synapse at spinal cord and relay pain signals to second order neurons

2nd order neurons decussate at spinal cord and pass into spinothalamic tract, where they project up into thalamus

2nd order neurones synapse onto third order neurons which help discern area of injury

Site of injury is contralateral to side of brain receiving information about pain

Question 30

Describe the descending pain pathway

Answer 30

Aim is to modulate pain

First order neurons arise from periaqueductal grey matter and synapse in medulla.

Second order neurones are seritonergic / noradrenergic and project into the dorsal horn of spinal cord. They inhibit first order neurons from the ascending pain pathway from synapsing with second order neurons.

Substance P is also inhibited

Question 31

Hemisection of the spinal cord results in what?

Answer 31

CONTRALATERAL loss of pain and temperature below lesion (as spinothalamic tract decussates at the spinal cord)

IPSILATERAL loss of touch (as DCML decussates at medulla)

IPSILATERAL spasticity and loss of motor function (as CST decussates at medulla)