Introduction to pain physiology

Question 1

State the pain pathway.

Answer 1

1. Pain stimulus
2. Transduction (nociception)- conversion of pain stimuli to nerve impulses by pain receptors
3. Transmission of pain information to the spinal cord by sensory neurones
4. Spinal cord processing
5. Transmission of pain info via ascending tracts in spinal cord to the brain
6. Processing of pain info in the brain.

Question 2

Define nocicoptors.

Answer 2

They are free nerve ending sensory neurons that can sense noxious stimuli. Nociceptors are found in the somatic and visceral structures.

Question 3

Describe pain stimulus.

Answer 3

This can either be physical or chemical.
Physical stimuli include intense or noxious thermal and mechanical stimuli.
Chemicals can be released as a result of tissue damage.

Question 4

There are two types of nociceptors, name them.

Answer 4

1. High threshold mechanical receptors

2. Polymodal nociceptors

Question 5

Define High threshold mechanoceptor.

Answer 5

This responds to intense mechanical stimulation.

Question 6

Define Polymodal Nociceptors.

Answer 6

This responds to noxious mechanical,noxious thermal and noxious chemical stimuli.

Question 7

State the four basic processes involved in nociception.

Answer 7

Nociception describes the normal processing of pain and the responses to noxious stimuli that are damaging to tissue.

1. Transduction
2. Transmission
3. Perception
4. Modulation

Question 8

Describe what is meant by the transduction of pain.

Answer 8

When the body is subjected to painful stimuli, mast cells release histamines. Neurochemicals are released for example substance P. This stimulation leads to ion channels opening in the nociceptors, with an influx of sodium ions.

Question 9

Describe what is meant by the transmission of pain and its processes.

Answer 9

The pain impulse is transmitted;

1. From the site of transduction along the nociceptor fibres to the dorsal horn in the spinal cord.
2. From the spinal cord to the brain stem
3. Through connections between the thalamus,cortex and higher levels of the brain.

Question 10

What is the difference between first and second pain.

Answer 10

The first pain is sharp and felt in a defined area, it is associated with A-delta fibres.
The second are burning or dull aching pain is associated with C fibres.

Question 11

Describe A-delta fibre.

Answer 11

A fast conducting myelinated fibre that signals an early, localized, intense pain. This also mediates the sensation of itching.

Question 12

Describe C fibre.

Answer 12

A slow conducting unmyelinated fibre that signals a later, poorly localized, long-lasting, dull pain.

Question 13

Where do A-delta and C fibres carry pain information.

Answer 13

To the dorsal horn of the spinal cord.

Question 14

What does grey matter consist of in the spinal cord.

Answer 14

The grey matter contains cells and central terminals of primary afferents from the periphery.

Question 15

What does white matter consist of in the spinal cord.

Answer 15

It contains ascending and descending fibres.

Question 16

Describe the transmission of noxious information in the brain.

Answer 16

Pain info reaches the brain via ascending tracts or pathways in the brain. The most important is the Lateral Spinothalamic Tract Pathway.

Question 17

Describe the three neurones involved in the Spinothalamic Tract.

Answer 17

Afferent fibres-
1.Synapse in the dorsal horn and 2. second order neurones cross over the other side of the spinal cord and carried in the spinothalamic Tract to the thalamus. 3.Third order neurones carry info from the hypothalamus to the sensory cortex.

Question 18

Describe briefly the processing in the brain.

Answer 18

Perception of pain becomes a conscious multidimensional experience. This has affective-motivational,sensory discriminative, emotional and behavioural components.

Question 19

What is reticular formation, in reference to processing in the pain.

Answer 19

Fibres from the reticular formation then radiate to all areas of the cortex, alerting it to the effects of sensory stimuli of all kinds. Information also goes to the thalamus and hypothalamus.

Question 20

Describe the role of the thalamus and the hypothalamus in the brain processing information.

Answer 20

The thalamus is central to the sensation of pain. Information is relayed through the thalamus to the cerebral cortex. This also gets projected into the limbic system, basal ganglia and hypothalamus.

Question 21

Describe the modulation of pain.

Answer 21

It involved changing or inhibiting transmission on pain impulses in the spinal cord.