9.1.1 Pain

Question 1

What is the definition of pain?

Answer 1

An unpleasant sensory and emotional experience associated with or resembling that associated with, actual or potential tissue damage

Pain can also be emotions basically

Question 2

What stimuli do first order sensory neurones detect?

Answer 2

Tissue damage nociceptors

Physical e.g. noxious, heat

Chemicals e.g. acids/alkalis

Question 3

What do A delta fibres and C fibres do?

Answer 3

Primary sensory neurones

A delta fibres- fast pain fibres e.g. initial sharp pain

C fibres- slow pain fibres e.g. burning

Question 4

Outline the pathway for pain transmission

Answer 4

Primary sensory neurone

Synapse onto 2nd order neurone in the dorsal horn

2nd order neurone transmits to the thalamus

3rd order neurone in the thalamus transmits cortex

Question 5

Where can pain be modulated by drugs?

Answer 5

In the dorsal horn where first order neurones synapse onto second order

This area is called the Pain gate

Question 6

What are the 3rd order neurone projections in the pain pathway?

Answer 6

Sensory dimension
Projects to the cortex to allow us to feel the pain and locate where it is

Affective dimension
Projects to limbic system, gives us emotional response to pain, hence why we cry in pain?

Question 7

At the pain gate what inputs do 2nd order sensory neurones receive?

Answer 7

• Inputs from first order sensory neurones
• Mechanoreceptors, synapse onto the inhibitory interneurones
• Descending pathways- inhibition

Question 8

What do inhibitor interneurones release?

Answer 8

GABA and endorphins e.g. encephalin

Question 9

What are endorphins?

Answer 9

Endogenous morphine-like substances

Question 10

What is released from descending pathways which act on 2nd order sensory neurones?

Answer 10

NorAD
5-HT

Question 11

What receptor does encephalin bind to?

Answer 11

µ opioid receptor

Question 12

What receptors does pain inhibition act on?

Answer 12

µ opioid receptors

Question 13

Where are mu opioid receptors found?

Answer 13

Found in the:
- Insular cortex
- Hypothalamus
- Amygdala
- Periaqueductal grey matter
- Rostral ventral medulla

Question 14

What regions in the brain synapse onto periaqueductal grey matter?

Answer 14

Insular cortex
Amygdala
Hypothalamus

Question 15

Outline the descending pathways from the brain to second order sensory neurones

Answer 15

Projections from the insular cortex, amygdala and hypothalamus synapse onto periaqueductal grey matter in the midbrain

Projects and synapses to rostral ventral medulla

This then synapses onto 2nd order sensory neurones in the spinal cord

Question 16

What effect does the amygdala have on pain?

Answer 16

Responsible for the stress response

Less inhibition of 2nd order sensory neurones during stress causing a lower pain threshold

Question 17

What effect does the hypothalamus have on pain?

Answer 17

Responsible for pain threshold

Varies during the menstrual cycle

Question 18

When pain is inhibited by higher centres, what is released?

Answer 18

Dopamine

Hence why opioids can be so addictive as the activation of µ opioid receptors leads to a sense of reward/euphoria