7.1 Pain

Question 1

Recall the purposes of pain

Answer 1

• Avoid harm
• Promote immobility and healing

Question 2

List three types of pain

Answer 2

• Nociceptive
• Inflammatory
• Pathological

Question 3

Physiological vs pathological pain

Answer 3

Physiological: normal and adaptive

Pathological: nonprotective, maladaptive

Question 4

What are the three classifications of nociceptive pain?

Answer 4

• Somatic (deep/superficial)
• Visceral

(Think of sensory modalities, like in cranial nerves)

Question 5

What are the three types of pathological pain? What characterises them?

Answer 5

• Neuropathic
• Phantom
• Psychogenic

Question 6

Threshold of inflammatory vs nociceptive pain?

Answer 6

Inflammatory: low
Nociceptive: high

Question 7

Which types of pain are pathological/physiological?

Answer 7

Patho: Pathological (wow!)
Physio: inflammatory and nociceptive

Question 8

What is nociceptive pain?

Answer 8

Pain in response to noxious stimulus (i.e., damage/potential damage to the body)

Question 9

Describe the tissues involved in the three different types of nociceptive pain

Answer 9

Sup. Somatic: Skin, superficial tissues

Deep somatic: bone, tendon, ligament, muscle

Visceral: internal organs

Question 10

Describe the stimuli that can cause the three different types of nociceptive pain

Answer 10

Sup. somatic: burns, shallow cuts, chemicals

Deep somatic: sprains, fractures

Visceral: stretching, hypoxia

Question 11

Describe the character of the three different kinds of nociceptive pain

Answer 11

Sup somatic: sharp

Deep somatic: dull, aching

Visceral: dull, deep & squeezing

Question 12

Which types of nociceptive pain are easy/difficult to locate?

Answer 12

Sup Somatic: Easy

Deep Somatic/Visceral: Difficult

Question 13

Two things happen before a nociceptive signal reaches the brain. What are they?

Answer 13

1. Motor pathway activation (e.g. withdrawal reflex)
2. Modulation

Question 14

Inflammatory pain is associated with…

Answer 14

Peripheral inflammation and tissue injury

Question 15

Inflammatory pain causes two phenomena related to pain hypersensitivity. What are they?

Answer 15

• Hyperalgesia: increased pain from a stimulus that is normally painful
• Allodynia: pain from a stimulus that isn’t normally painful

Question 16

Describe neuropathic pain

Answer 16

• Pain from nerve damage after initial insult, e.g.:

Postsurgical, diabetic neuropathy, cancer pain

Question 17

Describe the character of neuropathic pain

Answer 17

• Shooting/electric shock (like trigeminal neuralgia)
• Tingling, burning, aching

Question 18

In what kind of nerve endings are nociceptors located?

Answer 18

Free nerve endings

Question 19

What are the five kinds of nociceptors?

Answer 19

• Mechano
• Chemical
• Mechano-thermal
• Polymodal (all three)
• Silent nociceptors (respond to inflammation)

Question 20

Outline the full sensory pathway of pain from the face/head/mouth.

Answer 20

• Primary afferents from CN V head trigeminal spinal nucleus
• Decussate, and head to thalamus
• A delta head to 1° somatosensory cortex
• C fibres head to 2° somatosensory cortex

Question 21

Describe the role of the primary vs secondary somatosensory cortices in pain.

Answer 21

Primary: precise location of pain, assessing intensity

Secondary: Recognising pain, remembering past pain

Question 22

Define chronic pain

Answer 22

Pain that lasts beyond normal healing time of injury/illness.

Question 23

Describe how peripheral nerve sensitisation can cause chronic pain

Answer 23

• Chronic inflammation/nerve injury
• Concentration of voltage-gated sodium channels
• Lowered nociceptive threshold
• Chronic firing of silent nociceptors

Question 24

Describe two mechanisms of central sensitisation

Answer 24

1. “Wind up” from repetitive stimulation
2. Abnormal sprouting of axons causing unusual connections, meaning non painful stimuli become painful

Question 25

Describe 3 broad effects of microglial activation on pain synapses. What is the overarching consequence of this?

Answer 25

1. Increased pre/postsynaptic firing
2. Decreased inhibition
3. Decreased glutamate recycling by astrocytes

Result: nociceptive hypersensitivity