Nerves and pain

Question 1

List the different types of mechanoreceptors

Answer 1

• Nociceptors
• Pacinian corpuscle
• Meissner’s Corpuscles
• Merkel-cell-neurite complex
• Ruffini organ

Question 2

Define nociceptors

Answer 2

Free-nerve endings that sit in tissue to detect tissue damage

Question 3

Define Pacinian corpuscles

Answer 3

• Large receptive field
• senses high frequency vibrations (>500 Hz)
• Response briefly when stimulus applied and removed
• Rapid conducting axons

Question 4

Define Meissner’s Corpuscles

Answer 4

• Small receptive field
• Senses low frequency vibrations
• Response briefly when stimulus applied
• Touch sensitivity with active exploration

Question 5

Define Merkel-cell-neurite complex

Answer 5

• Small receptive field
• senses pressure
• Response throughout stimulus

Question 6

Define Ruffini ORgan

Answer 6

• Spindle-shaped

- Responds to skin stretch

Question 7

Explain the concept of ‘pain’, nociception and mechanisms of pain

Answer 7

Pain - both the perception of nociceptive event and emotional experience associated with actual or potential tissue damage.

Question 8

List the nociceptor classes

Answer 8

• Thermal
• Mechanical
• Polymodal = respond to multiple stimuli
• Silent = only activated when a very specific cytokine is present; produce a completely novel sensation

Question 9

Describe the different fibre types of nociceptors

Answer 9

A-delta fibres

• Thermal and pain sensors: pain and temperature
• Myelination
• Larger diameter
• Relatively fast conduction: causes ‘first pain’ = sharp mechanical pain.

C-fibres

• Polymodal sensors: temperature, pain itch
• No myelination
• Small diameter
• Slow conduction: causes “second pain” = visceral aching pain

Question 10

Describe nociceptor activation

Answer 10

• Tissue damage causes release of nociceptor-activating mediators: bradykinin, prostaglandins, potassium
• These mediators activate nociceptors only
• Nociceptors send pain signal to spinal cord

Question 11

Describe retrograde activation:

Answer 11

• sensory axons send signal away from spinal cord
• Substance P is released and activates mast cells
• Mast cells release histamine which increase swelling and sensitivity of nociceptors
• Histamine and substance P acts on vessels -> More bradykinin, PGs, and histamine from blood further activates and sensitizes nociceptors

Question 12

Define ‘alloydynia’

Answer 12

previously touch stimulus become painful

Question 13

Define ‘hyperalgesia’

Answer 13

Noxious stimuli are now perceived as more noxious

Question 14

Define ‘referred pain’

Answer 14

You can detect pain in a location distant from the actual source of the pain, due to the convergent of axons in the ganglion. Usually visceral pain is felt at cutaneous location. Brain isn’t used to feeling visceral pain.

Question 15

Describe facial palsy

Answer 15

Facial paralysis of facial muscles on one affected side; cause by disruption of Facial nerve.
Causes:
- Brainstem stroke
- Temporary paralysis via compression of facial nerve due to swelling
- Brain tumour or stroke
- Brain trauma
- Dentist cause: misplaced local anaesthetic (temporary FP)

Symptoms:

• Early: pain in jaw and numbness in tongue
• Late: involuntary contraction of affected side, watering eyes, and cornea ulceration (due to inability to close eyes)

Question 16

Describe early recognition of facial palsy

Answer 16

Early recognition to prevent permanent disability:
Clinical tests - inability to:
- smile (symmetrically)
- Blow out cheeks
- Tightly close eyes