Pathophysiology of pain and nociceptor classification

Question 1

What is the physiological definition of pain?

Answer 1

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

Question 2

Why type of damage does pain resemble or is associated with?

Answer 2

Actual/potential tissue damage

Question 3

What does the fact that pain is an unpleasant and emotional experience suggest about brain regions involved?

Answer 3

Indicates that pain is a conscious experience coming from integrated activity in multiple sensory and emotional centres in brain

Question 4

Is pain felt when unconscious?

Answer 4

No

Question 5

Why does the fact that pain is not felt when unconscious make it difficult to understand the physiology of pain mechanisms?

Answer 5

This means that pain isn’t a sensation and is multidimensional and there is lack of physiology of consciousness

Question 6

What are the 2 functions of pain as a protective mechanism?

Answer 6

Warns about ongoing damage

Promotes recovery

Question 7

When does perception occur relative to the stimulus?

Answer 7

Perception happens after reflex withdrawal from stimulus

Question 8

Define noxious stimulus?

Answer 8

Stimulus that is actually/potentially damaging to tissue and liable to cause pain, but doesn’t always cause pain in a situation

Question 9

Define nociception?

Answer 9

Neural process (brain function) of encoding noxious stimuli (eg. tissue injury)

Question 10

What are the 3 physiological processed that make up nociception when signals travel from periphery to CNS, and does nociception need consciousness?

Answer 10

Involves transduction, transmission, modulation of neural signals from periphery to CNS, and doesn’t need consciousness

Question 11

What 2 types of directional neuroanatomical pathways are involved in nociceptive transmission, and what is the resulting experience?

Answer 11

Ascending (afferent) and descending (efferent) neuroanatomical pathways

result in subjective experience of pain

Question 12

Define nociceptor?

Answer 12

Neuron that responds specifically to noxious stimuli

Question 13

What are the 4 types of noxious stimuli?

Answer 13

Mechanical (sharp)

Thermal (damaging heat or cold)

Chemical

Polymodal (combination of mechanical, thermal, chemical)

Question 14

What is the morphology/structure of a nociceptor?

Answer 14

Primary afferent pseudounipolar neuron

Question 15

What is meant by a nociceptor being primary?

Answer 15

It is a neuron that receives sensory input

Question 16

What is meant by a nociceptor being afferent?

Answer 16

It transduces info received in PNS and transmits it to CNS

Question 17

What is meant by a nociceptor being pseudounipolar?

Answer 17

Gives impression that it has more than one extension from the cell body, but actually only has one extension from the cell body

Question 18

What is the difference in length between proximal and distal axons of a nociceptor, and where does each axon project to?

Answer 18

Smaller proximal/central axon projects to spinal cord

long distal/peripheral axon that can terminate in fat or tissue that senses noxious injury except in brain eg. skin, muscle, tendon

Question 19

Where in the nociceptor structure are nociceptive stimuli transduced into electrical signals?

Answer 19

Free nerve endings: Dendrites that aren’t encapsulated by connective tissue

Question 20

Explain what is meant by a nociceptor being a functional unit of a glio-neural end organ?

Answer 20

End organ: specialised structure at end of peripheral nerve that acts as a receptor for a specific sensation

Glio-neural refers to interaction between neurons and glial cells, which provide support and protection of neurons and produce myelin

Question 21

What is the function of glial cells?

Answer 21

To provide support and protection of neurons and produce myelin

Question 22

What 2 structures is a nociceptor a part of?

Answer 22

Nociceptors form part of each spinal nerve and dorsal root ganglion (cluster of cells found in PNS) adjacent to spinal cord at each segment

Question 23

How do sensory neurons travel from the dorsal root ganglion to within the spinal cord?

Answer 23

Dorsal root ganglion found just outside dorsal root, where it allows the sensory neurons in the ganglion to enter the spinal cord via the dorsal root

Question 24

What 2 classes of neuron are nociceptors, and what kind of pain does each class transmit signals for?

Answer 24

Aδ nociceptors signal for fast nociception

C fibre nociceptors signal for slow nociception

Question 25

What are the 2 ways in which neurons are classified?

Answer 25

Diameter

Myelin sheath presence

Question 26

What 2 stimuli are detected by Aβ nociceptors, and do they have myelin sheath?

Answer 26

Detects touch and pressure

Has thick myelin sheath, which allows fast pain transmission

Question 27

What 4 stimuli are detected by C fibre nociceptors, and do they have myelin sheath?

Answer 27

Emotion, movement, heat, motivation

No myelin sheath, which allows slow pain transmission