Pain and neural transmission

Question 1

Where are nociceptors found?

Answer 1

• In the periphery as simple free nerve endings
• Branches and terminates as naked, unmyelinated ending in the dermis

Question 2

What does tissue damage and inflammation trigger?

Answer 2

Release of substances that sensitize peripheral
nociceptors → hyperalgesia

Question 3

What are the different types of nociceptors, and what do they do

Answer 3

• Mechanical → strong pressure
• Thermal → respond to extreme heat or cold
• Chemical → respond to histamine or other chemicals

Question 4

What stimuli do most nociceptors respond to

Answer 4

• Mechanical
• Thermal
• Chemical stimuli

Question 5

How do all sensory receptors work

Answer 5

• Stimulus deforms and changes the nerve ending
• Alters the membrane permeability of the receptor membrane → produces receptor potential
• Triggers an action potential travelling along axon to CNS

Question 6

How can sensory afferent nerves that innervate the somatosensory receptors be classified

Answer 6

• Conduction velocity positively correlates with axon diameter
• Large diameter: Rapidly conducting afferents
• Small diameter: Slow conducting afferents

Question 7

Describe first pain

Answer 7

• Fast Aδ fibres
• Sharp, prickling and easily localised
• Occurs rapidly for a short duration
• Mechanical or thermal nociceptors

Question 8

Describe second pain

Answer 8

• Slow C-fibres
• Dull ache, burning, and poorly localised
• Slow onset and persistent
• Polymodal nociceptors

Question 9

What are the skin and deeper structures innervated by

Answer 9

A rich, vast network of peripheral nerves

Question 10

Describe the primary afferents

Answer 10

• Feed into the spinal cord via a spinal nerve and the dorsal root
• Afferents bring information in from somatic receptors

Question 11

Describe the motor afferents

Answer 11

• Leave the spinal cord via a ventral root and the spinal nerve
• Efferents leave the spinal cord via a ventral root and the spinal nerve

Question 12

Where are the nociceptor fibre cell bodies found in the spinal cord segment

Answer 12

Within the dorsal root ganglion

Question 13

Where do the afferent terminals enter and travel down in the spinal cord segment

Answer 13

• Enter the dorsal horn
• Travel down a short distance within the Zone of Lissauer

Question 14

What do the afferent terminals synapse onto in the spinal cord segment

Answer 14

Synapse onto neurones within the superficial laminae of the dorsal horn

Question 15

How do the nociceptive afferents from internal organs enter the spinal cord

Answer 15

• Enter through common routes and target overlapping populations of spinal neurons
• Crossover of communication leads to referred pain, where visceral pain is perceived as having a cutaneous source by the sufferer

Question 16

Describe the contralateral pathway

Answer 16

Sensory inputs cross at level of spinal cord, ascend on opposite side

Question 17

Describe the ascending pain pathways

Answer 17

• Processes afferent inputs from peripheral mechano-, thermal and polymodal nociceptors
• Contralateral pathway: sensory inputs cross at level of spinal cord, ascend on opposite side
• Information relayed to the thalamus and then onto the somatosensory cortex

Question 18

What are the 3 components of the ascending pain pathways

Answer 18

• Lateral(neo-)spinothalamic tract
• Spinoreticulothalamic tract
• Anterior spinothalamic tract

Question 19

Describe the trigeminal system’s role in the pathway of pain and temperature from the face and head

Answer 19

• Small diameter afferents descend in the spinal trigeminal tract to the brain stem
• These synapse with second-order sensory neurons in the pars caudalis
• Axons ascend contralaterally to the thalamus in the trigeminothalamic tract
• Projection to the cortex via the ventral posteromedial nucleus

Question 20

What is phantom pain

Answer 20

Pain and touch sensations without sensory input

Question 21

What is endogenous analgesia

Answer 21

No sensations with sensory input

Question 22

What is pain modulation

Answer 22

Body alters the pain signal along the pathway

Question 23

What are hyperalgesia (increased pain) and allodynia (touch-evoked pain) features of

Answer 23

Chronic pain syndromes and pathological pain

Question 24

Where is the highest concentration of mu opiate receptors?
Where are intermediate levels of opiates found?

Answer 24

• Highest concentration in the thalamus
• Intermediate levels are in the cerebral cortex and basal ganglia

Question 25

What can hyperalgesia be seen as

Answer 25

• A reduced threshold for pain
• An increased threshold of painful stimuli
• Spontaneous pain

Question 26

(Acute pain)
What is nociceptive stimulation?
What type of pain does nociceptive stimulation cause?

Answer 26

• Thermal, mechanical, chemical
• Acute pain (protective)

Question 27

(Acute pain)
What is innocuous stimulation?
What type of pain does innocuous stimulation cause?

Answer 27

• Touch, pressure, brush
• Non-painful sensations

Question 28

(Chronic pain)
What does tissue/nerve damage, inflammation, disease

Answer 28

• Hyperalgesia (Increased pain, sensation)
• Ongoing pain

Question 29

(Chronic pain)
What does innocuous stimulation cause

Answer 29

Allodynia (touch-evoked pain)

Question 30

What is the gate theory of pain

Answer 30

• Non-nociceptive inputs will not activate projection
  neuron
• Pain inputs alone activate the spinothalamic
  neuron to the maximum
• Co-activation of Aα/β and C fibres will suppress
  activation of the projection neuron by C-fibres