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1

What is a nociceptor?

A nociceptor is a receptor of a sensory neuron (nerve cell) that responds to potentially damaging stimuli by sending signals to the spinal cord and brain

2

What stimuli in the periphery can activate a nociceptive afferent neuron?

- A noxious mechanical stimuli (harmful) e.g. a hammer
- A noxious heat and chemical stimuli e.g. fire/ chilli

3

What are nociceptive afferent neurons?

These are small diameter primary afferent fibres of the peripheral nerves. They are sensory nerves and have a high threshold for mechanical and thermal reception compared to other sensory nerves. Therefore, are activated by noxious stimuli. The noxious stimuli activates both non myelinated C fibres and myelinated Adelta fibres.

4

Noxious stimuli activate what?

The noxious stimuli activates both non myelinated C fibres and myelinated Adelta fibres.

5

What are the four types of primary afferent neurones?

A alpha
A beta
A delta
C

6

List the order of axon type from most myelinated to not myelinated at all (largest diameter to smallest diameter)

A alpha
A beta
A delta
C

7

Which axon conducts the slowest and why?

C. it non myelinated therefore has the slowest conduction due to lack of saltatory conduction

8

Which axon conducts the fastest?

a alpha

9

What are A-alpha fibres known as? What do they detect?

Proprioceptors. Vibrations.

10

What are A-beta fibres known as? What do they detect?

Mechanoceptors. Touch

11

What are A-delta and C fibres known as? What do they detect?

Nociceptors. Painful stimuli i.e, temp; heat or cold - frostbite, lactic acid (chemical)
OR
being hit by a hammer (mechanical)

12

Explain how and where mechanocetor or proprioceptor fibres travel?

The neurones travel to the dorsal root ganglia, where the stimulus is translated as non noxious stimuli rather than noxious. The neurone carries the signal to the spinal cord and goes straight the the dorsal column nuclei.

13

Explain how and where nociceptor fibres travel?

The nociceptor detects the painful stimulus and carries the signal to the dorsal root ganglia where it is translated as noxious. The signal is carried to the spinal cord, where it synapses at the substantia gelatinosa, with an afferent neurone (secondary neurone) and crosses over to carry the signal to the spinothalamic tract.

14

A beta innervates lateral

4

15

A delta innervates lateral

1 and 5

16

C fibre innervates lateral

2

17

PHYSIOLOGICAL PAIN (ACUTE)
Nociceptors respond to acute tissue-damaging stimuli either directly, through ___ channels on nerve terminals, or indirectly, through activation of TRP channels on keratinocytes (for example, _____) and/or the release of intermediate molecules (such as ____).

TRP
TRPV3
ATP

18

Cold _____ acts on _____ channels on nerve terminal

direcetly
TRPM8

19

Heat acts _____ AND _____.
The direct way, it acts on _____ channels on the nerve terminal. The indirect way it acts on _____ channels on keratinocytes.

directly
indirectly
TRPV1
TRPV3

20

H+ acts _____ on _____ and _____ channels on the nerve terminal

directly
TRVP1
ACIS

21

Mechanical stimuli act ______ and directly. They act indirectly, through releasing ____ and then acting on ____/_____ channels.
They also act _____ by acting on ____ channels

indirectly
ATP
P2X/P2Y
TRPA1

22

INFLAMMATORY PAIN (CHRONIC). After tissue damage, _____ ___, _______ and _______ are activated. Various immune mediators are released which exert their algesic effects by acting directly on nociceptors or indirectly through the release of other mediators, most notably prostanoids.

mast cells
neutrophiles
macrophages

23

Where are the cell bodies of these neurones located?

DRG (but also trigeminal ganglia)

24

Example of external tissues where these nociceptors are present?

skin
cornea
mucosa

25

Example of internal tissues where these nociceptors are present?

muscles
joints
bladder
gut

26

FACT:

The trigeminal ganglia are specialized nerves for the face, whereas the dorsal root ganglia associate with the rest of the body.

27

Define allodynia

a completely non-noxious stimulus like light touch causes extreme pain

28

Define hyperalgesia

low intensity stimuli from regular activity, initiates a painful sensation

29

What are the excitatory neurotransmitters for C fibre?

Substance P
CGRP (calictonin G-related peptide)
Histamine
Bradykinin

30

What is the difference in how acute pain is treated and how chronic pain is treated?

Acute pain is treated with local/general anaesthetics.

Chronic pain e.g. allodynia/ hyperalgesia is treated with NSAIDS, opiates, anticonvulsants