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Flashcards in Pain Deck (39):
1

Define analgesia

Inability to feel pain, without removing all feeling or ability to move muscles

2

Define analgesic

Drug used to achieve analgesia

3

Define anaesthetic

Drug used to eliminate all sensation, including pain

4

What is a neuromuscular blockade?

Also known as muscle relaxant
Works by blocking the neuromuscular junction

5

What is a perineural blockade?

Injection to selectively block a nerve root

6

What is radicular pain?

Pain that radiates into a lower extremity
e.g. sciatica

7

What are the 5 types of sensory receptors?

Mechanoreceptor
Nociceptors
Chemoreceptors
Thermoreceptors
Photoreceptors

8

What is the pathway of a pain signal?

Afferent peripheral nerve (nociceptor)
Synapses with interneuron in spinal cord in dorsal horn
Releases glutamate which binds to AMPA and NMDA receptors
Thalamus
Cortex

9

What is nociceptive pain?

Sensation of pain in response to detection of potentially damaging stimuli

10

What is neuropathic pain?

Pained caused by damage to the sensory nervous system

11

What is pain wind-up?

Perceived increase in pain intensity over time when the stimulus is applied repeatedly
Caused by repeated stimulation of group C nerve fibres and priming of the NMDA receptor response

12

What is Ketamine and how does it work?

Used as an IV anaesthetic
NMDA receptor antagonist
Leads to inhibition of CNS

13

How does Nitrous Oxide work as an anaesthetic (and what is it also known by)?

Antagonist of NMDA, AMPA and Kainate receptors
Also known as Entonox

14

What are the 4 types of receptor that opioids bind to?

Mu
Kappa
Delta
ORL1

15

What type of receptor are opioid receptors?

GPCR - coupled to Gi/o

16

What are the downstream effects if the Go receptor?

Potassium channels open
Potassium efflux
Hyperpolarisation
Less likely to reach action potential threshold

Also inactivates VOCCs, preventing neurotransmitter release

17

What 5 receptors are coupled to a Gi/o protein?

a2-adrenoreceptors
M2 and M4 receptors
All opioid receptors
5-HT1 receptor
GABA-b receptor

18

How does the GABA-a receptor work?

It is a ligand-gated chloride channel
Allows chloride ion influx
Hyperpolarisation
Less likely to reach action potential threshold

19

Is Glycine an excitatory or inhibitory neurotransmitter?

Inhibitory
Also works on ligand gated chloride channels

20

What are the two types of neuromuscular blockade?

Depolarising
Non-depolarising

21

How do depolarising neuromuscular blockades work?

Agonist of nAchRs
Causes persistent refractory depolarisation
Motor endplate becomes inexcitable
(Ach normally released in brief spurts and rapidly hydrolysed)

22

Example of a depolarising neuromuscular blockade
-administration
-structure
-how is it broken down

Succinylcholine
-Administered by IV
-Looks like two Ach joined together
-Broken down by plasma cholinesterase

23

How do non-depolarising neuromuscular blockades work?

They are competitive reversible antagonists of nAchRs

24

How does botox work?

Botox targets proteins in the SNARE complex
Prevents exocytosis of Ach

25

How does Neostigmine work?

Inhibits acetylcholine esterase
Prevents breakdown of Ach
Used to treat Alzheimers and Parkinson's

26

How is Ach recycled?

Acetylcholine esterase breaks it down into acetate and choline
Choline reuptaken into presynaptic membrane by cotransportation with sodium ions
Choline + Acteyl Coa makes more Ach
Repackaged into vesicles

27

What 3 things can anticonvulsant drugs be used to treat?

Seizures
Mood disorders/stabilisers
Neuropathic pain

28

How do anticonvulsant drugs work?

Block sodium channels
Block calcium channels
Enhance GABA function

29

By what 3 ways can GABA neurotransmission be enhanced?

Positive allosteric modulation of GABA-a receptors e.g. by benzodiazepines
Inhibition of GABA transaminase (preventing GABA breakdown)
Inhibition of the GAT1 reuptake transporter

30

Example of a drug that inhibits sodium channels

Carbamazepine
Specifically Na1.8 channels

31

Examples of 2 drugs that inhibits calcium channels
How do they work?

Gabapentin and Pregabalin
Block t-type calcium channels
Also prevent insertion of calcium channels into the membrane
Reduce expression of a2-delta subunits in calcium channels

32

How does neuropathic pain after injury arise?

Injury causes inflammation
Release of inflammatory mediators
Inflammatory mediates upregulate a-adrenoreceptors on the sensory nerve and upregulate NMDA receptors on the spinal cord synapse
Lowers nerve activation threshold

33

What is a nociceptor?

Sensory neuron that responds to potentially damaging stimuli
Detection of noxious stimuli transduced into electrical energy

34

What are the two types of nociceptor axon?

A-delta fiber axons
C fiber axons

35

What is the difference between A-delta fiber axons and C fiber axons?

A-delta fiber axons are myelinated and cause feeling of sharp pain. Action potentials are initiated through specific TRP channels
C fiber axons are non myelinated and cause feeling of dull, prolonged pain. They are polymodal - response to a range of stimuli

36

How do thermoTRP channels work?

Ion channel, opens in response to extreme heat
The TRPV1 channel opens in response to 42 degrees, also vanilloids present in chilli

37

What is hyperalgesia?

Increased sensitivity to pain, usually caused by inflammatory mediators

38

What are A-beta fibers?

Detect non-noxious, mechanical stimuli

39

What are 3 possible causes of phantom pain?

1. Neuroma (tumour on a nerve sheath cell), causing abnormal firing of action potentials
2. Degeneration of C fiber axons due to injury. A fibers branch into same lamina, so A fiber input becomes reported as noxious stimuli
3. Cortical remapping following amputation